Inspecting Direct Vent Water Heaters

Inspecting Direct Vent Water Heaters

Most new builds and retro installations utilize either an on demand water heater or powered direct vent water heaters. Inspecting powered direct vent water heaters is different from inspecting a conventional natural chimney vented unit. A powered direct vent water heater employs an electric induced fan. The flue gases exit to the outside usually through a PVC pipe, although some units use a metal flue pipe. The exhaust pipe terminates outside through a side wall. If a catch or drain pan is installed under a direct vent unit, ensure the pan does not restrict air flow to the unit. The drain pan must have a minimum length and width of at least 4 inches larger than the diameter of the water heater. In addition to our standard inspection of all types of water heaters, here are some items we should be looking for on powered direct vent hot water heaters:

• The PVC vent should be properly supported every 3’
• The horizontal run of the vent pipe should be sloped away from the induced blower not less than 1/8” nor greater than ½” per foot. This is to ensure any condensation drains away from the unit. This may not be necessary if a condensate trap is installed on the unit. Check with the manufacturer’s recommendation.
• A minimum of a 3” PVC pipe should be used for venting. A 4” PVC pipe may also be used.
• For 3” vent piping; the total equivalent feet of venting (intake plus exhaust) must not exceed 80 feet and the total equivalent feet of venting (intake or exhaust) must not exceed 40 feet. The total equivalent feet of intake must be within 20 feet of the total equivalent feet of exhaust. (Check with the manufacture)  
• For 4” vent piping, the total equivalent feet of venting (intake plus exhaust) must not exceed 150 feet and the total equivalent feet of venting (intake or exhaust) must not exceed 75 feet. The total equivalent feet of intake must be within 20 feet of the total equivalent feet of exhaust. (Again check with the manufacture)
• Subtract 5’ for each additional 90° elbow and 2.5’ for each additional 45° elbow for both 3” and 4” pipe.
• If a two pipe system is employed the exhaust and intake terminals must not be less than 16” apart. The exhaust terminal must be mounted above the intake terminal.
• The vent pipe should be at least 12” above the ground unless there is a snow concern.
• A three wire grounding type receptacle should be installed within 6 feet of the water heater if not directly hard wired. The line cord should not be plugged into a power supply that can be interrupted by a switch.