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Combustion air requirements

Without getting into the other air intake possibilities...code requires that the outside air intake ducts be covered with no less than a 1/4" screen. My concern is that there are a lot of bugs, mold spores, etc. that are much smaller. There's no way to fit this with a filter?

More details:
I bought a foreclosed house and the bank had just installed a brand new power vent water heater. Unfortunately, as I would like to seal up the house I am worried about providing combustion air to this appliance. A direct vent water heater would have been preferable but I'm not willing to shell out the cash to replace an 8 month old water heater.

Asked by Jim Johnston
Posted Aug 1, 2014 2:15 AM ET
Edited Aug 1, 2014 6:12 AM ET

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Jim,
If I understand correctly, this code-mandated air intake duct leads from the intake grille to a mechanical room or basement. Usually this type of duct terminates near the appliance it serves.

Unless you have noticed an infestation of insects or indoor air quality problems, I would stop worrying if I were you.

It may be possible to build a partition to separate your mechanical room from the rest of the house, if you are worried that your indoor air could be contaminated. But you need to be sure that the room meets minimum volume requirements, and that your fresh air duct is adequately sized, or you could further exacerbate the combustion air problem.

Finally, if you have chemical sensitivity issues, or if you have a particular medical reason why you need all outdoor air to be filtered before it enters the house, you may be happier if you swap the powered-vented water heater with a new sealed-combustion water heater.

Answered by Martin Holladay, GBA Advisor
Posted Aug 1, 2014 6:10 AM ET

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