Fans vs. A/C at night?

My 2000 square-foot house has a typical heat pump central air conditioner.
But at night, I run two window fans to blow the night air through the house. This brings the temperature down from 78° to 74° in the morning.
Running two window fans all night presumably costs less than using the A/C to get down to 74 degrees.

Do you think this really saves energy?
I know I get some extra humidity in the house by doing this, and the air-conditioning will run more to dry that out. Any other factors or issues I’m not thinking of? Has this been discussed elsewhere?
(I guess tonight I could ditch the fans and instead use the A/C to get down to 74 degrees, and Sense could tell me how much the A/C used. Just thought of that.)

I’ve been thinking the same thing in my place. Maybe your thread will be the impetus for me to actually investigate and run the numbers. Though, I don’t think my bedroom window fan gets us down quite that low and I don’t have a temp. sensor in there to know for certain.

In my case, my window fan pulls a constant ~50W. AC pulls around 3kW, but I’ll only run it for an hour or so before bed. So, that’ll be more expensive but I’m curious of the actual cost differences. I’ll report back!

What kind of humidity are you dealing with? On a night which may be 70* yet 80% humidity I’d rather run our AC systems than suck in humid air I need to recondition in the morning.

I agree based in n my experience. I live in eastern Kentucky where humidity runs near 90%. If I allow the house to get humid, the heat pump first has to remove moisture before the temperature “feels” right. The thermostat may show the temperature at 72 but it will feel 76 due to humidity.
Another consideration is flooring. I have all wood floors. Keeping humidity at or below 50% is best for them. Letting the humidity fluctuate wildly each day can cause other problems that could potentially cost much more than the extra electricity used for the heat pump.

My 2 cents… Leave the air on set at 74. It will not run as much for the sun is down as well as the temperature. Set the manual fan switch at low or medium to circulate the air for the air conditioner will not run as much to circulate the air. My thermostat keeps track of usage in kwh for continuous fan. That way you can abandon it if the usage is too high. Also a portable dehumidifier during that time may help. Later…Gerry

One thing I would say regarding H-V-A-C, given I am in the midst of reading John Hix’s excellent and probably forgotten “The Glass House” (1974!), is that there is “no V in A-C”.

With apologies to simple energy conservation through basic thermodynamics: unless you live in a really polluted city or unfortunate location, outside air, even with humidity, is generally much better than inside air. If you want to be convinced read this:

And apologies to people who like toast!

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I’ve toyed around with a couple of those smart air quality monitors (an Elgato one and now I cannot remember the other…but it’s quite popular). I quickly got rid of both, as the news was just too bad to handle. I live in an apartment building so there’s just very little I can do, other than stop burning incense, candles, browning steaks, and so on. And I’m not going to stop doing any of those. Need my nag champa and pan seared meat to get through the day.