Thermostats for Electric Radiant Heated Flooring

April 30, 2009 | by Fred (email) |

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?