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DIY radiant heat system HELP

DIY_BrianDIY_Brian Member Posts: 9
a few years ago we added on an addition with a basement. at the time we had to radiant heat but had the pex installed just incase we wanted to heat the basement in the future. Here we are in the future. I researched alot of designs, copied some of those systems at menards, bought a 5 port manifold, taco 007-F% pump from menards, WATTS 1" mixing valve from Menards, a bladder tank and a Plate heat exchanger is my heat source that connects to my wood boiler. so 180deg boiler water made me installed the mixing valve. I was super excited to test this all out and just finishing up my install now. I also added a sandwich style radiant heat to what will be a photography studio in our home. just hooked up that last line and re-purged the line of air with a garden hose from my water heater near by. Firing it up this week it all seemed good to me as the heat transfer plates we warm the basement thermostat was satisfied but i feel that i have some issue because my supply temp is about 130 but my return comes back like 80. i have the flow valves on my supply wide open and still that flow gage barely reaches .4gpm. When i purged with the garden hose i bottom those gauges out at 1.5gpm but with the pump running i cant muster any more flow. is my plate exchanger the issue, the mixing valve or just my pump not having enough Head to take on them both? ill post a picture i what i have going. I only have a total of 4 loops/2 zones controlled

with a taco controller and manifold actuators. but even 1 zone running i cant get a higher gpm but the rooms seem to be heating just not evenly as the beginning of the loops are warm then by the end they are cool

Mixing Valve


  • Jamie HallJamie Hall Member Posts: 12,947
    You just don't have enough flow. What you will need to do is to add up the head loss in your longest loop, plus everything else the pump has to pump through. Then take a look at the rating curve for the pump, and see if, at that head loss, you can get adequate flow through the system. You really don't want more than a 20 degree drop from inlet to outlet, and with a radiant floor 10 is better -- which means that you will get 5,000 to 10,000 BTUh per gallon per minute from the pump.
    Br. Jamie, osb

    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England.

    Hoffman Equipped System (all original except boiler), Weil-Mclain 580, 2.75 gph Carlin, Vapourstat 0.5 -- 6.0 ounces per square inch
  • DIY_BrianDIY_Brian Member Posts: 9
    edited January 8
    i have 4 loops, 2 zones the basement zone is 2-300ft 1/2" loops in 4" concrete. The other zone is 2, 1/2" loops 1 about 290ft the other about 270ft. those are the loops sandwiched style. the plates are still exposed because i havent installed flooring over it yet. as for head loss on the rest of the system im not sure how to calculate that with my plate exchanger and my mixing valve. according to the maximum head on the pump i listed its 11ft.
  • SuperJSuperJ Member Posts: 579
    edited January 8
    What is the CV of your mixing valve? Ideally you want to use a mixing valve with a high CV. DHW mixing valves often have high pressure drops.

    Make sure your manifold balancing adjustments are open. You have to take the control head off and turn the adjustment.

    Your pressure tank isn't really in an ideal position, you don't want any substantial pressure drops between the expansion tank, and the pump suction, your mixing valve is a substantial pressure drop. In the meantime make sure you have 15psi-20psi in the system. (and charge your tank appropriately while disconnected from the system).

    The maximum head pressure isn't necessarily relevant. You need to make sure the available head pressure of the pump at your design flow rate is equal to or slightly higher than your calculated pressure drop.

    As your flow goes from 0.5gpm to about 1gpm, your pressure drop goes from around 1fthd/100f to 3.5fthd/100ft.

    For example at 8gpm the 007 only has around 8fthd capability.

  • DIY_BrianDIY_Brian Member Posts: 9
    I'm guessing this is the issue, i noticed it says minimum operating pressure is 30 PSI. I bought it in the radiant heat section at Menards so i assumed it would do the trick. but I am a first time radiant heat DIYer so i dont know a ton of technical specs.
  • DIY_BrianDIY_Brian Member Posts: 9
    i dont know the CV rating. if this is my culprit then what would a better option be here?
  • SuperJSuperJ Member Posts: 579
    edited January 8
    From that chart you can kinda guess that the CV is probably around 1 (the flow at a 1psi pressure drop). And assuming 1gpm per circuit your pressure drop would be about 8psi (which is probably over 20fthd).

    If you choose a mix valve with a CV that match your design flow you can expect a 1psi pressure drop (about 2.3fthd) across the valve. With small circulators I don't think you want to budget much more of a pressure drop. Don't just look at the port size make sure you look at the pressure drop at your design flow (or use the CV rating). A lot of mixing valves have a high max flow but with an insane pressure drop if used in a heating application.

    With 4-1/2 loops you might be able to use a 1" caleffi mix valve valve CV of 3. I wouldn't go with any lower CV than that.

    Or to add a little more control go with the Taco I-Series Outdoor reset. The 3/4" 3 way has a spec'd CV of 4.5. This will improve comfort by matching the water temperature to the load and since it's a ball valve it has a higher CV. But it's more money than a thermostatic mixing valve.

    It's also available with a simpler fixed setpoint for a bit less $$$.
  • DIY_BrianDIY_Brian Member Posts: 9
    Wow thank you for that! 20fthd is about double my pump max rating. sounds definitely like the mixing valve. So a higher CV is better, meaning more GPM per 1PSI drop? this is all pretty new to me and if for a few dollars extra to get it running better im totally down with that. Like i found this just a few dollars more then the one you posted but a CV value of 3.9
  • hot_rodhot_rod Member Posts: 13,485
    .65 gpm is about the max you want to flow in 1/2" loops, .50 is typical. So 6 loops? X .65= 3.9 gpm total required.

