Proper operating pressure and temperature of a hot water boiler

• posted on December 4, 2003, 3:15 pm
Hi,
I am writing about a Dettson HGRC-170 hot water boiler which is part of my gas furnace.
Questions:
1) What is the proper operating water pressure for such a thing? Two pressure relief valves on the system are 30 psi so I assume the proper operating pressure should be somewhere lower...but not sure where...Currently it around 8 psi but that doesn't seem right to me (the upper floors are barely getting any water in the radiators furthest from the furnace).
2) What is the proper operating water temperature for such a thing? Mine hovers around 100 degrees F. Does that sound right?
Cheers
Theo

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• posted on December 5, 2003, 3:26 am
Theo. Assuming that the system you are describing is a forced hot water heating system having a closed expansion tank (diaphragm or air), you will want to have approximately 4 - 6 psi at the highest radiator. Easy way to figure this out is to calculate the difference in elevation between the pressure gauge on the boiler (measure in feet) and the highest radiator in the system. Multiply this height difference by 0.434 and add 4-6 psi to this number. For example, if your highest rad is 20 feet above the pressure gauge, go 20 x 0.434 = 8.68 Add 4 psi to that, and your gauge should read about 13 psi. The total length of pipe from the boiler to the furthest radiator does not affect this calculation. This calculation only takes into consideration the difference in height from the gauge to the highest rad. If you still have circulation problems, it could then be with the piping design, closed valves, etc. Of course, if your expansion tank is open to atmospheric pressure, you would disregard all the above information and make sure the tank has water in it :)
Good luck,
Dean

the

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• posted on December 5, 2003, 12:08 pm
Thanks Dean....
This information was very useful. I believe I have a faulty (or dirty) Mueller valve (some people call it pressure reducing valve). I have already made arrangements to get it replaced sometime today.
Cheers
Theo
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