Quote:
Originally Posted by photo1902
Huh? All new homes are required to have back flow preventers.
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I second your huh. The expansion tank provides a cushion of air so that the water pressure in your house is maintained at a constant level. Without it, there is a danger that, when you use a lot of hot water, and then shut off all fixtures, the water heater will heat up the tank, and the water pressure will rise due to thermal expansion. But, the expansion tank will allow the water to expand into the air filled expansion tank, and thereby maintain a more constant water pressure. AO Smith, a leading maker of water heaters, says that the expansion tank is needed, and that the pressure relief valve on all of their water heaters, is not sufficient protection against thermal expansion. It is only an emergency device, and they often become clogged and don't function. Expansion tanks are more necessary than ever because of better backflow prevention in the city water systems, and because of leakproof fixtures, which often create a situation where thermal expansion can occur. If you don't have an expansion tank, you should check to make sure your relief valve is not discharging water on a regular basis (put a cup under the discharge pipe), which will indicate that you are experiencing excessive pressure in your water system, and definitely need an expansion tank.