Water heater too tall for existing flue/chimney vent pipe

[bmaguire14]

I have installed new hot water heaters (2 x 40 gallon tanks) in my attic, but they are 1-2" taller than the old hot water heaters. As a result, there now isn't enough room between the top of the water heater and the bottom of the existing vent pipe (type B piping) for the vent hood to fit. I tried pushing the existing type B vent pipe up into the roof, but there isn't any give to it. Any ideas on what needs to be done? I have seen elsewhere that B vent piping is not to be cut/trimmed so that isn't the answer. I'm guessing whatever caulking was laid between the vent pipe and the flashing on the roof has hardened after years under the Texas sun. So I'm wondering if I need to get on the roof and cut the caulking out (and storm collar too) in order to be able the lift the B vent up 1-2" to give me my clearance. Is that the answer?

 

[Phog]

It depends on how the termination was done. The manufacturer method (in the application manual) typically involves a roof flashing + drip collar ring, and the caulking goes around the drip collar but not the roof flashing (which has a friction fit). This would allow you to slide the stack upward if there isn't caulk. But often the installer will go their own way & use caulk anyway, in which case you would have to cut the caulk. Even if there isn't caulk at the roof, there are probably also firestop supports at each story of the house which can be hard to push the stack through (friction fit), or alternately there can be support clamps you might have to be able to access and loosen. The way i would probably approach this is to take out the bottom most section of B-vent and put in a shorter / adjustable length section to meet your new height. This also might not be easy in your situation, it could involve opening up walls etc. Also be aware that B-vent connections are not intercompatible between manufacturers so to do this you would need to find the same manufacturer and order the appropriate part. And by the way, yes, you can't cut B-vent, you will break the double wall seal and this could lead to flue gases going up the wrong pathway and potentially lead to a fire. Sorry there is no easy answer, maybe one of the pros here has a tip for you.

 

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[bmaguire14]

Thanks for your reply phog. Since a picture is worth 1,000 words I am posting one below to show the situation I described in the original post. As you can see, its somewhat of a good situation in that there aren't any stories or fireblocks to navigate. It's a straight shot up through the roof. But, on the negative side, its all one b-vent pipe, so there isn't an option to take out a section and replace with shorter/adjustable length b-vent. I am trying to avoid a trip up on the roof (10 pitch slope), but it is looking more and more unavoidable to me. Hoping one of the pros on here has an easier solution.

 

[Phog]

Man you are so close. I assume you've already got the steel straps at the rafters loose so that you can lever the bottom of the stack back and forth. Can you rotate the stack at all? A standard roof flashing looks like this and there is a tight friction fit but nothing fastening the vent to the flashing.

If you can twist and rotate the vent then you should be able to gently push it upward through the flashing. (Hopefully the flashing was secured properly to the roof so you don't push it off!)

Up above the roof should look something like this

The thing up directly above the flashing is the drip ring. This is what is fastened to the B-vent (usually with caulk only) & what prevents rain from coming down the side of the stack through the flashing. It sheds the water away from the penetration. If that drip ring moves up too high then you can start getting water coming inside.

But you can hopefully move it upward a little way & it will still function fine. I can't remember exactly what the gap spec for the vent manufacturer I used was (Selkirk) but it was on the order of a couple inches max above the flashing, maybe 2-3"?

Or your stack could just be caulked to the flashing without a drip ring in which case you'll definitely have to break the caulk seal, move upward, and run a new bead. Good luck

 

[bmaguire14]

Thanks again phog. Trying to rotate it is a good idea. I'll try taking a strap wrench to it to get some leverage and torque. My fear had been that I'd disrupt the waterproofing seal by getting to rough with it, but as you show there should be a storm collar doing that work that won't be impacted by the force of rotating it. Thanks.

 

[bmaguire14]

Just to close the loop on this: I was able to use a strap wrench to rotate the B-vent enough to free it from whatever sealant/caulk was holding it in place. It took some effort, but after a while it broke through the hardened sealant and came free. Then I was able to easily push it up through the flashing/roof a bit more to fit the vent hood in place. Thanks phog for the tips. Fingers crossed no rain gets in now, but that should be what the storm collar is for!

 

[Phog]

Just keep an eye on it, worst case you'll have some drips gathering around the appliance connection at the top of the water heater. Some installers don't follow the instructions & just caulk the flashing instead of putting on the drip ring, so you'd be well advised to look up from the ground and see what you've actually got up there (if you haven't already). But glad to hear you've got things connected up, at very least you've got a functional water heater now.