Hole in flue

The last 3 homes I have inspected have a 1/4 " hole about 6’’ above the furnace. I have been recommending replacement of that section of flue for CO backup reasons.
After seeing the 3rd one yesterday I am wondering why these holes are there? Is it an inspection hole for a CO detector & should’nt it be replaced?

It is for taking co2 reading and smoke test, and temp are they oil furnaces?
Really they could asert a screw to close the hole but rarely done

What is that goop all over the flue?

I don’t know what the goop is.
It looks like someone tried to heat up somthing & it melted onto the flue
Should the hole be fixed?

No they are gas furnaces

It should be covered , but I doubt it will be a big issue.
Flue gasses would have a bigger tendency to travel up.

Think of draft hoods and how they are open.

Use you detector and I bet you get zero.

Roy, I’ve asked this question before and got same answer. The gas technicians don’t believe it’s a problem. For homeowner peace of mind, a big sheet metal screw wouldn’t hurt, IMO.

John Kogel

I never worried about filling them i never got anything from around the hole, I was a multiple certificated holder (License )in Ontario Canada normally you found them on oil furnaces. that is why i asked

I bet someone tried duct tape to cover the hole

looks like asphalt/roof cement product

i’ve seen this numerous times where the HO or goof ball roofer tried to patch a roof leak at the flue flashing and the stuff just melts down the flue pipe

i the call them for total replacement because now you have a potentially combustible products in direct contact with the flue

patching flue holes with high heat RTV silicone is what i’ve also seen :roll:

that is test hole that would be used in regular service if it is worry just use a screw to fill other wise someone will just punch a new one, In commercial we just left a stack thermometer in there

Instructions given at CO/Combustion training says the hole should be 12 inches from the draft connection. Sealing of the hole can be done with high temp metal tape, high temp silicone sealant, screw, lag bolt or metal snap cap.

Should the inspector cover the hole with heat resistance tape?