Water Heater Venting

rakes9720

Our 78% efficient furnace was recently replaced with a 93% efficiency furnace and it left a water heater venting into a 5" type B vent.
The water heater vent is 3" and it is connected to a tee where the furnace used to be. It is now covered with a four inch cap. I am wondering if the vent pipe needs to be changed to a 3" pipe all the way to the roof. The pipe goes through a garage and attic, is wrapped in insulation, and is about 25' long. The water heater input is 40000 btuh.

The water heater is 12 years old, so it might need replacing soon, any thoughts on power vented models?

Thanks for the help.

HVAC Doc

If you don't want the flue pipe to be corroding and falling apart in the next year or so as well as pilots being blown out or fear of backdrafts, then yes, get that flue pipe sized correctly!! Depending on your local codes, they may want a 4" inch pipe but 5" is too big.

Bestheating

I looked at this post when it came out, and didn't catch something. When you measured the 25 foot length, how much of that was horizontal? Typically, my inspectors like to see 4" on most water heaters. 3" is history and I don't know of any instance where it would be used. I might suggest a 4" liner through the 5" chimney and then 4" b-vent to the unit, but check with local codes.

locofoco

The original post here is a month old and you've probably figured it out by now. You may be okay leaving the 3" in the 5" stack. Go to Hart & Cooley's website and click on type B vent - Additional guidelines for single appliance venting (pg.9). Hart & Cooley makes Metlvent flue material. This is a great site for anyone with a venting problem.

rakes9720

Whenever we lit a fire in our fireplace on the other side of the house, the pilot would go out because the fireplace would pull air down the flue of the water heater. About a week later the pilot would not remain lit, and after relpacing the thermocouple it still did not work. Since it was so old, I got a new, loud but more efficient, power vented one. It solves the venting issue.

Thanks for the help.

By the way, about 10' of the old vent was horizontal.