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How to determine proper water temp for radiant floors

scott w.
scott w. Member Posts: 196
Would like to ask about proper water temp for pex tubing running through gypcrete poured floors. 1928 brick house was renovated several years ago. Installed new WM natural gas fired ultra 230 boiler with outdoor sensor.

House has cast iron radiators for zone one.
The other three zones are all in floor radiant heat. They all have a temp gauge above the mixing valve except for the theater room. Installer did not have a have a temp gauge that would fit the larger piping for that zone at the time so not installed.

May have made a mistake at time of renovation on the theater room. Did a gypcrete pour over concrete slab. Had to watch the increased floor height with pour over. Did not want to jack hammer out the old concrete floor so no thermal break between the gypcrete pour and old slab.

The other two zones are the kitchen, and have three bathrooms tied to the master bath thermostat.

All of the radiant heated zones have a mixing valve that is set by turning a dial to settings numbered 1 through 6.

My question: What is the optimal water temp to maximize savings for fuel use?

The mixing valves were never set by the installer. I have tweaked the valve settings so the floors don't get to hot to quickly and over shoots the thermostat.

I have noticed the pump on the theater room seems to run a really really long time before the room thermostat is satisfied and during that time the boiler cycles on and off. Is this the way it's supposed to work?
Any help or suggestions would be greatly appreciated.
Also would appreciate info on radiant heated floors, ie, theory, heated water going in, water loses heat as it passes through floor and heats room, colder water comes back to the boiler to be reheated




  • Ironman
    Ironman Member Posts: 7,170
    The only way to know would have been to do an ACCURATE heat loss calc and then to have designed the system from that. Heat loss; tubing size, length and spacing; flow rate, insulation; floor covering's R value; etc all determines what temp is needed.

    Also, using a fixed water temp is not the best method. A smart control with outdoor reset would have been. With a fixed temp valve, you should set it to give just warm enough water to maintain room temp on the coldest night of the year.

    It probably should be no more than 120*, but without proper design info, it's a guessing game.
    Bob Boan
    You can choose to do what you want, but you cannot choose the consequences.
  • Scoot
    Scoot Member Posts: 9
    An extensive heat loss calculation was done at the time of the renovation of the house including planning for all bathroom, kitchen, and theater room conversion to in floor heat and the installation of the new boiler which included an outdoor reset. Problem was the installer never came back in winter to set the valves.
    Am going to try to include photos.
    Maybe it's time to upgrade some of the 're technology to the system.
  • Scoot
    Scoot Member Posts: 9
    More pics.
  • Scoot
    Scoot Member Posts: 9
    Boiler pic.
  • Scoot
    Scoot Member Posts: 9
    Here are some more photos. All the radiant floors are ceramic or stone tile.
    Appreciate any comments if this system could be made more efficient.

  • DZoro
    DZoro Member Posts: 1,048
    The hard part is that you need high temp for cast and low temp for floors. A injection system with outdoor control would be best for the floors. Would need a re-pipe though. The extra concrete in the theater room is sucking up extra heat. Slab sensor would help maintain more constant temp/comfort.
  • Scoot
    Scoot Member Posts: 9
    I programmed the WM ultra for max water temp of 160 degrees. Read on the wall that lower water tempature means better fuel savings.

    The cast iron is now way over sized after all new energy efficient windows and the extra insulation. House used to have steel framed single payne casements, the cold air just rolled off them. Was uncomfortable to sit near them in winter.
    You can't believe how much heat the living room rad puts out. It's huge. 47 sections and 9 feet long. The zone all the rads are on runs the least.

    The theater room has French doors that separate it from the rest of the house. That zone seems to run the most.
    Want to get up to speed on what my options might be to increase the efficiency of the over all system.
  • Gordy
    Gordy Member Posts: 9,537
    edited December 2017
    After all the envelope upgrades that standing iron can take much lower AWT. Shoot for 130 return water temp, or lower.

    The theater room slab is sucking up btus. It will stabilize into the heating season, just takes unnecessary energy to do so.

    An EDR survey should have been done on the ci zone to determine the AWT needed.

    An IR temp gun will do wonders to check slab temps, and CI temps on the system to tune it.

    Do you use setback schedules? If so where?

    Radiant floors should run a 10 degree delta once stabilized. Example: 120 supply 110 return. Your delta may vary.

    Above all implement ODR, and tune it in.

    With out knowing heat loss numbers room by room. Pretty hard to determine flow rates, and AWT. Your installer has failed you in not finishing the job they started.
  • Scoot
    Scoot Member Posts: 9
    Please forgive me as I don't know all the abbreviations IR gun, AWT ??? I do know ci .

    Heat loss as mentioned before was calculated previous to the install of the boiler, for both cast iron and in floor heat for each room.
    Boiler WM ultra 230 has an out door reset. Unfortunately the installer has all that info on heat loss and all the calculations .

    I do not use set backs. Thermostat is set and left at one temp.

    My question, what is the proper way to set the manual mixing valves? ( see pics in above post)How does one check the temp on return water? Is the return water temp checked at the boiler on primary loop.
    I think through programming the boiler, return water temp can be checked.
    Not sure but don't think the pumps on the system are adjustable for gpm flow.

    Should I just give up and try to find some one who is knowledgeable, that can be a problem. Don't think i know enough to do this myself.

    I need to a aquire some knowledge about this so I can tell if the professional knows what he is doing.

    Am sure this system is not operating as efficiently as it could be.

  • ch4man
    ch4man Member Posts: 294
    edited December 2017
    or the highly inaccurate but very simple, real world, KISS method of just run that sucker until the boiler is cycling and the slab is stabilized. now go see whats the actual temperature of the floors surface. typically 84-87 degrees surfacetemperature works.

    note; im just a dumb service guy, not a designer or installer. but what are you gonna really do? rip it all out and start again. thats the cleanest, nicest mechanical room i've seen in a long time