Reply to Dual fuel (heat pump with auxiliary gas furnace) - what settings for maximum efficiency and/or cost savings?

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Reply to "Dual fuel (heat pump with auxiliary gas furnace) - what settings for maximum efficiency and/or cost savings?"

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[quote=Anonymous][quote=Anonymous]
The real benefit when turning the heat down is how long it's at equilibrium at the lower temp before it changes back - that's where the savings are. The cost to heat back up was your savings from letting it cool down - those are about a wash.

[/quote]

Right, if you don't run the heat for a few hours, you lose somewhat less heat by having the difference between your interior and outside be lower. But to the extent the house itself cools off, you have to put that heat back when you warm the house up again so that's a wash.

With heat pumps though it gets a little trickier, because the efficiency of a heat pump varies depending upon the outside temperature. The classic setback thermostat program is to turn the heat down when you go to bed, and have it come back on an hour or two before you wake up. But that's typically the time of day when it's coldest outside, and the heat pump is least efficient. So you may not even end up saving money because you run for fewer hours, but at lower efficiency.

Note that for cooling it can be the opposite. If you turn off the AC when you leave in the morning, and have it turn on again a few hours before you come home, you avoid having it run during the hottest part of the day, when it's least efficient. Also, AC gives better dehumidification if it runs continuously, having it run straight for a couple of hours will give better comfort than the same amount of cooling coming from cycling on and off during the day. [/quote]

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