How Thermostat Setbacks Save Money | Ask This Old House
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- เผยแพร่เมื่อ 14 ต.ค. 2016
- This Old House plumbing and heating expert Richard Trethewey explains how adjusting the thermostat can reduce energy consumption and save you money. (See steps below.)
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In most circumstances, thermostat setbacks will save energy. However, there are a few situations in which setbacks may not make sense, including heat pumps with electric resistance back-up, radiant systems with long recovery times, and homes with very tight building envelopes.
Steps for How Thermostat Setbacks Save Money:
1. Temperature setback is the act of adjusting the thermostat while you’re asleep or away from the house.
2. Lowering the thermostat in winter keeps the house colder, but the furnace doesn’t kick on as often, so you use-and pay for-less energy.
3. In summer, raising the thermostat makes the house warmer but prevents the air-conditioning system from running all day, which lowers your electrical bill.
4. There are several types of thermostats, including manual single thermostat, programmable clock thermostat, and smart thermostat with motion sensor that you can access via a smartphone.
5. R-value is the amount of heat that transfers from the inside of a home to the outside during the heating season, and from outside the home to the inside during the cooling season.
6. Delta T refers to the temperature difference reflected by heat transfer.
7. Imagine it’s zero degrees outside and the thermostat is set at 70 degrees, which is called the target temperature.
8. If you lower the thermostat to 60 degrees, less heat will transfer to the outside because there’s less of a temperature difference between the indoor and outdoor temperatures.
9. According to the Department of Energy, for every degree you lower the target temperature, you’ll save 1% of fuel over an 8-hour period. In the above example, you would save 10% on your heating bill.
10. The amount of energy it takes to reheat a home will always be less than if you didn’t lower the thermostat and the furnace kicked on and off all day. The same is true in summer with air-conditioning costs.
11. Don’t use a clock thermostat with an electric heat pump, super-insulated house, or radiant-heat system.
For more information, visit: Energy.gov [www.energy.gov/energysaver/th...]
Expert assistance with this project was provided by Nest Labs [bit.ly/36i4bPX].
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How Thermostat Setbacks Save Money | Ask This Old House
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Great explanation….thank you!
Could address impact LEEDS heat pumps and ducting installed to LEEDs requirements. Why new homes have multiple Heat pumps. Best cold air return locations. How adding additional attic insulation above local code impacts heating cooling costs.
I have a "Honeywell" thermostat. I really don't need my whole aprtment heated as I live alone. Can I just keep the setting @ 56 and run a small personal fan when needed to save money? I heard some say lower it to 55-57 during night and bring back up to 62-68 during the day. Just wanted to know if I can keep it @ 56 to save the most money during winter rather than adjusting it daily and before bed? I'm not worried about pipes freezeing as it hasnt below 37 degress Fahrenheit yet.Thanks in advance!
If you set a thermostat to78. When does it turn on 79? Or is there a few degree swing?
I don’t think it makes much sense for me. I have an old brick house that I have sealed fairly well with decent windows. It takes hours and hours to cool down and hours and hours to heat back up. I have hot water radiators and thick plaster walls and ceilings. It’s closer to a radiant in floor situation than a forced air system with super Leaky envelope.
My question is:
How can I figure out how much more I’m spending if I leave my thermostat at 69 vs 72? If it’s only 3% more I’m doing it. Why live like an Eskimo? I guess I have to ask myself how much I support fracking... hmmm
Good work guys. As always there's nuance. But set backs help.
No one uses hot water when they're sleeping or at work. How can I save money using an electric water heater ? Can it be controlled to only provide hot water during those times it is needed ?
I use a timer. It's called "the little grey box". I bought it on Amazon for $47. I have my water heater come on for 1 hr, from 04:30 am to 05:30 am. That's all I run it for. I have plenty of hot water all day and night. I live by myself and it works out great for me. My electric bill is half of my neighbors. But I am very frugal using electric anyway. It was very easy to install.
Homestead Homie That sounds exactly what we are looking for. My wife and I only use hot water during our morning showers. What a waste of energy leaving the water heater on all day. The only concern is our dishwasher. It has a "hi-temp wash" setting which we always use but I don't know if the dishwasher uses hot or cold water to start. Thanks for the information. I wonder why This Old House hasn't discussed this.
Glenn Watkins
I still use my dishwasher, but not on a daily basis. Your dishwasher will still work just fine, it will just use the hot water you have. I turned my thermostat on my hot water tank down. So now I never have to turn the cold water on to make the shower nice. I just turn the hot water handle on and it comes out at my preset temp. You can also wrap insulation on your hot water tank to keep the water hotter longer. I should do a hot water temperature reading from when I get up, until I go to bed. Just to see how much the temperature difference is. Maybe check it every hour. Sounds like a plan! LOL! I will keep you updated!
