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Cold air intake - sizing

Bob W._3
Bob W._3 Member Posts: 561
Is there a rule for sizing cold air intakes on steam systems? My current boiler has a 10" flue; the replacement will have either a 7 or 8" flue. There is also a 50 gal. gas HWH in the boiler room. Currently there is no cold air source other than infiltration. I am planning to add an 8" intake through a window (all masonry home - no box joists, etc.) and running flex duct into a large barrel, which should act as the plug or damper. Any thoughts on this? Thanks.


  • Plumdog_2
    Plumdog_2 Member Posts: 873
    Contact your local Building Authority

    for the code adopted in your region. There are plenty of rules depending on the design of your Combustion Air System. I don't think using a large barrel is mentioned anywhere in any code book. You may want to look into Fan in a Can or the Enforcer as an option to having permanent openings that can cause freeze-ups or drafts; but check with the Permit Man (remember the Money Pit?) for his recommendation.
  • Mike
    Mike Member Posts: 94
    combustion air intakes

    Here in N.J., 2 openings are required. One openning high and the other low. The local utility co., wants 1 sq.in. per 1000 btus, of open free area. With a minium size of 100 sq.in. With this you really need to consider freeze-ups! Fans and or dampers, should be used instead of natural draft. But need to be wired to operate with each appliance. Always, check with the local code official, first. See what the require. Why do things twice.
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