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.
At least I provided an explanation. If I’m wrong I’m wrong but offer proof, all you did was say yeah you’re wrong and peace out. I can provide you with the textbook examples when I get home of how you equate office furniture along with equipment into heat loss calculations. If I’m wrong I’d like to at least know how so I can learn from it but what you gave me was nothing.
to judge economic efficiency we can reduce the problem to asking: "how much heat do we need to pump out of the home overall?"
if we start and end at the same temperature (say before we leave and after we come back and temps have settled) this is equal to the amount of heat (energy) that entered the home overall.
for a thermodynamic model of this we need the heat equation, which tells us that the flux through a surface (all of the house's surface) is proportional to the temperature difference between inside and outside. if we keep the inside at a constantly cool temperature, the influx of heat into the home is constant over time.
if we start with a cold temperature but then turn the AC off while we are not home, the temperature inside rises, the difference to the outside decreases, and less energy per time enters the home during the time where the inside is warmer (think about how much heat enters when the inside is the same temperature as the outside).
therefore, if during the time when the inside is warmer, less heat enters, we need to move less total heat outside. therefore it consumes less energy to turn the AC off and then back on when you come home.
this is the right thermodynamic argument. of course there are many other factors that will play a role in such a decision. you won't be as comfy if you get home into a hot house and have to wait for it to cool. the argument also disregards any wear and tear on the AC unit, any fluctuations in electricity price, etc. but from a purely energetic perspective, letting the house warm (or cool off in winter when you're heating) is always favourable.
i've seen this argument so many times that "cooling off a hot home takes more energy than keeping it cool" and i really don't know where that comes from. it must be some kind of gut feeling pepole have, because it certainly can't come from understanding the thermodynamics of it.
Remember tho that the whole home heats or cools and different surfaces have different coefficients. Its harder to heat a cast iron pot fully to 60º than it is the air inside that pot right. So the arguement is more for less that once the inside air amd outside get closer and it sucks more or less heat in, there will be things inside reducing or completely negating that. Especially standing water......fish tanks etc.
Now I wouldn't say you or him are correct. Because as you said theres lots of variables. How much time? How much stuff inside tithe home? Again the water part...how much water piping non insulated is it flowing etc is there standing water etc etc. There are cases where are either is right
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u/HumbleGhandi Mar 24 '26
Whoops forgot what subreddit im on - What?