Replies

1. 
   rjw | Mar 15, 2010 05:13pm | #1

   >>how is this different to

   >>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%

2. 
   Clewless1 | Mar 25, 2010 07:55pm | #2

   Generally

   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.

3. 
   Tim | Mar 30, 2010 03:11pm | #3

   No different

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   I don't know what the previous practice was, and since it is no longer applicable, who cares.

4. 
   Jeff_Clarke | Mar 31, 2010 12:58am | #4

   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.