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January 20, 2009

Don’t Set Your Programmable Thermostat Too Low (Myth!)

Category: Conservation,Household,Save Fuel,Tips – Tom Harrison – 4:00 pm

programmable-thermostatA recent conversation reminded me that many people believe it’s a bad idea to set your programmable thermostat too low, asserting that it will use more energy to bring your house back up to temperature than it would to leave the temperature closer to normal.

This is wrong. False. Myth. Not true. No way, no how.

(Update: 12/2010: More detailed scientific theory about why programmable thermostats will indeed save money, if you use them correctly in a new post.)

Every moment your house is warmer than the outside air, (heat) energy is leaking out. The greater the difference, the more energy leaks out.

Every moment your home heater is on, energy is being used. The longer it’s on, the more energy is used.

Period.

Say you set your thermostat to 68° in the afternoon after school or work, then down to 50° at night. Your neighbor, who lives in an identical house (I guess in some condo complex or something :-) also sets her thermostat to 68° in the morning then down to 60° at night. It gets cold at night, say 20

It will indeed take longer to raise the temperature of a house from 50° to 68° than it would to raise the temperature from 60° to &68deg; for the same house and outdoor temperature.

Over the course of a given day your neighbor’s heater will be on longer. And that’s all there is: a burner is either on or off, so length of time on is pretty much all that matters in energy consumption. (There are some ways to optimize, such as running a circulator pump after the burner is off, but that’s not relevant, here).

It is true that it will take longer for your house to get to 68°, and your floors may not heat up as fast as the air. I read a couple things about issues with condensation which might apply to summer, but not winter.

The link above is to a 5 + 2 day thermostat with four settings per day, from Honeywell — $28.90 right now. That means you can have different weekday and weekend settings. It installs with a screwdriver — no, really, it’s super easy — there are two low-voltage wires to disconnect from your current thermostat and attach to the new one. They are very light, so don’t need any fancy mounting to the wall, and use a 9V battery. If you’re home during a time it expects you to be away, there’s a simple override; it will switch back into automatic mode at the next change time.

We have ours set to:

  • 4:30 am — 67° (morning warm-up)
  • 8:30 am — 50° (burner usually off 7 hours)
  • 3:30 pm — 67° (afternoon warm-up)
  • 9:00 pm — 55° (burner usually off 7-1/2 hours)

It would be really nice if there were a thermostat that could adjust it’s start time to “reheat” the house based on outside temperature, since it takes longer the colder it is outside.

68 Comments

  1. Another common myth is that a house will warm up faster if the thermostat is turned up higher. If the temperature is 62 then set the thermostat on 80 rather than 68 with the mistaken belief that it will speed up the heating process and reduce the time needed to get the house to 68. The problem is that the thermostat is forgotten and the house warms up beyond 68.

    Comment by Paul Lambert — January 21, 2009 @ 12:52 pm

  2. I think people don’t have a mental model of a thermostat. Maybe if they were called a “temperature switch” it would make more sense. But probably not…

    Comment by Tom Harrison — January 21, 2009 @ 1:05 pm

  3. Does anybody have any science to PROVE that programmable thermostats use less energy? I cant find any. We stopped using our programmable thermostat because at 20F outside temp., the furnace would run continuously FOR HOURS in order to get the house back to 68F in the AM. Ours is an 8 year old house with 6 inch insulated exterior walls, triple pane windows, 12 inches of attic fiberglass insulation ect ect.

    T in Michigan

    Comment by troop — February 2, 2009 @ 3:11 pm

  4. Hi troop –

    The science behind this is based on the fact that it takes as much energy to raise air temperature one degree whether the air is 10° or 100°.

    The problem is not much more complicated than that. Of course your furnace will have to run for a longer period to raise the temperature from 50 to 68 (18 degrees) than 60 to 68 (8 degrees) — about twice as long if the outdoor temperature is the same. However, the savings come because the furnace is not running as long the rest of the time.

    Often the misconception comes because the house seems colder in the morning and that’s different, and yes, not as nice :-). If you set the thermostat to go on early enough, you can awake to a nice warm house instead.

    In my house, it usually takes about 60 minutes for the burner to run to heat up the house in the morning when it’s modestly cold out (say 25°F), and another 60 minutes to heat up the house in the afternoon — so about 2 hours per day. If the house were maintaining a constant temperature, the burner might go on for 30 minutes every 3 hours — or about 4 hours per day. Your house will be different based on your burner’s efficiency, insulation, heating system, outside temperature, and so on.

    I am working on building a device to measure and record the amount of time our burner runs every day (in my head now, but it looks doable). For most heating systems, they are either on or off, and when on burn a constant amount of fuel. In these cases, the length of time the burner runs is directly correlated to energy used. Until then, one of the two of us will need to find two days during which the temperature is the same, and sit by the burner in the basement recording when it goes on, and when it goes off.

    I promise, the programmable thermostat will win. Scout’s honor!

    Comment by Tom Harrison — February 2, 2009 @ 5:00 pm

  5. Tom, Thank you for your thoughtful response. My question remains unanswered: Can we find any PROOF that a house with variable temp. uses less heating energy than another with constant temperature? I cannot. All the info I find is anecdotal and/or from manufacturers of patented equipment.

    Two thoughts drive my skepticism:
    1. My 2000 sq/ft house contains (for the sake of argument) 80000 lbs of material INSIDE the well-insulated exterior walls/roof. This includes all the interior walls, floors, plaster, trim, cabinets, furnishings and personal stuff. Right now all of the 80,000# is 68F.

    If the thermostat is lowered overnight to 60F, all of that 80,000 lbs will be 60F in the morning. My experience with my own house and my very basic understanding of physics leads me to believe that my properly-sized furnace will take many hours of continuous running to re-acclimate a mass of 80,000#.
    2. Consider driving a car for 100 miles at variable speed vs constant speed. Most cars use less energy at constant speed Getting all the mass moving again takes more energy than maintaining the motion.

    Interesting stuff.

    Respectfully,

    Todd

    Comment by troop — February 3, 2009 @ 10:52 pm

  6. Todd –

    We should probably move this over to a physics forum :-)

    Considering your item #1 … all stuff holds heat energy, so if you apply a given amount of heat to the stuff, it will tend to get warmer, whether the air in your house, your sofa, your floors, or perhaps even that huge pile of stones in your in-house sauna (for example). It will take longer to warm up the denser things like your sauna rocks and floors. But likewise, they hold that heat, so will take longer to cool down. I don’t think this is a better explanation than I attempted before, but it’s a nuance perhaps you hadn’t considered.

