Sizing Chimney Vents

[michael333]

Here are my givens for the application:

(3) gas-fired furnaces: 80000 btu/h input ea. (240000 btu/h)
All three furnaces are side-by-side in an enclosed mech
room. Volume of the space is approx. 20'L x 12'W x 10' high
Will (1) 10" diameter vent connected to all three furnaces
via a manifold to them work?? Or does each gas-fired
furnace need it's own independent vent up through the roof?? 3 separate vents?? Is the 2006 IFGC code the best place to go to answer this?? Where do I look in the code??

Thanks for any help that someone may offer.

Mike V.

 

[cdxx139]

Depends on the codes in your area.
For Category I appliances, we use NFPA 54
For Category II, III, IV, use manufacturer's recommendation, check the IOM.
The vent from the furnace cannot be smaller than the actual vent connection to the furnace.
Another option is to have a chimney vent manufacturer size it for you, but you are ultimately responsible.
Typically the more vertical vent you have the better.
Dont forget the combustion air.
Good luck

 

[TBP]

Why not just ask the vendor? Surely there must have been installations like this before. It may even be included in the installation instructions.

If you're unsure about which gas code applies in your jurisdiction, ask the people at the gas utility supplying the fuel.

 

[cdxx139]

ask the vendor,
but don't trust the vendor,
use it as a check

knowledge is power

 

[DrRTU]

If furnaces can be vented with B vent, then you could use

http://www.hartandcooley.com/vent/all_vent.htm

and the code the AHJ requires. Make sure you are good on the combustion air with the code.