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Decreasing pipe sizes on zones

you are good with the numbers . Yes , I mean connecting the main to the circulator on the supply . Usually less than 2 feet on a replacement .

We rarely see 3/4 takeoffs to the convectors , even on an 1 1/4 inch zone .

Thanks again Brad for the insight and the math . I really appreciate it .


  • Is there a significant decrese in flow

    if hypothetically , on an 1 1/4 inch copper supply pipe going to convectors , it is connected to the supply of the boiler in 3/4 inch pipe less than 2 feet long ? I know flow through the same size circulators is not impeded for different pipe sizes because the distance through the circulator is so short . But how far can you keep the pipe choked down ?

    What this is basically about is on our boiler replacements I was thinking of using a universal size for every zone ( no need to get the right size flanges , adapters and valves for every job , and the smaller parts are less expensive ) . Since we usually only have to go 2 feet or less to connect each individual zone supply , would substituting 3/4 inch for other sizes for this short distance be a bad idea ? Of course I would keep my black supply manifold 1 1/4 inch up to the circulators . Thanks in advance .
  • Ron SchroederRon Schroeder Posts: 998Member

    Hi Ron Jr.

    The inlet/outlet of many circs is closer to 1". That would be preferable to choking down to 3/4".

  • Brad White_63Brad White_63 Posts: 24Member
    What is the flow rate, Ron?

    And how many convectors are being served off of the 1-1/4" main?

    If the 3/4" pipe is carrying 4 GPM or so, even more, I see no problem over a short distance.

    In my experience, the mains are designed to get flow near the emitter (fan coil, coil, radiator, convector, what have you) with limited loss, saving the "restrictive" piping with valves, fittings, offsets, for near the emitter.

    The "hook-up" should be accounted for in the pump pressure drop of course. Say the convector connection is 1/2". I would usually go up at least a size to accomodate valves, fittings, unions, etc. and keep the connection size short. But if the connection size is 3/4" and the flow is, what, one GPM or so? Nothing to worry about.

    Did I grasp your concerns correctly?


  • I was thinking 1 inch also

    Typically we see only one zone in a home bigger than 3/4 inch . And more than likely the other zones were split off parts of the home that were served by the larger pipe . So , in essence the larger zone size is bigger than needed . Thanks Ron . Any info yet on how to keep a .25 GPH nozzle going ? I read your post on OTT .
  • The flowrate

    This isn't a specific home , but typically there will be less than 8 convectors . 1 - 8 footer in the living room , 3 or 4 footers in the bedrooms , and smaller ones in the kitchen and bath . I'm guessing 1 1/4 is way oversized if other zones were added without adding space in the home ? I really should do the math , but we go by the " one Taco 007 fits all " credo . Thanks Brad .
  • Brad White_63Brad White_63 Posts: 24Member
    Flow Rates

    If your mains are 1-1/4" and you have eight convectors as you say (probably less than one gpm per given the lengths), using 3/4" runouts, even 1/2" runouts should not be a problem. Even if Monoflow/One Pipe, so long as the temperature dilution is taken into account in convector sizing, I still think you will be just fine. In my book you could handle 9 to 12 GPM off of that main. A 3/4" runout can comfortably handle 3 GPM (30,000 BTU's!) and 1/2" will handle half that (15,000 BTU's!) so you can see how this has lots of wiggle-room.

    And nothing against Taco, the Grundfos or other 3-speed circulators will serve your HO much better, IMHO. One size does not fit all and some savings may be had. Fractional but 20-30 Watts adds up over the life of a system.

    My $0.02

  • Yep

    I'm learning more and more about proper circ sizing . I figured out that 2 of my heat zones need only 006s so I'm looking for a few in good shape off a couple of used aquaboosters .

    Thanks for the numbers Brad . OK another question to make it a little more clear for me ( my math is horrendous ) . Say you have an existing system like I said before - 1 1/4 inch supply and return . We know the flow rate and btus that can be delivered . Is there any way to figure how how much those numbers would decrease if we connected the supply with 2 feet of 3/4 inch ? There will definitely be a drop , but would it be a huge drop ?
  • Ron SchroederRon Schroeder Posts: 998Member

    Hi Ron Jr.

    I was thinking that you were driving a zone on it's own circ., that needed a 1 1/4" feed (more than 10gpm) where you could get by with a short section of a little smaller pipe.

    If you are talking about numerous smaller zones from a 1 1/4" common supply, just follow the old rule of thumb of 1.5gpm on 1/2", 4gpm on 3/4", 8gpm on 1" etc. Just make sure that you aren't over pumping or use a pressure differential bypass. It's all a system, look at the head loss and pump curves and match to what you need. You might be surprized in how small of a circ that you really need. I am running 15 zones from a circ. that draws less than 1/5th the wattage of a 007. Why waste the electricity.

    I ran the .25gph nozzle for almost 2 months with some degradation in flame shape but no plugging. I am not ready to reccomend it yet. I have another nozzle that can fire down that low that should be much more tolerant to fuel than even a conventional .85gph nozzle that I hope to run this summer.

  • Ron SchroederRon Schroeder Posts: 998Member

    Hi Ron Jr.,

    Are you thinking of going from a 1 1/4" supply down to a 3/4" pipe, the circ, a couple of feet of 3/4" and then back up to 1 1/4" before branching to the zones?

  • Brad White_63Brad White_63 Posts: 24Member
    When you say \"connect the supply with two feet of 3/4 inch\"...

    do you mean where you feed the mains from the boiler? Or just feeding to a given radiator? If you mean neck down the mains to 3/4", the question becomes, how much flow is being carried at that point?

    My own home system main circuit has a 1-1/4 inch main splitting to two 1-inch mains which then run reverse-return around the house, returning to the boiler via a common 1-1/4 inch return main. The system carries 6.5 gpm incidentally, so really low PD. Still, the supply at the circulator reduces to 3/4" in order to meet a balancing valve at that size. It roars a little bit but nothing of consequence.

    What I am saying is, you may generate a little noise but the pressure drop overall being so low, you make it up elsewhere.

    The way to figure the flow loss is to know the pressure loss of that tiny section of pipe versus if the pipe was kept at the full 1-1/4 inch main size. Then plot the head difference on the pump curve. I do not think you will see much difference, personally, but let's work it out to be sure:

    Take 2 feet of 3/4 type L copper pipe at 8 GPM. The pressure loss is 15.73 feet per 100 feet of pipe. The loss is multiplied by 0.02 (two feet of pipe) so the net loss is only 0.315 feet of head. Something, not much.
  • Ron

    I'd keep the circulator header 1 1/4 inch on the supply , maybe using 1 1/4 by 3/4 blk tees for the circs . Downstream of the circ feeding the 1 1/4 inch zone would be reconnected using 3/4 pipe . Short length .
  • Brad White_63Brad White_63 Posts: 24Member
    Thank you, Ron- and you are most welcome.

    Any chance you could 'up' that 3/4 inch to 1-inch? I mean for two feet and all... probably not a big deal either way.

    Thanks for the kind words and not to be ungracious but point of fact is, math was my worst subject bar none. Never "got it" until later in life and still struggle sometimes, then it "clicks". Part of thinking differently. I loved the word problems which were detested by the kids who were good at the theoretical aspects of math.

    Of course, being a Swamp Yankee on Dad's side and Swedish on my mother's side, I am, shall we say, a tad stubborn? :)

    -Actually in others, the trait is "stubborness". In me it is "highly principled" :) So that I got into engineering is a testimony to bullheaded willingness to defeat my weak spots. Never ends!

    But thanks-

This discussion has been closed.


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