DIY Home Improvement Forum banner

finished basement freezing in summer (AC)

4632 Views 4 Replies 3 Participants Last post by  beenthere

I have a finished basement, with no supply or return registers/vents. I live in New England where the summers are hot enough to need the AC on, but the finished basement gets uncomfortably cold, with all the cold air eventually finding its way to the lowest point. The house is a cape and the second floor is a bit warmer than I'd like, 1st floor is comfortable, basement is freezing.

The furnace is vented to the chimney, as is the hot water heater (oil.. combustion). There is a swinging damper in that exhaust system, and I wouldn't want to pull gases backwards through the system.

The 'furnace room' area is walled off from the finished area with a door -- furnace, water heater are in that room. The good news: ** There is also a 10 inch combustion air intake in that room **, flexible duct into a 5 gallon bucket (to help slow the rate of cold air pouring through in winter).

I added a pellet stove in the finished area, and have a small fresh air intake immediately behind the pellet stove, but it's not connected/sealed... i.e. it's in a wall register a foot behind the pellet stove.

Radon is present through the state, and the house has a mitigation system with negative pressure underneath the foundation, with a negative pressure indicator visible on the pipe that goes up through the wall to vent through the roof.

Winters are fine -- insulated well enough that it is usually comfortable without needing the pellet stove. If it's brutally cold outside, like -5 F, the pellet stove is required. Interestingly, it's the summers that are the problem being too cold, not the winters. All concrete floor and wall were drylok sealed, and all walls insulated. Like I said, winters aren't even really cold down there. It's the summer AC that gets too cold, and there are no supply vents providing that air, it's just from what finds its way into the basement throughout the day + night (stairway, etc).

Summary: In the summer, the air is a bit stale, and freezing cold. What can I do? I'd love to:

* re-use this freezing cold air to help with the AC on 1st and 2nd floors...
* freshen the basement air (a bit stale)
* have the basement be a little warmer than it is today, when the AC is on

So.... if I place an air return on the wall close to the ground and open during the summer, I would be pulling in a ton of cold air from the basement floor. But how to replace the air? If I add a supply vent (the supply trunk for the 1st floor is in the basement ceiling, I could cut in to it...) -- would I be 'stealing' too much of the air that would otherwise be destined for the 1st floor? Both the proposed return and supply would now be the ones closest to the furnace -- they'd be the 'strongest' and I'd worry I'm stealing too much of the air destined for upstairs.

If I didn't add a supply vent, and only added a return, I assume that the air would be replaced by a combination of the air that falls down the stairs (though there is a door at the top of that stairway, if closed, has a 1-2 inch gap under the door.....), and the air that might get pulled in from the combustion air vent that I have behind the pellet stove (again, that is not part of the pellet stove venting, it was actually there before I put a pellet stove there, it was the original combustion air intake for the house before I walled off the furnace and water heater).

Thanks for reading this small novel. :) But I wanted to give you answers to the questions you would have undoubtedly ask.
See less See more
1 - 2 of 5 Posts
A return and supply would make the basement even colder then it is/already gets.

A return would be okay since you have an undercut door. Should seal off the combustion air intake in the summer.

re: seal off the combustion air intake -- you're referring to the one in the finished area (behind the pellet stove), not the one in the furnace room, correct? The hot water heater (in the furnace 'room') would still need combustion air.

Yeah, the one behind the pellet stove.

Regarding adding a return only (near the basement floor), with air it takes in then being replaced by the air that it pulls down the stairs, am I correct in understanding that while it might accelerate the rate in which air comes "down" into the basement (of which the knee-jerk reaction might be that it would accelerate the cold air migrating downstairs more than it naturally does...) -- it would balance itself out due to the fact that it's finally mixing that freezing cold air with the rest of the circulation overall? That's what I'm hoping, but want to make sure I've got the idea down right.
Yes, the air coming under the door won't be as cold as the air coming from a supply would be.
1 - 2 of 5 Posts
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.