    On item #2, it is true that a car uses less energy going a constant speed than when it starts and stops. But this is due to several unrelated reasons. First, when a car stops by braking, the energy of the car is converted to heat by the friction applied to the brake rotors; that heat dissipates and is lost. Accelerating back up to speed uses gas to add that energy back to the system. (A hybrid car like my Prius actually tries to get back some of that lost energy by charging its battery when you apply the brakes instead of just wasting the heat energy into the air). I don’t think this analogy fits the house heating case.

    Maybe a simple experiment to demonstrate my assertion would be to warm up a pot (your house) of water (the air in your house) on a stove (your furnace) to a temperature like 150° F. Keep the house at a constant temperature of 68° (to represent the colder outdoor temperature). Once the water gets to 150°, set the stove so it stays at that temperature; now you know the proper setting, let’s say that’s the “low” setting.

    Test 1: With the water at 150°, turn off the heat and come back 8 hours later. Turn the heat to the “low” setting and measure how long it takes to get to 150° — let’s call this “re-warm-up duration”. Maybe it takes 1 hour to get back to 150°.

    Test 2: With the water at 150° and the stove set to “low”, go away and come back 8 hours plus the “re-warm-up duration” time later (9 hours in my example).

    In test 1, the heat was on for 1 hour. In test 2, the heat was on for 9 hours. The time the heat is on, maintaining that water at 150° is roughly analogous to the amount of energy used. Your results may vary, but I assert that test 1 will always use less energy than test 2.

    Variant A: put a rock in the pot (representing the stuff in your house) and do both tests again.

    Variant B: simulate your thermostat by letting the water in the pot vary by 20° for test 1 and 5° for test 2. Vary the temperature by turning the stove off, then back on to the “low” setting.

    Variant C: do variants A and B together.

    Each variant gets us closer to a real representation of your house situation.

    Variant D: sit in front of your burner for two cold days (same outside temperature). First day set your thermostat to 68° constantly; second day, set your thermostat down and back up as your programmable thermostat would. Measure the total time the furnace is on.

    (Note: for variant D, I strongly recommend purchasing either a good book or a bottle of Scotch :-)

    Variant E: Trust the folks at EnergyStar.

    Please write back after you have the results of your tests carefully recorded.

    Tom

    Comment by Tom Harrison — February 4, 2009 @ 6:31 pm

  7. Tom,

    Haven’t been in your site for a while but thought that maybe I could find an answer to my question. About a month or so ago, I found, I believe in a Popular Mechanics online article, some info on a product that will shut off all electric when not in use, except for those items it knows (somehow..mystery to me!) continue to need electricity, i.e. the frig, furnace, clocks, etc. I just spent an hour online trying to find this, but guess I didn’t save it as I thought I had…I believe this device sells for between 25-$50.

    Yesterday at Lowes I enquired, but the salesman said he hadn’t heard of such a thing yet, albeit he thought it a great idea. So, knowing that you are an expert in all things energy saving related, where do I buy this and what is this device called?

    Good job on your website…lot of good stuff there. I had the same question as your guy from Michigan, but had a hard time following your answer to him…sounds like a good book or scotch would help one forget what one wanted to know…heh!
    actually it reminded me of Timothy Geithner’s talk this week on the Senate floor when asked a question..by the time he was done, no one had a clue as to what he had said.

    At any rate, I had my programmable taken out a couple of years ago, and life is much better heat wise in my unit..I hate those darned things. I found out that they use more heat than the old fashioned ones. And for the life of me, how can one programme these when mother nature is not the same from day to day..this past week I had windows open to bring in fresh air..and the heat was off for hours…I couldn’t have done that with a programmable.Having windows open for a few hours only dropped a degree, and actually when I closed the windows and went to the thermostat to turn furnace back on, the temp had gone up a couple degrees…no doubt due to the southwest exposure in liv rm/din rm. Lots of sun helped a great deal.

    Just got my last heating bill…ugh…for having the smallest unit here, my bill last month was over $700! If I am paying over $700, my neighbors are paying between $ 800 – $1,000 depending on the size of their three floor units…arrrggh.
    Is there anything I can do with solar that isn’t mounted outside? Or wouldn’t create problems with the condo association?

    Lastly, I am so glad that I had those Hydrosil heaters installed in both the basement as well as my studio a yr ago…room heats so fast and so nicely…unlike dumb heat pumps we have here.

    Comment by Jean — February 14, 2009 @ 12:54 pm

  8. The device you’re looking for is a Smart Strip power strip. Read the linked article for information on how it works and where to buy.

    Sorry you can’t get your programmable thermostat to work as you want. It may be that you have a different expectation as to what it is intended to do; this seems to be at the root of why people don’t think they “work” and thus how to set it in a way that works for your particular heating situation.

    As a result of the long thread here, I have created a little device to measure how long my furnace (and hot water heater) are on during the course of the day. I have one set of data now for a 30° day using the programmable thermostat in use. I’m waiting for another day that’s about the same temperature so that I can perform the same measurement with the programmable thermostat off. From this I will be able to demonstrate that less energy is used than a thermostat set at a particular temperature.

    Comment by Tom Harrison — February 14, 2009 @ 2:36 pm

  9. Hi Tom,

    My questions stands: Does whether changing the thermostat temperature in a home several times daily save energy? I still have not seen ANY SCIENCE that shows it does. In fact, my skepticism grows with each visit to this site.

    Fact: Stop and go driving uses more energy. period. Regenerative braking (like a Prius) lessens the loss from the speed variations. Go to the Toyota site.

    Boiling rocks on a residential stove top with thermometers and… ?

    That is not science.

    Science: Two identical houses. One with a temperature that varies daily, one with continuous temperature. A guage on the electric and gas meter.

    Todd

    Comment by todd — February 14, 2009 @ 6:54 pm

  10. Todd –

    Our differences cannot be reconciled in this blog as it appears that your definition of science differs from mine.

    I am sorry, but we have nothing further to discuss here.

    Respectfully,

    Tom

    Comment by Tom Harrison — February 15, 2009 @ 1:07 pm

  11. Tom wrote: “… it appears that your definition of science differs from mine…”

    I agree. Wiki’s definition of scientific method: “a method of inquiry must be based on gathering observable, empirical and measurable evidence subject to specific principles of reasoning.”

