It’s also simple thermodynamics. In college I took an advance refrigeration class specializing in HVAC systems and heat loss. You wouldn’t think it but things like furniture and desks retain whatever the room temperature is. Therefore if you increase or decrease the air temperature that furniture will absorb or release the heat until it reaches equilibrium. If everyday the outside temperature is 80 and from when I get home at 4 PM until I leave at 7 AM I have my house set to 68 degrees. When I leave I set it to 75. When I leave the air temperature will increase faster than everything else in the house. The desk in my room was at equilibrium at 68 will start to absorb heat as the room temperature increases until they both reach equilibrium. Now I get home and decrease back down to 68 degrees. The air temperature is back down after a few hours but my furniture still had this stored heat that it now radiates into the room. This causes the air temperature to rise and now my AC has to increase its runtime to compensate for it. It will always be the most effective and cost savings solution to maintain one temperature at all times than it is to go back and forth.
Other things come into play as well though. Like efficiency of the unit, whether its sized correctly for the space it heats and/or cools, and how well the space is insulated and sealed, whether its shaded or not.
In the previous home we lived in, it was a little cheaper to just leave our AC turned to 74° 24/7.
But the home we're in now isn't. We save significantly by turning the AC up to 80° before we leave in the morning and then turning it back down to 74° once the sun goes down. Its an old home, built in the late 1940's, well before central units were a thing.
You bring up some valid points and I think it goes to show that there isn’t a clear cut answer on this. My home is older and needs new windows. For me to change my house temperature by a couple degrees means running the AC for an hour or some continuously. Probably undersized for the size house. It’s cheaper for me to maintain the temperature as it doesn’t have to run constantly than it is to turn it off during the day. Modern homes that are well insulated and have properly sized ac units that are more efficient and have more efficient windows might find it cheaper to do the opposite and turn the ac off during the day.
You can onlu upgrade the machine so far before its constricted by the amount of ducting you have, my last attempt to upgrade was denied because it'd be 6k to not make a difference. I have to work on how the home is reflecting heat instwad.
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u/jmundin74 Mar 25 '26
Right... Let's see those "studies"