If you pull air from the basement, it's going to get replaced with warmer, wetter air from upstairs. As it cools the air is going to deposit that water on the coolest surfaces. You might be trading this problem for another, more damaging one.
this post was submitted on 21 Jun 2024
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Wouldn't the AC still be dehumidifying the air circulation on the upper floors?
Good point, I'll have to keep that in mind. I would think that after the initial temperature equalization, it shouldn't be an issue as long as the temp remains relatively stable afterward, so in theory, if the rate of the initial equalization is gradual enough, I would think it wouldn't cause any long-term issues.
Though that does depend on how exactly any possible solutions would work, and how controlled they could be. I might just re-evaluate after I get the insulation work done.
I've had this conversation before.
I live in a geodesic dome and the finished basement is always noticeably cooler than the main floor and top floor.
As a test, I got a blower fan and put it at the basement stairs blowing the air from the very bottom of the house up towards the middle floor.
After about a day the temperatures equalized enough that it was difficult to tell the difference between the Middle floor and the basement.
Doing that causes the colder air to mix in with the warmer air upstairs, and the registers pull the warmer air in and blow out dehumidified air back into the basement, so no moisture build up.
The only downside is the noise and energy costs to run a fan. Probably 400 watts.
What I want to do is get a 4 inch duct fan and place that in the wall and run ducting from the basement up to the top floor so that the cold air is constantly being reblendid back up with the rest of the air upstairs.
I feel like that would use much less power and do a decent job of blending the two.
Maybe you can find something like that that will work for you.
When I was a kid some family friends had put an air-moving fan in the floor from the basement to the first floor. On hot summer days it would pull the cool air from the basement, and in the winter it would circulate the air from near their woodstove in the basement to the upstairs.
Maybe that would help? Wiring would be the hardest bit to figure out. After that it's just cutting a hole in the floor.
I know there's a floor insulation issue, but what about redirecting air, and other sources of leaks? Does your basement have vents in it? Turn them off and maybe consider getting bent covers that can seal in the summer. Close the vents on the first floor so that (the majority of) the cool air comes in at the second floor and sinks down. Weather-strip and baffle the basement door.
Also, see if your electric company offers a home energy assessment. It takes about an hour, and there are usually two tiers: free, and a second tier where you pay for a blow test. They can make some recommendations on making your home more energy efficient.
My house has a similar issue with a lower level that is perpetually much colder than the upper level. The main way we have somewhat alleviated the problem is by opening/closing registers. In the summer, we close all the registers in the lower level, forcing all the cold air from the HVAC into the upper level, then letting it sink down naturally. Our lower level is still cooler, but it isn't as stark a difference. Due to the layout of the stairs linking the two levels, a fan is not terribly effective at exchanging a lot of air between the two on its own.
If you're looking for a commercial product it's called a whole house fan. The tl;dr is there are vents in the places you want cooled connected to this fan that sits in your attic. Twice a day or so it exhausts the hot air letting it be replaced by the cooler basement air. Depending on the humidity you might need to run the AC to dehumidify the air a bit.
I initially had the opposite problem where my uninsulated cinder block basement was too hot in the summer and too cold in the winter and my basement didn't have any HVAC registers or returns. The only air conditioning it got was from a window AC unit and leakage from the HVAC ducts. Over several years I ended up adding 2" foam insulation internally to all the exterior walls, insulating the ceiling to the basement (mostly for sound absorption but it also helped with floor temperatures), and adding returns and registers in the basement. I also added an inline booster fan to help pull air up to a second floor bonus room that was an addition. Now the basement is always comfortable, the second floor is much more comfortable, and the energy costs are about the same. My moisture levels are 30-50% in the summer.