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Posted by Dave on January 26, 2007 at 11:05:03:
In Reply to: Re: Size expansion tank posted by Ron on January 26, 2007 at 08:32:53:
: With all being correct you should not see much change in pressure when the water heats up. From a cold start to 180f you may see a 5 psi change. Sounds like you may have a low air charge or too small of a tank. What type of radiation do you have? This makes a differance. What size boiler? What is the tank pressure? This must be checked with "0" water pressure. The above information would allow us to better assist you.
I replaced the tank with a new one becasue I'm not always at this house and I wanted to make sure. The old one was OK, no water in it and still 12psi. The tank size is a 30. I added a bit more makeup water and when all the zones are hot the pressure is now about 22 or 23. It's all fintube baseboard and a indirect Superstor water heater. Total system is approx 30 gallons of glycol. I can't really get a cold reading right now, it's near zero degrees today. It does seem to have a wider psi swing than 5 degrees though, it's closer to 10 (or more). When you heat 30 gallons from 60 degress to 190 it apparently expands enough to change the pressure that much. It does seem that a cold start would be subject to a greater PSI change than when everything is always hot. I would think a larger expansion tank, a 60, would buffer that expansion and result in a smaller PSI change between cold and hot. But if it's OK to run at approx 23 psi then it's probably OK the way it is. Oh, and the boiler is a Peerles 4 section, WBV04.
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