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Old 07-24-2020, 08:24 AM   #1
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What do you seal AC lineset and PVC vent through brick with?


Had furnace/AC replaced yesterday and part of the install was running a new AC lineset and pvc furnace vent through the exterior brickwall. After they left, I noticed it wasn't properly sealed around both items and had gaps that went straight through to basement.

What is the proper sealant for around the AC lineset and the pvc furnace vent/intake?

I also noticed that the sealant there had a lot of movement in the somewhat large gap. If a caulk product is used, should you use some sort of backer rod in there?

As a final point, these holes are basically at ground level because our basement barely extends above ground level so there isn't much of a choice. Not sure if this changes what product you would use.

Looks like some clear caulk/sealant with the brick dust thrown on it to somewhat color match to the brick


Just clear sealant
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Old 07-24-2020, 09:10 AM   #2
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Re: What do you seal AC lineset and PVC vent through brick with?


They probably just didn't use enough. No real biggy, you can fix it. A mouse/small rodent can get it a hole the size of a dime.

If there is a really large gap through the brick, i use xpand foam, then dress it up on the inside/outside with silicone or in your case mortar caulk. it looks better. Just my opinion.
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Old 07-24-2020, 09:14 AM   #3
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Re: What do you seal AC lineset and PVC vent through brick with?


Clear DAP silicone ( not the dollar store stuff ) works well.

You don't want to seal the furnace pipes tight as they need to expand and contract with temp changes. Don't use cement on them. Silicone is flexible enough.
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Old 07-25-2020, 12:55 AM   #4
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Re: What do you seal AC lineset and PVC vent through brick with?


Does anyone use Duct Seal Compound for this situation? That gray putty that is supposed to remain flexible for decades. I believe it is found in the electrical wiring section in Home Depot, implying it is usually used for conduit penetrations. The second photo looked like it might be using this gray putty.
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Old 07-25-2020, 06:24 AM   #5
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Re: What do you seal AC lineset and PVC vent through brick with?


Quote:
Originally Posted by RustNeverSleeps View Post
Does anyone use Duct Seal Compound for this situation? That gray putty that is supposed to remain flexible for decades. I believe it is found in the electrical wiring section in Home Depot, implying it is usually used for conduit penetrations. The second photo looked like it might be using this gray putty.
Nobody uses it outdoors anymore. It dries up and crumbles and then water can leak in and damage occurs.

Silicone is fairly cheap and lasts 4ever.
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Old 07-25-2020, 07:52 AM   #6
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Re: What do you seal AC lineset and PVC vent through brick with?


We would is a colour matching caulk for this. In a pinch we use general purpose clear silicone, but I've had people complain about the look. Yuri is correct about the flexibility needed.

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Old 07-25-2020, 08:24 AM   #7
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Re: What do you seal AC lineset and PVC vent through brick with?


Yep, just caulk it.
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Old 07-27-2020, 08:58 AM   #8
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Re: What do you seal AC lineset and PVC vent through brick with?


Sounds good all.

I forgot to mention in first post that the grey blobs next to the clear'ish caulk IS duct seal. I temporarily stuffed a couple blobs to plug the holes next to their caulking from bugs until the guys who installed the furnace/AC can come back. They need to come back anyway with the correct fitting to plumb the humidifier in.

I think the gaps are too large for normal silicone without some sort of backing, but doing a shallow fill with a low expanding foam (maybe the window/door version) and then dressing outside with silicone sounds reasonable.

Mortar caulk was also mentioned above. Could you link a product at home depot specifically? For example, typing in mortar caulk in HD search brings up DAP dynaflex 230 and dap concrete & mortar filler & sealant. How would these compare to 100% silicone?
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