I started to install a new light fixture in an upstairs bathroom and found something that concerns me. The mounting for the old light fixture was attached to the wall with 2 sheet metal screws. Investigating further, the sheet metal screws are into the vent stack. The screws are about 1 1/2" long, and the last 1/2' appears rusted like they had penetrated the inner wall of the vent pipe. The furnace no longer connects to the vent, but the water heater still does.
Is it safe to simply reinstall the sheet metal screws to plug the holes? Will the screws conduct heat from the inner wall of the vent pipe? Will that section of vent pipe need to be replaced or is there another fix?
BTW - It has been like this for the 35 years we have lived here.
Put new screws in. Cover them with RTV high temp silicone from a auto parts store or silver foil duct tape. The space between is a air gap and there is no way a tiny 1/8" shaft from a screw can conduct enough heat to be dangerous.
Those B vent chimneys can eventually need to be replaced if the outer wall rusts thru where it leaves the roof etc. They don't last forever. Very hard to find replacement sections as each manufacturer can be off by a 1/16" to 1/8" fit from another brand or a different style of clamp etc.
"Cut it twice and it is still too short".