Does any natural draft appliance must have a draft hood? 1

[Hydronican]

I'm working on the flue vent design where there are boilers and furnaces. Some appliances clearly specify a draft hood, but the others do not say anything about draft control devices. I checked the code. It looks like it depends on appliance combustion chambre design (positive, zero, or negative pressure combustion), only zero-pressure combustion appliance requires a draft-hood. The problem is: if the appliance is designed as negative pressure combustion, we don't have to put a draft-hood at all, even the chimney draft is super strong? what's the limit of it?



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[lma1]

You must first check with the manufacturer whether the boiler or furnace is one used with a draft hood or draft regulator. One should not by or on himself determine whether the gas appliance requires a draft control device or not.

A draft hood equipped appliance is a category I appliance operating with non-positive vent static pressure. An appliance not equipped with a draft hood or draft hood not required could still be a fan-assisted type I appliance for venting into a type B vent.

The type of chimney or vent to use is always listed with the appliance. You must check with the manufacturer or its installation instructions, the gas Code &/or Regulations in your area to see what kind is required.

There will always be limits as to its height (vertical or lateral), size (ӯ), type and material depending on the input rating of the appliance.

For example, a 3” Ø 15’ high type B vent with a 2’ type B lateral can only serve a max of 69 MBH (input rating) fan-assisted category I domestic gas water heater or a 48 MBH drafthood-equipped one, according to our gas installation code.