I've been researching this and have landed on just leaving it on a reasonable temperature. We used a geo-fenced smart thermostat with our boiler in a cold climate and were 100% for turning the heat down in most circumstances. Now we are in hot humid NC with a heat pump, a dog, no insulation, and a spouse that works from home. Outside is never more than 30 degrees from our set temp (77 cool, 62 heat) and we need dehumidifying in the summer. I've not installed a smart thermostat yet (need to run a C wire), but given the circumstances and slow temp changes and my research, I'm not inclined to set the temp up/down further, except when on long trips. (My lovely neighbor takes care of our dog for free while we are away, but she sets the temp down to 66 (for the dog?) and doubles our electric bill, but I can't question her about it!) I am looking at attic insulation once I've done some electrical work and an attic exhaust fan plus some air sealing, but am not seeing a huge need as our electricity is <$150/month and no gas, which makes solar less compelling (also not expecting to be here terribly long).
With your setup I think just leaving it set makes sense. What you really want to get there is a heat pump water heater (HPHW). That'll dehumidify and cool your house and give you free hot water as a byproduct! See my thread on my new one here.
Looks compelling for sure. Our resistance HWH was put in right before we bought the house a year ago. Mostly my wife wants to go tankless to reclaim on of our two closets, so I don't think I can sell her on a HPHWH!
Also, I appreciate the transportation advocacy and civic action on your Twitter!
The BTU savings doesn't include the amount required to rewarm the house so the savings is a bit less. Any chance you can do a spreadsheet showing the kilowatt hours or cubic feet of natural gas required to rewarm the house?
This can be kind of tough to wrap your head around. Think about how the cooling house is not running heat at all while cooling down, but the house that is kept hot is constantly running its heater to maintain the set point. We could measure, or calculate all of that, but in the end it doesn't matter because all we really care about is how much heat is LOST from the home to the outside. This lost heat is the real difference between the two, because they had the same amount of heat trapped inside before the thermostat was lowered and they again have the same amount of heat inside once the thermostat has been raised once again. This is a scenario of basically doing more math to get the same result.
The main thing my math is missing is the heat lost from the home while it is heating back up, but this is very small. You could find this by basically graphing the temperature as it goes back up, converting that temperature to BTU heat lost and then integrating under that curve. That seems overkill though as it will only take a few minutes to heat back up generally. I avoided this by simply assuming that the home rises back up to the thermostat set point the instant it is changed. This fails to quantify some savings because in reality it takes minutes to reach that and the temperature of the house is lower while it is warming and thus heat loss is less. This is minimal compared to the energy saved over the hours the setpoint was lower and is basically a rounding error so I didn't calculate it.
I've been researching this and have landed on just leaving it on a reasonable temperature. We used a geo-fenced smart thermostat with our boiler in a cold climate and were 100% for turning the heat down in most circumstances. Now we are in hot humid NC with a heat pump, a dog, no insulation, and a spouse that works from home. Outside is never more than 30 degrees from our set temp (77 cool, 62 heat) and we need dehumidifying in the summer. I've not installed a smart thermostat yet (need to run a C wire), but given the circumstances and slow temp changes and my research, I'm not inclined to set the temp up/down further, except when on long trips. (My lovely neighbor takes care of our dog for free while we are away, but she sets the temp down to 66 (for the dog?) and doubles our electric bill, but I can't question her about it!) I am looking at attic insulation once I've done some electrical work and an attic exhaust fan plus some air sealing, but am not seeing a huge need as our electricity is <$150/month and no gas, which makes solar less compelling (also not expecting to be here terribly long).
With your setup I think just leaving it set makes sense. What you really want to get there is a heat pump water heater (HPHW). That'll dehumidify and cool your house and give you free hot water as a byproduct! See my thread on my new one here.
https://twitter.com/ProfitGreenly/status/1566436175677722624?s=20&t=csBrcHi79XLg1PTNyh7Tog
Looks compelling for sure. Our resistance HWH was put in right before we bought the house a year ago. Mostly my wife wants to go tankless to reclaim on of our two closets, so I don't think I can sell her on a HPHWH!
Also, I appreciate the transportation advocacy and civic action on your Twitter!
The BTU savings doesn't include the amount required to rewarm the house so the savings is a bit less. Any chance you can do a spreadsheet showing the kilowatt hours or cubic feet of natural gas required to rewarm the house?
This can be kind of tough to wrap your head around. Think about how the cooling house is not running heat at all while cooling down, but the house that is kept hot is constantly running its heater to maintain the set point. We could measure, or calculate all of that, but in the end it doesn't matter because all we really care about is how much heat is LOST from the home to the outside. This lost heat is the real difference between the two, because they had the same amount of heat trapped inside before the thermostat was lowered and they again have the same amount of heat inside once the thermostat has been raised once again. This is a scenario of basically doing more math to get the same result.
The main thing my math is missing is the heat lost from the home while it is heating back up, but this is very small. You could find this by basically graphing the temperature as it goes back up, converting that temperature to BTU heat lost and then integrating under that curve. That seems overkill though as it will only take a few minutes to heat back up generally. I avoided this by simply assuming that the home rises back up to the thermostat set point the instant it is changed. This fails to quantify some savings because in reality it takes minutes to reach that and the temperature of the house is lower while it is warming and thus heat loss is less. This is minimal compared to the energy saved over the hours the setpoint was lower and is basically a rounding error so I didn't calculate it.