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Radiant floors hardly ever get warm

In my house which is new construction. The floors are very rarely warm to the touch. It’s 3/8 Uponor  joist track at 8” spacing. 3/4” plywood and 3/4” hardwood. Fiberglass insulation below. The house is 2x6 construction with r30 mineral wool in walls and r38 closed and open cell roof insulation. Right now I’m running 125 degrees at -10 and 70 degrees at 70 with min boiler temp of 80 degrees. Today is 33 degrees out and the boiler is running at 96 degrees. Thermostats are set at 69 degrees and the floors don’t feel warm. The whole house is always either 68 or 69 degrees whether the heat is running or not. It seems like the heat doesn’t come on long enough to heat the floors. Is there anything I can do to make the floors warmer more often without overheating the thermostat set point? I’ve tried lowering the water temp but I’m not sure how much lower I should go. Maybe I should be raising the water temp? 


  • Jamie Hall
    Jamie Hall Member Posts: 21,109
    Let's see here. Your thermostat is set at 69. The house is at 68 or 69. This is a problem? Remember, you are trying to maintain the house space temperature. If you make the floors warmer the whole house will be warmer... but you have it set for 69.

    You are generating plenty of heat in the house -- that's a very well insulated house -- that you don't need toasty warm floors to maintain temperature.

    Yes, you could get the floors warm -- change your thermostat setting and the boiler reset curve -- but that would make the house warmer, too.

    Now I do have a question: with the house that tight, what are you doing about air quality? You should have a minimum of two air changes per hour of outside air to maintain indoor air quality at something reasonable.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • Hot_water_fan
    Hot_water_fan Member Posts: 1,276
    Yup they're working as designed. This is a common misconception about radiant floors. The better constructed your house is, the cooler they will be. You might even be able to lower water temps further!
  • Sal Santamaura
    Sal Santamaura Member Posts: 482

    In my house which is new construction. The floors are very rarely warm to the touch...

    Where do you live and who was the builder? Sounds like a great recommendation! :)
  • GroundUp
    GroundUp Member Posts: 1,573
    Open some windows, the floors will become warmer
  • sunlight33
    sunlight33 Member Posts: 378
    If you raise the supply temperature but maintain the same room setpoint, the boiler will cycle more.
  • BirchwoodBill
    BirchwoodBill Member Posts: 11
    I am in Zone 6… reset is between 70 to 95 degrees which is the Warmboard guideline. We keep the bathrooms at 72f and the bedrooms at 68F.
  • ordellrobbie
    ordellrobbie Member Posts: 10
    The house being able to maintain the thermostat setting easily is not a problem. I guess I don’t have a problem. What I’m trying to figure out is if there is a way to have the heat on more often without overheating the room. I think I can keep lowering the temperature. Reset curve is already way lower than what the rep designed for. 
    We didn’t do anything for indoor air quality. The insulation contractor said we didn’t need too.  I only did spray foam where I had to meet code. I can still add an ERV. The bath fans have timers on them. Is that enough?

    I live in Massachusetts. I GCd the house myself. 

    I don’t want to run the heat with the windows open. I’m not looking to waste fuel. Just trying to have the floors warm as often as possible without overheating the house. 

    I’m going to try lowering the high limit temp more. 
  • KC_Jones
    KC_Jones Member Posts: 5,409
    If you are tweaking the reset curve, the goal is to get as close to running all the time as possible. On that note, what boiler are you using to power the system? Your desire for warmer floors is sort of counterintuitive to that goal. You actually need to lower temps to get more run time. The floor should feel neutral, not really warm.

    If you built a very tight house, you always have to consider indoor air quality, I'm honestly shocked the system designer you used didn't say anything about this, that should have been part of their job. The insulation contractor isn't really the one to consult for that, the HVAC system designer is.

    Think about it, the insulation contractor tells you he made a nice tight house for you, now you need to install a few thousand in equipment to purposely let air into the house. He'd probably lose a lot of work. The reality is, with a tight house, you decide the "leak" rate, and in the process recover some of the conditioned air, something those of us with old houses don't get.
    2014 Weil Mclain EG-40
    EcoSteam ES-20 Advanced Boiler Control
    Boiler pictures updated 2/21/15
  • hcpatel78
    hcpatel78 Member Posts: 150
    edited November 2021
    We have done a retrofit install between the joist with the extruded plates. We have hardwood and I am keeping the thermostat setting(75 with floor sensor). That gives a nice 69 to 70 room air temperature. We are located in zone 5 (NJ-North).
    SWT is between 80-120F and it is following ODR.
    Thank you,
    Hiren Patel
  • ordellrobbie
    ordellrobbie Member Posts: 10
    Boiler is a Burnham Aspen 110 which allows me to set the lower end of the reset curve at 70 but the min boiler temp oy goes to 80.  IAQ is controlled by 3 bath fans that run at 30 cfm which I didn’t know. Not sure if that’s sufficient. 
  • kcopp
    kcopp Member Posts: 4,188
    Forced air leakage w/ bath fans is really not a great approach although it may be "accepted".
    A hrv or Erv is really the best option. This way you are filtering what you exchange...
  • Zman
    Zman Member Posts: 7,446
    This article does an excellent job of explaining the concept https://www.pmmag.com/articles/83903-heating-a-thermos-bottle-house-br-john-siegenthaler
    Depending on your layout, you might consider turning off some loops in areas where you don't walk.
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
  • hcpatel78
    hcpatel78 Member Posts: 150
    Zman said:
    This article does an excellent job of explaining the concept https://www.pmmag.com/articles/83903-heating-a-thermos-bottle-house-br-john-siegenthaler Depending on your layout, you might consider turning off some loops in areas where you don't walk.
    Thank you,
    Hiren Patel
  • Dave H_2
    Dave H_2 Member Posts: 526
    Radiant floors are warmer than traditional heating systems (Duh!).
    Typical floor temp with a radiant system is around 75F. Forced air or baseboard systems, the floor temp is around 62F.
    Skin temperature is around 80F, so when you touch a radiant floor it "feels" cooler.

    As you stated, tstat set for 69, house is 69 = it's working!

    How to get the floors warmer, it's simpler than you think. Don't touch the boiler, change the reset curve or raise the design temp.......Raise the thermostat setting, it'll run longer trying to satisfy the air temp.

    Simple enough and enjoy!

    Dave H.
    Dave H
  • hot_rod
    hot_rod Member Posts: 19,275
    any time the floor surface temperature is warmer than the ambient it is adding heat. About 2 btu/ sq ft for every degree difference.

    75F floor surface in a 68F room= 7X2 or 14 btu/sq ft. A well insulated home may only need 14 btu/ ft on the coldest (design) day!

    The issue becomes skin temperature, it runs 82 or so F, so any surface below that temperature doesn't feel warm. In. your case warm floors may = over-heated rooms.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream