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We have an A/C (and gas-fired heat) unit in the attic. It uses (forced) air ducts going to the ceilings in the rooms. I was in the attic today when the A/C turned on. I felt cold air come on my leg when I was near the unit. I then looked to see that this small amount of air was coming from near the copper tubes coming out of the sheet metal of the unit near the evaporator area.

I took pictures and marked the area where cold air seemed to be coming out in red.

Is that normal? I am guessing that the installer didn't seal it. There are two holes in that area. One with more tubes (on the right-side) that has some rubber seals but the other has bare tubes coming out.

Should I somehow seal it with perhaps rubber seals sold in the market or improvise something?

Thanks for your help.



 

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I would try move the small line a wee bit and put some rubber between it and the metal so vibration does not cut a hole in it and create a freon leak.

Then you can seal the holes with clear or white silicone or if you are handy use silver foil tape and cut in into smaller workable pieces.

You can buy a product called Thumb Gum but for such a small area I would use silicone or tape. Contractors use Thumb Gum but we buy it in 1 or 5 lb chunks and it goes a long way.

https://www.homedepot.com/p/Gardner-Bender-1-lb-Plug-Duct-Seal-Compound-DS-110/100212441

https://www.amazon.com/Bramec-1003-Thumb-Sealing-Compound/dp/B002SSGARY
 

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+1 on cushioning between the copper tube and the edge of the hole; do that right away.


I'll disagree on the silicone, though, since this is a heating system also. Some silicone caulks get soft with heat, and may not hold up when heating season comes around. A few layers of the aluminum foil tape is the best option for sealing it up. I would suggest taping up around the other 2 holes there while you're at it.
 

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My installers use HVAC, higher grade white silicone all the time. If you buy a high grade one it should be OK.

My Uncle uses high temp RTV silicone on his wood stove door gasket and has no problems.

Use high temp RTV grade if you feel unsafe.
 

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I feel like the tape would eventually peel off because it is so hot in the attic and the adhesive would melt off or else condensation would build between the tape and pipe.

I'm not familiar with thumb gum, but my guess is it would work better.

My guess is that it is leaking out of that joint which looks poorly welded together.
 

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That tape is very difficult to remove and will not come off.

Thumb Gum if you can find it at HDepot lasts 4ever but dries out after 10 years and then you need to rework it back on.

The tape is a pain in the butt to work with in a spot like that.

Silicone is the easiest and that area does not get very hot. 150-165 deg F max.

On a chimney exhaust pipe yeah it would not be good unless you use the high temp RTV type.
 

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An old standard of the industry in the US is Permagum. I see they sell it at HD and others now. Used to be strictly a HVAC/Refrigeration dealer item. You can get a 1# slug of it for about 3 bucks at HD.

Otherwise, I'd shoot some rtv silicone on there and call it done.
 

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What about the big main trunk line that attaches to the air handler? I've seen some kind of white compound coating the insulation and tape to build a more permanent, protected layer. Obviously that's different than wrapping a copper pipe. I think HVAC techs use some sort of masking compound on trunk lines.
 

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My Uncle uses high temp RTV silicone on his wood stove door gasket and has no problems.
I replaced my inducer last winter and since they didn't send the glass gasket with it, I shot some GE RTV standard grade clear silicone on the flange and slapped it together. I put a small dab on the flue pipe at the hottest point so I could see if it was up to the job. I check it occasionally and notice that it still looks like it did when I first shot it on there. That stuff is good to 500°F (260°C) so they can keep their special "glass" gasket and stuff it somewhere else. :vs_laugh:

BTW, the high temp type silicone is good for up to 650° F (343° C.). Your uncle's stove door shouldn't get anywhere near that hot! :smile:
 

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What about the big main trunk line that attaches to the air handler? I've seen some kind of white compound coating the insulation and tape to build a more permanent, protected layer. Obviously that's different than wrapping a copper pipe. I think HVAC techs use some sort of masking compound on trunk lines.
That a water based duct mastic that is pretty much standard stuff for duct installing.

Here's an example:

Duct sealant
 

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I feel like the tape would eventually peel off because it is so hot in the attic and the adhesive would melt off or else condensation would build between the tape and pipe.

Not on the aluminum foil tape. It's made for HVAC ducts, so it handles heat and cold very well. In the years between replacing my windows and replacing my siding, it functioned as flashing around the windows fairly well, too.
 

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My installers use HVAC, higher grade white silicone all the time. If you buy a high grade one it should be OK.

Sounds good to me. My caution was against using just any old silicone. Obviously, high temp silicone can be found, but I didn't know what might be available outside of the stuff typically sold for automotive use.


So the aluminum foil tape or the high temperature silicone, or a combination of the 2 should work. My suggestion would be to use the foil tape to cover the larger open areas of the hole and then use the proper silicone to seal around the pipes.


Don't forget to like a medium-hard rubber cushion of some kind between the copper tube and the edge of the hole before sealing it up.
 

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Don't buy the dollar store cheap bathtub grade stuff but a higher grade DAP product and it should be OK.

I would do the tape and then silicone trick also.

We used to use thumb Gum outside to plug the hole where the lines exit a house. That hole was a lot larger and you needed the 5 lb plugs of it.

That stuff would dry up and fall off and now we use HVAC grade silicone and it lasts forever.
 

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Have you searched the HVAC unit manufacturer's website/database for their info on how it should have been installed properly? If that step is available it should reveal how to address the issue. Might also call their toll-free number and talk to their help desk if they have one. They might give you an email address to send the pics you posted here, so the makers might advise a fix.
 
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