Hello_there

The guy works on software for like a decade and it’s completely free with regular updates, and you insult his ethnicity? Wtf is wrong with you

Sell them used and reduce the cost of entry to other people

Call a tech and get your heater serviced. Yes you’re supposed to get those looked at annually. When they’re doing your heater, ask them what they think.

Imo, duct tape the shit out of that. I had a similar hole in my apt, and I just did maybe paper over it and then long strips down, layering them a bit, and then over, and it all gets a bit fucked in the middle, but point being you can get a seal. Cost is a half a roll of duct tape

“this is for a rental unit so I’m trying to keep cost low”

This sounds like the kind of BS that gives you apartments that are infested by bugs and still somehow charge 4k a month.
He says there are bugs already. Just lucky it’s silverfish and not cockroaches. Do the job correctly and it will save money in long term.