I moved from California to Montana 5 years ago, and every winter I struggle with how to set my thermostat at night.
I don’t care how cold it gets at night since I have a heated bed, but the last article I read said that forcing your heating system to heat a house 10 or more degrees in the morning was 1) overworking your heating system, and 2) more expensive than just turning the temperature down a few degrees and letting it cycle throughout the night.
We keep the house at 65 degrees during the day, and if I turn off the heater completely the house will cool down to 55 degrees by the morning. The temps at night routinely drop to below 0 during the winter months.
I have a 3,500 sf house that is well insulated, except for a doggy door that leads into an unheated garage, and a ground source geothermal heat pump. If the temperature drops too low the system will initiate “emergency heat” which I think means electric heating coils which is costly.
So should I do what I am doing now, drop the thermostat to 63 from 65 and let it cycle throughout the night, or turn off the heater completely and let it struggle, as in run for an hour, to get the house up to temperature in the morning?
It is a cold hard law of physics that your lose less energy by letting the house get colder - heat transfer is directly proportional to the temperature difference between inside and outside. Less energy lost means less energy to replace, so other things being equal you should always save money by letting the house get colder and heating it back up. Other things are not necessarily equal.
I don’t know that I’d call having a heating system run for an hour “struggling.” That’s just running in my books, but then my heating system is radically different from yours - radiators fed by a circa 1926 boiler, originally coal-fired but with a gas burner retrofit. To make up a 3C setback on a cold day (by Saskatchewan standards) can easily have the circulation pump running for 3 hours, though the gas wouldn’t be going that whole time once the system was up to temperature. I’m pretty sure my system is more efficient (or rather, less inefficient) when running for extended periods, though, so I kinda intentionally set things up so that it does.
That said, I’m not sure why having a heat pump running for an hour would be less efficient. I think it should have a small efficiency gain if it’s heating a colder room (greater temp difference in the heat exchanger), so unless the compressor duty cycle doesn’t like long continuous runs I don’t see the problem. Obviously tripping emergency heating coils sounds like a bad thing.
you ought to be able to look up your system online and see what the manufacturer recommends. I have a well insulated house too and keep mine about 65-68 all the time. If I had a heated bed I don’t think I would ever get up and go to work…
I have a geothermal heat pump in central Missouri. My installers said to set it where I want it and don’t set it back at night. If the desired temp is more than 3 degrees higher than the actual temp the system will run the electric coils until the temp are within the 3 degree difference. After that it will just run the compressor system.
Mine is a Water Furnace system and yours may not work exactly the same. It may be possible to over ride the electric coils. I’d suggest talking to you HVAC guys and explain what you want to do and get their advice.
You haven’t told us waht your goal is: minimum wear & tear on equipment, minimum energy consumption, minimum spending in dollars, or some compromise between spending & comfort.
Lowest cost. My preference is to turn it off at night, but I keep reading that the emergency heat mode is the most expensive, so I guess keeping it running on and off all night, even though I don’t need the heat when I am sleeping, is the cheapest way to go.
No, I mean, can you set the temperature to vary on a schedule? For example, my weekday schedule has the temperature set to 17 (sorry, too lazy to convert to F) overnight, bumped up to 19 for breakfast, back down to 18 during the day when I’m off at work, then up to 21 for when I get back. I don’t touch the thermostat to make it do this.
Whenever someone says that it is more economical to keep the thermostat at the same temperation all night I ask them if they were baking a cake before they went to bed and plan to bake biscuits for breakfast, would it make sense to keep the oven at 375 degrees all night long?
Of course not.
But that said, wear and tear on the furnace (or heat pump) is not factored in.
But I do know that I could not sleep at night if I did not turn the thermostat down. Awake/At home setting = 65-66 deg. Sleep/Away setting= 60 deg
They make thermostats that allow you to set the temperature at which your backup electric heat will come on.
So you could set it at 55 degrees as a fail safe incase your compressor failed when you weren’t home. The rest of the time you would only be running your compressor.
