Click here to Find a Contractor in your area.
Welcome! Here are the website rules, as well as some tips for using this forum.

If you've found help here, check back in to let us know how everything worked out.
It's a great way to thank those who helped you.
Need to contact us? Visit

Air Diffuser In Boiler Room NYC

eric_38eric_38 Member Posts: 2
My plumber recently told me that I need to install an air diffuser in my boiler room (20 family apartment house) to pass NYC boiler inspection. Does anyone know what this is and the appropriate place to find one? What I have now is an open window, with wire mesh (to keep out vermin). How about sizing? This is a 1,000,000 btu (input) gas fired boiler. There is also a large gas water heater in the boiler room.


  • Brad WhiteBrad White Member Posts: 2,392
    I am guessing

    a good combustion air system is in order here. One is known colloquially as a "Fan in a Can". Tjernlund is one company, perhaps that is their model. The other is Exhausto out of Atlanta, GA.

    The simple ones have a pressure switch wired in series to the burner so if there is no established flow the burner cannot fire. The Exhausto and Tjernlund models I specify use a pressure differential basis. The fans are ducted and have VFD's to maintain a positive pressure in the boiler room. The principle is that if the room is positive in pressure there is enough air getting in for proper combustion. Air pressure switches govern and lock out the burner if not at setpoint.

    I take it that the boiler room is land-locked and not on an outside wall? NFPA-54/ANSI Z223.1 is one national code (National Fuel Gas Code) which may or may not be accepted but has principles they are probably looking for. So many square inches of free combustion air area (per BTUH input) to the outside if air from the inside is not practical.

    For example, if directly ducted to the outside, one square inch per 4,000 BTUH input is a minimum. If ducted horizontally any distance, it doubles to 1 square inch per 2,000 BTUH input. The input number refer to all appliances in the enclosure, firing or not. I also take the area numbers as equivalent in and the same out, so double them.

    One opening has to be within 12 inches of the floor and the other within 12 inches of the ceiling of the space enclosing the boilers/heaters. If this passive arrangement is not possible then an engineered system (such as I describe and as you were being directed) seems to be what they are looking for.
    A lot to explain but get a copy and see what you find.
    "If you do not know the answer, say, "I do not know the answer", and you will be correct!"

    -Ernie White, my Dad
  • eric_38eric_38 Member Posts: 2

    This boiler room is not landlocked but is on an outside wall. The venting now is essentially an always open window with a wire mesh screen. This window is at the ceiling level. As the boiler is in a basemnt it is not possible to provide any lower air access.
  • Brad WhiteBrad White Member Posts: 2,392
    If the window is large enough

    to satisfy both full areas required, you build a sheetmetal plenum dividing the two paths and duct one of the halves down to a foot above the floor. No one really expects you to open the wall that far below grade, but if you did, you might get lucky and find your own personal entrance to the transit authority which could save you the fare :)

    I imagine that the inspectors think that the opening is not adequate, in which case they are requiring a ducted powered system. Give Steen at Exhausto a shout. Their MCAS system might be a good place to start.

    [email protected]

    "If you do not know the answer, say, "I do not know the answer", and you will be correct!"

    -Ernie White, my Dad
  • Could be the plumber

    ment to say "louver", rather than diffuser. If so, ask him to procure & install the properly sized piece.

  • tim smithtim smith Member Posts: 2,288
    Regarding combustion air grill

    Depending on if your muni adopted the international fuel gas code (IFGC), the ifgc now allows for only one opening to outside located w/ in 12" of the ceiling of mech. room. sizing is 1 sq. inch per 3000 btus. The uniform mech. code still say's 2 openings, one at ceiling and one at floor. divided ducts, 1 sq inch per 4000 btu per each opening. Most muni's I deal with have adopted the IFGC code. Just some tid bits. Tim
  • Brad WhiteBrad White Member Posts: 2,392
    That is good to know, Tim


    Here in MA they have been talking about moving to the IBC and IMC for years. What we see coming in would still have chapters "entirely unique to Massachusetts". I guess we are like that :)

    Nice to see the code pendulum swing toward more practical applications.

    We are still under NFPA-54 here, which used to be printed verbatim in the Mass. Fuel Gas Code. But the odd thing is, under the Fire Prevention Regulations, they allowed much less area for large boilers, on the order of 1 square inch per 17,500 BTUH input. Go figure!
    "If you do not know the answer, say, "I do not know the answer", and you will be correct!"

    -Ernie White, my Dad
This discussion has been closed.


It looks like you're new here. If you want to get involved, click one of these buttons!