Calculating Combustion Air - HVAC - Contractor Talk

Calculating Combustion Air

Thread Tools Search this Thread Display Modes
Old 03-08-2017, 09:03 PM   #1
3 Jacks 2 Nines
bwiab's Avatar
Trade: Wannabe Homebuilder
Join Date: Mar 2006
Location: Arvada Colorado
Posts: 392
Rewards Points: 2

Calculating Combustion Air

Looking at two 50 gallon power vent water heaters. Not direct vent so I need combustion air. Total BTU is 80,000 so if I follow the code

2009 IRC - Combustion air requirement = 80,000/1000*50CF = 4000cf.

I got 1920 cf in the utility room and 7500cf in the basement adjacent. So My understanding is that I only need two 100 square inch louvers in the wall separating the utility room and the basement. One up high and one down low. That sound right? Apreciate your insight!
bwiab is offline  

Warning: The topics covered on this site include activities in which there exists the potential for serious injury or death. DOES NOT guarantee the accuracy or completeness of any information contained on this site. Always use proper safety precaution and reference reliable outside sources before attempting any construction or remodeling task!




Old 03-08-2017, 09:30 PM   #2
General Contractor
greg24k's Avatar
Trade: New Home Construction-Additions-Remodeling
Join Date: May 2007
Location: NJ
Posts: 7,835
Rewards Points: 8,902

Re: Calculating Combustion Air

You need 2- 12x12 louvers one installed 12" from the ceiling and second installed 12" from the floor and that should do it.


I never lost a cent on the jobs I didn't get!
greg24k is offline  
The Following 2 Users Say Thank You to greg24k For This Useful Post:
belangerheating (03-11-2017), bwiab (03-08-2017)
Old 03-09-2017, 12:19 AM   #3
Fouthgeneration's Avatar
Trade: Masonry
Join Date: Jan 2014
Location: Middle
Posts: 2,720
Rewards Points: 9,917

Re: Calculating Combustion Air

Why not use outside air to save $, a insulated 3" or 4" pipe to the sunny side of the house above the snow line,saving the cost of burning A.C. in the summer, Heated air in the winter?

A back up flapper vent on the doorway to the Hot water heater closet...

Do you have to adjust the jet or air flow at your altitude?
Fouthgeneration is offline  
Sponsored Links
Old 03-09-2017, 05:23 AM   #4
beenthere's Avatar
Trade: HVAC
Join Date: Mar 2009
Posts: 2,471
Rewards Points: 1,256

Re: Calculating Combustion Air

That would be 2-100 sq in free area louvers. So as posted earlier, 2-12x12s.
beenthere is offline  
Old 03-09-2017, 06:27 PM   #5
Fouthgeneration's Avatar
Trade: Masonry
Join Date: Jan 2014
Location: Middle
Posts: 2,720
Rewards Points: 9,917

Re: Calculating Combustion Air

You could build an insulated room around the HW heaters to isolate the waste heat by slowing the heat flow into the Air conditioned spaces during the A.C./dehumidifier seasons, closing any air returns or supplies from the A.C./furnace duct-work.

And of course reopening the ducts to spread out the "waste" heat in the heating season.

In modern super tight home, the suction of a radon gas blower, bath vent fans and appliances such as cloths dryers and Range hoods need to be considered regarding the creation of a negative draft that would cause exhaust gases to fill interior spaces....

Even a dry floor drain trap can allow the DVW roof stack to suck air out of confined basements. Or emit toxic sewer gases.
Fouthgeneration is offline  

Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes Rate This Thread
Rate This Thread:

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off

Similar Threads
Thread Thread Starter Forum Replies Last Post
Question about workin on my own oil burner InterCounty HVAC 6 04-29-2013 12:05 AM
calculating crown spring angle Mrmac204 Finish Carpentry 12 12-26-2012 08:08 AM
Calculating Mud and Tape MasterBuilt Drywall 4 01-06-2011 08:08 PM
Combustion Air Calculations MechAcc HVAC 2 04-02-2010 05:42 PM
I Need cheap Combustion Analyzer delavan Tools & Equipment 9 02-15-2010 04:56 PM

Join Now... It's Fast and FREE!

I am a professional contractor
I am a DIY Homeowner
Drywall Talk is for

At we cater exlusivly to professional contractors who make their living as a contractor. Knowing that many homeowners and DIYers are looking for a community to call home, we've created DIY Chatroom is full of helpful advices and perfect for DIY homeowners.

Redirecing in 10 seconds
No Thanks
terms of service

Already Have an Account?