Author Topic: Outside air intake for power vented water heater  (Read 1191 times)

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Outside air intake for power vented water heater
« on: December 03, 2018, 08:26:06 AM »

I recently had my propane system inspected when changing propane suppliers and was given a conditional pass based on a correction required for the hot water heater.
We were told per B149.1 8.2.3 we need to install an outdoor air supply for the water heater.
The water heater is 75,500 BTU and power vented with a vertical run of 2' and horizontal run of 3' to outside.  It is in an open half of the basement approx. 400 sq ft in area with the furnace that already has it's own outdoor air supply direct to it (2" diam).
My question is do I actually require an outdoor air supply, and if so what diameter pipe would be required?  Would it need to be run right down to the bottom of the water heater or just supply fresh air to the room?


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Re: Outside air intake for power vented water heater
« Reply #1 on: December 03, 2018, 08:49:25 AM »
Technically it’s Clause 8.2.1 or 8.2.4 that require an outdoor air supply.  Clause 8.2.3 is just an exemption for water heaters 50,000 BTU’s or less.

Without doing a depressurization test to determine how tight the house was built or knowing other factors the safe bet is using Table 8.1 which for 75,000 BTU’s requires a 4” round insulated outdoor air supply.  There may also be something written in the water heater manual that requires an air supply.

Have you looked outside to see if an intake vent is installed?  Sometimes they would run it directly into the return air duct, in which case you disconnect it and extend it over to the water heater.

If the outdoor air supply duct is longer than 3m, certain areas like Ottawa, require R8 insulation and not the standard R4.2. 

A screened intake vent must be installed outside and the duct would terminate within 2’ horizontal and within 12” above the water heater burner.