    Good luck,

    Todd

    Comment by todd — February 15, 2009 @ 8:16 pm

  12. [...] they do not freeze.  It may run for some time to warm back up, but nowhere as much as when it is running during the day while you are not there.  Another concern is about family pets.  If you do feel that it is too [...]

    Pingback by Programmable Thermostat to Save you Money | Pays to Live Green — February 17, 2009 @ 10:09 am

  13. Troop
    There are 2 reasons why a programmable T-stat saves energy:
    1. The bigger the difference in temperature between outside and inside the house, the greater the rate of heat loss. The house loses heat at a faster rate. If you can decrease that difference (Delta T) you’re decreasing the rate of heat loss.

    2. Heating systems run more efficiently when they’re running continuously – at a steady state. No cycling losses or wasted heat as you do when the heating sys cycles on and off, unless you have a power vent. So when the heating sys is bringing the temp back up in the morning, it’s running more efficiently than when it’s trying to maintain the higher temp.

    I’ve been doing energy audits for 20 yrs and in my experience, a house that has 6″ walls and a foot of ins in the attic should be perfect for a programmable T-stat. It shouldn’t be taking you that long to bring the temp back up. I probably wouldn’t go below 55 at night, unless your setpoint is below 68, then you can probably go lower with your setback. Do not use setback T-stats with radiant heat in cement floors or with heat pumps, especially air source versions.

    Comment by Tony — February 17, 2009 @ 11:57 am

  14. Thanks Tony, I hope you will join me in my search to find an an actual field study or trial that supports this widely accepted reasoning.

    Could it be that adjustable thermostat energy-use trials have been done and not published? Why would that be?

    Waiting now for Tom to block my heretical posts.

    T

    Comment by todd — February 17, 2009 @ 1:52 pm

  15. Hurrah!.

    A real-world ongoing thermostat experiment in Canada. Up to 13% savings in heating cost!

    http://www.homeenergy.org/article_full.php?id=566&article_title=Thermostat_Setbacks%E2%80%94Do_They_Really_Work

    They also tested things like closing window shades:
    Letting full solar in during the day and closing the blinds at night resulted in about a 7% saving in overall heating performance.

    Thanks,

    Todd

    Comment by todd — February 17, 2009 @ 10:44 pm

  16. Hurrah indeed! I’ll use this article as some good solid proof as I write my next post about the measurements I have been making of my hot water heater and gas burner.

    Thanks Todd.

    Comment by Tom Harrison — February 18, 2009 @ 8:42 pm

  17. I’m hoping you can answer this question for us. We were away all of a frigid January last year. We set our furnace at 60 degrees instead of an average of 67 degrees. Still according to our gas bill, we used more gas than the previous January where we were only gone 12 days. The woman we spoke to said that because our furnace was set so low, it worked more because it was so cold outside. Said we should have set it at 63-65 degrees instread.
    Does this make sense?

    Comment by Micheline Chaput — December 3, 2009 @ 2:26 pm

  18. Micheline –

    The woman you spoke with is mistaken. It’s a common misconception, and strongly held by many people. It’s just not right.

    If last year was frigid, then this is probably why you used more gas, even with a lower setting. If you were so inclined, you could find the number of “Heating Degree Days” for your location for the two periods and do a little math. But it is a very, very difficult problem to work out — if you were gone (and had the temp set at 60°) for 12 days, then back for the remaining 19 days with the temp set at 67° it gets tricky already. When you’re home, doors are opened letting in cold air, but stoves and lights are on and bodies heat the place up.

    Looking at it more simply, the difference between when you’re gone and when you’re home is 7°. If the outside temperature were an average of 15°, for instance, the furnace would need to run long enough to raise the inside temperature 60 – 15 = 45°. 7° is only about 1/4 of the amount the furnace has to work, so a slightly warmer January, or even just a few days extra in the billing cycle could make all the difference.

    Let me know if you’re feeling intrepid — if you can find the degree days for your area for those two time periods (try http://www.degreedays.net/) and you have the two heating bills, I have a spreadsheet I can post that will help you do the calculation.

    But the simple answer is: the higher the temperature in your house, the more the furnace has to work, all other things being the same.

    Myth: Busted :-)

    Comment by Tom Harrison — December 3, 2009 @ 2:55 pm

  19. Thanks for the quick reply. So the short answer is that our gas usage went up compared to the previous year because it was so darn cold? Had some -40 degrees Celsius days !

    Comment by Micheline Chaput — December 3, 2009 @ 4:46 pm

  20. Yes, -40° would definitely do it! Yikes. Boston is looking better every minute.

    Comment by Tom Harrison — December 3, 2009 @ 4:53 pm

  21. Todd, I am baffled by your logic with Tom. I have one question for you: If you turn the heat off for a month with the outside air temperature of 20 degrees and then warm the house (and its contents) back up to 70 degrees in one day will you use more energy then keeping the house at 70 degrees the whole time?

    Comment by Jack Frost — December 23, 2009 @ 10:45 am

  22. Jack Frost — I think the exchanges in the comments resolved Todd’s questions — see comment #15.

    The reason I wrote the post is that I have heard (and continue to hear) people having or repeating the myth.

    Comment by Tom Harrison — December 23, 2009 @ 11:59 am

  23. Hi Jack,

    Call me Captain Kirk…irrational. Yes, the ongoing study of two identical houses in Canada (see link at post #15 above) proved to me that proper use of a programmable T-stat can potentially save up to 13% on heating costs. We started using our programmable T-stat again in March – and stopped again in May. 13% savings was not worth waking up and stepping onto a still-cold wood floor into still-cold ceramic tile shower -taking a cold coffee mug out of the cold cupboard… These tactile, difficult-to-quantify comforts are the human element that science finds difficult to measure.

    It’s a Spock v. Kirk thing. Define love. ;-)

    Comment by Todd — December 28, 2009 @ 10:10 pm

  24. Todd –

    On this point, I completely agree. You heat your house to be comfortable, and your comfort isn’t a quantifiable matter of science.

