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optimal system pressure baseboard hot water

Ken_40 Member Posts: 1,320
Any pressure that assures the uppermost point of the system never goes into vacuum, is all that's necessary.

Never means: when the house is cool, the system completely off (extended vacation?) and the circulator is pumping away from the PONPC.

If the circ. pump is connected to the return and the expansion tank is on the supply side, all bets are off!

The reason? The circ. pump may induce a vacuum in areas of the system none should experience - like the eye of the impellor - where water will boil in the 170 to 211F range - by virtue of that vacuum...

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  • mark schofield
    mark schofield Member Posts: 153
    lowest possible pressure OK ?

    There was a thread a few days ago concerning the system fill pressure for a two story house. Brad White gave some numbers to figure the system pressure in different circumstances. In my situation - a one story house with 6' between the boiler pressure guage and the top of the slant fin baseboard - the calculations show 7.1 psi. Is there a relationship between performance and pressure? Currently with a new #30 tank at factory 12 pounds charge, my system is filled to 12 psi at 130 degrees (low limit all summer) and will raise according to the high limit as determined by the OAR. With a 4 degree difference between supply and return, on a design day the supply pressure after circulator ( pumping away)is 22psi. Would I gain anything in efficiency by dropping the charge in the tank to 7 or 8 pounds an then adjusting the fill pressure accordingly? The system runs fine, never goes above 22 or 23 psi, relief valve never blows. Taco 007 bundled with the WM WTGO3. Thanks for any thoughts. Mark S.
  • mark schofield
    mark schofield Member Posts: 153

    that should read 4 psi difference between sypply and return. The delta is between 15 and 20 degrees.
  • Brad White
    Brad White Member Posts: 2,398
    Ken Nailed It

    The "12 PSI for a two story house, 18 PSI for three" is a good start. Indeed it could be less, just enough to ensure no vacuum and to keep those bubbles small. 12 PSI should not be a problem though. If your expansion tank is 12 PSI charged, that will define your system pressure. If you wanted to lower it (no need but just suppose), you would bleed off at the Schraeder valve.

    But if you have not measured the actual tank charge, I suggest that you do so. The sticker says "12 lbs." but the reality may be above or way below that. The fact that you have a 4 PSI rise cold to hot sounds perfectly fine to me.
    "If you do not know the answer, say, "I do not know the answer", and you will be correct!"

    -Ernie White, my Dad
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