Radiant Heat Mechanics

Discussion in 'HVAC Heating & Cooling' started by FMcCracken, Feb 23, 2020.

  1. FMcCracken

    FMcCracken New Member

    Jan 20, 2015
    New York
    I'm a contractor in NYC and have a client whose radiant heat hasn't worked 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.

    Floors and walls are slab marble.

    Remote sensors are under the slabs. The Powder Rm does not have a sensor so it needs to be paired with one of the three zones.

    Outdoor air temp has little impact on a. Master as all the heavy lifting is done by central air and none on Powder as it is windowless.

    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?

    Last edited: Feb 23, 2020
  2. fitter30

    fitter30 Active Member

    Feb 2, 2020
    Retired service tech
    Peace valley missouri
    Radiate heat water normally run 5-10* over thermostat setting. Most flooring has a recommended hi temp limit marble probably doesn't. Cast iron boilers have a minimum water temp of 140* so piping is critical. Sounds like you need a serviceperson that understands radiate heat to go through the controls and look at boiler. Controls that old could of failed. Any control that measures temperature works 24/7 since it was made. To make domestic hot water boiler temp 150*-160*.
    try this site to look for a contactor
    Last edited: Feb 25, 2020
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