Can I put a fine mesh metal screen on my chimney cap. The current cap has a screen but the mesh is large enough to let stink bugs in. I'd like to put a finer metal screen over the existing screen. Does anyone even make such a product? The chimney is for a gas fireplace which is never used.
Good question. if you reduce are flow to much, then you are at risk of carbon monoxide CO₂ poisoning. You can get good battery operated detectors, that will warn you if there is a problem.
Check the specification for the flue diameter. Then calculate the area. Compare it with what you have after partially blocking it with the mesh. There main still remain a problem with turbulence causing the affective flue size to be reduced. Or with the mesh becoming blocked.
A better solution may be to block it at the other end, with something solid. That way you stop drafts as well. And make it impossible to use the fire, while it is blocked. (If this is practical)
No, this is a bad idea. In the winter, the moist combustion byproducts or plain leaky indoor air can condense and freeze on the cold metal screen. After a while and in the right conditions, enough condensation can freeze to slightly prevent airflow, which makes the whole thing freeze over very quickly. I don't think I need to explain why a frozen-shut chimney is a very bad thing...