The Money Mustache Community
Learning, Sharing, and Teaching => Ask a Mustachian => Topic started by: singpolyma on October 18, 2018, 04:22:59 PM
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It's that time of year again! (If you live in the more-northern parts of the Northern Hemisphere.) We run on a pretty simple schedule: 19C all day and 15C all night. Manually set to 15C when leaving the house during the day and back to 19C when returning.
One thing I've been wondering is if there are good resources on how low to go at night / when away? Obviously it might be high enough to keep the pipes from freezing, but we're far above that. However if the temperature is allowed to fall too much then the energy needed to get it back up to 19C might be so much that the cost offsets the time spent not heating. Not sure where the break point on this tends to be.
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For those of us in the USA 19c is 66.2f and 15c is 59f.
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It's that time of year again! (If you live in the more-northern parts of the Northern Hemisphere.) We run on a pretty simple schedule: 19C all day and 15C all night. Manually set to 15C when leaving the house during the day and back to 19C when returning.
One thing I've been wondering is if there are good resources on how low to go at night / when away? Obviously it might be high enough to keep the pipes from freezing, but we're far above that. However if the temperature is allowed to fall too much then the energy needed to get it back up to 19C might be so much that the cost offsets the time spent not heating. Not sure where the break point on this tends to be.
There há no break point... You don't use more energy to bring back from 45f to 65f,than if you maintain a set point of temperature constant.
Away temperatures I turn off my heat and have emergency power on if temp inside the house falls below 45
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One thing I've been wondering is if there are good resources on how low to go at night / when away? Obviously it might be high enough to keep the pipes from freezing, but we're far above that. However if the temperature is allowed to fall too much then the energy needed to get it back up to 19C might be so much that the cost offsets the time spent not heating. Not sure where the break point on this tends to be.
45F is reasonable in most areas, though if it's particularly brutally cold and you have pipes in exterior walls, 50-55F might be wiser. I've got exterior pipes and outside gets to -10F, so I don't like it below about 50F in the house.
If you're heating with a gas furnace or electric furnace, there's no such thing as "too much energy to come back up to temperature." Temperature loss through walls is (for a good handwave) directly proportional to the temperature difference, so you lose less heat from the house at 50F internally than 65F internally, and that means less energy to heat with.
Heat pumps with backup coils are a slightly different case, though if you're using a "dumb" thermostat with them, you'll save money switching to something smarter. The dumb thermostats have a little panic attack and turn on the backup coils (resistive heating elements) any time there's more than a few degrees difference between "set" and "actual," which leads to very silly things like turning on the backup coils in the spring, when it's 70F out, and you want to "bake the house" to drive off VOCs before moving in.
A smarter thermostat can run the heat pump more efficiently, and start early to bring the temperature up. Our heat pump starts to struggle around -5 to -10F, and will run the backup coils more in the morning. This winter, I'm going to play with leaving the night time temperature up a bit higher and turning the backup coils off. In theory, it's a bit more efficient to hold a few degrees higher overnight with the heat pump churning away at a 1.5-2 COF than having to run the backup coils in the morning.
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One thing I've been wondering is if there are good resources on how low to go at night / when away? Obviously it might be high enough to keep the pipes from freezing, but we're far above that. However if the temperature is allowed to fall too much then the energy needed to get it back up to 19C might be so much that the cost offsets the time spent not heating. Not sure where the break point on this tends to be.
45F is reasonable in most areas, though if it's particularly brutally cold and you have pipes in exterior walls, 50-55F might be wiser. I've got exterior pipes and outside gets to -10F, so I don't like it below about 50F in the house.
If you're heating with a gas furnace or electric furnace, there's no such thing as "too much energy to come back up to temperature." Temperature loss through walls is (for a good handwave) directly proportional to the temperature difference, so you lose less heat from the house at 50F internally than 65F internally, and that means less energy to heat with.
Heat pumps with backup coils are a slightly different case, though if you're using a "dumb" thermostat with them, you'll save money switching to something smarter. The dumb thermostats have a little panic attack and turn on the backup coils (resistive heating elements) any time there's more than a few degrees difference between "set" and "actual," which leads to very silly things like turning on the backup coils in the spring, when it's 70F out, and you want to "bake the house" to drive off VOCs before moving in.
A smarter thermostat can run the heat pump more efficiently, and start early to bring the temperature up. Our heat pump starts to struggle around -5 to -10F, and will run the backup coils more in the morning. This winter, I'm going to play with leaving the night time temperature up a bit higher and turning the backup coils off. In theory, it's a bit more efficient to hold a few degrees higher overnight with the heat pump churning away at a 1.5-2 COF than having to run the backup coils in the morning.
+1 Great explanation of heat loss and energy-sucking backup resistance heating. When I lived in a colder climate with a heat pump, I left it set at 68 degrees all the time. Reading my dumb thermostat manual, if there was a two degree difference between set temp and actual temp, it would kick on the coils, and there was no option to disable that. When I had gas heating, I would set it to 50 degrees during the day and 68 when I was home.
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72 degrees
I work at home and don't mind paying $160/mo for Gas/Electric.
I hate being hot and working in Maryland summer humidity.
I hate being cold and typing on the computer with cold hands.
I am tall and thin and don't have blubber to insulate me.
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Reading my dumb thermostat manual, if there was a two degree difference between set temp and actual temp, it would kick on the coils, and there was no option to disable that.
I'm not generally a fan of the "Internet of Things" devices, but I am convinced that the Nest thermostat paid it's cost the first winter of operation with a heat pump for exactly that reason - it would light off the backup coils only if absolutely needed (or if the defrost cycle called for it).
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64F day, 58F night.
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68-69 constant. Older cold House!