Learned to turn the water heat temp down then it heats up when you use it more and doesn’t heat all night and Day but may get a few showers that aren’t super hot
Most are set a a scolding temp when you have to use cold with it if it gets turned down a few notches can save
See my wife thinks keeping the heat off saves during the cold months not really if it’s set around 69 to 65 it’s not gonna run as much just enough too keep your house a little warm
setting it back wont lose you energy when reheating.. but if you turn it off completely over night it can cost more
Depends on the heating system you have. Like he mentioned, if you have a heat pump with a backup electric furnace, the savings would be minimal.
There is no instance in which setting back your thermostat will not save energy. Literally none. Not one. Ever. Under any circumstance, with any system, any house, located anywhere. It's extremely simple physics. If you want it to be hotter inside than outside, you heat the structure. This will make the inside hotter than outside, so the building will loose some of its energy to the outside. It will always loose energy until the inside and outside are at the same temp. Now, the real trick is that the building will loose less energy when the difference between inside and outside is less. So, if you heat the building 10º less, or warm it up 10º outside, its the same impact. The longer you can minimize the difference between inside to outside, the less heat will be lost. In a house where the furnace comes on every ~5 minutes, you will have some savings even with a 10 minute setback. It's going to be nearly zero, and is kinda silly, but it WILL save energy.
Be aware, unless you are set to auto, setting the temperature back 10º does not cool the building off. It just means the system won't run, until the building cools 10º. If the building never cools down over the span of time you have the setback, you're not going to save much. What you want, is the building to be as cool as possible for as long as possible, since this means the least heat is lost to the outside. If the building performs very well, and you set the thermostat back 10º, but it only cools off 1º over hours, you won't notice any savings. That's not to say you won't save energy, you will, it just will be very little.
Of course the building always has to be reheated, but unless theres something very wrong with your system, it will NEVER cost more to reheat than it would have to maintain the temperature. This is especially true with high efficiency gas furnaces and heat pumps that take 15+ minutes to get near rated efficiency. You want those systems to run as long as possible, with the largest thermostat deadband tolerable. However, most heat pump systems are not oversized enough to recover from a massive setback in any sensible amount of time, and often the thermostat will kick in emergency heat if available. While you will still loose less heat, its probably not going to save you any money, and likely would end up costing more with some systems. Saving energy does not always save money.
Exactly like Frank said, and if you don't believe it, do a quick study at your house, track how many times in an hour your furnace or AC comes on and for how many minutes - then multiply that by 8 hours (equivalent of overnight), this is your baseline of regular energy use. Then turn off or way down (winter) the thermostat overnight and time how long the heat runs in the morning to warm up. We figured it out here and figured out that it's the equivalent of about 2 or 3 hours of cycles versus 8 hours of cycles that would've run overnight.
@@EricsiPhone I have a "Honeywell" thermostat. I really don't need my whole aprtment heated as I live alone. Can I just keep the setting @ 56 and run a small personal fan when needed to save money? I heard some say lower it to 55-57 during night and bring back up to 62-68 during the day. Just wanted to know if I can keep it @ 56 to save the most money during winter rather than adjusting it daily and before bed? I'm not worried about pipes freezeing as it hasnt below 37 degress Fahrenheit yet.Thanks in advance!
Funny thing here he's right but this is also misleading. Setbacks are a good idea for very leaky homes using a conventional ducted air handler (which is most of them). If the house is built tight its hit or miss if you'll save or lose energy using setbacks especially for split systems or radiant systems. Many very energy efficient heating and cooling systems depend on being able to spread out the load because they are not high load systems so they are less efficient if they have to be loaded all at once. Thats why this is misleading because really you save money doing this because your duct work is so incredibly inefficient its best to run the heating and cooling cycle when the outside temp is the most moderate. But if you're building a new home or a major retrofit it might be a better idea than setbacks to simply insulate your roof, insulate those ducts, etc.
Where is the anesthetic. Man
6 yrs later.. Covid... Now everything is double
Science Heresy! "one degree setback saves 1%"???
Depends on delta T! For example If it is 68 outside and you reduce from 70 to 69, you have changed delta T by 50%!! If it is 69 outside and you reduce setting from 70 to 69, you save 100%!
Typical government numbers that barely make sense for anyone. File that estimate with the 2000 calorie diet and the body mass index.
2nd hi this old house
It takes more energy to bring the house back up to tempertaure because the burner is on longer raising the room ten degrees than the half to two degree difference it raises it during a normal cycle.
That’s simply not true. Consider this example. If I keep my kettle boiling all day and night (cycling on and off as needed) will it use less energy than if I only boil the water for coffee in the morning? Obviously not.
Keeping a high temperature differential will always result in more energy use.
At a constant temperature the heat only works sporadically the heat has to run continuously which means more fuel is consumed during that time.