    A 3 Cv valve would be fine, here is the pressure drop thru a 3 Cv valve at that flow rate. As Jamie mentioned, add everything in the circuit. Should not be much pressure drop in the HX at that flow rate.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    The magic is in hydronics, and hydronics is in me
  • DIY_BrianDIY_Brian Member Posts: 9
    Thank you everyone! Ill get a new one on order and update when that happens but it sounds like we are all on the same page and i had the right idea just new to all the technicalities so i appreciate all your input!
  • GroundUpGroundUp Member Posts: 990
    So, with the photos provided you have only got 2 loops of 1/2" connected to the 007, nothing else. Were the rest added post-photo to the same manifold? Did you remove the red caps and crank the flowmeters wide open or are you just relying on the white knobs? That particular mixing valve has a pressure drop of 4ft of head at 1 GPM or 7ft at 2 GPM, but as was mentioned you will not likely get above .7 per loop regardless of circulator or mixing valve with a 300ft loop. There is nothing wrong with a 50 degree delta T if it's heating the space adequately, and with 1.6 GPM at 50 degree delta you're emitting 40,000 BTU- pretty impressive for a staple-up system! If you haven't opened up the flowmeters, I might suggest that first. If you have, and the house is heating adequately, don't worry one bit about the flow rate or the mixing valve- it is just fine.
  • hot_rodhot_rod Member Posts: 13,485
    Odd that they do not give a Cv on the valve, the graph is not a lot of help. Running their numbers backwards, flow and pressure drop seems to be 2.? Cv.

    Also odd that a valve with 1" available connections would be a lower than 3Cv? What would be the application?

    Low Cv, say 1.9- 2 are generally point of use, single flow, a faucet or two applications, a 1070 listed valve.

    That valve shows both 1017 and 1070, to be a 1070 listed it must be limited to no more than 120F setting.

    Is 120F adequate for your design?
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    The magic is in hydronics, and hydronics is in me
  • mattmia2mattmia2 Member Posts: 1,408
    You need a pressure relief valve on the radiant side of the system as well.
  • DIY_BrianDIY_Brian Member Posts: 9
    to respond to "ground up" the photo is a bit out dated. that photo does not have my actuators installed and also does not have my second zone installed. so there is actually 4 loops of 270-300ft. and yes i can get over .4gpm with the red caps fully open. it would be nice to get atleas that .5-.65gpm to get a better Delta then 40-50deg.

    new issue i just came across and a bit off subject is we are looking at flooring Coretec flooring to be exact. they have strict warranty rules for radiant heat applications. floor temp cant be above 80deg. dont thing thats a problem as i dont thing i will need my room any warmer then 72-75 anyway. but they say i cant install it over my sandwich style as is, that i need at least 1/2" material between the plates and the flooring. i already lacking head room as it was 8ft to start, then 3/4 rigid foam over concrete, then 2 layers of 3/4 OSB to accommodate my pex. now they want 1/2" more plus the .3in flooring. if i do decide what 1/2 material should i use? a plywood? 1/2 concrete backer board maybe it will help hold the heat longer like a slab?
  • Jolly BodgerJolly Bodger Member Posts: 209
    I think the problem with the sandwich system and floating floors is the SWT (supply water temp) usually needs to be high. This will make a hot spot on the flooring right above the tubing. I suspect it would result in bad heat striping on the surface. The 1/2" material Coretec requests is to help distribute the heat. I would thing that something high density like hardibacker would help transfer and distribute the heat. Or pure a self leveling underlayment?
  • ZmanZman Member Posts: 5,870
    What brand and type of flooring. Do you have an idea of the heat loss of the space?
    When you really read most warranties, they have so many clauses like that they become worthless.
    In my experience, you have to really cook a floor to damage the flooring. If you go with the taco valve and outdoor reset the chances of damaging the floor will be much lower.
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
  • GroundUpGroundUp Member Posts: 990
    Back to the quest for more flow, why does it matter what the delta is? Is the space not heating adequately?
  • hot_rodhot_rod Member Posts: 13,485
    ∆T will depend on when you measure it, with a cold start expect a wider than designed for number. Typical radiant floor design is 15°. All things being equal tighter ∆ will cost more circulator.

    More flow or higher SWT is the way to more radiant panel output in an existing system.

    On a new design tighter spacing provides better output and more consistent floor surface temperature.

    My next home will be 6" oc designed around a 100- 110° SWT.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    The magic is in hydronics, and hydronics is in me
  • DIY_BrianDIY_Brian Member Posts: 9
    Just an update. i got the mixing valve suggested above and got it installed, but a little set back i put a screw through a loop putting down 1/4" OSB over the transfer plates because our flooring company said it had to have a barrier. so i have to pulle up 300ft of pipe and re run a loop because i dont like the idea of a fitting in the floor that has no access to repair and wont know if theres a leak in 6 months. thank fully i caught it no and not after the room was finished. Any way the new MV is installed and i did get a small improvement on the flow gauge. i still cant get more then .6 on the guage but thats assuming its actually accurate. what i do notice now though is the return lines are actually hot where as before they we very cool to the touch, almost cold. My temperature guages are all over the board. the Mixing valve has a guage that says its 125deg coming out but my supply manifold gauge says its 138, and my return manifold says about 120. so again i dont know the accuracy of the guages but i can definitely see and feel a change in the floor temp being more even from the beginning of the loop to the end. so thanks for the tips. Now waiting on new pipe tomorrow. plumber for Pex-AL-Pex wanted $350 to splice the leak. the pipe was $130 shipped and reassurance that it wont leak in a few years
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