Article 1036976 of alt.home.repair: Path: news.misty.com!not-for-mail From: nicksanspam@ece.villanova.edu Newsgroups: alt.home.repair Subject: Re: Water heater overpressuring water system? Date: 2 Aug 2008 15:25:43 -0400 Organization: Villanova University Lines: 25 Message-ID: References: NNTP-Posting-Host: acadia.ece.villanova.edu X-Trace: max.inside.misty.com 1217701406 20539 153.104.44.130 (2 Aug 2008 18:23:26 GMT) X-Complaints-To: abuse@misty.com NNTP-Posting-Date: Sat, 2 Aug 2008 18:23:26 +0000 (UTC) Xref: news.misty.com alt.home.repair:1036976 Theo wrote: >Recently replaced old electric water heater with a 40-gallon SuperStor >running off oil furnace. It now overpressures and vents several times a >week. Feed pressure is about 30 PSI. A cheap max-indicating pressure >gauge confirms that pressure jumps whenever a lot of hot water is used, >though it doesn't always reach the 150 PSI needed to vent. Are you on city water, with a check valve? A well pressure tank could handle the hot water expansion, if the water heater has no check valve. >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, Water's density at temp T (F) is about 62.46-0.01(T-68) lb/ft^3. Copper pipes can expand a little. A larger house with more pipes would have a smaller pressure increase. >and that some kind of expansion tank (like the one in the heating system, >right next to the SuperStor) is needed. If so, put it on the cold water side. Hot water may ruin it. Nick