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Make up air

Jason_22 Member Posts: 39
Where can I find the chart for amount of air per BTU input?


  • Make up air are you

    referring to air required to replace air removed by mechanical exhausting, or dryers.

    Or are you looking for "Air For Combustion"?

    If it is air for combustion look in NFPA 54 2002 edition section 8.3 starting on page 54-29.

    If it is make up air due to exhausting then you have to know how much air is being removed from the building. If it is relative to dryers:


    In an earlier section we mentioned the need for air as it applies to gas dryers, in particular Type I Dryers for residential use. This is an important part of the air for combustion and ventilation requirements, which is often over looked by technicians. This is being added to the end of this section to reinforce its importance in the overall coverage of the air for combustion subject.

    From time to time questions have come up about Air for Combustion . In particular DRYERS and the affect they have on air requirements.

    In the National Fuel Gas Handbook authored by Ted Lemoff PE he states the following concerning dryers: "Type I clothes dryers (residential dryers) exhaust fans typically range from 180 cubic feet per minute (cfm) to 200 cfm. Higher exhaust models may exhaust up to 250 cfm. The air exhaust rates include air for removal of moisture, as well as the air needed for combustion of the fuel gas. For example, models with 180- cfm require 10,800 cubic feet per hour of makeup air. A gas dryers energy input ranges up to 35,000 btus per hr regardless of exhaust rate. Which at a rate of 10 to 1 for complete combustion is 350 cubic feet per hour. Therefore a dryers combustion air is only about 3 percent of the total air required for dryer operation.

    It goes on to say farther on in the code section that list requirement for installation of dryers, that it is a mandate to provide "make up air". Because this amount of air would include sufficent combustion air, the code requirements for combustion air need not be applied.

    In the section on requirements for make up air it states the following: "The quantity of make up air required for dryers exceeds that of other gas appliances. Generally, five to ten times the air required for an appliance of similar heat input should be allowed (similar would be say a 35,000 BTU water heater)." That means the typical 350 cubic feet of air required per hour would be 350 times 10 or 3,500 cubic feet for the dryer not including all the other equipment. Even on the low end it is 1,750 cubIc feet.

    Provisions for Make-Up Air

    Make-up air shall be provided for Type 1 clothes dryers in accordance with the manufacturers' installation instructions. In Figure 16 Dryer Installation Requirements make note of the opening for “Make Up Air”.
    The quantity of make-up air required for a Type I clothes dryer exceeds that of other gas appliances. The manufacturer's installation instructions, must provide opening requirements to allow sufficient air makeup. Note that Section 8.3 National Fuel Gas Code, Air for Combustion and Ventilation, has been revised in the 2002 edition to exclude clothes dryers with make-up air provided in accordance with this section from the air for combustion calculation. This exclusion recognizes that a large amount of make-up air essential for proper performance includes the small amount required for combustion.

    Generally, five to ten times the air required for an appliance of similar heat input should be allowed. If several gas appliances are installed in a space with insufficient air for; combustion and ventilation (see Section 8.3), or in a limited space (e.g., a utility room or service porch), provisions should be made for adequate combustion and ventilation air. Type I dryers that can be installed in closets will be identified as such by the manufacturer's installation instructions. In replacing a dryer in a small space, one listed for installation in a closet must be selected.

    Let it be noted that in many cases I have found that equipment installed in a confined area in the basement do not have adequate air for combustion. People get alarmed when I walk in and without any measurements tell them they have insufficient air. It is a no brainer - when I see the dryer and no provision for air I do not need to measure anything. The dryer creates a definite problem no matter what.

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