House under extreme negative pressure NOT due to the hvac system depressurizing the house. How can I fix it?
Homeowner in Long Island ny. We have a Vented attic that is extremely well air sealed with R-60 blown in cellulose insulation on the attic floor. HVAC system and Ducts are in the attic but they are throughly air sealed recently and covered with new duct insulation. The ducts are also buried under the cellulose. I have no attic fans or whole house fans. The chimney is well sealed.
Our house is under a lot of negative pressure and as a result it’s very cold in the winter. This air pressure is independent of the hvac system, as you can feel an influx of air through any little opening on the Lower floor at all times, even when the hvac is off.
I tried to seal as many openings in the basement as possible but it is very hard to get it all. This isn’t moderate air infiltration It’s almost like someone is standing outside with a giant fan blowing air into the house
the driving force for all this negative pressure on the Lower floors has to be from an opening on the upper floors. But I cannot air seal or insulate the attic better than it is now. I think there must be some giant hole on the upper levels somewhere.
my guess is water damage to some of the sheathing has caused holes in the sheathing on the upper levels that are driving this negative pressure. Any thoughts would be greatly appreciated
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Replies
It sounds like stack effect. The solution is air sealing. Have you tried blower-directed sealing?
Mike,
As DC says - start with a smoke pencil and see what that tells you.
Or temperature gun/IR camera
I also had this done when the blower door test was being performed. It indicated some clear problem areas which I tried to address.
I had that blower door air sealing test done as I mentioned to DC. I haven’t done a smoke pencil test myself.
I did have a blower directed air sealing test done but it seemed that the air was coming from everywhere. I patched up all the areas that showed infiltration but was never able to figure out the source.
Try to find out where the air IS GOING, not where it's COMING FROM. If it seems to come from everywhere, there is probably one big place where it's all leaving (or maybe several places), and that's what you need to look for.
I'd check all upper level vents for things like bathroom fans, and any recessed lights. I'd check the attic hatch, which is a common place for leaks. That's probably all the easy stuff. If none of that stuff is leaking, then I'd start to suspect something in the framing, such as a missed upper level band joist, something like that, that didn't get air sealed.
Go around with the smoke pencil and see what tries to suck the smoke out. Whever the smoke get's "sucked to" is probably the problem, or at least connected to a nearby problem.
Bill
Bill thanks. Good tips. Any advice on a brand for a smoke pencil that’s reliable and effective?
I usually just use cheap incense sticks. Find some that are as smoky as possible without being too stinky. These are usually way cheaper than "proper" smoke pencils.
Amazon has a few types of proper smoke pencils that are reasonably priced, but still expensive for what they are (IMHO). These are much nicer to use than incense sticks, at the expense of, well, their expense :-)
I do not like the little "wind checker" bottles that puff out dust. Many of those use what is basically a very fine silica powder, which is a known respiratory hazard and I avoid those like the plague.
Bill
Thanks bill for the incense stick idea. I’ll try that
"I think must be some giant hole on the upper levels somewhere."
You are probably correct.
Double check the function of the dampers on the exhaust fans, bathrooms and kitchen.
Thank you!
Every Walmart sell incense sticks that make great smoke for leak detection. A bright LED flashlight is helpful.
Taping a box fan in a window or 2 will make the air move when you want to.
Start at the highest point and work down about 20% then work on the lowest 20% the stuff in the middle has very little affect.
Walta
Incense sticks are a great idea. Thanks!
Just out of curiosity, when you had the blower door test done, what was the result?
The report says “BD 4091 cfm50.” The person doing the blower door said that it shows a leaky house but nothing too bad. That number came down after the attic was meticulously air sealed.
There is a disconnect between blower door and lived experience. If I cover and tape the sliding glass door that’s well installed in the basement with plastic on the inside, there’s so much air coming through it in the winter, it’s like a balloon. You push the plastic in and it immediately bulges out. So there is a problem that’s not being captured by the blower door test.
How big is the house, square feet?
3700 square feet or so
OK. Infiltration is usually measured in air changes per hour, ACH.
Assuming 8 foot ceilings that's roughly 30,000 cubic feet. 4091 cfm is 245,000 cubic feet per hour, that's just over eight air changes per hour. That's not great but it's not terrible either, probably average for about a 40-year-old house.
Thanks dc for the blower door analysis. I don’t think I fully understand the disconnect between the blower door score and what I’m experiencing. Hope I can figure it out
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DC any explanation about the disparity between the blower door and the lived experience?
Sometimes in the blower door test they tape off things like doors, windows and ducts.
VALAR5391@mathi
Hi Isabella not sure I understand your response
Have you looked into this?
https://www.greenbuildingadvisor.com/article/aerobarrier-for-air-sealing-existing-homes
Thanks! I’ve heard of it but never tried it. If I can’t find the source with the smoke pencil maybe that’s the next step
Are you windows just as leaky as the door?
I didn’t test the windows but that’s a good question.
Your house is leaky. 8 air changes per hour isn't good. If your sliding glass doors are "ballooning", that's one area that needs to be seriously addressed. There are obviously many others.
You keep saying the attic is/was meticulously air sealed, yet you think there may be a big hole up there somewhere. Leaks are the bane of your comfortable existence. I think of them as when mice are intruding into my homes. You need to go to war against how the air is getting in.
The most revealing experience for me was when the blower test guy left the fan running and we walked around the house looking/feeling for air infiltration. That gave me the most obvious areas to seal.
You need to go to war against air infiltration. Tough to do in an old house but achievable. A box fan taped closed blowing out in an open window with all other openings closed is a good start.
Nynick, thanks! I agree with you that they are a huge issue. The blower door score dropped by about 1/3 after the attic was air sealed. That helped some. I walked around the house during the blower door test and felt a lot of air coming in from everywhere. I agree with you that it needs to be sealed everywhere but my overarching concern is that the only way there can be these massive air leaks at lower levels if that’s being accompanied by air leaving at the higher levels. So I think as others have suggested using a smoke pencil to find the source might be the first step. But certainly your suggestion would also help!