Correct size flue for Furnace and water Heater?

yazkSeptember 24, 2010


I have a Gas furnace and a Gas water heater that each have a 4" flue pipe from them. These two are then connected into a single 8" pipe that goes up through my chimney. I was told that 8" is too large and it has probably been there for years and no one bothered chnaging it when they installed the new furnace.

Can anyone confirm what size flue I should use to cater for two 4" pipes?

Thank you for reporting this comment. Undo

Look in the flue sizing tables in the gas code. Depends on your total BTU output.

    Bookmark   September 24, 2010 at 1:06PM
Thank you for reporting this comment. Undo

And since your furnace is 4" it sounds like a fan assist so you should be looking at the NAT + Fan total BTU chart with correct vent connector length and chimney height.

Heres a link why there needed and sizing charts, assuming its gas appliances

    Bookmark   September 24, 2010 at 11:26PM
Sign Up to comment
More Discussions
Who do I call about a whole-house fan?
I'd like a whole house fan. This might be a DIY project,...
I need help in deciding on a replacement central air conditioner
I need help in replacing 38 year old 1 1/2 ton 8 Seer...
HVAC billing question
Question for the pros...... So I had a faulty capacitor...
No Fully Trained Mini Split Installers
Reading threads about mini split heat pumps I got curious...
1 vs. 2 stage cooling? 80% vs. 95% furnace?
I'm in SoCal near L.A. (zip 91354). Two story house...
M. A.
Sponsored Products
Christopher Knight Home Modern White Leather Roundback Chair
Fortebraccio Table Lamp
Eastwood Single Arm Sofa - Key Largo Ruby Red
Joybird Furniture
Massaud w083 Table Lamp by Wastberg
$625.00 | Lumens
Pulse Vinyl Office Chair in Brown
$89.00 | LexMod
Solar Goes Green Path & Landscape Lights Solar Powered Black Outdoor Spot Light
$85.99 | Home Depot
Harris Tweed Dog Collar
$79.50 | FRONTGATE
Frameless Deco Mirror
People viewed this after searching for:
© 2015 Houzz Inc. Houzz® The new way to design your home™