Or you could simply turn off the circuit breakers to your electric heat.
Personally, if I had your setup I would leave it at one temp, perhaps setting back a couple degrees at night.
I don’t really think that’s a valid comparison because the oven doesn’t have an “economy” mode. If you could run your oven in a fashion that would only use 10% of the energy in a special mode and save your having to preheat the oven and save your valuable time it might make sense to do so. Check out Aga cookers. They are on all the time.
And that’s what I do. 65 degrees during the day and 63 degrees during the night. It’s discomforting for me because I hear the heater cycle all night long, and heating a house that doesn’t need to be heated just seems wrong… but it’s the only way to ensure that I am never in emergency heat mode.
The key I guess is how much energy does it take to keep the house at 63 degrees through the night versus raise the house temperature from 55 degrees to 65 degrees, day after day. I wish I could somehow measure this and know for sure.
Yes, my thermostat can do that too. In the summer I have it going up and down at different times, but I don’t need to run the heater at night of course.
You can be quite confident that the former requires more total heat energy to be delivered to your house. As has been noted, vagaries of particular heating systems can affect the cost of delivering that heat energy.
If your heating system is electrically driven (e.g. a heat pump), you could check your electric meter each morning to see how much you consumed in the prior 24 hours. But for accurate comparison, you must then correct for temperature and wind …
It seems to me that you need to find out exactly what triggers your system’s emergency heating coils. If they’re simply tripped by what is in effect a separate thermostat, can you set that to say 50? Then let the nighttime temps fall to 55 and who cares if the compressor takes an hour in the morning to bring temps back up. Or is the emergency heat tripped by a high difference between actual temp and set temp? In this case you’ll have problems because when the thermostat starts calling for 66 again and it’s actually 55 it’ll decide it needs the emergency coils to achieve this in a timely fashion. In that case, depending on your thermostat, you might be able to use multiple setpoints to ramp temps back up in the morning - 58 at 6:30, 61 at 6:50, 64 at 7:10, or whatever. Then it’s never seeing a 10 degree difference, just 3 degrees at a time.
But really, what you’re saying is that you’re happy letting it get cold overnight, and this should result in lower heating costs, provided that you can heat the house back up in the morning using only the heatpump. So you have to find out how to make your system heat the house back up using only the heatpump.
Whatever energy you save by turningyour heat off at night you lose when you turn
it back on in the morning to get it back up to temperature.
So if you hear it cycling at night just think that its just that much less it will have to run in the morning:)
The savings is just as Gorsnak said in post 2, Its the difference between the outside temp and the inside temp, thelower that number,the less heat loss you will have.
If you have to, replace your thermostat with a better one that is smarter about when it activates the emergency heat. I bet the heat pump is driven by 6 wires or so to the thermostat, and there are dozens of electronic thermostats you can purchase from amazon that will be able to connect to it.
Quite clearly, you lose the least energy if you let the temperature fall during the night. But least cost is another matter. It would be a tradeoff involving knowing the cost of operating the heat pump vs. the heat coils. The best would be to fix the system so that it would require a 10 degree difference before the electric heating came on. But this would not work well if the electric heating was needed during the day time. What you need is a complex thermostat that would use one difference at night and a different one during the day. Does the house temperature really fall by 10 degrees during the night?
As for wear and tear on the equipment, a pump is not a person that requires regular rest. It will wear out when it wears out, which I think depends only on total usage. If it required rest for five minutes in every hour, then presumably would be designed to turn off for five minutes in every hour. Sounds like an old wive’s tale to me.
I am not an HVAC expert, and it sounds like you need to talk to someone who is very familiar with your system and thermostat, or do some real research on both. If you have a ground source geothermal, then I presume it’s pretty new and should be pretty advanced/sophisticated. The worst thing you can do is actually turn the system off and then back on, because it will for-sure turn on the resistance coils to heat up the house. From what I know about geothermal, I would be tempted to set it back only a few degrees at most. Allowing the system to maintain a consistent temperature will likely be more energy efficient as well as more comfortable.
