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.

Hydronic Floor Heat Aquastat

FrankieS Member, Email Confirmation Posts: 5
I'm a contractor in NYC and have a client whose radiant heat isn't working well for the past 4 years. The system was installed 16 years ago. I think its been a problem since the beginning but when an actuator failed, it focused his attention.

3 Zones - A. Master Bath Floor + B. Powder Room Floor; C. Master Bath Towel Wall; D. Master Bath Tub.
BUT, there are 4 Uponor valves - A, B, C, D.

The Uponor actuators and the TruFLOW supply and return manifolds are new replacements and have visual flow meters.
The Powder Rm does not have a sensor so it needs to be paired with one of the three zones.
Floors and walls are slab marble.

We still can't regulate the heat. Too hot or too cool.

The 3 aquastats controlling the Uponor actuators are the Johnson A419 - 3 units, 1 for each zone. Floor and Tub zones are set to 85* and the towel zone is set to 80*
There is an aquastat on the dedicated hot water heater. It is a Honeywell Type L4006A, 100*- 240*F, "switch opens on temperature increase." It was set at 160* (!) but I turned it down to 100* and floor and wall temps are more regular/ even. Temperature spikes are a lot less extreme.

#1. The Honeywell aquastat controls the temperature in the hot water tank/ heater, right?

#2. How does the circulator know when to turn on? It should be wired to the Johnson A419 Aquastats, right? I'm not saying it isn't. Just confirming understanding.

#3. My research tells me that we should be using a floor heat Set Temp 5* hotter than the temperature we want the room and a water temperature same as the Set Temp. Hence we need 80* water. The Honeywell aquastat needs to be changed, since its low limit is 100*F, but to which one? Note - the current unit has an immersion well.

According to SupplyHouse.com my Honeywell choices are:
L4006A1959, High or Low Limit Aquastat, 40* - 180*F Range.
L6006C1018; High or Low Limit Aquastat & Circulator Strap-On Aquastat, 65* - 200*F Range, 5*F - 30*F Adj. Differential.

What would you recommend?

#4. If I use the L6006C1018, can it be installed as an immersion type unit rather than as a strap-on?



  • GroundUp
    GroundUp Member Posts: 1,495
    Are the controllers relying on probes embedded in the slabs somewhere or what? What is the differential set to on each unit? Long story short, this is not a place for aquastats or temp controllers like the 419A- this is a place for thermostats. An 80 degree floor temp might have a 75 degree air temp if it's warm and sunny outside but may also have a 50 degree air temp if cold and dark outside, you cannot rely on floor temp only to regulate air temps. Do not worry about the aquastat on the tank- it does not need to be swapped. If I were you, I'd hire a heating contractor that know's what they're doing. But if I were me, I'd turn that Honeywell back to 160 where it belongs and pipe the loads either through a mixing valve or with injection mixing to set the proper delivery temps, as well as swap all three 419A controllers for Tekmar 519 stats with both air and floor sensing capabilities.
  • FrankieS
    FrankieS Member, Email Confirmation Posts: 5
    Thank you for the reply. Good points.
    The 419A's have probes under the slab marble. I should have mentioned this.

    The heavy lifting of the air temp is pretty much regulated by the adjacent rooms. Outdoor air temp has some, but little impact on room temperature in Master and none in Powder.

    I should have also noted that the radiant heat is primarily for feet comfort. With the 160*, it would warm the room by 15*-20*.

    Wouldn't mixing valve require additional water to enter system? This is supposed to be a closed system.
  • nibs
    nibs Member Posts: 499
    5 rooms, 7 loops one thermostat, Supply water max 110 F. this winter have adjusted two flow valves 1/4 turn, at manifold for balancing, adjusted the thermostat once for run time, and changed the thermostat setting once. Master bedrm stays at about 67F, living rm stays at about 72, bathroom stays at about 76. Design days supply water goes up to 110 F but most of the time is running at 90 +.
    Keep it simple.
  • GroundUp
    GroundUp Member Posts: 1,495
    Mixing valves use the return water from the zone to temper down the supply water to the appropriate temperature. Say you had 160 degree boiler water but wanted 100 degree supply water to the slab, the return water from the slab might be 80 degrees so the thermostat within the mixing valve would recirculate as much 80 degree water as needed while injecting as much 160 degree water as needed to attain 100 degree supply water. Same rule applies to injection mixing. If proper floor temps cannot be maintained without overheating the space, some sort of economizer should be used to combat the issue. You say the floor heat water is being fed by a water heater. Is this like a tank style domestic water heater, or are you actually referring to a boiler? Most boilers (unless high efficiency, typically vented with plastic piping) will run into trouble if operated at low temperatures due to flue condensation and that's why I suggested turning the temp back up. We need some more information about that before a proper recommendation can be made. Some pictures would be fantastic
  • FrankieS
    FrankieS Member, Email Confirmation Posts: 5
    If I understand correctly, this would require a mixing valve on each loop. Correct?

    The mixing valve (Honeywell-Sparco AM100R-USTG-1) would be installed at a return Tee, so it could feed the new supply and dump the balance back into the hot water heater, right? This way the slab could never over heat.

    Water heater is a 10 gallon electric tank style domestic heater.

    Thank you,

  • FrankieS
    FrankieS Member, Email Confirmation Posts: 5
    Nibs -
    That's is what I've been trying - balancing the heat by controlling the flow rate - but before I lowered the tank temperature it was a loosing battle. The Uponor Flow Meters are a great visual help. I'm getting there now, especially with 100* supply.

    Thank you for the reply. Tells me I'm on the right track and it might simply be more about fine tuning.

  • hot_rod
    hot_rod Member Posts: 18,209
    See what the on/ off differential if the water heater is. For radiant you want the lowest supply temperature and a 10- 15 degree delta from supply to return on the loops

    Adding an outdoor reset controlled mixing valve would be a good control option
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • GroundUp
    GroundUp Member Posts: 1,495
    Okay, with the electric tank style it can be run cooler as you are with no mixing valve- sorry for jumping the gun. Odd it uses an aquastat instead of a regular old thermostat behind the access panel, usually below the heating element. Perhaps you could reuse one of the 419A controllers to operate the tank temp to lower than 100 when you swap them out for thermostats? You never did say what the differential is set to on the existing 419A controllers
  • FrankieS
    FrankieS Member, Email Confirmation Posts: 5
    edited February 2020
    Differential is set at 3 and I can't tell you why.
  • GroundUp
    GroundUp Member Posts: 1,495
    Dropping it to 1 will further dial in your temp swing issues