Filling in a hole in the floor

[jkindt]

I would probably cut some sheet metal a little bigger than the hole and attach it from below with either short metal screws or rivets, with a little sealant to keep the moisture out. Then if you replace the plywood floor you just go over it, and if you choose to keep the plywood floor, cut some plywood circles and drop them in with some building adhesive or other sealant. OR...use the hole to plumb in your toilet or sink or shower.

 

[bus-bro]

Fiberglass tape and epoxy resin works well for something like that.

 

[bus-ted]

Doesn't look like holes for heater....or that they've been there for nearly 20 years.....lol, metal isn't even rusty.

Smitty

...or 2" thick! Sorry- couldn't resist.