    However, my family wakes to a warm, comfortable house. The trick with programmable thermostats is to anticipate — it takes our house between 30 and 90 minutes to come up to an air temperature that’s comfortable for us, depending on how cold the house is to start, and how cold it is outside. We’re usually up by 6:30 on weekdays, so we set the heat to come on at about 5:15 (and may adjust in the winter a few minutes earlier). Yes, the air heats much more quickly, and it we wanted to have the floor get warm, or the coffee cups, we might need to start earlier, or have the target temperature higher.

    But let me take a moment to encourage you to look at this problem emotionally, but also (Kirk-like) altruistically. Is it not our duty as humans to make responsible decisions about how we conduct our lives? 13%, if that is the number, is rather incredibly large, if you think about it. Whether you are concerned about climate change, energy security or costs, or any of them, household energy conservation is one of the largest and also easiest changes we, as individuals, can make to help.

    As I recently wrote, the real difference we make as individuals may not be in saving 13% of our personal consumption (which is of course a mere drop in the bucket), but in influencing others to make changes by showing how easy some changes are.

    Todd, while your cold tootsies are certainly a factor, perhaps there are other simple solutions that don’t interfere with your comfort too much and which you could make in conjunction with your thermostat changes. A pair of slippers, a bath-mat and a little twiddling with the timing of your programmable thermostat (even if you don’t save the full 13% possible) are all small, reasonable steps you can take.

    Through your comments here, and hopefully through your thoughtful conversation with others you are finding ways that do work, or at least understanding the small trade-offs we need to be willing to accept.

    Having gone through this recent economic collapse, brought on by our self-centered beliefs, it is perhaps a time when we need to consider how our actions affect others, in particular, that we have some responsibility to find new ways to be comfortable, even if those ways involve changes. Change is often not simple; it sometime requires other adjustments. While it doesn’t mean “reduction”, I think most changes require a certain amount of effort, and accommodation to new ways of doing things.

    I hope you’ll reconsider your programmable thermostat, and perhaps make it a five year mission to explore new worlds. :-)

    (And of course, Todd, I am using your comment as a foil, only — this is in no way intended to be a personal assault on you. Your point is indeed correct — it’s not as easy to quantify the human impact of changes.)

    Tom

    Comment by Tom Harrison — December 29, 2009 @ 9:52 am

  25. I live in a 10 year old 2 story house. The problem is that my digital thermostat is located in the hallway above a tile floor located near the front door & the door to the garage. We have vaulted ceilings in our living room and we cannot get the temperature regulated in our house. if the heater is on all of the bedrooms, up stairs and down stairs get hot but the living room, kitchen and hallway stay cold and since that is where the thermostat is even if we have it set on 63 degrees, it never shuts off. it will run constantly. What can we do?

    Comment by Robin — January 8, 2010 @ 1:10 pm

  26. hi

    Very interesting discussion. thank you for providing so much information. I just bought a 10 year old home and I am a new home owner. Your discussion has shed light on many questions that i had.

    But one answer I couldn’t find is what’s the lowest temperature i can set without having my pipes burst or something.

    I have 55F during nights and 67 during evening and 64 during day. but some one told me if i set it up anything below 64 i will run risk of having a pipe burst. is that true.

    Please let me know what’s the safe low temperature i can set.

    Thanks

    Comment by Anwarul Kabir — January 8, 2010 @ 1:28 pm

  27. How cold you set it depends on how much insulation you have and if you have any water supply pipes in outside walls…which get cold first.

    T

    Comment by Todd — January 8, 2010 @ 3:20 pm

  28. Anwarul — as Todd says, the low setting can vary. My brother in law reported setting his down to 50° but had a freeze up because there was an air leak in an area where the pipes were and it got really cold one night.

    We set our heat down to 55°F at night and have no problems, but our house is also very tightly air-sealed.

    So, just set the temperature down lower and lower, and once your pipes freeze, you can set it up a few degrees from there.

    Just joking ;-)

    Tom

    Comment by Tom Harrison — January 8, 2010 @ 6:23 pm

  29. Robin –

    Your plight is one that many people with relatively new houses suffer — they were built to look great, but not to be efficient or practical, in some cases.

    Some things I would suggest:

    1. Ceiling fans — great to move air down from vaulted ceilings
    2. Get a heating contractor to look things over — even if the house is on a single zone (which would be surprising for such a new house), there may be ways to balance things out better, so that the right heat gets to the right places
    3. Get an energy audit — newer houses often tend to be the least efficient of the lot (sadly) and suffer from air infiltration; a blower-door test will identify where the leaks are and where more insulation might help — in our case, we were able to seal some rather major “holes” in our house with simple remedial methods — caulk, foam, and a few other tricks. The energy audit is totally worth the money.
    4. Maybe move the thermostat — sounds harder than it is
    5. Consider some circulation fans to move heat from one room to another
    6. Hope this helps. Check out my new company, Energy Circle for home energy efficiency advice.

      Tom

    Comment by Tom Harrison — January 8, 2010 @ 6:33 pm

  30. I am also absolutely baffled by Todd’s logic. How is it not retardedly obvious that lowing the set temperature for ANY amount of time will reduce energy consumption? My mind is boggling.

    Also Todd, why don’t you anticipate how long it takes your house to heat up/cool down and change the programmable times accordingly? you say you don’t like getting out of bed and feeling cold floor, or cold tile, or a cold coffee mug. Why not program the thermostat to turn on 2 hours earlier so its nice and toasty? And if I know anything about thermodynamics, and I do, your house (floor, tile, and mugs) will also take a long time to cool back down to unacceptable temperatures so you can also program your thermostat to adjust the temperature back down and all these items will retain their residual heat while you get ready for work or whatever.

    Comment by Brandon — January 25, 2010 @ 9:04 am

  31. @Brandon — let’s give Todd a break. I beat him up pretty badly in the early comments from last year, but he came around after he found proof that they actually work as advertised (but then found another reason not to use his).

    In truth, programmable thermostats can be tricky to set just right, and, as they saying goes, “You can lead a horse to water, but you can’t make him drink”. Some people only kinds of want to do a little as long as it’s easy. My goal here is to help people see how it’s easy to do some things. I can’t make them do it.

    We see this discord between people who believe different things, even if they may not be true. It’s frustrating when what we’re arguing about is really a law of physics, as in this case, and perhaps even more frustrating when it’s clear, accepted science, as in the case of climate change.

    Anyway, we do what we can do to help inform those who are willing to open their minds, put in a little effort to make change, and stick with it for a while. Sadly, this seems like a small slice of the pie these days, but I am always hopeful that more will be coming to join the party.

