Sealing Vent Pipe To Metal Chimney Cap - InspectionNews

Michael Thomas · #1 (**permalink**) 05-29-2009, 03:28 PM

Three-story condo, the unit in question is a first floor unit duplexed down into a garden apartment - looks to me like was perhaps originally designed as an in-law setup, there are units on the second and third floor above, and a fireplace in each unit (except the garden apartment). I've not been able to identify their relative positions at the top of the chimney

Whenever there's a hard rain there is water at the ceiling in the garden apartment directly below the first floor fireplace, in IR there's an almost perfectly circular drip pattern directly below the fireplace, and a few feet from over from that an irregular linear area of moisture that crosses several truss spaces and appears aligned with the outer edge the hearth extension (the three vertical objects are track lights.)

At the chimney top the cap is fairly flat and there are various small sealant failures where the vent pipes pass through it, per the owners when there's heavy rain and you are standing in the first floor living room beside the fireplace you can hear a steady drip from somewhere in or near the fireplace, however I could detect no evidence of excessive moisture anywhere within the firebox or at the exterior of its enclosure - my assumption is the water is dripping down the outside of the vent pipe and fireplace and making its way down to the ceiling below..

Anyway, up at the chimney cap (as you can see in the pictures) it appears to me that someone had originally installed storm collars and sealed them to the vent pipe (at an angle ???), and then (I would presume because there was leaking) pushed them up as far as they could below the terminations and then attempted to re-seal the vent pipes to the cap.

My question is: what is the correct way to achieve a durable seal between the vent pipe and the cap, and where will I find this documented?

Bob Harper · #2 (**permalink**) 05-29-2009, 03:40 PM

Michael, you can get all the info. you need in the Heatilator listed instructions. This is a 'chase top' or 'chase flashing' in the industry. The round things are 'round vent terminations' or 'round vent caps'.

Yes, it is incorrect for the storm collars to be up high. They are intended to be just above the 2" raised collar in the chase top, which is missing from this installation. Also, HL specifies the separation minimums both laterally and vertically when you have adjacent chimneys.

This chase top is pieced together with many seams. Is it flat or pitched--I can't tell from here but it looks like it pitches up to that central rectangular area, which is flat. What is supporting all this? I'll bet there is combustible plywood under that cover that does not meet clearance.

Get the model of the Fps, then go online and download the manuals. There is also an insert that is packaged with each temination cap showing how to finish it whether using a pitched roof flashing or a chase top.

As for the caulk, HL will specify a 300*F rated sealant but most everyone uses regular high temp. silicone at the storm collar. You cannot caulk the raised collar to the pipe as this area must breathe and each mfr. should state their min. clearance. This space provides cooling air for the system and prevents the top of the chase from concentrating heat. Failure to ventilate chase tops is a very common contributing factor to unfriendly fires.

HTH,
Bob

Michael Thomas · #3 (**permalink**) 05-29-2009, 04:11 PM

Bob,

Thanks as always for your quick reply... I had not thought about what was supporting that cap.

I posted here because I was not finding that detail specified in the Heatilator installation instructions, I'll bet this is another case were it's specified (as you note) only in the instructions packed with the termination cap... and nowhere else

---- Later

OK, found the termination cap instructions - for future reference they are here: http://www.heatilator.com/downloads/...uals/31445.pdf

Michael Thomas · #4 (**permalink**) 05-31-2009, 04:10 AM

Quote:

Originally Posted by Bob Harper

Yes, it is incorrect for the storm collars to be up high. They are intended to be just above the 2" raised collar in the chase top, which is missing from this installation...

For anyone who wants it for reports, here's an edited grab of the relevant Heatilator instructions:

Michael Thomas · #5 (**permalink**) 05-31-2009, 02:38 PM

Quote:

Originally Posted by Bob Harper

You cannot caulk the raised collar to the pipe as this area must breathe and each mfr. should state their min. clearance. This space provides cooling air for the system and prevents the top of the chase from concentrating heat. Failure to ventilate chase tops is a very common contributing factor to unfriendly fires. Bob

Does heated air escape through the gap, or does cooling air enter it (which way is the flow at the exterior of the pipe?)

- Thanks