A version of this article appears in the July/August 2005 issue of Home Energy Magazine.
July 01, 2005
With HVAC, Size Does Matter I have been facing the HVAC-sizing problem for my new house on the central Gulf Coast of Texas for some time now. I had a Manual J run by an independent engineer, and I ran one myself using a commercial software program (I am not an HVAC professional). The numbers were within 1,000 Btu of each other.However, the HVAC professionals I’ve talked with say that there is no way the Manual J sizing will work because of “insufficient air movement.” None of these professionals has run an actual Manual J, and I don’t know what to think other than to insist they run a Manual J (which they are reluctant to do) and explain any differences. My house has 3,567 ft2 of cooling space, and the Manual J calculations call for 40,000–41,000 Btu of cooling (includes both sensible and latent), with 1,300–1,400 CFM of air movement. Should I stick to my guns or listen to the “professionals”? David CarltonWest Columbia,Texas House Doctor John Proctor responds: Stick to your guns. “Insufficient air movement” is an old concept that is really applicable to commercial buildings with lots ...
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