Make-up air for Kitchen Range Hoods
EarthCraft Sean
| Posted in Mechanicals on
I have a builder that insists on installing a 1200 cfm range hood. What is recommended for make-up air (rate and preferred installation)
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It's tough to do it right. The right answer is that the makeup air fan has to have the same cfm rating as the exhaust fan; and if the clients expect to be comfortable, the makeup air needs to be conditioned. Ouch! That fan suddenly got expensive, didn't it? Here's a link to a 600 cfm makeup air fan:
http://www.sheltersupply.com/shelter/product.aspx?i=0&p=Make-Up%20Air
By the way, don't bother to contact the range hood manufacturers — most of their tech-help people don't know the meaning of "makeup air." (I'm not making this story up; I've called several.)
Some clients just crack a window; not a great solution.
It's best to talk the clients into a much smaller exhaust fan.
Get another builder!
For a conventional residential range, a 250-300 cfm exterior vented hood is more than adequate.
Assuming you're building a tight house with mechanical ventilation to maintain the minimum 0.35 air changes per hour for indoor air quality and moisture control, then spot ventilation in kitchen and baths needs to be sufficient only to remove source pollutants (including moisture).
In a 2500 sf house with 8' ceilings (20,000 cf), a 1200 cfm fan will move 3.6 air changes per hour - the equivalent of an old leaky house. Not only will an equal amount of make-up air be required, but the heating and cooling costs will be exhorbitant.