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Parallel reverse return

NYplumberNYplumber Member Posts: 487
How well does parallel reverse return work when the emitters are of different size (such as in a recessed cast iron convector system)?

Will balancing be required? If so what's the eastward way to balance?

Thanks in advance.


  • Greg MaxwellGreg Maxwell Member Posts: 211
    Parralel Reverse Return

    In most reverse cases, you will need to supply some sort of balancing valve on the returns of each rad.
  • NYplumberNYplumber Member Posts: 487
    ball valves or

    Should I balance with ball valves or the Caleffi product which comes sized to a specific flow rate?
  • Greg MaxwellGreg Maxwell Member Posts: 211

    Ideally, you would know the flow rate, and set each unit to its own individual flow, but this sounds like a retrofit job, so you probably dont, so I would recommend a ball valve here. Make sure your supply & return piping is such that you can keep your velocity as low as possible, so as not to get velocity noise. 5ft per second is generally considered the "safe" flow rate.
  • Jean-David BeyerJean-David Beyer Member Posts: 2,532
    Ball valves vs. Balancing Valves.

    I have a radiant zone in a slab. Five 1/2 inch copper tubes enter the slab (one for each of 5 rooms) with a ball valve for each. The trouble with ball valves is that they really are not designed to run almost closed, and unless you need only a slight flow redution, they are difficult to adjust. One of the rooms I have requires very little heat, but I do not dare to turn it completely off for fear it would freeze the tubing in the slab. What I have done is to slowly turn it to off, and listen to it. When it is almost closed, I can hear the water rushing through it. I have left it at that.

    But there are valves designed for just this described in John Siegenthaler's big book. He shows several different types.
  • NYplumberNYplumber Member Posts: 487
    caleffi flowcal

    What are the thoughts of the caleffi flowcal balancing valves? Assuming they aren't too pricey I will give them a try on this job.

    Greg, its actually a new install from the ground up. Boiler, buffer tank, new rads, piping, etc.

    Just curious what would happen if I didn't balance and let the water flow the way water does. Would it all heat up? Or would I end up with cold rads?

    Parallel reverse return makes the most sense to me, but I'm always open to experimenting new ideas, or even old ideas.
  • Mark EathertonMark Eatherton Member Posts: 5,584
    Allow me to quibble... while educating :-)

    The pressure drop through a typical cast iron radiator is nil. Not even sure it is measurable, assuming a flow rate that would give a 20 degree F drop in fluid temperature.

    With that said, provided that the MAXIMUM difference in pressure between the highest and lowest PD in a parallel reverse return circuit are within 10% of each other,AND the system is truly piped parallel reverse return, then a balance valve is not necessary.

    If your distribution system is parallel DIRECT return, then you MUST have a means of balancing out the flow.

    As for the use of ball valves to balance flow, they are not recommended because you have to close them to 98% of their valve handle throw capacity before they start affecting flow. They also can experience what is known as "wire draw erosion" which scores the ball and or seat and renders them useless as a shut of valve.

    An inexpensive balance valve, like a Thrift Balancing valve, may also require near complete closure to affect flow. It is not intended to be used as a complete shut off, and in fact will not stop water under pressure from flowing past it.

    A true proportionally graded balancing valve will have a needle and seat type of shut off, with some means of being able to detect and determine flow passing through the valve.

    Residentially speaking, they are as rare as hens teeth :-)

    The truth is, most residential systems are extremely over pumped 98% of the time... Especially when used as zone pumps.


    It's not so much a case of "You got what you paid for", as it is a matter of "You DIDN'T get what you DIDN'T pay for, and you're NOT going to get what you thought you were in the way of comfort". Borrowed from Heatboy.
  • NYplumberNYplumber Member Posts: 487
    hens teeth

    Hey there Mark, thanks for the reply. You are most certainly correct. Properly designed systems are also as rare as hens teeth.

    With that said i may skip balance valves all to tether since the radiators will be very closely sized from one to another. It will be my first parallel reverse return system with many photos to come.

    As a teaser, look forward to seeing some low bills and a happy customer come December time. The last job of this design yielded a reduction in 50% of gas usage.

    Thanks HH guys.
  • Jean-David BeyerJean-David Beyer Member Posts: 2,532
    My house certainly needs some kind of balancing.

    My downstairs is radiant heating on a slab. There are 5 rooms, and 5 tubes going into the slab, and a bigger one coming out. It seems that each tube heats one of the rooms. If the tubing is spaced the same in each room, the lengths are all different, with the bathroom the shortestt and the living room the longest. I do not know the length of the tubing in any of the rooms, though I might be able to guess if I knew the spacing, which I do not.

    I am almost certain it is not parallel reverse return. I think each supply finds a way to the start of each room, and the returns all get themselves to one-inch return pipe. It might have some 3/4 inch in there too, but I do not know how to find that out without an x-ray machine and access to the underside of the concrete slab.

    So balancing is definately required, an I use ball valves because that is what my installing contractor put in. It replaced a little 5-port manifold casting that no longer worked. The adjusting screws would barely turn, and turning them did not seem to change the flow at all. Mark correctly describes what is wrong with using ball valves. When I look up balancing valves on the Internet, I find many clever ones that have calibrated passages with pressure ports so a sensitive pressure difference meter can read out the flow; many of these are ball valves too. For me, that is no use, because I do not know the piping layout, and I had to make a lot of assumptions in calculating the heat losses of the rooms that are not really good enough for setting a flow control valve anyway. I have to run the system and measure the room temperatures and floor temperatures to see if I am about where I want to be. It was tricky enough to see what valve went to what room. So unless I had a friend in a parts warehouse, I could not even use the Caleffi non-adjustable ones, because I would have to find some way to determine the required flow..

    I imagine the room where the valve is very nearly closed (I can hear the water rushing through it) will have that valve wear out prematurely. This is obviously a situation where a suitable needle valve should be used, if there are any for this service.

    I do not even know if mine is overpumped or not. I have a Taco 007-IFC and the slab is about 750 square feet. Five rooms in parallel. But since I do not know the lengths, this is meaningless. I do not hear the water rushing around the pipes, except where it goes through that nearly closed balance valve (ball valve), so it is not fantastically over pumped. But I get no where near 20F drop through that slab, even when it is 5 degrees below design temperature outside. So it is probably somewhat over pumped.
  • TonySTonyS Member Posts: 849
    Mark is right on the money

    I have converted quite a few gravity system(parallel return)to reverse return and even though the radiators are different sizes throughout the home..Like Mark said.. the pressure drop is nil.

    everything goes right into balance.

    Before cutting in all those valves I would try it.
  • Mark EathertonMark Eatherton Member Posts: 5,584
    You're welcome NYP...

    I did forget to mention purging. If you have a bunch of emitters in parallel, the presence of ball valves makes purging MUCH easier. Kind of like trying to purge a RFH manifold. Without balance/isolation valves, purging will take forever.

    Proceed with caution :0-)

    It's not so much a case of "You got what you paid for", as it is a matter of "You DIDN'T get what you DIDN'T pay for, and you're NOT going to get what you thought you were in the way of comfort". Borrowed from Heatboy.
  • NYplumberNYplumber Member Posts: 487
    edited August 2011
    ball valve

    Mark, what so you recommend to make purging painless? Placing a ball valve on each rad between the rad return and the main (basically on the branch)?

    I was aware of the erosion effect on the ball valves, but not that they had limiting capabilities. I remeber reading an artical of gate valves vs ball valves vs globe valves vs etc... but didnt recall ball valves being all that bad, however, with that said, I see how that can be limited.

    JBD, Caleffi sells adjustable valves called QuickSetter balance valves. I have no experience with them, but if you get the itch to modify your radiant system before winter, give them a try.

    While I'm here sounding like a newbie to the heat industry I may as well go ahead and ask what PD is.

