TOPIC: Cobustion Air

Hey guys I've been seeing a trend around here on combustion air pipes for closets.

I have been noticing a lot of new homes having only one large combustion air pipe for closets instead of the two high low configuration I was taught.  I have asked a plumber friend of mine about this and he said he doesn't know of any code changes. 

Anyone here know more about this?  Are they just trying to cut corners here?

Is that a water heater in that 2nd picture?

Hey guys I've been seeing a trend around here on combustion air pipes for closets.

I have been noticing a lot of new homes having only one large combustion air pipe for closets instead of the two high low configuration I was taught.  I have asked a plumber friend of mine about this and he said he doesn't know of any code changes. 

Anyone here know more about this?  Are they just trying to cut corners here?

Yes I've seen different ways of supply also. Hi/lo and sometimes one.
Check with your local HVAC guy in your area. all building jurisdictions differ. usually related to btu's of appliances that are being served. 

Is that a water heater in that 2nd picture?

Most of the time the hot water and the HVAC are in the same closet here.

John, I have seen those setups more than once and what appears to make the decision is the amount of make up air require for a burner.

ASME Section VI Recommended Rules for the Care and Operations of Heating Boilers
Reference 6.04 states:

The boiler room must have adequate air supply to permit clean, safe combustion and to minimize soot formation. An unobstructed air opening should be provided. It may be sized on the basis of 1-square inch free area per 2000-btu/hr maximum fuel input of combined burners located in the boiler room, or as specified in the National Fire Protection Association standards for oil and gas burner installations for the particular job conditions. The boiler room air supply openings must be kept clear at all times.

From experience the ASME rule of 1-square inch free area per 2000-btu/hr (Unit Converter) maximum fuel input of combined burners located in the boiler room works.

So if the amount of free air is available for one or two burners, it should be ok, although it is not set up like you said, hi and low.

Here in Maine some commercial air intakes have to have motorized dampers on them so they only open when the burner starts, due to the cold in the winter time.

Hope this helps.

Marcel 

Yes, reminding me of the numbers is always a good thing.  I guess technically it doesn't really matter if its one or two. 

I just remember something somewhere about the reason they went to the high low duel pipe configuration.  It was something about it allowed the air to circulate better.  Also there was something about the low pipe needed to be within 6" of the burner chamber. 

All this is making me think, I need to hit the books for a refreasher!  lol