Make-Up Air Formula - http://www.hvacmechanic.com/ Forums

Original message

jmon

65.196.54.199

"Make-Up Air Formula" , posted Wed 17 Sep 18:14

Does anybody know what the make-up air formula is for how much fresh air you need for a basement?

The basement only has 2 small windows, and it is about 700 square feet. The inspector said we have to mechanically introduce fresh air through the vents or tap into the HVAC system for fresh air. We have a Trane XE 90 (central air and heat system).

Any help will be apreciated. Thank you!

Replies:

rlj1117

24.181.246.138

"Re(1):Make-Up Air Formula" , posted Fri 19 Sep 07:39

i had to do this once in raleigh , nc i cant remember the formula but the inspector made me do and provide the calculations to him , so i would ask the inspector if he needed the calculations and if not i would just tap a duct from outside into the return side of the furnace , hope this helps

jmon

65.196.54.199

"Re(2):Make-Up Air Formula" , posted Fri 19 Sep 19:57

There is a building code, but I can not make heads or tails of what they are asking for. But from what I can gather, we need at least 4% of the air for make up air for the total size of the room. So if the room is about 700 sq ft I am thinking we need at least 28 sq ft of make up air. The 2 windows are only 14" x 20" so that is not enough. The fan we got creates 82.6 cfm per minute, whatever the heck that means. Trying to find the "formula" online, but still no luck. I am no math genius or mechanical engineer either, so that doesn't help.

Jojo98

152.86.133.139

"Re(1):Make-Up Air Formula" , posted Thu 18 Sep 12:15

Do you have a furnance in the basement?

jmon

65.196.54.199

"Re(2):Make-Up Air Formula" , posted Thu 18 Sep 12:26

Nope, there is no furnace down there.

Jackson Mon

theduke03

68.9.234.3

"Re(3):Make-Up Air Formula" , posted Thu 18 Sep 20:09

I'm not sure what your inspector is saying but I've never heard of a "make-up air" requirement for a residential basement. If that is a local code then ask the inspector what would be appropriate.
Make-up air is for applications such as a commercial kitchen or auto repair shops where exhaust fans are drawing lots of air from the building. As a result this air must be replaced with outdoor air and conditioned hence the term "make-up air".

"My dad was the most feared furnace fighter in Northern Indiana."