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Navien Tankless installation on OSB plywood

N

No Soup for you

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Feb 13, 2020
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New York
I did a search couldnt find.
Sorry didny know whether to put in plumbing section or mech etc...

Did an inspection and the Navien tankless water heater is mounted on a sheet of OSB plywood. I am thinking probably not a great idea as it is combustible.
So i look up mounting instructions from Navien, no mention of this,
I call the technical dept they say not to be mounted on combustible material, he says its in the instructions. I cant find it...
I call back and I am on hold forever , so I try the "chat" thing from website, I specifically ask about OSB as its combustible, they say not to use OSB because it will not be strong enough to hold the unit which is BS.

I checked fuel gas code, refers back to plumbing code, Cant find anything about combustible material.

Am I missing something?
Should I let it go?
Any discussion?
 
I would not have thought twice about it.

Google says that OSB may ignite at temperatures above 400 degrees F. Paper burns at 451. Sheetrock is covered with paper.

I don't know about any requirements off the top of my head.
 
Many tankless water heaters have a label with the required clearances (top, side, back). I would not have an issue with mounting over the OSB as long as the minimum clearance, which might be 0", is there.
 
steveray said:
If the exhaust doesn't melt PVC, it's not likely to set anything on fire...
Click to expand...
I think your remark raises an additional concern. the discharge temp of the condensing flue gas can turn PVC Brown and the manufacturers usually don't rate PVC for that use (only DWV) SO me thinks it is less than clear about PVC vs CPVC for the discharge Flue Gas.

Anyone got the complete story, I would like to understand this better
 
Most high-efficiency tankless water heaters and furnaces are rated to discharge into PVC piping, and it is a very common installation. Because they are high efficiency, they waste a lot less energy in the form of heat that is exhausted, which means that the temperature of the flue gasses are much lower. I believe the code refers to this as a Type IV appliance.

https://structuretech.com/gas-appliance-categories/
 
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