Article 1031405 of alt.home.repair: Path: news.misty.com!not-for-mail From: nicksanspam@ece.villanova.edu Newsgroups: alt.home.repair Subject: Re: It's Hot Upstairs More Insulation or Attic Fan? Date: 8 Jul 2008 00:59:09 -0400 Organization: Villanova University Lines: 38 Message-ID: References: <71743544-60b9-4a7d-997e-1b8578c97e98@25g2000hsx.googlegroups.com> NNTP-Posting-Host: acadia.ece.villanova.edu X-Trace: max.inside.misty.com 1215489444 24825 153.104.44.130 (8 Jul 2008 03:57:24 GMT) X-Complaints-To: abuse@misty.com NNTP-Posting-Date: Tue, 8 Jul 2008 03:57:24 +0000 (UTC) Xref: news.misty.com alt.home.repair:1031405 Tom in PA wrote: >We have a two-story home in Flagstaff, AZ. It's normally cool enough >around here that, without using our central air, the downstairs stays >pretty comfortable during the day if we open things up at night to >cool the house down. But the bedrooms upstairs get pretty toasty. >The attic gets very toasty, naturally. I'm thinking about either >adding insulation in the attic to keep that heat out of the bedrooms >or putting in an attic fan... Sounds like more insulation or a radiant barrier under the roof would help. Warm air rises. Whatever a fan can do, more attic ventilation can do... For instance, 250 Btu/h-ft^2 of sun shining on a 1200 ft^2 roof with 60% solar reflectance over an attic with a 1000 cfm fan and a roof with a US U2 (2 Btu/h-F-ft^2) conductance to 100 F outdoor air makes an equivalent electrical circuit like this, viewed in a fixed font: T = 100+I/1000 = 135.3 F attic temp | 0.5/1200 | 1/1000 ----------www----------www------ 100 F outdoor air | -------------------> | I = (150-100)/(0.5/1200+1/1000) = 35.3K Btu/h | | 100+250(1-0.6)0.5 = 150 F sol-air temp --- - | - We can also make 35.3K Btu/h flow with 2 A ft^2 vents with a 35.3 F temp difference and an 8' height difference if 16.6Asqrt(8)(35.3)^1.5 = 35.3K, ie A = 3.58 ft^2, eg 2'x2' high and low gable vents with doors to close them up in wintertime. Nick in PA