Correct combustion intake location/configuration?

Specific Inspection Topics Inspecting HVAC Systems
1

This regards a basement installation of a sidewall-vented cat III gas boiler/furnace with combined use of inside and outside combustion air (50/50, not direct-vented), in Massachusetts.

In the diagram below,
A = gravity outside air intake, extends 12" down
B = dryer vent (electrical), louvered cap
C = exhaust, terminates with a horizontal z-vent box (deflects sideways)

and FWIW this is what the z-vent termination box looks like:

http://www.prowaterheatersupply.com/media/catalog/product/cache/1/image/313x/9df78eab33525d08d6e5fb8d27136e95/Z/-/Z-Flex-Z-Vent-2SVSRTF04_185.jpg

Anything wrong with this configuration? I have not seen this long of a downward extension for the intake before; one nearby unit has a similar kind of layout, except that the intake ends at the elbow and does not extend downwards (they seem to have gone with NFPA 54 12.9.3 instead of 12.9.2).

Thanks for your insight!

2

Are you saying that “A” doesn’t connect to the unit? It’s just a glorified hole in the wall?

You seem to have done a significant amount of research just to make your post. Why not find the manufacturer’s installation specs to determine if correct? I see similar setups to that all the time, what are you specifically questioning: measurements, the z-vent cap, the intake length?

3

Correct, “A” is not connected to the unit (the unit is not sealed/direct vented), so yep “A” is essentially a hole in the wall.

The diagram lacks the additional detail, but the “wall” pictured is a decorative wall that separates the great outdoors (on its left) from about 4ft of under-deck space (on its right); the foundation wall is 4ft to the right of the decorative “wall” pictured, see below:



        
                    | |
                    | |     deck
                    |XXXXXXXXXXXXXXXXXXX|~~|=========
                    |X|                 |~~|
decorative wall --> |X|   under-deck    |~~|
                ____|X|_________________|~~|_
               /  ___________________________  <-- hole in the wall
               | |  |X|                 |~~|
               | |  |X|                 |~~|
               +-+  |X|<----- 4ft ----->|~~|
                    |X|                 |~~|   <-- foundation wall
          outdoors  |X| under-deck      |~~|
                    |X|                 |~~|
                    |X|                 |~~|
          ------------------------------|~~|
          \\\\\\\\\\\\\\\\\\\\\\\\\\\\\\|~~|
          \\\\\\        \\\\\\\\\\\\\\\\|~~|  basement
          \\\\\  ground  \\\\\\\\\\\\\\\|~~|
          \\\\\\        \\\\\\\\\\\\\\\\|~~|
          \\\\\\\\\\\\\\\\\\\\\\\\\\\\\\|~~|__________

My two specific concerns are the following:

  1. downward extension of “A” to meet the 12" “below vent” clearance requirements in 12.9.2; looking at the NFPA and mechanical codes I can’t find anything prohibiting that, but I never saw something quite like it before either so I was wondering, e.g. assuming no problems with snow height, how badly could this 1ft downward extension impede intake during winter months by forcing COLD outside air to travel 1 extra foot UP with an additional 4ft horizontal run at outdoor temps?

  2. exhaust vent “C” is essentially blowing exhaust sideways under the dryer vent “B”; although “B” is louvered, when the dryer is not operating, should one be concerned with exhaust from “C” making its way through “B” through the dryer into the basement if e.g. “A” becomes obstructed?

The manufacturer lists no specific requirements other than quoting from NFPA 54 (pages 4, 9-12 from http://www.gogeisel.com/geiselonline/support/Burnham/Series_2PV_Service.pdf)