ACCA Manual D does not endorse the panning of joists.
Too many air leaks and a rough surface that causes air turbulence. But, if you look in Chapter 6, Duct Systems in the 2012 Mechanical Code, panned joists are allowed for return air.
Take a look at Section 603.18 on page 61, Return-air intake. Notice that the Fpm value for return air grilles shall not exceed 450 Fpm. Get your Manual D out and turn to Appendix 1. What is the maximum Fpm value for return air grilles?
The last piece of the puzzle can be found on pg. 51, Section 603.2 Duct sizing. “Ducts installed within a single dwelling unit shall be sized in accordance with ACCA Manual D or other approved methods.” Approved methods mean it is the AHJ’s call. If your building Inspector allows it, then it is legal.
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One of the key skills required for passing the exam is quickly deciding which reference book the exam question is asking for. Is the question referencing Manual D or the Mechanical Code? To develop this key skill, enroll now? We have solutions to your problems!