Home Temperature Question That Defies Logic

[RainMaker]

This has been driving me crazy for a year now and I just can't figure it out. I've looked online but can't seem to get a good answer.

My place has the A/C set to 73 degrees most of the time. We've had a mild summer so temperatures get down to the 60's at night outside. So I say fuck it, turn off the A/C and just open up the windows. For some reason though my place goes up in temperature. Within 30 minutes it's up 76 and if I left it for hours would get up to 78.

I don't get how this is happening. How can my home be 73 degrees, I open the windows to 60 degree weather, and the place goes up 5 degrees.

I know there is probably a simple reason for this but I can't figure it out. It just makes no sense to me. It's like my place is creating heat out of nothing.

[cartman]

Must be some sort of air pressure thing. Are you on a hill? If so, the old "hot air rises, cold air sinks" might be coming into play. When you open the window, the AC cooled air is being sucked out of the house, while the cooler outside air isn't coming in. In due time, the pressure should equalize, and the outside air should start coming in. That's all I can think of off hand.

[JPhillips]

Are you in a two-story? I have that issue in my house, but only on the second story. My best guess is that the air in the attic is much hotter than 73 as well as the outside of the walls, especially if you have a dark paint color. Add in all the heat generated by all of your electrical appliances and, if the air isn't moving through the house, the hot air builds up in the second story.

You should be able to lower the air pressure in the house and hence get more outside air if you have fans blowing out in some of the windows.

[JonInMiddleGA]

Create some circulation with some window fans pulling the cooler air in & it should solve whatever the problem is.

And if it doesn't, you might consider calling a priest or a paranormal expert ;)

[RainMaker]

Yeah it's a 2-story and the problem is upstairs. Might get a window fan tomorrow at Home Depot.

[CU Tiger]

We keep therms in attics my guys are working in, because on a 95 degree day the attic can exceed 140.

When its 72 in your house and 95 in your attic (usually hotter than ambient high...and I dont fully understand this part) that heat passes down.

this also indicates a poor insulation value between the attic and the house.

[RainMaker]

I don't really have an attic though. It's a coach house in the city with a flat roof.

That is what gets me about the whole thing. If it's 73 inside and 60 outside, you would think that opening the windows for many hours would eventually bring down the temperature. If I kept the windows shut, my A/C would still be running on and off all day/night.

I don't get where the heat is coming from. I could understand if parts of the house were hotter and that heat started getting blown around once the A/C was off. But after 6+ hours, wouldn't it start to cool down toward the temperature that is outside? I mean it is around 80 here during the day so I'm wondering if it's somehow storing the heat from the day somewhere. The whole thing just boggles my mind as I can't figure out why a 73 degree house being opened up to 60 degree air is getting warmer.

[JPhillips]

If you're in the city there's a lot of radiant heat from the streets and surrounding buildings. Also if your roof is black it's gotten very hot during the night and will take quite a while to cool off. Finally, if you go around at night and check every electric appliance you'd be surprised how much heat you are generating.

[RainMaker]

If you're in the city there's a lot of radiant heat from the streets and surrounding buildings. Also if your roof is black it's gotten very hot during the night and will take quite a while to cool off. Finally, if you go around at night and check every electric appliance you'd be surprised how much heat you are generating.
That's what I'm thinking. Lot of concrete everywhere. I used to have the place covered mostly in ivy till a contractor fucking cut the trunk of it. The ivy was great insulation.

[fantom1979]

I am no expert, but I would probably get two fans and if you have two windows, set up a wind tunnel. Put one fan blowing in on one side, and one fan blowing out on the other. If that didn't work, I would point both fans in.

[kcchief19]

I don't really have an attic though. It's a coach house in the city with a flat roof.
CU Tiger still has the most likely cause but there are plenty of ways your home can store and create heat. Anything in your home that's electric and plugged in will create heat. Any lights, TVs, computers, appliances, etc. will create heat that increase your temperate a few degrees. I was stunned to discover that items in your home that aren't electric do the same thing -- for example, furniture can absorb heat from lighting or sunlight and continue to emit.

Everything in your house is giving off heat. When you stop cooling the air inside, those items continue to heat the air, which is why it will continue to get warmer. You need to get hot air pumped out of your house so you can bring in the cool air.

When I was a kid, we lived in a large ranch house with no a/c. We had an attic fan that helped a lot but we could also put fans in the windows -- one blowing in and one blowing out, just like fantom suggests.

[NewIdentity]

My place has the A/C set to 73 degrees most of the time. We've had a mild summer so temperatures get down to the 60's at night outside. So I say fuck it, turn off the A/C and just open up the windows. For some reason though my place goes up in temperature. Within 30 minutes it's up 76 and if I left it for hours would get up to 78.

Asks the guy with the 60" plasma TV. :)

[flere-imsaho]

I don't get how this is happening. How can my home be 73 degrees, I open the windows to 60 degree weather, and the place goes up 5 degrees.

The issue isn't so much that the 60 degree weather isn't making it inside, the issue is that you've turned off the AC but there's still plenty of stuff in your house that's generating heat, causing the internal temperature to rise.

Since hot air expands, you almost certainly have positive pressure in your house, which means that although you've opened windows, the cold air isn't getting into the house because in general air is being pushed out of the house.

The key is to work with circulation, to get a lot of the hot air going in one direction (and exiting the house) so that cold air can come in from somewhere else and cool off the house. A window fan or two, combined with opened internal doors, should help. I know what I've done in the past is put a window fan pushing OUT somewhere on the east side of my house (the general airflow in my area is west-to-east) with another on the west side of my house and very quickly I'll get a full change of (colder) air from the outside.

[Autumn]

If yo'ure on the second story you've also got the floor below pushing its heat up to you constantly. As the above posters said, you're not getting any outdoor air in because your floor is just filling up with hotter and hotter air.

[Huckleberry]

The solution to the puzzle is that the thermometer on your thermostat is off by 10+ degrees.

;)

[jdavidbakr]

The reason is probably because your roof, walls, concrete, etc. absorb the heat from the sun all day long, and it takes most of the night for those objects to release the heat that they have stored up. It's the same reason that it takes several days of cold weather/snow before the ground is cold enough to allow the snow to stick, especially on the sidewalks and streets. The solution is definitely to get the air flow passing through the house, an attic fan is the best because it blows the air from the house into the attic and then you open up all your windows and it just sucks the air right into the house from outside, but since you don't have an attic, putting fans in windows - one side of the house blowing into the house and the other side blowing out - you should get some of that cooler air circulating nicely through the house.

[RainMaker]

Thanks for the help guys. I'm trying out some window fans I bought at Home Depot. They are built so that one pushes air in and the other out. Hopefully I get a few cool nights where I can try them out in the near future.

My bills haven't been high or anything since we've had a mild summer. I just feel like an asshole running my air all night when it's 60 degrees out.