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.
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, and that some kind of expansion tank (like the one in the heating system, right next to the SuperStor) is needed. They think I'm nuts.
Can anyone here offer relevant experience or practice?
Dont you mean it runs off your boiler, what vents, the boiler or heater, On my old pipes I would never let them get over 75, 150Lb ! I think you are crazy to run it at all. The installer was a hack if it actualy goes to 150lb. Whay do you even need 140f water, lower it now to the lowest temp you need to take a hot water shower, with no cold added. for me thats 95f, it will lower pressure before you break alot of stuff. Pressure should not be more than incomming. Also you now run the boiler to heat water in summer, likely that will cost you alot more in summer.
If you run a dishwasher you need 140°F water for optimum operation. If you wash white cotton fabric in the clothes washer, you need similar temperatures. Believe it or not.
Dont all dishwashers have electric heaters to bring the temp to what is needed, mine does, whites, I use Bleach. No wonder this country uses 25% of the worlds energy with only 5% of its population, nodody cares about conservation. 140f is a waste, and if you really think about where that hot water goes, down the drain. I keep mine around
there should always be an expansion tank. Especially if you are on some kind of pressure regulator, or if your city meter has an antibackflow valve in it.
PO's of my house were like that. I immediately turned the water temp up so I could take a comfortable shower. Plus if you don't have it at least 130F you can get nastiness growing in the water. I think before the hot water was about 110F and I'd take a shower with all hot water and it'd still feel cold - and then run out halfway.
Oh, and I have a solar tank feeding the gas heater, so I'm only heating the water from maybe 90F to 130F not 65F to 130F - before you accuse me of being wasteful.
Water expands when heated. Most water systems tend to be closed (regulator, backflow check etc) and in a closed system it needs someplace to expand so it is definitely standard practice to install an expansion tank. Small house has nothing to do with it.
Many or most dishwashers have a "heat assist" to help maintain water tempeature, but will not raise the temperature to correct operating levels. Only some (usually high end) models have heaters with enough power to heat (or preheat) the water to the correct operating temperature. Our dishwasher is one with "heat assist". When we first moved into this house (it was a new house), the water heater was set much lower than 140°. The dishwasher was doing a really lousy job. When I increased the setting on the hot water heater, the dishwasher's performance was superb.
In a prevous house we installed a high end, all bells and whistles dishwasher which had water pre-heat cycles. We kept the water heater set at a reasonably low temperature. The dishwasher performed flawlessly, but because of the water heating cycle, the total operation time for a load of dishes was well over 2 hours. In part, it depends on where you want to spend your energy. I'm sure it wasn't exactly cheap for the heating element in the dishwasher to preheat each batch of water to the correcct temperature before running that part of the cycle.
We live in AZ where the incoming water is one the warm side most of the year. Because of this, we also do not need a large water heater, nor are ever having to raise 35-40° incoming water to proper temperatures. Ours is only a 30 gallon quick recovery electric tank. I doubt seriously if we are wasting a lot of energy.
We do have gas or oil service in our area, so electric was the only choice in town.
I presume you DON'T have anti-pipe knocking "water hammer" arresters on your hot water piping.
Many DIY home improvement books show you how to make your own with copper piping. Fun DIY project for long rainy weekend. Good training for sweating copper.
Commercial versions just for visual demo: (click on link in write up for Water Hammer.
There is definitely a purpose, whether you think so or not. Obviously I can afford to piss it down the drain whil using it as neceessary, and you obviously cannot. So piss off!
Here in Scottsdale, I was once able to take a shower with just the "cold" tap water. It had heated to 110 during a brief circuit around an outside wall.
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.
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.
If so, put it on the cold water side. Hot water may ruin it.
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