    Tom

    Comment by Tom Harrison — January 25, 2010 @ 9:16 am

  32. Thanks Tom.

    The short answer to why we no longer turn down our thermostat: Comfort. We really do not like being cold. Maybe we should move to Florida.

    Big Picture: We all need to do things to use less energy, yet we are all different. We save energy in ways that fit our lives. My wife gets up at 5am. I go to bed at midnight. I suppose we could turn down the thermostat from midnight to 3am.

    WE DO -1. use half as much gasoline as we did 5 years ago. 2. wear a layer of head-to-toe Nuwool from Oct to April. 3. Use all-CFLs at home and at our businesses. We also have a super-insulated home we designed from scratch.

    Respectfully,

    Todd
    Michigan

    Comment by Todd — January 25, 2010 @ 10:51 am

  33. Thanks Todd –

    Yeah, Michigan can get cold. I spent one winter in Chicago and there was a two week period where the temps never got above -10°F — it sucked. I was cold all the time.

    I’ll bet your contribution to energy savings far, far exceeds most of the rest of us — and I guess my point earlier sort of assumed that you had given the thermostat a try and gave up; clearly quite the contrary.

    And this is an important point. There are literally hundreds of things we can all do to make reductions in our energy usage and our contributions to climate change. I haven’t done all of them, and none of us is likely to. Becoming aware of the issue, making the changes that work for you, and being open to the process of continued adaptation to new habits and new ways of living our lives takes time, and we should all feel good about whatever direction or speed we are taking … as long as it’s forward!

    Onward. And to future commenters (including me) — let’s keep the discourse civil and non-personal.

    Tom

    Comment by Tom Harrison — January 25, 2010 @ 11:48 am

  34. Tom, I’ve finally discovered why a programmable t stat never worked for me. Before I had little control over my heat. Had an electrician here a few times, and 2 years ago, he simply ripped it from the wall, and replaced with an old fashioned thermostat which has served me well ever since….well, sort of, more on that later. He told me that he didn’t find too many folks who liked them. I’ve learned that programmables don’t go well with heat pumps, especially when the heat pump freezes over outside and you have to whack off the chunks of ice and use a blow dryer in an attempt to melt ice off the blades so they can turn again. The other problem with a programmable for me is having a cathedral ceiling in a greatroom with southern exposure..

    That room has two southwesterly double windows allowing sun in all day, so between that fact and the opposing one of the dumb heat pump outdoors, it’s no wonder the first few years in my condo were miserable in the heating dept. The thermostat was simply not computing all the craziness of the heat pump’s major problems vs southwest windows.
    But I have improved my heating situation greatly since then by installing some hydrosil baseboard heaters in my studio as well as the basement..and they don’t cost anything near what a heat pump and back up electric would cost. I now have a toasty studio to work in and supplemental heat in the other bedroom…studio and bedroom are both above the garage, the latter which is often colder than it actually is outdoors, thus making bedrooms so cold.

    My latest attempt to get more warmth for my larger space/greatroom has been accomplished recently by my purchase of an infrared heater which I use in that space well over 500 sq ft. This little portable charmer is working wonderfully for me. It is terrific insofar as I only have to turn it on in the morning from seven to nine, then shut it off for the day and the heat is retained like nothing I’ve had before. Then when the sun is going down, I turn it on again from four to six pm, then to the nursing home with dinner for friend. When I come home later, I then put it on again for two hours and then OFF for the whole night. Essentially I have it on only for six hours a day and am warmer than ever before, not to mention cleaner air and easier breathing. AND NOT RUNNING EXPENSIVE HEAT PUMP/ELECTRIC.

    Infrared heat is a terrific and efficient way to turn electrical energy into heat energy as it uses thermal infrared, short wavelengths to produce heat, thus enabling heat to penetrate objects much faster than conventional gas/electric heat. Up to 80% of heat generated by the infrared is absorbed by all room objects. This is done in minutes, not hours. It doesn’t uselessly dissipate through the walls, floor and ceiling, so the warmth stays for hours while off. For a senior this is a plus healthwise too for it penetrates the body. One of the most fantastic things about this other than the hugh savings I should see in my next bill, is the negative ions making the air ‘greener’, healthier. I notice such a difference in the air quality, like it is really clean, fresh and easier to breathe. I wish I had discovered this long ago…would have saved big bucks for sure.

    Oh, and did I mention this will pay for itself in three days..yep. The cost of the heater was close to $400 and no shipping fees or taxes. Additionally I got a $300 gas card which I use once a month for $25 each month, thus you can knock off 300 from 400. They also took off another $50 discount bringing $100 down to $50 total. Even if it only lasts for the three year warranty, this was a no brainer for me.

    My last bill from CL&P was $600 for the month, averaging $20 a day to heat this condo, and not really even warm at that. With the infrared and the six hours I have it on, I should reduce that amount to about $2 a day..and be warm at long last….talk about a hugh savings…sixty vs six hundred. I’ll be thrilled if I even cut that bill in half, let alone more.
    For clean air, warm heat and cutting your energy bill all in one fell swoop, check out this super heating at
    http://www.czinfrared.com/how-does-infrared-heat.html

    Comment by Jean VanBael — January 25, 2010 @ 4:16 pm

  35. I just installed a programmable thermostat this evening. We’ll see how it works. We’re using diathermic oil space heaters, one in our room and one in the kids’ room, at night, and I’ll try to find the lowest comfortable setting for those heaters (they have thermostats and are supposedly fairly energy efficient). Right now, I’ve decided to run them on the medium (900 watt) setting at medium heat and see how that goes. I’m doing this based on the assumption that, while some of the energy savings I’m realizing by lowering the house heat to 58 (that’s my “sleep” setpoint now) will be neutralized by heating the two bedrooms, heating those two rooms in this manner will still be more efficient than heating the whole house. Tom, does this make sense?

    Also, I want to commend Tom and Todd for their very reasonable interchange. The tone was respectful, thoughtful, and utterly uncharacteristic for the internet. I was convinced by Tom early in the exchange, but was impressed that he parried all attempts to flame Todd for his reasoning and persistence in continuing to argue the point. Kudos to both of you for maintaining a level of civility that is all too rare these days in and forums like this.

    Comment by Matt Weiss — January 8, 2011 @ 12:02 am

  36. No disrespect to the dude doing stove top experiments – air and water have different rates of response to heating and cooling. For example, water heated holds heat longer than a comparable air space heated at the same rate. Love the science…it’s just not a valid comparison.

