Article 30967 of alt.solar.thermal: Path: news.misty.com!not-for-mail From: nicksanspam@ece.villanova.edu Newsgroups: alt.home.repair,alt.solar.thermal Subject: Re: Water heater overpressuring water system? Date: 3 Aug 2008 04:47:52 -0400 Organization: Villanova University Lines: 28 Message-ID: References: NNTP-Posting-Host: acadia.ece.villanova.edu X-Trace: max.inside.misty.com 1217749534 2567 153.104.44.130 (3 Aug 2008 07:45:34 GMT) X-Complaints-To: abuse@misty.com NNTP-Posting-Date: Sun, 3 Aug 2008 07:45:34 +0000 (UTC) Xref: news.misty.com alt.home.repair:1037129 alt.solar.thermal:30967 Tony wrote: >Theo wrote: >> I've tried to convince the installers that 40 gallons of water expanding >> from 55F to 140F is going to strain the pipes in this small house... With a density 62.46-0.01(T-68) lb/ft^3 at T (F), 40 gallons at 55 F weighs 62.59 pounds per ft^3, ie 62.59x40/7.48 = 334.7 pounds. Heating it to 140 F raises the volume from 5.348 to 5.421 ft^3, an increase of 0.073 ft^3, or 0.55 gallons. In a large house with a working check valve on a city water supply, those 2 quarts might expand the pipes elastically with no damage at say, 60 psi, but that seems unlikely, since copper doesn't stretch much at that pressure. >If there is an inlet supplying pressure at 30psi, the pressure rise due >to expansion of heated water will just push a tiny amount of water back >up the pipe, "Tiny" as in 2 quarts :-) But we can't push water back through a check valve, which is often a safety requirement with city water supplies... This could be a non-problem if the water heater were a more elastic $60 1"x300' 13-gallon black plastic HDPE pipe coil in 140 F solar-heated water in a 4'x8'x3' deep plywood box tank with a folded 10'x14' EPDM rubber liner. Nick