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High Mass Radiant Control, again.

LuckyDogLuckyDog Member Posts: 22
I am building a house in the White Mountain region of New Hampshire. The boiler guy I am using has told me ODR isn't a good choice for the radiant floor. OAT (outdoor Air Temps?) can swing pretty wildly here and I will be overshooting.

After a LOT of reading on here, I see where / how his experience is correct. (I still believe we can control this beast though). I had ODR on a non-condenser Buderus with fin-tube baseboard down in RI. Took awhile to dial it in, but loved the steady heat and comfort. So, I am not afraid to take the time to adjust it to work. Whatever 'it' turns out to be.

Basement: Slab on grade; 4 loops at about 250 ft. per loop.; DD -9°F, SWT 90°F
Control system?
1st Floor: gypcrete over pour; 4 loops at about 250 ft. per loop; DD -9 / 125
Control system?
2nd Floor: Radiant Panels from Beacon Morris; 3; DD-9 / 125
Considering Wall T-stat w/ maybe TRVs on the panels?

Boiler selected but NOT purchased yet;
Lochinvar Noble NKC110N (LP conversion) (combi)
It comes with an ODR sensor. Modulates to 11k output. It appears to only have one input for "Call for Heat".
The other boiler the boiler guy wants me to install is a Bosch Greenstar ZWB-28-3 combi; No ODR installation.

I looked at the Tekmar 519 and Uponor A3100101 thermostats that also have slab/floor temperature sensors. They are PMW control. My fear is that I would be short cycling the boiler when the floor and air temps are very near the set-point.

I have read here about other control schemes; like room temperature reset. From the limited reading I have done, it looks like they want to modulate the boiler. The Noble doesn't appear to accept that kind of input.

I understand and like ODR. I know that short cycling is bad. I understand how and why the 'fly wheel' effect of the floors causes over-shoot. I am sure I'll need a zone control box. I plan on using circulators rather than zone valves.

PID control works great on some of my systems at work, mainly because they are rather steady-state. Mother Nature is not what I call steady-state. :)

@Zman @hot_rod @SWEI and some others whose names I forgot.

Ok, the question....
What control system should I be looking at? Recommended model numbers?
Do I need to chose a different boiler?

Building a house in NH


  • hot_rodhot_rod Member Posts: 14,397
    First off you need two SWT temperatures, 90 for the slab, 125F for the other emitters, correct?

    Be nice if you could run all one temperature, upsize the panels and tighten the gyp tube spacing? If they were closer together, within 10- 15° required SWT I'd just do one temperature.

    If not run the boiler at the higher temperature on ODR.

    Simplest would be manual mix valve for the lower temperature it would track along with the ODR controlled boiler.

    Or more costly would be a modulating valve for the lower temperature on it's own ODR setting. Many here rave about the Taco 3 way modulating valves for that.

    Anytime you add sensors to the wall stat you gain more control resolution. I would add a slab sensor if possible in the basement.

    Or the next more $$ option, a thermostats stat with indoor and outdoor feedback, a more expensive tekmar control platform option.

    If the boiler cannot turndown to the lowest load on the mild days, few can:) there will be some cycling. A buffer, or a higher mass boiler lessens the cycling further.
    Until boilers modulate from 0- full output, expect some cycling.

    IF you spend the time to dial in the control accuracy you could get near constant circulation, which helps lessen flywheel type swings.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    The magic is in hydronics, and hydronics is in me
  • ZmanZman Member Posts: 6,322
    It should be easy to get this running at the same temp. You might just consider not running tubing in areas of the basement where you don't walk and running all of it at 125. You will still get the nice warm floor feel without overshooting.

    I would strongly disagree with your contractors view on ODR and boilers with 3-1 turn downs. You absolutely need outdoor reset. The Lochinvar would be a good choice. Since your contractors qualifications seem questionable, be sure he intends to pipe it per manual. I have found contractors who don't use outdoor reset often have "creative" ways to mis-pipe the boiler
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
  • LuckyDogLuckyDog Member Posts: 22
    I'm glad you agree with the ODR and Lochinvar. I get the feeling my boiler guy is just ol' school and seen slabs-on-grade controlled with a wall 'stat and ODR. He has said things like "If the circulator runs all the time, you aren't getting enough heat." That is, I guess, pedagogically (fun word) correct; but 'almost' all the time is the goal, correct? :)

    @Zman I will be watching closely. (I have studied the iDronics series from Caleffi .) He has said enough things that match the books that I am not scared. (and I know, I don't have experience)

    @hot_rod I like the idea of a floor stat for the basement slab and a manual mixing valve to just keep the temp proportionally lower (90 to slab when SWT is 125)

    Is the first floor considered 'High Mass'? it is a ThermoFLoor gypcrete product about 2 inches thick.

    What if I just use a normal bang-bang floor stat and wall stat in parallel? The PWM stats are making me nervous.

    The 1st floor stat would be set to keep the slab at 68-70 minimum temperature. The wall stat would try to keep the room air at the correct temperature. If the air temp went up, it would stop the boiler because the floor should already be above 70. Might still get a little overshoot.

    If the floor 'tried' to fall below 68, then boiler would kick on again. Keeping the floor from falling below 68 should, I think, help with any under-shoot.


    Wire them in series? Then they both set upper limits. Either one would turn off the boiler when a set point is reached.


    Series Parallel? The series floor sensor prevents too high of a floor temp. The two parallel stats do what the first scenario does.

    WAIT!, the Tekmar 519 already does that. (Except it is PWM) I don't like the idea of the boiler and circulator 'bumping' on and off because I am near setpoint.

    Yes, I over think things. But it has done me well at my paying job. :)

    The house is over insulated and pretty tight. I have found it to hold the temperature very steady even without heat yet. But no one is living in it yet.

