Fred

Thermostats for Electric Radiant Heated Flooring

April 30, 2009 | by Fred (email) |

radiant heated flooring thermostat

As we’ve written here in a dozen different articles, radiant heated floors are growing in popularity as a luxury upgrade to modern homes, and DIY radiant installation is a relatively easy project. There’s nothing quite like a heated bathroom floor early in the morning, or the cozy feel of a warm family room floor old a cold Winter night.

With each radiant flooring installation, you’ve got a couple of control options for how the temperature of the floor is set and maintained.  Each has implications for the floor, the room, and your radiant floor’s energy consumption.  Here’s the rundown of control types available to homeowners.

Plain Switch Only – No Thermostat Installed

The simplest electric radiant installation isn’t controlled by a thermostat at all.  Instead, its simply turned off and on by a switch.  This option, which costs nothing more than a $2.00 switch at installation, is likely to cost much more in the future.  Inevitably, switches are left on by accident, which could allow the floor to heat up into the high 80s F (or in some installations, even hotter).  Also, since radiant floors can take time to heat-up, a switch is only a good option when a delay is acceptable between the time the floor is turned on and when it needs to be warm.  Unless you are doing a bargain-basement installation with some pretty unsual circumstances, avoid this option.

  • Pros: Simple installation.  Inexpensive installation cost.
  • Cons: Likely to waste energy and cost more in the long run.  Delays usability time.  May cause the floor to heat up to an uncomfortable level if accidentally left on.

Timer – No Thermostat

One step up from a plain switch is a standard timer-style switch.  Standard timer switches eliminate the need for the user to remember to turn off the floor, which dramatically reduces waste.  These switches still require the user to set them before the floor heats up, which means they retain the delayed gratification downfall of the standard switch.  For certain installations, including bathrooms, a timer switch may be a good, inexpensive option.

  • Pros: Simple, inexpensive installation.  Saves money by automatically turning off a floor that isn’t in use.
  • Cons: Delays usability time.  May have to be constantly reset if the room is being used for more time than the max set time on the timer.

Simple Thermostat

Next up is the simple thermostat, which allows the user to set a temperature at which the floor will cycle on and off based on a temperature sensor. Both standard and programmable thermostats can be governed by in-floor, in-room, or both in-floor & in-room sensors (see below for a discussion on these).

In some ways, the simple thermostat is as bad as the plain switch option, but costs more to install. Unless the floor is the sole heating source for the area, it likely shouldn’t be allowed to run all day which a simple thermostat will allow. The only advantage: the simple thermostat will prevent a floor from over-heating or running when it really makes no sense (e.g., when the temperature of the sensor exceeds the thermostat setting).

  • Pros: Maintains comfort & prevents the floor/room from overheating.  Saves energy over a plain switch, but likely not over a timer.
  • Cons: Wastes energy by running the floor even when not in use.  More expensive than simple switch & timer  installations.

Programmable Thermostat

The best (but most expensive) installation option is the programmable thermostat.  Programmable thermostats work similarly to their non-programmable counterparts and much like programmable thermostats for traditional HVAC systems. A typical programmable thermostat will offer 4 cycle times on weekdays (wakeup, leave, return, and sleep), and 2 cycle times on weekend days (wakeup and sleep).  These thermostats will also have a manual override setting that allows the user to hold a temperature on holidays.  Over the long haul, a properly set programmable thermostat offers the best comfort / cost tradeoff, which makes the most of energy dollars.

  • Pros: Optimizes energy use / comfort of the floor.
  • Cons: Higher installation cost.  May be difficult to program which discouarges proper use.

Sensor Types for Radiant Floor Thermostats

Thermostats for electric radiant floors will require a sensor to detect the temperature of either the floor or the room.  There are three types of thermostat sensor control systems.

In-Floor Sensor: In this setup, the thermostat only controls the temperature of the floor.  This type of installation is appropriate when an electric radiant system isn’t the primary heat source for the space.  At least one back-up sensor should be installed for each active sensor.

In-Room Sensor: In this setup, the thermostat controls the temperature of the room.  This type of installation is appropriate when an electric radiant system is the primary heat source for the room.  It is also an easy replacement option if the floor sensor goes bad.

In-Floor and In-Room Sensor: In this dual-sensor setup, the thermostat primarily controls the temperature of the room, but may be secondarily limited by the temperature of the floor.  This setup is appropriate if there is concern over the floor becoming too hot while the room does not heat up (for instance, in poorly insulated rooms).  Our take: this setup is probably a waste of money and indicates a flaw in either the room or the flooring installation.

What do you think? Have you installed radiant heated floors? Which thermostat / sensor option did you choose… and why?

9 Responses
  1. simon thibault says:

    Just a question

    I have radiant floor with floor sensor…..
    my thermostatd as a “breaker” and it automatically jump
    I know I did wrong I used staples one or twice…. I have a little “ground”….
    But directly in the main braker 20amps it heats well with no jump….
    My thermostat with floor sensor is ultra sensitive to milliamps….
    can i use a standard thermostat with room temperature sensor and no (build-in breaker)

    thanks

    Simon

  2. Fred says:

    Simon! Staples? Buddy, what were you thinking?

    You’re taking a risk by not identifying the ground fault… hard to know what the leakage is. Are you sure it’s not just a defective thermostat? Have you measured resistance between the hot wires and ground using a multimeter?

  3. simon thibault says:

    thanks for the answer

    I tried a brand new thermostat… no change

    for the resistance between the wires and the ground I didnt measure it.. I will what it should be????that will tell me the leakage???

    But I did mesured the voltage and the amps and it’s exactly what it should be according to the cable infos

    For the few staples I used I remember me double checking them to make sure they were not in the wire…. Im SURE there is no major ground fault….

    thanks again

    Simon

  4. Fred says:

    Simon – resistance should be infinite between either hot wire and ground… make sure the power is off before you test. If you get any resistance between the wires, it means there’s a ground fault.

    Most meters indicate “infinite” resistance with a -1

    If there’s no ground fault, it’s hard to imagine why you’d have a trip.

  5. simon thibault says:

    SO….

    I measured the resistance between hotwire and ground… I have 50 ohms….so I definitively have a problem….
    But I tried to plug it direct in the breaker the red with the red, the black withe the black and the ground with the ground….. my floor heat well ,the 20 amps breaker dont trip….i used a laser thermometer i can’t find a hot spot… is it safe to put a standard thermostat with air temperature sensor and let it go????? By the book the answer is no I know, but in realty is it dansgerous… my ceramic is sealed and all my pipes are in plastic….

    thanks again

    Simon

  6. Fred says:

    Simon, I’m honestly not sure what the real danger would be. Certainly overheating or fire comes to mind… but I’m just not certain what real risks you would face.

  7. george says:

    my heated floors require 17.5A my thermostat has maximum 15A what can i do and not have to put in two thermostat.

  8. Fred says:

    George,

    Buy a new thermostat? The ones from Thermotile are rated for 20Amps.

  9. Jared chua says:

    Hi, I just recently bought a 37 y/o house. I had no idea about radiant heat floor before when I started feeling the floor is warm. I don’t see any switch or floor thermostat, so I don’t know if it’s radiant heat or something is wrong below the slab. Can u help me on this. Ty!

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