Furnace flue how close to wood

I did an inspection and am curious how close the flue can be to wood? What types can be how close to wood.
If i remember right, some are 1 inch and some are 3 or so?
Tell me once and hopefully it sticks!

Kenny cottage 068 (Small).jpg

Kenny cottage 067 (Small).jpg

Kenny cottage 066 (Small).jpg

What type of furnace


If that’s a vent, then you definitely have clearance issues there…

Single wall metal connectors - Depending on the appliance and installation, clearance to combustibles should be 9 to 18 inches. If the listing of an appliance specifies a different clearance, the listed clearance applies.

Double wall, uninsulated, or “B” vent - Clearance to combustibles is typically 6 inches. “B” and “L” vents may be in accordance with the appliance and vent listing.

Double wall, insulated - Clearance to combustibles should be 1 or 2 inches, or as the appliance or vent listing allows.

Is that in a closet?

Is that duct tape?

This is a forced air. I am not sure what type of flue it is. YES, Duct tape!!! and in a closet.
Thanks for the info.
How do i know what type of vent flue it is? Is there some place i can research adn learn this?
THanks ALL


Is that a hot-air supply vent or an exhaust vent?

Something else to consider about that flue, assuming it’s an exhaust flue of any kind, is to try to see if it is installed with the correct end up. The lower pipe should slip inside the upper pipe to “receive” it. I’ve seen flue pipes installed upside down (some even have an UP arrow embossed on them) If it is installed incorrectly, it is a carbon monoxide gas poising hazard to the occupants, aside from also being a fire hazard as it appears to be now (assuming its an exhaust flue)


I am appreciating all your inputs.

Too close to combustibles…

Yes, i am just going to mention it (clearance) and let the tech decide.
Thanks for all the comments.


It’s quite easy determining a single wall vent from an insulated vent.

Just tap on the outer shell. If you hear a thud, it’s insulated. If you hear a ping, it’s single wall and should not pass through floors.

Another thing I don’t understand is why that duct tape is not frayed on this hot vent. I swear…Duct tape is the only band-aid homeowners think of when there’s a defect.

It is a cottage and the furnace probably rarely gets used.

Is it an optical illusion, or is the lower pipe a larger diameter than the upper one?

Also, typically, single wall flues for gas furnaces have a 6" clearance to combustibles, and double wall (Type-B) flues require 1". Gas- and wood-burning appliances have different clearances, as you probably know.

In your area, aren’t there draft-stopping/fire-stopping issues that might also be in question here?

In any case, that is a scary flue! Recommend to have it inspected by an HVAC guy.

Be careful not to overlook the flue in contact with things like sheetrock too. The sheetrock is paper lined (combustible). I cite it all the time.