Article 30977 of alt.solar.thermal: Path: news.misty.com!not-for-mail From: nicksanspam@ece.villanova.edu Newsgroups: alt.solar.thermal Subject: Re: Water heater overpressuring water system? Date: 3 Aug 2008 15:17:01 -0400 Organization: Villanova University Lines: 19 Message-ID: References: <1217779415.911.1217754052@bayman.org> NNTP-Posting-Host: acadia.ece.villanova.edu X-Trace: max.inside.misty.com 1217787282 5195 153.104.44.130 (3 Aug 2008 18:14:42 GMT) X-Complaints-To: abuse@misty.com NNTP-Posting-Date: Sun, 3 Aug 2008 18:14:42 +0000 (UTC) Xref: news.misty.com alt.solar.thermal:30977 David Williams wrote: >-> 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. > >But you are assuming that the pipes do not expand as the temperature rises. I assumed the temperature in most of the piping did not change, but the OP said the T&P valve popped at 150 psi, after a lot of hot water use, so maybe the hot water pipes are already expanded after the hot water use, and they shrink while the water in the heater tank expands. Nick