Leaking furnace pipe

What can I try to stop a small leak between the pipe and the wall flashing? I’ve already used hitemp silicone on the storm cap.

I would try cutting out shingles to form a channel around the boot so the water has a place to go, but the flashing and shingles go right under the wall flashing.

Thanks for lookin’

Tear that area apart, replace pipe flashing and cut it in properly. Maybe just the picture but this roof looks way too flat for shingles. If you keep caulking things you’ll chase this leak for years.

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What size boot for a pipe thats 24" circumference, about 7.5" dia ? The one’s Home Depot sells are for B Vent, mine looks like a single wall.

Talk to a HVAC supplier.


You can get a tapered flange from HVAC supplier and trim for an exact fit. You will also want a weather ring/ storm collar for above the flange. I would get the largest one possible and or solder an extension to the right side so it is long enough to bend it 3" up the wall. Then install it as one big step flashing.


I’m having a hard time understanding what you mean, is there some visual depiction I could see? Surely I’m not the only one who has had to put a boot right up against a wall.


What MPA is describing is really the best way to handle the issue. However, its not really a diy job.

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I think The leak is more likely at the wall.
The water is running under the flashing.
The flashing is supposed to be under the shingles.

Re-seal where the sealant has wore away
Where the flashing meets the shingles
The top of that flashing too(wall side)
And you might solve the issue.

It really needs to be torn out and done right.
But that might solve it for a while.

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I have that flashing sealed up to the ridge and beyond, I can’t comprehend the path of entry

I would guess that you do not have proper step flashing at that wall. I would also guess that previously the metal that flashes that wall was originally under the shingles. Caulk generally does not stop a roof leak, even if feels like it will work when you apply it. Are you in a financial position to have a roofer or two come and take a look at it?

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Thanks for your reply.

The flashing you see is original to the duplex, as every other duplex has the same arrangement. It goes up and around the party wall, and comes down the neighbors roof in the same way. Would they originally have put step flashing under that flashing I see?

One guy quoted over the phone $375. I’ll pay it if I must, I’d just like to understand how it’s getting in.

Do you have a picture of the area along the wall that is above the pipe? I know you have caulked a lot of the flashing and vent. However, caulk will not only keep water out but also keep it in. So if there is any open hole, no matter how small, then that vent hole is the first place it coild escape once its in. I would assume that its either a hole in the metal flashing that was missed or a hole in caulk running along the length of flashing.

There is a shingle seam right at the top of the boot.


I can’t not comprehend the point of entry. I would be shocked if that hot mess didn’t leak.


Look close and you will see the seam at the top of the boot, the top of the underlying shingle may be missing which would result in a leak.

Not sure if this is it or not but it is a common issue.


Thanks for making me laugh!

I’m sure I’ve found the leak in the spot some have noted, can this be patched for a few years instead of tearing up the whole mess?

it would be best to replace the shingle in such a way so that the seam is farther to the right as looking at the picture.

If you are just going to use caulk it would be best to get the caulk under the seam 2" on each side and 2" up.

Thx Axiom,

If I go the caulk route, I’m assuming I’d need to free the base of the shingles which are cemented to the boot. Wouldn’t this create more entry routes for water?

At this point just smear tar (I feel like such a hack saying that) over the shingle butt joint. Make sure you feather it far enough out on the top and sides so no water can get in. I’m only saying this because you already have such a mess on your hands its not gonna make it any worse. If it still leaks its time to open your wallet and hire a pro to tear off the shingles around it and fix it the right way.


Also axiom offered great solutions however imo they are a little out of the skill level for most homeowners.