    "highest and lowest PD in a parallel reverse return"
  • Jean-David BeyerJean-David Beyer Member Posts: 2,532
    Caleffi adjustable QuickSetter balance valves.

    "Caleffi sells adjustable valves called QuickSetter balance valves. I

    have no experience with them, but if you get the itch to modify your

    radiant system before winter, give them a try."

    I know they do. Where mine are located makes it very difficult to change the valves. I will not do it before this winter. Three of my ball valves run full open, so they should last forever. One is partly closed (less than half way, I estimate). The last one is almost off. That is the one that is likely to fail. I do not know how long it will take to erode the stainless steel ball. I suppose it is the teflon around it that will quit. I am 73 now, so I do not know if the valve or I will quit first. When the valve quits, I may put a Caleffi one in, if I still have enough marbles left to think of it.

    Actually, If I did not have two computers constantly running in there (one runs a measured 376 watts most of the time, the other much less), I could open that valve a little more and prolong the life of that valve.
  • Greg MaxwellGreg Maxwell Member Posts: 211
    Parrallel Reverse Return

    Hopefully you are going to be using modulated water temp on outdoor reset as well.
  • Mark EathertonMark Eatherton Member Posts: 5,584
    edited August 2011
    Balls are fine....

    It matters not whether it is on the supply or return, just so that each branch can be individually closed. Close all but the first branch, run water till air free, then open the next, close the first, and so on and so forth until everything is purged, then work backwards to open the rad's, giving a couple of minuted for each branch to flow purge.

    You will have your pressure reducing valve bypass set on full pressure, hence the reason you want to open the next branch before you close the first branch, otherwise you will have an inadvertent pressure relief valve test, and that usually only happens when the homeowner is standing right there watching you :-)

    PD = pressure differential. Sorry for using alphabet soup... And there is no such thing as a stupid question. Just stupid mistakes made by good people who are too afraid they will look stupid for asking questions :-) Funny thing is, the guy standing next to you wanted to ask the same question, but out of fear....kept his mouth shut.

    It's not so much a case of "You got what you paid for", as it is a matter of "You DIDN'T get what you DIDN'T pay for, and you're NOT going to get what you thought you were in the way of comfort". Borrowed from Heatboy.
  • NYplumberNYplumber Member Posts: 487

    Greg, as you may know, home owners want everything for nothing. We don't discuss price here, however, let's just say that this homeowner splurged by using us over the others. He wanted fan forced, yet I explained the pros and cons of.both systems, then the difference between my competition. For example he was on a budget (an unrealistic one) and asked for radiant heat too but didn't want the added controls to make it safe for the cast iron boiler, nor did he want proper reset curves...etc.

    The system will be able to be converted to reset with the addition of a few more dollars if he decides, however, these customers tend to stay with the bare minimum.

    It's a shame since he is spending money to relocate the chimney and still skimps on the mod-con. Had he thrown all the money for the chimney, new dhw tank... into a pot it would all come out at the same (or close) amount, with significant more long term savings.

    That's all for now. Pics to.come shortly.
  • Greg MaxwellGreg Maxwell Member Posts: 211
    Outdoor reset

    Check the pricing on the Honeywell AQ251 boiler/zone control system. It comes w/outdoor reset, and compare it to your current zoning control. I think you may be surprised at how easy it is now to convince homeowners about features/benefits now that the cost is much less.
  • NYplumberNYplumber Member Posts: 487
    edited August 2011

    From experience, is it easyer to run the feed/return pex lines in the perimeter studs behind the rads with short branches in 1/2 or 3/8 or run the feed/return mains in the basement ceiling and run longer small diameter branches up to each rad? I suppose the latter is a smarter less labor intense option.

    Greg, I stand corrected about the odr. I speced a tekmar 256 to control odr when the taco zvc relay box calls for heat.
  • NYplumberNYplumber Member Posts: 487

    Bump.... Any advice on piping preferences?
This discussion has been closed.


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