Propane water heater flue through a SIP roof

**Mike Wakefield** · 12-07-2009, 11:21 PM

What a great forum! I am building a new home in the Colorado mountains, and have a propane water heater on the second floor. The class B flue must pass through a SIP (Structural Integrated Panel) 12/12 roof, and I'm looking for guidance. The roof panel has 1/2 inch of Fiberock on the inside, bonded to 1/2 inch of OSB, bonded to 11-1/2 inches of expanded polystyrene (EPS), and topped by 1/2 inch of OSB. The water heater is 36,000 btuh input, and has a 3 inch diameter vent. I'm having trouble finding hardware that works on the 45 degree slope, and can't find the clearances required to the roof components, especially the EPS. Any comments would be appreciated!

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**Bruce Breedlove** · 12-07-2009, 11:32 PM

Originally Posted by Mike Wakefield

The class B flue must pass through a SIP (Structural Integrated Panel) 12/12 roof . . .

SIP is a Structural Insulated Panel.

You will need 1" clearance around your B vent.

Stay warm. 4 degrees here in the Springs.

**John Arnold** · 12-08-2009, 04:41 AM

The way people spell on this forum, at first I assumed you meant "propane water heater flew through a SIP roof"! Boom!

**Bob Harper** · 12-08-2009, 05:38 AM

Mike, I strongly recommend you have a professional install the venting and follow it up with combustion analysis. Any house built with SIPs will be rather tight and not a good candidate for a B-vented water heater. It will most likely spill carbon monoxide at the first wind gust or exhaust fan. Go with a power vented WH instead and don't put holes in that roof. Vent out the side.

Bob

**Scott Patterson** · 12-08-2009, 07:18 AM

Originally Posted by Bob Harper

Mike, I strongly recommend you have a professional install the venting and follow it up with combustion analysis. Any house built with SIPs will be rather tight and not a good candidate for a B-vented water heater. It will most likely spill carbon monoxide at the first wind gust or exhaust fan. Go with a power vented WH instead and don't put holes in that roof. Vent out the side.

Bob

I agree with Bob, SIP homes are tighter than a jar of pickles! A power vent WH would be your best bet and any time you don't have to put a hole in a good roof you are better off.

**Mike Wakefield** · 12-08-2009, 09:20 AM

The suggestion for a powered vent on the WH is a good one. Being SIP, the house is very tight. I have two 4 inch diameter combustion air ducts from a side wall feeding the high and low areas of the closet containing the WH, but wind is an issue, and there could still be some spillage. Unfortunately, the side walls are only 4 ft high, so a powered vent thru the wall could not be above the level of the WH. I wish I had opted for an electric WH at this point, but have installed and passed inspection on the gas supply lines.