Combustion air opening

[MagicJS]

Hi, I'm hoping someone here can clarify NFPA 54 requirement for outdoor combustion air for me.

Section 8.3.3 calls for openings in boiler room enclosure of 1 sq.in./2000,3000,4000 Btu/hr of input depending on method. The openings shall communicate directly, or by ducts, with the outdoors or spaces that freely communicate with the outdoors.

While opening sizes in the boiler room is quite clear, what's not clear is the area required for the connecting duct and louver. Someone said to size them at 12 CFM/HP at .005" pressure drop, someone else emailed me a chart of manufacturer's recommendations, another said to use same area as required openings in the boiler room.

Need a little guidance here on code compliance. Thanks.

 

[imok2]

This may help you:

http://www.energysolutionscenter.org/BoilerBurner/Eff_Improve/Operations/Air_Supply.asp

 

[lzh007]

same area as required openings in the boiler room.

 

[DuctPipeMan]

MagicJS,


Here in Tennessee, code officials interpert that to say that the free area of the duct and the free area of the louver are to conform to the SqIn/BTU rule.

ie. A 1000MBH boiler requiring 1 sqin/4000 btu will need 250 sqin area duct. If you use a std louver with ~ 75% free area the louver will need to be ~ 333 sq in.

For large boilers, (Where there is not enough wall to satisfy the natural ventilation or where freeze protection is important) I engineer a combustion fan sized to provide the CFM of air required for combustion and interlock fan with boiler safties. This sometimes takes a little explaining to the boiler official.



Earl M Keith, PE
Tennessee

 

[cme]

that 12 cfm / bhp is based upon excess air combustion calculations