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parallel plumbed baseboards

I have a customer with a parallel plumbed baseboard heating system. The feed and return pipes are 60ft with 7 loops plumbed in parallel. Initially the farthest zone didn't get circulation, so I replaced the circulator, no change. I then put balancing valves on all 7 loops and achieved flow in the farthest loop, but now there are two baseboards in the middle of the line that do not circulate (they were working before the balance valve were installed). The valves to these two baseboards are wide open, but no heat. All other 5 baseboards are working, both closer and farther on the feed and return lines. When I pump the system with a purging pump, there is heat. Do I just increase the pumping power? Install a series circulator on the return side? It seem like the pressure in the middle is equal on both feed and return, hence no circulation at those points. Any suggestions? Could the circulator be cavitated? HELP PLEASE


  • Gordy
    Gordy Member Posts: 9,537
    edited September 2013
    Did the system

    Work before? Or is this a new problem?

    If it worked before then if there were changes made since could be a red flag.

    Are you SURE the loops are purged of air?

    A cavitating circulator would sound like rocks in the impeller.

    With True parallel piped emitters head always is equalized, but flow to the different loops will not be the same depending on loop lengths, and pipe sizes of each baseboard loop.

    What size are the supply, and return piping?

    Is this reverse returned?
  • atomic
    atomic Member Posts: 9
    edited September 2013
    parallel paradox

    I was brought in to fix the problem, but have only been partly successful.

    NOT reverse return plumbed, but far and near ends work, the middle base boards don't.

    Force pumped with 1/2HP pump to eliminate air. Has air scoop and several air vents, including on one of the cold baseboards.

    Increase pump power?

    Feed and return 3/4" copper.
  • JStar
    JStar Member Posts: 2,752
    edited September 2013

    60 feet of 3/4 pipe with fittings accounted for may give you around 4 feet of head. A 1/2 HP circulator is about 12 times oversized. Yes, twelve.

    You have other issues. Can you post a drawing of the general piping layout? What size is the boiler?
  • Gordy
    Gordy Member Posts: 9,537
    edited September 2013
    Btu carrying capacity of pipe paradox

    3/4" copper pipe can carry 42000 btus. With out knowing the heat loss of each zone, and total heat loss of the dwelling it's hard to say if the supply, and return piping is of sufficient size.

    How many feet of baseboard are connected to each loop?

    What size boiler?

    Piping diagram for sure.

    I think Joe may be leading up to this.
  • Gordy
    Gordy Member Posts: 9,537
    edited September 2013
    So in other words

    42000 btus with a 20* delta t would require a flow rate of 4.2 gpm

    IF each loop had the same length baseboard piping fittings etc that would be .6 gpm to each loop which would produce 6000 btus to each loop. Highly unlikely the piping schematic is exact, but you get the just of it.
  • atomic
    atomic Member Posts: 9
    Back story

    Originally the baseboards were hooked to a water woodstove, and was a closed loop, atmospheric system. It's 30 years old, and had replaced, circulators twice. One Taco 007, on the problem loop, a B+G rf-22, on the good loop. After the second 007 proved not up to the job, I replaced it with a higher head lower flow 009 model. This was working mostly, but I had to use the balance valves to get the heat distributed to all baseboards Since the wood heater died, I switched to a pressurized system with 80kBTU boiler, have the same circulators, and now the issue of no flow in the middle.

    Let me regress to draw a mental picture; two 3/4"( supply and return) lines run the 60ft length of the house. Branches to baseboard elements go off the left and right of the supply, and loop back to the return, for the entire length of 60ft. The entire 2-loop system has 160ft of baseboard, of which the problem loop has about120ft. Well insulated and in good shape, pipes are clear of corrosion, in and out. Boiler treatment was always added.

    I did add 1" near boiler piping, about 20ft, 4 L's and 2 T's, and the boiler to the system's head, and used the original direct plumbed design, not primary/secondary. The 009 shouldn't have any trouble, and does go to the farthest baseboard.

    The owners are elderly and can't be sure how the system used to operate, so I have more experience with it than them. I just want these nice people to have their heat working in all rooms. What would you try next?
  • Gordy
    Gordy Member Posts: 9,537
    The real deal

    You have 160 feet of baseboard at 550 buts a foot with 180 water is 88000 buts possible output.

    You have an 80000 btu boiler.

    You have 3/4" supply return able to deliver 42000 buts at 4.2 gym at 20* delta t. A 25 delta would get you 55000 buts.

    First question is how many buts do you need?

    If it's more than 42000 then you need to increase pipe size, or delta depending on how much more nuts you need.

    If not then you have an over sized boiler, and over radiated.

    Is it possible that the wood boiler ran wild and the base board we seeing higher temps than 180 before. If so the flow issue may have went unnoticed because the house was warm
  • atomic
    atomic Member Posts: 9

    There's two 3/4" loops in the system, @ 42000BTU each, by your calcs. The load isn't an issue at this point, and I think things are sized appropriately. The hydraulics are the mystery.

    The delta T is small at the boiler, like 5 degrees, but the first two baseboards on the problem loop return very quickly to the boiler where the delta T is recorded.

    Could too high a flow rate cause problems? The 009 does 9gpm@ 0' head, decreasing up to 35' head. I figure it's doing about 5-6gpm @ 10-12' system head. More pump? Less pump? Suggestions?
  • Gordy
    Gordy Member Posts: 9,537
    Delta as a trouble shooter

    Low DT

    can mean to much flow.

    To low of a flow rate

    A 5* DT is real low at the boiler loop suggests to much flow, or seething is array with the piping.

    Not sure what you mean by suggesting two 42000 btu loops.
  • Gordy
    Gordy Member Posts: 9,537

    Out of 160' of baseboard only 40' is working properly. You may need to split the 120' loop into two 60' loops it gets the loops closer in length thus head and flow rates would be more balanced.

    Cant solve everything with a circulator.
  • atomic
    atomic Member Posts: 9
    Problem solved

    I found another balancing valve in the system and it was wide open. It's near the boiler and was short circuiting a lot of flow. When closed half way, everything started working again. Thanks for everyone who helped me over-think this one. Whew!
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