Negative House Pressure
My house built in 2004 is suffering from some pretty bad stack effect. And I'm trying to figure out how to alleviate it and hoping I could get some advice here. If I open a window or front door I get a decent gush of cold air coming into the house. My direct vent gas fireplace feels like an open window if it's off. When off, my down draft stove top just dumps in cold air and the damper is fairly well closed.
I already had an energy audit and they determined that my house was too tight. At the time of the audit they said my house was exchanging ~5.06 volumes/day. And I needed ~5.9-8.4 volumes/day.
It's funny, because I thought my house was too leaky exacerbating the stack effect. The energy audit company told me not to seal the house any further until I got mechanical ventilation.
Following their advice I got a whole home ventilation system professionally installed, an Aprilaire 8126. The stack effect hasn’t changed at all. I still have a good solid stream of air trying to get in the house whenever I open a window or door.
I've sealed all the major mechanical penetrations in the attic hoping to slow down the loss of air to the attic and there still doesn’t seem to be much of a change. I also sealed the heavy leaks identified on my audit report. I’m at a loss of what to try next.
I need additional insulation in my attic, but I’m hesitant to add more until I get the stack effect solved. If there’s a problem in the attic, sifting through more attic insulation will just make it harder.
Could it be that I just need to add the attic insulation to slow down the conductive loss?
I don’t have enough insulation in the attic and it’s poorly distributed (this is stated in my energy audit). In some spots I’m as low as 2”, average of 6" range of 2"-10". I’d really like some insight before I have the contractor out to beef up the insulation. The insulation company doesn't think sealing all the top plates is cost effect since my house is already too tight. Is this correct? As I said, I'd hate to have them dump in a load of insulation to only have to shovel it out of the way to seal the top plates.
If it helps, I'm located in Montgomery County Maryland.
Thanks in advance!