Interpretation #7435
Published December 15, 2014
Original Request
- Code Version
- 2010
- Code
- MECHANIC
- Code Description
- Mechanical
- Chapter
- 6
- Section
- 601.4
- Topic
- Balance air and undercut doors
Question
Is it the intent of 601.4 exceptions 1 and 2 to require the door to be undercut when already requiring properly sized transfer grills to achieve balanced return air?
Answer Published 12/15/2014 at 10:04 AM
Yes to the question and No to the comment.
Commentary
When this code section was proposed in order to achieve
close to the 0.01 W.C. across closed doors, the equivalent
cross sectional duct area for a transfer duct would be
approximately twice the size of the supply duct. The 1”
undercut door was introduced to the code in an effort to
provide additional square inches for return air. By doing
this, the return duct cross sectional area was reduced to 1-
1/2 times the supply duct and transfer grills were reduced
to 50 sq. in. per 100 c.f.m.