    Comment by Mark — January 28, 2011 @ 12:29 pm

  37. He isn’t comparing the rates of cooling of water to air. He is comparing the rates of cooling of water to other water to illustrate how thermodynamics works. The exact same holds true for your house. Maintain a constant temperature over a period of time, or don’t maintain it and heat it up all at once at the end. The point is that the laws of thermodynamics apply and you will always lose heat from a hot source (either your house OR a pot of hot water) to a cold source (the outside OR the outside of the pot [your kitchen]).

    A house kept at 80* for any period of time will lose more energy than a house kept cold and heated up to 80* at the end of the identical time period. The loss of heat must be greater for the house that was kept at a higher temperature, just as the loss of heat of a pot of water maintained at an elevated temperature will also be greater than a pot allowed to cool in between. This is thermodynamics and was illustrated just fine by Tom.

    Comment by Brandon — January 28, 2011 @ 1:25 pm

  38. Hi Mark (and Brandon) –

    For a more complete and scientific explanation of these issues please seem my more recent blog post on how heat works.

    Tom

    Comment by Tom Harrison — January 30, 2011 @ 3:51 pm

  39. Great article and interesting discussion in comments. :)

    I think this may be a decent analogy, incorporating Tony’s spot-on reminder that houses lose heat more quickly as the inside/outside temperature differential goes up.

    Imagine you have a bucket. It leaks, because there is a line of small holes drilled up the side. So the fuller it is, the faster it leaks.

    Sometimes you need the bucket full; other times you can live with it half empty. Clearly you let it be half empty when you can be, because it leaks less that way. And filling it to the top only when necessary doesn’t take any “more” water….

    I dunno if that’s a useful thought experiment or not.

    Anyway, keep fighting the good fight ;)

    Comment by Eric — February 9, 2011 @ 12:12 am

  40. What a great discussion. I’d been wondering about many of these issues and I feel much more informed now. I’m planning to move my programmable thermostat from near the woodstove to outside the bedrooms so I can maintain a better temperature in them but I’m thinking that it’s a job better done in the summer when a non-functioning thermostat won’t be a disaster. Hoping for the best, preparing for the worst.

    I have hot water baseboard heating with the pipes and registers mostly on outside walls. Is there any kind of alarm system that would let me know if the pipes are getting close to freezing – say on a really cold windy night? This is a 60′s era house so who knows how much insulation is in the walls.

    Comment by Karen Hamblin — February 13, 2011 @ 5:40 pm

  41. Karen, if you get an energy audit, especially one with an IR camera, you can find out about the insulation. We had kitchen sink pipes on an outside wall that froze a few times each winter, thankfully they never burst.

    After we retrofitted wall insulation, the freezing problems went away. An unexpected and very welcome benefit.

    Comment by Eric — February 13, 2011 @ 5:47 pm

  42. Karen — Eric beat me to the answer (well done, Eric :-).

    The way to find out is through an energy audit — remarkably inexpensive and remarkably useful.

    We have possibly the opposite problem as Eric — after sealing and insulating the water pipes that run up to the second floor, and too the kitchen are outside of the insulation, so are actually getting colder. So far no freezes, but, next Spring to be sure I’ll work on caulking areas on the outside where I know air is still leaking in.

    I have actually been pretty impressed with the Black & Decker TLD100 Thermal Leak Detector — it’s no substitute for a real energy audit, but when you’re looking for spot problems, it’s a good option.

    Tom

    Comment by Tom Harrison — February 13, 2011 @ 7:54 pm

  43. Myth or fact? It is cheaper to heat a occupied home versus an empty home? Assuming the thermostat on the un-occupied home was not turned down to say 50deg. If you have the home set to 68deg, is it going to be cheaper heating the home occupied by the natural stirring of heat within the home? Thanks for the input.

    Comment by Glenn — March 10, 2011 @ 6:38 pm

  44. Glenn –

    Answer: it depends upon far too many variables to make a categorical statement.

    I can say that the answer does not depend on whether you have the thermostat set to 50° or 68° — if the setting is the same for the two test conditions (occupied and unoccupied), the result would be the same.

    Consider for example: sunlight exposure, convection currents, thermostat location, ceiling fans, heating system type, leakiness of house, windy or not, size of the space, and scores of other factors.

    Then consider: if you are home, you are generating some heat, but you’re probably also doing things that cause heat loss, like opening the external doors, or, for that matter the refrigerator door (the fridge is a very costly and inefficient way of heating your house).

    In the end, one thing I can say, assuming it’s cold outside: it costs more to heat a house to 70° than it does to 68°.

    Comment by Tom Harrison — March 10, 2011 @ 10:07 pm

  45. I use this in my house and it helps a ton. Read about it at their site. You can monitor the run time of your unit(s) at their online portal.

    http://www.ecobee.com

    Comment by Joe — August 1, 2011 @ 4:22 pm

  46. Joe — thanks for the link. I have heard good things about this (other than being a little pricey) from the guys at MapaWatt.com.

    Comment by Tom Harrison — August 1, 2011 @ 5:24 pm

  47. Hi,

    How low can I set the thermostat for the air conditioner in Arizona house? I was told not to set it lower than 72, otherwise the pipes inside of the air conditioner unit will freeze.

    Thank you

    Comment by Irene — February 12, 2012 @ 1:52 pm

  48. Oops! I wrote this with the incorrect assumption that thermostats are used to control the heat in your house. Typical Northeast liberal elite. :-)

    Everthing I wrote for heating applies for cooling, ‘cept backwards. “Low” goes to “high”, “hot” to “cold” and vice-versa, etc. In short, if you’re out of the house for some hours during the day, it makes sense to cool less using a programmable thermostat.

    Comment by Tom Harrison — February 13, 2012 @ 8:41 pm

  49. I manually adjust our thermostat everyday, usually 70 when we’re there and awake and about 62 when we’re gone or in bed. This DOES save money, and my heating bill proves it. I am going to install a programmable thermostat eventually which will basically do the same thing.

