We live in the desert.

At night when the temperature outside drops below the thermostat's AC setting I like to open the windows on the "hot" end of the house.

That way the cool morning air can help cool those rooms.

My wife says that the AC cannot be on if the windows are open.

I say that as long as the outside air is cooler than the AC setting, that it is ok to open some windows.

By sunrise the outside air temp can be down in the 50's or 60's, and I want that colder air to leak in through the windows all night.

My wife thinks that it is wasteful to leave the AC on while the windows are open at night under these conditions, but I say that leaving the windows closed on cooler nights will cause the AC to work longer and more often than if the indoor air temp was being cooled by letting hot air out of the windows at night.

I know that the AC will still kick on with the windows open at night, I just contend that it will kick on somewhat less often if supplemental cool air is allowed in over the night hours.

Help me settle this bet.

Question from user HalfaBubbleOffLevel at hvacadvice at reddit.

Answer:

Let me put it this way.

Youre in the desert.

If your particular area is low humidity when youre running the A – C, its not a problem to open the windows at night.

If the temp is cooler than indoor ambient, and your thermostat is set, it wont run the unit once the temp drops below that threshold.

Thats talking strictly about temps and energy usage.

Its not factoring in allergens, air quality, and whatnot.

Answer from user na_ro_jo at hvacadvice at reddit.

ac on at night with the windows open yes or no