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Tankless water heaters vents and foam Post New Topic | Post Reply
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Jimmy Eaton
Posted: Nov 29, 2007 07:39 AM
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Tankless water heaters vents and foam
I am building a new home and am installing tankless hot water heaters which vent through my roof. I am having foam insulation installed against the roof deck. My question is: How much separation should there be between the foam and the vent duct?
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mason
Posted: Nov 29, 2007 08:26 AM
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A rule of thumb is never install sprayfoam to any substrate 200 degrees F or above. At this temperature and above the foam will discolor and lose some physical properties, adhesion would be affected also, at higher temeperatures (250 to 300 degrees F) it will char next to the hot substrate. So, in this case typically 3-4 inches of separation should suffice, if you install a heat resistant insulation next to the vents. Hope this helps. Hope this helps. |
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mason
Posted: Nov 29, 2007 08:32 AM
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PS, there should be pre-insulated vents that can be used as well, that you could spray foam against. Check with your heater installer. |
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SprayFoamSupply.com
Posted: Nov 29, 2007 09:42 PM
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By preinsulated vents, do you mean metal bestos or similar? George |
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mason
Posted: Nov 30, 2007 08:28 AM
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Yes, some vents have insulation fabricated into the vents themselves. The key is to have the metal surface that you spray foam to to be less than 200 degrees F. (note; some suppliers call for no more than 180 degrees F to be safe.) |