    Comment by Wes — February 27, 2012 @ 2:47 pm

  50. Tom, great site. I was researching for information regarding this very dilemma with respect to our church sanctuary, which is essentially used 1 day a week in NH.
    I’m determined to find the optimal temperature to set for Monday-Saturday, with the goal to reach thermal comfort for Sunday morning when the doors open. Aside from concerns over the piano being affected by the temp swings, I’m sure that the lowest possible setting that does not create other problems (like pipe issues) is the way to go.
    Are there are any other special considerations for a building used this way?

    thanks
    Bob

    Comment by Bob — April 9, 2012 @ 8:36 pm

  51. Hi Bob –

    I did another post here that may provide more details. But short answer: as low as it can go without freezing pipes or causing other damage for as long as possible.

    Comment by Tom Harrison — April 9, 2012 @ 8:56 pm

  52. Tom,

    I haven’t heard anyone talk yet about the Nest thermostat in this forum. It was designed specifically for people who find it difficult to program a thermostat. So far, all the feedback and reviews on the web have been quite positive for the Nest. You should review this on your site sometime and let everyone know what you think.

    http://www.nest.com/

    Comment by Kevin — September 27, 2012 @ 12:55 pm

  53. I haven’t bought or installed the Nest, but it definitely addresses a major issue with programmable thermostats, namely that people don’t program them correctly.

    I trust Sage’s review at EnergyCircle (disclaimer, I used to work there), and the MapAWatt one, too.

    In reality, it may be that there’s not a lot of data yet, as they sold out when they were first available, and it hasn’t been cold enough yet in most parts of the country for a thermostat to get in people’s minds.

    Tom

    Comment by Tom Harrison — September 27, 2012 @ 9:51 pm

  54. Over the weekend my house has dipped into the 59-61 range on constant basis day and night. I turned on my furnace in the evening for the last 2 evenings about 6-7pm and warmed it up to 68 and then shut the furnace off. Over night it gets back down to 61 and stayed there until the next evening when I did the same thing. I was told that it is harder on my furnace to have it run for long periods of time versus just letting it run a little bit to warm it up to the set temp.

    I like everyone else is just trying to save money on my energy bills and just need to know the smartest way to do this. I live in Indiana nearly in Michigan, and the temps have been in the 50s by day and low 30s at night, but my house stays 59-61 no matter day or night. Two years ago I had insulation blown in my walls and attic, and last year I had my basement and crawl space walls and sill plates spray insulated.

    I when I am at my most comfortable I like it at 68, but can sleep much cooler and we have even been just fine at the 59-61 temps through the night and day. I just want to know what the smartest way is to run my temperature control to make it the most efficent…is it having it set no more than 10 degrees less than my “comfortable” number or having it set as low as we can take it during the day ok and no matter how long the furnace has to run to get it up to “comfortable” is not harmful to the unit. It took about 45 min the first time going from 60 to 68 and about 35 min the second night going the same distance in temp. Thanks for any insight you can provide. I too am interested in the Nest information that was posted too.

    Comment by Shannon — October 8, 2012 @ 4:42 pm

  55. Hi Shannon — it’s not harder on your furnace to have it run for longer periods of time; unless you let your house get down to near freezing, there’s no basis for thinking your furnace will somehow be damaged.

    The only real trick (and the one the new Nest thermostat is supposed to do for you) is knowing about how long it takes for your house to get up to your “comfortable” setpoint from the cooler temperature at night. This will depend on your furnace and heating system, house insulation, and outside temperature.

    In my house, it takes about 45 minutes on a cold morning, so I just set my (dumb) programmable thermostat to come up to comfortable 45 minutes before we get up. Likewise, I set it to revert to the cooler setpoint a while before we go to bed. (We are all out of the house during many days, so the same for our daytime cycle).

    That’s all. Keep it simple :-)

    Comment by Tom Harrison — October 9, 2012 @ 8:16 am

  56. This is an amazingly helpful site. A while back, someone wanted an alarm to signal freezing temps on some outside pipes. While such are available, alarms are always coupled with the question of what happens when the alarm goes off? Knowing there is always a tradeoff with any solution, I solved a similar problem with a timed water circulating pump installed on the water heater.

    This works by forcing hot water into the line where it is bypassed by a pressure sensitive shunt at the end of the circuit and returned to the heater via the cold line. It takes a surprisingly small amount of run time to keep the pipes from freezing, and if we are talking sinks or tubs, we also eliminate the wasted water run while waiting for the heated water to arrive. The timer can be set at 15 min intervals and so adjusted to minimize wasted energy.

    Comment by Robert — November 18, 2012 @ 7:32 pm

  57. Some thoughts on programmable thermostats:
    a) Some (e.g., my Honeywell model) have a “usage” button. It tracks the total hours/minutes the furnace (or AC) was actually running today, yesterday, and since you last reset it. I love this feature. Also would help with some of the above mentioned tests.

    b) Some (e.g the one I have) are “smart” / adaptive. You program when you want it to reach the desired set point. Initially, it “guesses” how long this will take. If it is wrong, next day is turns on the heat earlier or later. As the weather changes, it gradually adjusts. If the weather changes fast, it may be a day or 2 behind. Not perfect.

    But how many people think to reprogram their thermostat to come on 30 mins early tomorrow morning because the weather dude(ette) on TV said there was a cold snap coming? So my thermostat is a good balance of comfort and energy saving. I love this feature too. (And if you have one of these, you need to remember to set the times differently than if you didn’t.)

    c) For most people, a 5 day / 2 day ‘stat is easier to set. And on the 80-20 principle, less-is-more, better to do something, etc. I recommend this.

    However, my kid comes home earlier on Wed, and I always go out on Friday evening, get home late on Monday, etc., so I have a 7 day thermostat. I can have different settings for every day. It has a “copy” function, so I copied Tuesday settings to Thursday, since my schedule is the same those days. For me, best of both worlds.

    Comment by Glyn Garside — November 19, 2012 @ 3:54 pm

  58. What an informative and civil discussion! So much good info here.

    I’ve been looking for ways to finally convince some stubborn friends that yes, turning the temperature down at night will use less energy. It’s amazing how some people with no understanding of thermodynamics can nevertheless still argue against it.

    Anyway, regarding one guy’s comment about there being hundreds of small changes we can all do, I’ve written a simple book about this and I’ve got it on the Internet available for free download. (http://greenifyyourlifebook.blogspot.no/)

    Feel free to take a look and let me know if you have any comments / suggestions, and of course pass it on :)

    Comment by Victor — November 24, 2012 @ 9:43 am

  59. Check out http://www.ecobee.com
    I have one of their thermostats and it is has “Smart” recovery, outside temperature and it learns your homes response to the weather and how rapidly your system heats/cools. You can set it to be 70 at 5am and it will determine what time it needs to come on and it will be at 70 at 5am.

