We are redoing our basement and closeting off the boiler and hot water heater. With our layout, it makes most sense to vent it out of the chimney. However, I want to make sure we are getting enough air draw. Does anyone know if slated doors are enough? Is there a better system I'm not thinking of?

  • 1
    That's a fairly loaded question for a potentially dangerous situation and with very little information. Perhaps update your question with a model number or accurate description of the unit?
    – isherwood
    Dec 18, 2015 at 21:10

1 Answer 1


According to NFPA 31, you'll need two openings. One near the top, and one near the bottom. Each of which must be 1 in.² per 1000 Btu/h of the input rating of all the appliances in the confined space.

NFPA 31 Standard for Installation of Oil Burning Equipment.

Chapter 5 Air for Combustion and Ventilation.

5.4 Appliances Located in Confined Spaces.

5.4.1 All Air Taken from Inside the Building. The confined space shall be provided with two permanent openings as shown in figure, one near the top of the space and one near the bottom. Each opening shall have a free area of not less than 1 in.² per 1000 Btu/h (140 in.² per gal/h) (22 cm²/kw), based on the total input rating of all appliances in the space.


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