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Just installed tankless heater - insulation suggestion on expose concreate


limron's Avatar
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Join Date: Feb 2010
Posts: 2

02-01-10, 08:02 AM   #1  
Just installed tankless heater - insulation suggestion on expose concreate

Hello everyone

I'm a newbie who just joined the forum. I'm seeking advise on dealing with an exposed concrete resulting from a recent tankless water heater installation.

My basement concete wall is insulated with fiberglass from the ceiling to just about 6" off the floor. About 3 weeks ago, I replaced my tank water heater with a tankless unit. The installer mounted the unit on the wall directly on the insulation. He had to cut the concrete wall for the stainless steel duct for the exhaust. The insulation had to be removed where the cutout is for the duct.

The problem I'm having now is we're in the midst of winter in Canada and the concrete area exposed without insulation is icing up due to condensation. The concrete literally freezes and ice up when the temperture dips down to -10 to -20 degrees in the evening. When it warms up during the day, the exposed concrete becomes wet as well as the surrounding fiberglass insulation. I'm concern that mold may form over time if I don't deal with it.

Also, when the installer cut the hole for the exhaust duct, I notice a hugh gap between the duct and the wall. Can I spray foam insulation into the gap?

Any suggestion on insulating the concrete around the duct? The installer advised me to leave it as it ...

Thanks

 
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ME

02-01-10, 09:22 AM   #2  
Hi limron and welcome to the forum.
To seal around the duct to concrete hole, I would use a high temperature silicone. I know it's not hot, but for a small job, the better stuff will avoid any one questioning it later.

As for the exposed concrete, I would normally cover concrete with rigid insulation. It simultaneously insulates and blocks any air from accessing the cold concrete. You'll need to check to see if any clearances are required between combustibles and the duct/vent. If a space is required, then the gab can be covered with sheet metal, but something should fill the gap that acts as an insulator and meets the codes.

Be sure to seal any openings that were created where warm moist inside air can reach those cold concrete walls. You know the results.

ROXUL is a mineral based insulation that can withstand over 2,000 degree temps, according to their flyer. I know Canada has been using mineral wool for years so perhaps a product along those lines.

Bud

 
limron's Avatar
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02-01-10, 10:58 AM   #3  
Thanks BUD9051 for your quick response. Just some questions for clarification..

As for the exposed concrete, I would normally cover concrete with rigid insulation.
- Is this similar to a styrofoam insulation sheet which can be held in place by contruction adhesive?

ROXUL is a mineral based insulation that can withstand over 2,000 degree temps, according to their flyer.
- I've seen those at Home Depot and will check it out. I'll have to remove the silicon and the exterior vent. I assume it's a matter of stuffing the gap between the duct and the concrete hole with the ROXUL insulation?

Thanks

Posted By: Bud9051 Hi limron and welcome to the forum.
To seal around the duct to concrete hole, I would use a high temperature silicone. I know it's not hot, but for a small job, the better stuff will avoid any one questioning it later.

As for the exposed concrete, I would normally cover concrete with rigid insulation. It simultaneously insulates and blocks any air from accessing the cold concrete. You'll need to check to see if any clearances are required between combustibles and the duct/vent. If a space is required, then the gab can be covered with sheet metal, but something should fill the gap that acts as an insulator and meets the codes.

Be sure to seal any openings that were created where warm moist inside air can reach those cold concrete walls. You know the results.

ROXUL is a mineral based insulation that can withstand over 2,000 degree temps, according to their flyer. I know Canada has been using mineral wool for years so perhaps a product along those lines.

Bud

 
Bud9051's Avatar
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Join Date: Oct 2008
Posts: 9,773
ME

02-01-10, 02:44 PM   #4  
Yes, the rigid insulation is the pink or blue type stuff and construction adhesive if it says it is ok for foam board. I think liquid nails, but read the label first.

Obviously I can't see the installation, but the primary issue is air sealing. that was the high temp silicone, but sounds like that may already be done???

The mineral insulation was to insulate where the rigid foam cannot be placed too close to the duct, assuming that is the case. If there is a large gap between the duct and the concrete, as long as it is air sealed, you probably don't need to pull it apart. But I'm here and you're there so your choice.

Bud

 
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