over sized hot water heater flue

[spaz]

Installed a new 90% furnace and vented out the side wall. The hot water heater is still vented in to the 6” b-vent flue. Has anyone had a problem when doing this?

[blitz]

it could have problem with condensation and possibly down draft/spillage... you might be able to fit 4 inch liner down the hole. you need to do your venting calculation.

[hearthman]

You are allowed x7 the cross-sectional area by code but combustion analysis will tell you if it is working or not.

[Crimzin Shadow]

Condensation will be the main issue. Also depending where you are, but here in Ont, you can only go one size larger on a forced device then the flue collar size. so if you're a 4" flue collar you'd have to change the size to 5" to be in code.Blitz nailed it. vent size calculation chart

[rob williams]

I know this sounds petty, but in our trade, it is a "water heater" not a hot water heater. 6 inch b-vent should be fine, depending on the vertical height. In some areas, because of the vertical height of the main stack, when you orphan a water heater, the connector pipe must be b-vent, to keep the flue gas temperatures up enough before they get to the 6 inch stack. In our area, which is WSSC territory in Maryland, if you touch the flue pipe for a furnace install, you own the entire furnace and water heater flue piping, even if the water is 20 years old. It is up to you, to bring everything up to current code.