Replies

1. 
   mwalter1 | Oct 16, 2015 04:44pm | #1

   Thank you.

2. Expert Member
   Dana Dorsett | Oct 16, 2015 04:46pm | #2

   There are two issues here- one is the duct system balance, the other is whether the crawlspace is sufficiently insulated.

   The crawlspace walls have to be insulated, not just the rim-joist, to at least the IRC 2012 level appropriate level for your climate zone:

   http://publicecodes.cyberregs.com/icod/irc/2012/icod_irc_2012_11_sec002.htm

   Supply ducts need sufficiently low impedance return paths, but it doesn't necessarily have to be a return duct. A grille way or open hatch between the crawl space and the basement might be enough, if there is a return register of adequate capacity in the basement.

3. GBA Editor
   Martin Holladay | Oct 17, 2015 07:19am | #3

   Martin,
   I'm not sure why you want to heat and cool your crawl space. (Very few homeowners spend much time in their crawl space.)

   Of course, you want your crawl space to be tight, with as few air leaks as possible, because air leakage causes all kinds of problems and raises your energy bills.

   In most cases, you also want your crawl space walls to be insulated, for similar reasons.

   You want your crawl space to be warm enough to prevent your plumbing pipes from freezing.

   You also want to control moisture accumulation, so some understanding of humidity control is necessary.

   To achieve these goals, it's rarely necessary to provide direct heating and cooling. At most, you need a little bit of air exchange to prevent moisture problems.

   Here is a link to an article that explains how to can achieve these goals: Building an Unvented Crawl Space.