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Outside Combustion Air?

kaorisdad's picture

Outside Combustion Air? (post #186151)

kaorisdad on Mon, 03/15/2010 - 11:36
in

The new California Mechanical Code (Section 701.3) requires that separate combustion air is provided for a FAU.  Not being familiar with this, how is this different to previous practice?  What is required now?

-A +A

>>how is this different to (post #186151, reply #1 of 4)

by rjw in reply to kaorisdad [original] on Mon, 03/15/2010 - 14:13

>>how is this different to previous practice? 

Presumably, the prior code allowed conditioned air to be used for combustion.

>>What is required now?

Tye code will provide specifics.... In my area it means air supplies from out doors (or crawl spaces and attics) to both the top and bottom of the combustion zone.  The size of the supplies will likely be specified in the code.

General rule of thumb is 1 sq" of free vent space per 1,000 btu.

Free vent space includes the effects of a grill over the opening.

Rule of thumb there is 50% reduction (Usually, grills say).  I believe that if there are 2 such grills, one inside the wall and one on the outside, the net air supply is reduced to 25%

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Generally (post #186151, reply #2 of 4)

by Clewless1 in reply to kaorisdad [original] on Thu, 03/25/2010 - 16:55

this probably means air ducted into your furnace room from outside. Details of requirements MAY include a motorized damper to interlock w/ the furnace (which is a good idea to prevent unconditioned air leakage into the house when the furnace is not on. Previously, the furnace could draw combustion air from the house or mechanical room in general ... if not in 'a confined space'.

There will likely be specific requirements as the other poster elluded to ... e.g serving the space high and low and be a certain size.

There ain't NO free lunch. Not no how, not no where!

No different (post #186151, reply #3 of 4)

by Tim in reply to kaorisdad [original] on Tue, 03/30/2010 - 12:11

http://www.iapmo.org/California%20Mechanical%20Code/Chapter%2007.pdf

I read the Code section and compared to most Mechanical and/or Fuel Gas Codes Iv'e dealt with in recent years, there is no new requirments.

I don't know what the previous practice was, and since it is no longer applicable, who cares.

If you use a direct vent (post #186151, reply #4 of 4)

by Jeff_Clarke in reply to kaorisdad [original] on Tue, 03/30/2010 - 21:58

If you use a direct vent model it will take it's own combustion air in through the PVC intake (or PVC concentric vent).   Case closed.

Otherwise see my post on creating dampered makeup air.