Makes sense since the draw from basement pulls air from wherever it can, through the floor vents.If you see my picture I posted of the vents. A piece of paper dropped from the air will be sucked onto and trapped onto those vents. So air is being pulled from the upstairs through the return vents even though they have been taken out.. idk if that makes sense to you
I think I’m understanding you a bit better after rereading. Where would I drill the hole for this? Sill plate?Makes sense since the draw from basement pulls air from wherever it can, through the floor vents.
I’m guessing when the thermostat closes and the stove only gets idle air, the draft slows and is being overpowered by the lower pressure in basement.
Since you know of those two air leaks, I would put an air flap of some sort on them preventing unwanted flow.
Then give the basement its own air intake.
When I installed gas burning appliances in utility rooms or tight basements, I installed a PVC pipe through wall. I used an elbow facing up on the inside, and an elbow facing downward on the outside with an insect screen on the outside. This prevents warm air inside from dropping down and out, and allows the higher atmospheric pressure outside to push in. It needs to take the path of least resistance, instead of down both chimneys.
The basics of what makes the stove work is hot gases lighter than outside air rising up the chimney causing a low pressure area in chimney flue, pipe, and stove. Atmospheric air pressure PUSHES into intake feeding fire. This is measured as draft. This is an exceptionally minute pressure differential that mechanical blowers, and rising air from basement competes with chimney. Going back to the basics will diagnose these issues.
Yes, I go through wall above sill plate if possible. Normally 3 inch pipe. A short elbow up, inside, and drop down the outside with a pipe where snow will not be an issue.I think I’m understanding you a bit better after rereading. Where would I drill the hole for this? Sill plate?
I making a U tube manometer to see what pressures are like and see if that gives me any other info I might be missing