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Gravity question for the experts

Ironman
Ironman Member Posts: 6,562
I have a down feed gravity system like this:
https://heatinghelp.com/assets/Uploads/heating-p14-262x300.gif

It has O/S fittings like this:
https://heatinghelp.com/assets/Uploads/heating-p15-160x300.gif

A gas boiler and pump was installed 50+ years ago and it works fine except for 3 rad's which were moved about 25 feet away from the down feed riser. Obviously, these get no flow. I can access the piping beside each rad, but nowhere else except near the boiler.

My question is this: if I put a small circ on each rad, would this create any flow problems in the risers. It would basically be doing p/s for each of the 3 rad's. What circ would you recommend? They would each have to stay on constantly since there's no practical way to wire them back to the boiler.


Bob Boan
You can choose to do what you want, but you cannot choose the consequences.

Comments

  • Danny Scully
    Danny Scully Member Posts: 1,329
    edited December 2017
    Were they originally 25 feet from the downfeed riser? And enough with the modesty gentlemen, you’re an expert @Ironman! :wink:
    Ironman
  • Paul48
    Paul48 Member Posts: 4,470
    edited December 2017
    Why not split the loop to the troublesome radiators and put a valve in. Force them to be, at least in part, series vs. parallel. I'd try one, and see what kind of results you get. Oops........Sorry, I'm not an expert, but even a broken clock is right, twice a day.
    Ironman
  • Ironman
    Ironman Member Posts: 6,562
    @Danny Scully
    No, some knucklehead did this in recent years before the present owners bought the house. They moved the rad's during a remodel.

    @Paul48
    I can only access the piping at the rad's, not the risers. The HO doesn't want to tear stuff up to get to the risers. It's 3 separate risers, not one.
    Bob Boan
    You can choose to do what you want, but you cannot choose the consequences.
  • Paul48
    Paul48 Member Posts: 4,470
    Oh crap....and of course it's probably plaster walls?
  • Ironman
    Ironman Member Posts: 6,562
    Yep.
    Bob Boan
    You can choose to do what you want, but you cannot choose the consequences.
  • Harvey Ramer
    Harvey Ramer Member Posts: 2,217
    How many downfeed risers are there?
    Since the system is pumped, would it be possible to get to the main distribution point through the attic floor? If so, you could install balancing valves to each downfeed riser and get the flow back up in the problem riser. Considering the fittings that are used, this would perhaps be enough to reestablish the thermal siphon to the rads in question and get them heating again.
  • Ironman
    Ironman Member Posts: 6,562
    @Harvey Ramer
    Thanks for your insight. I don't believe the issue is flow in the riser, but in the branch. By moving the rad's so far away, the plumber created far more resistance in the branch and so the flow just goes straight through the riser. It's the same as when someone puts too much pipe in the branch of a monoflo; it's easier for the flow to go completely through the diverter T.
    Bob Boan
    You can choose to do what you want, but you cannot choose the consequences.
  • Harvey Ramer
    Harvey Ramer Member Posts: 2,217
    Ironman said:

    @Harvey Ramer
    Thanks for your insight. I don't believe the issue is flow in the riser, but in the branch. By moving the rad's so far away, the plumber created far more resistance in the branch and so the flow just goes straight through the riser. It's the same as when someone puts too much pipe in the branch of a monoflo; it's easier for the flow to go completely through the diverter T.

    Thats true, but you also have 3 risers and likely very low resistance in the whole system. By moving the rads away from the problem riser, they created more resistance in that riser, however small it may be. This likely diverted some flow to other risers. If flow were reestablished in the problem riser, it MIGHT be enough to overcome the thermal trap in the piping leading out to the rads. Once it does that, gravity flow would be reestablished to the rad and would work in concert with the little bit of pressure drop created by the fittings.
    One way you might be able to determine if it has a chance of working is to valve off the other to returns in the basement and direct all the flow through the problem riser.

    It's a crap shoot, but aesthetically, it would be better than mounting a pump on the rads.
    Do the rads have covers?
    Ironman
  • Paul48
    Paul48 Member Posts: 4,470
    How did he hide those 25' pipes?
  • Harvey Ramer
    Harvey Ramer Member Posts: 2,217
    Also, have you been able to ascertain that the supply and return piping to the rad are in the correct orientation? If they happen to be reversed, there would be no gravity flow helping the rad.
  • Ironman
    Ironman Member Posts: 6,562
    I can't tell how the pipes are run or if they're reversed because they're concealed.

    The HO said they wouldn't mind seeing a pump on each of the rad's that's effected.

    Everything is finished including the basement which is an apartment. The only exposed piping is in the boiler room, and that's not much.

    My question is still whether the flow in the riser would be effected if I pump the rad?

