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.