    Building a house in NH
  • hot_rodhot_rod Member Posts: 14,397
    I consider gyp or thin slab, less than 2", to be medium mass. I'm not sure there is a true definition.

    I doubt your basement slab with heated space above will see wide temperature swings and suffer from "flywheeling"
    Constant circulation and ODR responsive control should all but eliminate over-shooting. assuming it is all put together and dialed in properly.

    ODR fine tuning requires some operator participation :)

    A t-stat in each zone. The tekmar and Uponor allow "not to exceed" slab sensor settings, that is plenty of control when used along with ODR.

    The PWM control logic attempts to smooth out the temperature control, I would not fear it, really.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    The magic is in hydronics, and hydronics is in me
  • LuckyDogLuckyDog Member Posts: 22
    @Mark Eatherton Way back in Nov. 2011
    You mention Mean Radiant Temperature (MRT) thermostats weren't reasonably available. Has this situation improved?

    Do you or someone have a recommended thermostat for radiant floors? I totally understand why an 'air' thermostat is not a good choice.

    Building a house in NH
  • hot_rodhot_rod Member Posts: 14,397
    at days end a thermostat is just a high limit switch And you and your comfort are in charge of it🤔 Don’t over complicate things
    If MRT controls were that much better, you’d see them more readily available, me thinks
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    The magic is in hydronics, and hydronics is in me
  • ZmanZman Member Posts: 6,322
    I have an older version of the Uphoner with PWM in my own house. The cycles are very gentle. It does not short cycle the boiler.
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
    LuckyDogTim Potter
  • Jean-David BeyerJean-David Beyer Member Posts: 2,665
    I am building a house in the White Mountain region of New Hampshire. The boiler guy I am using has told me ODR isn't a good choice for the radiant floor. OAT (outdoor Air Temps?) can swing pretty wildly here and I will be overshooting.

    I have a high mass radiant slab at grade in my house (and baseboard upstairs); no basement. I am not a heating contractor, but in a past life, I used to design feedback control systems, which the thermostats, boilers, resets, etc., are.

    It used to be heated by a 1950s GE oil fired boiler that rapid cycled all the time, and the temperature swings were pretty bad. I replaced that boiler with a gas fired mod-con with outdoor reset.

    The installing contractor did not wish to install the ODR (even though it came with the boiler) because he said they did no good. Well he installed oversized boilers, so they would modulate all the way down and still put out too much heat. And into a slab that meant severe overshoot and undershoot.

    I insisted on the smallest boiler and that the ODR be connected, which he did. It took me several years to get the ODR curves correct (my boiler has two thermostats connected and a different reset curve for each, so I have two zones, one for the slab and one for the baseboard). On good days, the thermostat would call for heat for 18 hours or so, and then stop. And the ODR would adjust the boiler supply temperature to just what was needed to compensate for the heat loss. In shoulder seasons, my boiler will not modulate down far enough so it cycles on and off a couple of times a day.

    But even right away, I got the curves good enough that it controlled the temperatures very closely, much better than the old boiler. Because on a day when little heat is needed, it reduces the supply temperature accordingly. On quite a warm day, it puts only 80F water into the slab, so how much overshoot can there be when I heat the room to 69F? It also cut my heating bills in half, but how much that difference is due to lower gas prices compared to oil, and how much is due to the more efficient boiler I do not know. But I do know about the increased comfort from much smaller temperature swings in the house. It holds 69F +|- 1F all winter long. Right now, it is about 78F inside, but that is because I do not have A/C.
  • hot_rodhot_rod Member Posts: 14,397
    I feel the bigger piece of the puzzle for ideal comfort is the air quality control, IAQ. For years this was ignored with radiant heating systems, still is in too many cases.
    We have good technology, controls and products now to deal with humidity, air turns, and good filtration.

    Humidity is most responsible for your wood squirming, furniture, cabinets window trims, flooring, etc.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    The magic is in hydronics, and hydronics is in me
  • Dave H_2Dave H_2 Member Posts: 413
    Here is my control system FWIW.

    Everyone has their own ideas and this is what works for my house and the way me and my family use it.

    Whole house is radiant on Long Island, NY. Outdoor design temp is 15F above 0.
    First floor is slab on grade, embedded 12"o.c.
    Second floor is underfloor with some rooms with heavy plates, some rooms, suspended pipe.
    Addition is also underfloor with plates.
    I broke the house into those three areas based upon water temp design.
    First floor - 95F
    Second Floor - 125F
    Addition - 145F

    The house is broken down into 9 zones and have a combination of zone valves and zone circs. A mix of different thermostats, none have a floor sensor; Taco 562 on/off stats, two nests, honeywell lyric, ecobee 3, ...

    The boiler used is on ODR and set for 145F to match the addition target water temp.
    The first floor gets its water temp from a Taco i-valve on ODR set for 125
    And the first floor uses another i-valve on ODR set for 100F.

    I do use setback on several of the zones, some do not move settings at all.

    In theory, if you can dial in all of the ODR curves perfectly, you would only need the thermostats to act as a high limit. Unfortunately we install heating systems in homes, not on paper and therefore so tstats are needed ....

    This install occurred 7 years ago, the only thing I wish I did and I may be doing it real soon is add a buffer tank to the system.

    Dave H.
    Dave H
  • LuckyDogLuckyDog Member Posts: 22
    Thank you all for the inputs.
    I have an HRV installed.
    I also have mini-splits for AC and knee/shoulder seasons.

    The Lochinvar Noble NKC110 will mod down to 11k. From the heat loss calc and plotting against the MiniSplit Heat BTu, I see a cross over point at about 25 to 30 degrees. Above those temps, I think I'll be using the MiniSplit system for the heat

    Building a house in NH

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