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old radiant system

drhvac Member Posts: 190
Im working at an old ( 40 - 50 ) year old levitt house if anybody is familiar? Its a ranch on a slab with radiant heat. There are two manifolds placed in closets of the house with manual dampers. One manifold is in the center closet for the main part of house, and the other in the bedroom closet for the bedrooms. The people are complaing of the bedroom s being cold.  Even though the pressure is around 12psi, I feel the prv is slightly restricted. Maybe the gauge is wrong, and the water isnt getting to those further areas? The other thing I noticed is the circulator is a B&G series 100. That is a low head pump, maybe a little to much piping and head to over come. How do you size a circulator when you dont know how much piping your dealing with? wouldnt a higher head pump work better with radiant systems. How about a variable speed pump? thx


  • Gordy
    Gordy Member Posts: 9,537
    edited December 2012
    Trouble shooting

    Are the bedrooms getting any heat, or just not enough?

    Is this a new development?

    Are the owners setting back the thermostat?

    Series 100 was probably the size circulator always on that system, and it worked. Does it look to be original? Maybe the impeller is worn.

    One way to check unknown head of piping if you know the circulator is operating properly.

    A little plumbing involved, but install a 0-30 psi pressure gauge at the suction side, and at the discharge side of the circulator. When the circulator is operating note the difference in psi between the gauges, suction side will be less than the discharge side.

    Take that difference, and multiply by 2.31, and that's the feet of head the circulator is seeing. Then go to the chart for that model circulator, and plot the gpm for the head you calculated.

    Now divide that gpm by the number of loops in the system, and that's a rough idea of how many gpm each loop is getting IF they are all same diameter, and length circuits.

    Or if it looks to be the original circulator assume it has always worked before for the last 50 years.
  • drhvac
    drhvac Member Posts: 190

    the bedroom supply manifold is warm and the return cooler but a little warmth. This an older development ( 40 - 50 yrs old ) and the pump is the original. They say it worked better at one time, but not in a long time. the main area of house is 70, and the bedrooms 65. The t-stat is set on hold so I dont think they are setting back. How could i tell if the propellers are worn, and the pump isnt circulating properly?
  • Gordy
    Gordy Member Posts: 9,537

    I was editing my post when you replied see above.to check impeller you will have to disassemble the circulator.

    Are you sure there is no air in the loops in question.
  • drhvac
    drhvac Member Posts: 190

    I forgot to mention that I did bleed the individual loops and got hardly any air. The other thing that was weird was that the water was crystal clear? theres about 8 loops, and only one of them had a little air, and that nasty brown water that you see when you bleed a system that hasn't been bled in awhile. Maybe there is a leak somewhere? Thats when I noticed that the water pressure wasnt that good even though I had the gate on the prv up? If there was a leak, if i shut the water feed ball valve, the pressure should drop, corrrect?
  • Gordy
    Gordy Member Posts: 9,537

    Was the feeder valve always open?

    If the feeder valve is closed, and the system is air free there should not be a drop in pressure.

    If the feeder valve is always open, and there is a small leak then that could be the reason for clarity of system water. But not all copper systems have dark water. If system is clean, and air free water,should be clear. Usually dark water is an indication there was air trapped some where for a long time.
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