    I appreciated the insight on other options, but if I have to experiment, trying the pump on one of the rad's is the easiest option.
    Bob Boan
    You can choose to do what you want, but you cannot choose the consequences.
  • Harvey Ramer
    Harvey Ramer Member Posts: 2,217
    Ironman said:

    I can't tell how the pipes are run or if they're reversed because they're concealed.

    The HO said they wouldn't mind seeing a pump on each of the rad's that's effected.

    Everything is finished including the basement which is an apartment. The only exposed piping is in the boiler room, and that's not much.

    My question is still whether the flow in the riser would be effected if I pump the rad?

    I appreciated the insight on other options, but if I have to experiment, trying the pump on one of the rad's is the easiest option.

    Gotcha.

    I don't think adding a pump to each rad is going to have a negative effect on the riser, unless the supply and return pipes happen to be reversed. In that case it would.

    Were it me, I believe i would install a line voltage thermostat to act as a high limit and shut off the pump and also allow it to be turned off during the summer. The pumps will likely induce a greater flow rate in the riser and increase the output of the rads in disproportional to the rest of the system.
    Ironman
  • ratio
    ratio Member Posts: 2,925
    If the pump is sized/throttled to just counteract the head of the additional piping, I'd expect the system to fall back into balance. Perhaps a ΔT pump, if one could be set to the same ΔT as a correctly-operating radiator.

    It works out in my head, but IANAE.

    The restrictors aren't still in place, are they? It'd be odd if they weren't left out by the knucklehead, but stranger things have happened.

    Ironman
  • leonz
    leonz Member Posts: 421
    edited December 2017
    Did anyone ask which floor the suspect radiators are on?

    I bet they left the restrictor's out when they changed the location of the radiators. It would be easy enough to check.
  • Ironman
    Ironman Member Posts: 6,562
    All the rad's in question are on the first floor, but different risers. No orrifices.

    I think a delta P circ set to its lowest pressure setting would be the correct choice? It seems that a delta T could over-pump the riser when it's cold hindering flow in it.
    Bob Boan
    You can choose to do what you want, but you cannot choose the consequences.
  • Ironman
    Ironman Member Posts: 6,562
    @Harvey Ramer
    If the branch lines are reversed, then all I should have to do is flip the pump over?
    Bob Boan
    You can choose to do what you want, but you cannot choose the consequences.
  • EBEBRATT-Ed
    EBEBRATT-Ed Member Posts: 10,287
    I would use a pump that just meets the flow the radiator needs and pump it as lightly as possible so as not to disrupt the riser flow.

    This was the exact reason that Gil Carlson invented primary secondary back in the 50s. On that original job they had monoflow tees and the branches were too long so he installed pumps
    Ironman
  • Harvey Ramer
    Harvey Ramer Member Posts: 2,217
    Ironman said:

    All the rad's in question are on the first floor, but different risers. No orrifices.

    I think a delta P circ set to its lowest pressure setting would be the correct choice? It seems that a delta T could over-pump the riser when it's cold hindering flow in it.

    I seem to think they make a reverse acting TRV which could be used with a delta-p pump to regulate the flow. With the sensor mounted to the return line, and the TRV set for the design water temp minus the desired delta-t of the rad, it should automatically maintain the proper flow.

    But i guess the same could be done by installing a globe valve and setting it to the proper flow by physically measuring the delta-t.
  • Harvey Ramer
    Harvey Ramer Member Posts: 2,217
    Ironman said:

    @Harvey Ramer
    If the branch lines are reversed, then all I should have to do is flip the pump over?

    I doubt it. If the supply were to come in at the bottom, the return has to come from the bottom on the other end. Otherwise the rad won't heat evenly.
  • Ironman
    Ironman Member Posts: 6,562

    Ironman said:

    @Harvey Ramer
    If the branch lines are reversed, then all I should have to do is flip the pump over?

    I doubt it. If the supply were to come in at the bottom, the return has to come from the bottom on the other end. Otherwise the rad won't heat evenly.
    The new branches are copper, so I could switch them at the rad fairly easily if needed.

    Bob Boan
    You can choose to do what you want, but you cannot choose the consequences.
  • hot_rod
    hot_rod Member Posts: 15,029
    These are about the smallest circs I have been able to find if you need to mount them on the radiators.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
    Ironman
  • Ironman
    Ironman Member Posts: 6,562

    I would use a pump that just meets the flow the radiator needs and pump it as lightly as possible so as not to disrupt the riser flow.

    This was the exact reason that Gil Carlson invented primary secondary back in the 50s. On that original job they had monoflow tees and the branches were too long so he installed pumps

    Exactly!

    Bob Boan
    You can choose to do what you want, but you cannot choose the consequences.
  • Paul48
    Paul48 Member Posts: 4,470
    Maybe sizing the system circ like a regular gravity system conversion , per Steamheads document would help. You are dropping the most remote radiators....the same thing that document is written to correct . I know you have extenuating circumstances, but maybe some additional flow in the system would not be detrimental.