Welcome! Here are the website rules, as well as some tips for using this forum.
Need to contact us? Visit https://heatinghelp.com/contact-us/.
Click here to Find a Contractor in your area.

radiant heat system advice

Mark_23 Member Posts: 1
Could someone advise me on the best place to place the pump,expansion tank,air vent and air scoop on a radiant slab heat system?Would the best place be the supply or return on the system?What the plan is for is a slab heat system for a 32x36 foot garage.I also want to know what the best side(return or supply) to install the balancing valves.
Thank you in advance for any advice.It is greatly appreciated.


  • John Ruhnke1
    John Ruhnke1 Member Posts: 154
    Good Books............


    In order to properly install a radiant heating system you need to know alot more stuff then that. It is always best to pump away from the air eliminator and boiler. I suggest that you hire a good radiant contractor or take a few seminars and buy a few good books. Dan's book pumping away is good for starters. Try taking a radiant basics class from the RPA. John Sigenthaller has two good books out,Modern Hydronic Heating and Radiant Basics. You should at the very least buy and read those three books.


    To Learn More About This Contractor, Click Here to Visit Their Ad in "Find A Contractor"
  • Dave H_2
    Dave H_2 Member Posts: 545

    I agree, get as much info shoved between your ears as possible.

    There are many to skin a cat and it will depend upon the design that was performed first. Water temp, flow rate. loop lengths.......

    But here is one example.

    Dave H.
    Dave H
  • Mark Wolff
    Mark Wolff Member Posts: 256
    Radiant Slab Upgrade

    To properly add radiant capabilities to a standard high temp baseboard system, you will need to repipe the supply and return manifold on your boiler, then choose between floating action mixing valve or variable speed injection pump, the latter is preferred. Then pipe in your thermal jogs to eliminate ghost flow, install the single zone piping connect that to your remote manifolds, and you are nearly on your way. OR

    Hire a professional that does it every day, and let them explain how the system works after they've installed it.
  • Radiant Wizard
    Radiant Wizard Member Posts: 159
    Why is the latter

    preferred and who say's it's preferred? There is no system advantage between injection and 3-way mixing. If anything it just adds cost but that's my opnion.
  • Radiant Wizard
    Radiant Wizard Member Posts: 159

    How do you know what size pump to use? What water temp you need? What type of control strategy are you using? Here's my best advice.

    Before you do anything get a heat loss and radiant design done by a experienced/reputable contractor. There is no set plan on any system. You don't need balancing valves if you use radiant manifolds. They are already there. I take it you already set the tubing and did the pour. I hope you insulated below the slab and around the permimeter, sleeved the tubing at the points it exited the slab and that your loop lengths are withing the given lengths for this type of application.

    What are you using for a heat source? By the way your heat loss is somewhere around 18,720 btu's or 16.25 btu's per sqft. But that's just a guess. You also need 1,152 feet of tubing or 4-Loops of 288' at 12" on center of 1/2" Pex. Just a guess though.

    Good luck
  • Duncan_6
    Duncan_6 Member Posts: 26
    More advice (and opinion)

    Like the man says, get an accurate heat loss done.

    16.25 btu/sq.ft. sounds a little low to me, considering a typical garage has large, leaky, poorly insulated doors. In your case, maybe two of them.

    But that's just another guess. You need to do the math.

    Generally, pumping away from the expansion tank is a good idea. Usually (but not always) pumping away from most boilers is a good idea, too. Any restrictions in the system, like balancing valves, are better off located at the circ outlet rather than the inlet.

    If you take John Runkhe's advice you'll get the bigger picture. Don't wannna get lost in the forest looking at a couple trees.
  • Wiz, how do you protect the boiler?

    Or do you only use condensing boilers?

  • Radiant Wizard
    Radiant Wizard Member Posts: 159
    Let's See

    How about a return sensor.

  • > How about a return sensor.

    Pardon me for not being specific.

  • Pardon me for not being specific.

    How does a three way mixing valve on a radiant floor keep the boiler return water mixed above the temperature that condensing occurs at?

    You know what I meant.

  • Jed_2
    Jed_2 Member Posts: 781
    Which 3-Way Mixing Valve?

    And just which 3-way mixing valve configuration are you refering to? I can think of a few. And they could be Thermostatic, motorized, or just balancing valves with tees. This is a GARAGE; where's the JUDGEMENT for COMFORT level? Is it stand alone with it's own heat source? Is it an add on zone? And I don't make assumptions that most garages are massive leak zones(another poster).

    Mark, visit hydrinicpros.com and, look into Dan's many books on radiant heating. Your conception of what you want,
    simply stated, is probably a little more complicated than you might have counted on. But, it just might be as simple as you desire, given the many options available with radiant heating applications today.


    p.s. Oh, and I might make that 5 loops of approx. 250'(with tails) to keep the head well below 10', which 300' loops would create.
  • Radiant Wizard
    Radiant Wizard Member Posts: 159
    Modulating 3-Way Mixing Valve

    with outdoor reset. Control has a supply, return and outdoor sensor. Now I bet your going to ask where's the boiler by-pass. If your using 1950's technology ie. pinned type single pass boiler I guess you need one.

  • I deal mostly in 1800's technology, sorry.

    Cast Iron boilers are my main diet.

    I wanted to understand why you prefer one mixing method over the other.

  • Floyd_5
    Floyd_5 Member Posts: 418

    got out of the wrong side of the bed this morning!!!
This discussion has been closed.