Larry asked in Science & MathematicsWeather · 9 months ago

# ac temps vs heat temps?

My wife and I are "discussing" whether 77 degrees we set the AC in summer is different than 77 degrees with heat in the winter.  Any help?

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• 9 months ago

They can feel different, for sure. How much different tends to depend on the place.

The idea here is that the thermostat location is the place where temp is at the target value.  In summer, heat tends to enter from outside, so the coolest spot in the house tends to be at the location of the thermostat (heat is coming in at the periphery so the center is the least hot spot).  The reverse tends to be true in winter, because cold is attacking the periphery, so the outer reaches of the space will be colder than the central location of the thermostat.

Also, on top of it all, the system stays off until change triggers it to turn on.  In summer, change will be toward hotter, so the thermostat temp is the MINIMUM that you will experience. The opposite is true in the winter, when the thermostat temp will be the MAXIMUM.

You are always more than or equal to the thermostat in summer, but less than or equal to the thermostat in winter, so while the temperature of the setpoint is always the same (in this case), internal temperature variations are not the same at all.

Also, there are a number of other things which contribute to our perception of temperatures. We tend to habituate to the cold in winter (ever notice how 32F is cold in the fall yet warm in spring?) and heat in summer, and humidity matters a lot to how we feel warm, as does the presence of drafts (winter) or breezes (summer); even how we are dressed matters.

It can even be that AC in the summer seems cooler even if set to a higher temp than heat in the winter set to a lower temp. My house is like that, I use 24C in summer (AC) and 21C in winter (heat), to make the house feel about the same to me.

(EDIT: I ought to have added that sometimes the cool from AC makes the bulk of the house colder than the setpoint, or heat makes the bulk of the house warmer than setpoint.  My house has forced air so the heat and the cool tend to overshoot the setpoint in most rooms (not all). )

• no
Lv 6
9 months ago

They're basically the same.

• 9 months ago

77ºF is 77ºF ... how could you think otherwise.

However, the room temperature and humidity could be a few degrees different as thermostats are not very accurate (and you are comparing the one for the heater with the one for the AC), and they all have a dead band of a few degrees on each side of the set point.

And, in the winter, even with a perfect thermostat will result in a temperature that starts at the set point at the thermostat itself and grades down in temperature as you move from that point to the coolest point in the room, probably near a window. So you could see the thermostat setting, minus perhaps 3º, at the thermostat, grading down to 10º lower at the window.

In the summer, the opposite, temps being lowest at the thermostat of the AC and warmest at a door or window.

• Anonymous
9 months ago

wrong forum.  belongs in Home & Garden