My 20 year old natural gas WH’s (water heater’s)hot water is only enough for one person to shower, so I want to replace it before it leaks too. However, its 3″ vent pipe is “T”d into the 6″ double wall vent pipe that my new high-efficiency furnace no longer uses. The furnace and WH are side by side in the basement about 1′ from the wall.
The 6″ pipe runs through the concrete block basement wall (5′ up) then under & parallel to an interior door to the garage and then up between the wall (contains the door) between the attached 2 car garage and the family room (no basement) into an attic then up through the roof above the garage and family room.
On the phone, the Borough engineer thought the existing 6” metal vent pipe may be too big for just the WH, though one of the engineers inspected the new furnace installation about 7 years ago and didn’t mention it. Also, the code may have changed.
What are my options for venting a replacement WH other than switching to a power vent WH & venting through another basement wall, which has its own problems?
Hi there, based on the Seven Times rule, the largest permissible chimney diameter for the water heater with a 3″ draft hood would be 7″ (49.455sq inch), so your 6″ almost completely concealed within the house structure (warm chimney) should be OK.
But I’d highly recommend to use Gamma tables, where you can input BTU, vent pipe length and # of all connectors –http://icpindexing.mqgroup.com/documents/076416/gama%20vent%20tab.pdf Power-vent equipped water heater will cost you a few hundreds $$$ more than regular, savings per year are roughly $30.00 (based on energy guide), so you’ll need 10 years to get that extra money back.
Also, it needs electricity to run the motor, and the motor runs a lot (before and after the burner stops). High efficiency water heater or tankless type will save you more money, but it costs much more. Tankless is probably the best choice, but it must be installed as close as possible to the faucets to give you biggest savings, it usually requires larger gas pipe diameter and special venting. If your current chimney will match the Gamma tables, getting another regular WH will be of course the cheapest way. Did that information help? 🙂