    There is a full compliment of data and it can be controlled from any Internet based computer and smart phone.

    Comment by Charlie — January 5, 2013 @ 5:40 am

  60. Hi all, so here is my (non-scientific) opinion, and to me….it is the most easy to understand.. in my head, let me try to explain…
    For my typical (winter) work week, I leave the house at 7am and return home at 5pm, my “comfy zone” temp is set at 70 F while I’m home, so… I set my T-stat to 60 F while I’m at work, starting at 7am, and 70 F at 4pm (this gives my house an hour to warm up before I get home) outside temperature is 18 F, (Idaho) ok so the inside temp drops down to 60 F, and there is a 7 degree differential I believe, so once the temp goes down to 53 F the furnace kicks on and warms the house back up to 60 F then shuts off…back down to 53…kicks on…back up to 60 shuts off etc. This same thing is happening when I’m home…70 F…drops down to 63…kicks on…back up to 70…shuts off…back down to 63 etc.
    So my point is, the furnace/energy is still being used throughout the day even when you’re not there, it’s still running, just 10 degrees cooler. You can set the T-stat down to 40 F, or 30, as long as the outside temp is 18 it will get down to 30 F in your home. I sure hope this makes since, cause like I said, in my head, this is a no-brainer…wait, what?

    Comment by Mark M. — January 15, 2013 @ 7:22 pm

  61. Mark M — thanks for the comment.

    I hope your explanation helps — it’s a good way to think about the problem.

    For many, the logic is far from a no-brainer, and that’s largely because the actual science is not quite as simple as all that (as I wrote about last year in another post.)

    Maybe even simpler is this:

    You turn your heat down during the day when you’re at work, and turn it back on before you get home so your house is comfy. One day you get the flu so come home at noon to your cold house: you crank up the heat to “comfy” for the afternoon. Compared to a normal day, does your boiler/burner run longer, the same, or less?

    If it runs longer (hint: it does), you use more energy.

    Thanks for your comment!!

    Comment by Tom Harrison — January 16, 2013 @ 9:01 pm

  62. One item not noted in the cool down/warm up situation is house damage. I’ve noticed more nail popping in my drywall when I cool down too much (or fast) to below 62 F. when -20 F. outside. Plus moisture could also be an issue with cooling down too fast/much. Anyone heard of any research on cooling rates vs home damage? I’ve used a 5 time period thermostat & it seems to have lessened nail pops.

    Comment by Ronald Christopherson — January 29, 2013 @ 6:36 pm

  63. Hi Ronald,

    If your home cools fast, you may need to evaluate the building envelope to find out why. My house was built in the 1840′s and I have had a programmable T-Stat in it for 20 years with no noticeable house damage.

    Comment by Charlie — January 30, 2013 @ 12:37 pm

  64. Tom,

    I actually ran my furnace at a steady setpoint for one night and the next night the temperature and wind conditions were the same. The 2nd night I set it back to 50F. Although the home did not drop to 50F, there was a good drop. My burner runtime was 40 minutes less on the programmed setback night. The time period was from 10PM until 730AM when another setback occurs.

    The Ecobee TStat has a downloadable csv file that gives you all of the parameters that you would ever want. The data on your web portal is updated at 5 minute intervals and furnace run time is reported in seconds.

    Comment by Charlie — January 30, 2013 @ 12:41 pm

  65. Hi Tom, thanks for replying to my statement, and I would like to “attempt” to answer your question about the furnace “staying on longer if I come home earlier in the day”, not trying to be argumentative, but if my thinking is wrong, I gotta figure this out. I believe that the furnace does not stay on longer…I just turn it up…sooner. so instead of it coming up to 70° at 4pm, I turn it up to 70° at noon, now once it’s reached 70°, the cycle on/off time will be the same as when it was 60°, or any other normal days. And btw, my thermostat differential isn’t 7 degrees like I thought, it’s more like 2 degrees. Ok so maybe I’m looking at this the wrong way, perhaps its the “therms” in the heat that the furnace is producing, that is drawing more “energy”? so obviously 70° heat will produce more therms than 60° heat, and isn’t that how the gas company calculates payments ?

    Comment by Mark M. — January 30, 2013 @ 1:31 pm

  66. With regards to nail pops, I have also been told that letting the temperature in the house drop to low can lead to cracks in the walls and ceiling, due to different degrees of shrinkage during cooling and expansion during reheating of the various structural elements in the house. Is this really a concern?

    Comment by David — January 30, 2013 @ 4:51 pm

  67. We installed a Honeywell wifi thermostat in our church sanctuary and its been great in many ways. The convenience of being able to modify the schedule remotely is fantastic. We typically keep the temp at 50 in the winter except for Sunday morning and evening. The unit learns when to start to ensure its exactly 68 when we walk in Sunday AM, regardless of outside temp. Meanwhile, the other 3 dumb programmables need to be adjusted to earlier start times the colder it gets. One thing we could use is a smart wifi stat that has separate fan schedule (this one has ON, OFF, or AUTO (when heat is on), as we have a large open space, and running the fan longer would help move the air around. The Honeywell also does not have usage tracking to see how often the furnace cycles. Will the Ecobee do these two things? How about any others? thanks!

    Comment by Bob — January 30, 2013 @ 7:54 pm

  68. Just to echo the comment half way down about programmables and heat pumps….not always a good idea, and usually not a good idea with a geothermal/ground source heat pump. With oil and gas, there is typically only one stage of heat. No matter how high you turn the thermostat,or how much of a set back it’s recovering from, the heating uses a constant amount of energy. Not so with heat pumps. They are often sized very closely to the space they are heating. Raising the temp by more than a few degrees, or trying to recover from a large set back, will often engage auxiliary heat strips, powered by electricity, negating any savings from the heat pump.

    From experience in my home with a geothermal system, having setbacks in winter caused second stage and many times aux heat to engage, costing $6 or $7 per day to heat the home. Now I’ve locked the programmables at 70f, and the usage is about $3 to $4 per day.

    Home is in bucks county, pa, 2000 sq foot, two story. Cinder block 1st story, new full 2nd story in 2010.

    Comment by Stuart — March 9, 2013 @ 9:37 am

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