We have had a water spot appear and not go away in our master bath. After looking around I found out that the flue pipe, B-Vent, is dripping with condensation when the furnace is running.
I have changed the heat cycle on the thermostat to a slow cycle so it stays on and off longer to hopefully allow the flue to heat enough to get the gas out.
I also took a look at the rain cap to see if it looked good. It did but I also noticed it seemed to be bottlenecking the gas badly. When I lifted it up, a lot more steam pushed out.
So my question is, could a too restrictive rain cap cause condensation on furnace flue pipes? Should I replace it with a more open one?
UPDATE: Changing the thermostat to slow cycle helped dramatically but there is still a small wet spot. Going to try a new rain cap.
Best Answer
To answer your question I suppose it could although I have never seen it. I doubt your vent cap is too restrictive unless you have or have had in the recent past a bad sooting problem. I rather suspect the B-vent is not being kept warm enough. It has to be in a warm space basically all the way to its termination. No drafts. No cold spots. Warm. It should be run straight up or nearly straight up. And as short as possible and the very least number of bends. Bends are a killer. Happy Venting. P.