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.

2 Answers 2


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)

  • Good idea, it has a dark glass screen so I can block it off behind the screen and it won't be noticeable and no one can start a fire if it's blocked just behind the screen. I also like the part about minimizing drafts. Oct 10, 2017 at 22:00

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...

  • 1
    Not only moisture but cresode buildup Ald loss of draft.+
    – Ed Beal
    Oct 10, 2017 at 21:14
  • Two good comments/answers but since it's a natural gas fireplace that I don't use ctrl-alt-delor gave me an answer that will work for me. Oct 10, 2017 at 21:49
  • @PlatinumGoose: be careful: often chimneys have more than one chase, so it might not be only your unused fireplace venting out the cap. i agree plugging the lower end is a better bet, if your damper is somehow not working.
    – dandavis
    Oct 10, 2017 at 21:54
  • I'm going to block the fireplace opening not the chimney and the chimney is strictly for the fireplace, furnace vent is separate and water heater is electric. Oct 11, 2017 at 19:09
  • I have a duravent wire mesh bird guard?, standard product on my chimney cap. Dandavis's scenario happened verbatim, 11:30 pm, Nov 19, 2020, central NC, 31-32 degrees, no wind, humidity 87%, clear sky, 30.61 in. pressure, dew point 28 degrees. Started a fire with paper, kindling, cedar shavings, some small cedar split wood. Fast, hot, instant fire. After 15/20 seconds, smoke started pouring out of all stove pipe connection points. Freaked me out. After opening all windows and shutting down air supply to fire, smoke stopped. Upon inspection, all square openings of wire mesh were sealed with soot
    – csbkip
    Nov 19, 2020 at 5:40

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