We have a Concord 80 Plus (Lennox) furnance, and it has three pipes outsides; for intake and outake. I suspect that the ladybugs may be entering from there. (Or is that impossible?) I am thinking of putting in a bug screen, but realize some problems. If the screen is outside of the pipes, then freezing rain in the winter may block the air flow. If the screen is on the inside, then would bugs nest or die there and block it as well? I'd like to do something.
(I am in Ottawa, Canada, where the summers can be +30 C and winters -30 C. Freezing ice is very common, and so it lots and lots of snow during the winter. I do not have air conditioning yet, but plan to in the future.)