Question: We have an air-to-air heat pump. Is it still beneficial to lower the temperature every night? At one point we had heard it was not efficient to do that.
Marilyn, a Smart Choices reader
Mr. Tight Watt asked Randy Camblin, Camblin Mechanical, and member of the Iowa Geothermal Association, to answer Marilyn’s question.
Answer: Like its big brother the geothermal heat pump, an air-to-air heat pump spends a lot of its working time getting your house to the temperature you set. Therefore, once the house surroundings get to that temperature, it costs just pennies to keep the temperature at the set point.
Your goal as a homeowner of either type of heat pump is to avoid using the auxiliary heat (backup or second stage) as much as possible, because that is a more expensive source of heat.
Most setback thermostats operate in a time mode, so if the thermostat does not see a gain or drop in temperature in a certain number of minutes, it brings on the next stage. Excessive temperature swings will cause this to happen every time. So this part of the answer to whether it pays to lower your thermostat is “no.”
Most air-to-air heat pumps have a break-even point of approximately 20 degrees outside temperature. At this point, the energy in has the same value as the energy out. At this outside temperature and below, the heat pump mode will be locked out and the backup/auxiliary will take over. So if it will be this cold for a very long time, you COULD choose to set back your thermostat to keep the house colder and keep the backup heat off longer since you are already in that mode.
The problem is that most consumers do not know WHEN Mother Nature will warm up above 20 degrees! So short of sitting by your thermometer and thermostat to adjust it (the “yes” part), the answer is really “no.” You must also remember that if you time this adjustment incorrectly, your house will be cold when you get back into the air-to-air mode and it will turn on the backup heat anyway!
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