The new controller programming seems to be working quite well so far. The attic hasn't been getting quite up to temp with the overcast days we've been having. So, the fan hasn't been coming on at all. Previously, it would have been turning on and off intermittently blowing cool air down into the kitchen. I'm very glad to have that sorted.
So, the time has come to improve the system a bit. I just ordered one of the dampers shown below.
American Aldes Spring Return Back Draft Damper - 6 Inch
This is to replace my home made damper. I had glued in some foam pieces, cut a hole in them, and then made a hinge out of plastic bag. Its been working okay-ish, but it doesn't seal well. The new damper has a gasket to seal better and is spring loaded. My damper also really reduces the diameter of the opening which I'm sure is reducing the airflow to some degree.
The opening is probably less than 4 inches as is. The new opening will be 6 inches in diameter with the new backdraft damper. This should be especially helpful as I do plan to add another fan or two to the setup. I estimate that each fan will move at most ~100 CFM based on what most bathroom fans move. With two fans I'll be moving ~200 CFM and the recommended duct size for 200 CFM is 5 inches in diameter. For 300 CFM a 6 inch duct is recommended, and 400 CFM recommends a 6.5" duct. So, 6 inch will have to do which happens to be the size of the hole in the brick.
I noticed the other day when I was up in the attic that there was a small amount of air leaking around the wooden base of the fans. I'll have to seal that up. Does anyone have any recommendations on a caulk that will hold up to attic temps (~115F in summer)? The normal acrylic stuff I had on it has cracked since I first applied it.
