Electric Floor Heating

 Depending on the size of your project or access to a hydronic heat source you may decide to use an electric floor heating system. Electric floor heating systems are made by installing electric heating cable in a concrete substrate. The heating cable is set by the manufacture to deliver a fixed amount of heat at the designed voltage. They wire length can not be changed in the field. The heating cables come in different power outputs for various applications. 

Electric floor heating systems can be much cheaper to install than hydronic heating systems. Labor costs are almost nothing compared to hydronic systems as some of them recur no more effort than that of rolling out a mat.   The material costs can be very affordable as there is no boiler, pumps, etc. Operating costs can be lower as well since electric systems are 100% efficient. That means 100% of your money goes into heating the floor and not up the chimney. Lastly there are no maintenance costs since there are no moving parts and no combustion. Virtually no wear-and-tear on the system.

Heating applications include; 

• floor warming - heating cable usually put in the mortar bed under tile. This is used for kitchen and bath floors to take the chill of the floor. It can sometimes produce enough heat to be the only heat source for the room
• slab heating - medium heavy heating cable put in a concrete slab either on grade or in a basement. This can be the only heat source for the room since it is a higher heat output that the floor warming cable.
• snow melting - a heavy cable or high output applications. Installed in concrete walks and driveways. These systems produce a high about of heat and can melt snow, ice and drive off water. Some customers have used them in Greenhouses under beds and in the floor. These cables should always be used with a slab temperature sensing control to keep from over heating the slab.

The concrete substrate can be; a mortar bed under flooring tile, a self leveling underlayment under a floating floor, a concrete slab on grade or a concrete walk or driveway. Due to to small surface area of the wire and high heat requirements the wire may get fairly hot. The concrete increases heat transfer from the heating wire but it also gives the wire a UL fire rating. The concrete substrate can be as thin as 1/4 in up to 4 in. depending on the application and system requirement.

Power requirements: Due to the high amounts of heat needed to be delivered by the heating cable the designer and installer need to be very aware of the power requirements of the system.

•  Small Bathrooms can be heated with up to 15 amps of service at 120 VAC.
• Larger rooms should consider using 240 VAC service as it can deliver the same power as 120VAC at half amperage load.
•  The manufacturers can also make cables set at commercial service voltages like 208 VAC and 277 VAC. Consult the product literature for power output and amperage loads.
•  Always keep in mind the total amperage load on the circuit. Multiple floor heating cables can be connected to the same service circuit but should not exceed the total amperage load of the circuit or control. 15 amps is usually the max load in a residential application. If more that 15 amps is required, the system can be supplied by a second circuit from the electrical panel and controlled by a slave relay to power additional heating cables. More circuits and more relays can be added to provide additional power to more cables.
•  Finally keep in mind the total load on the electrical panel. You don't want the heating system to take all the service and leave nothing on the panel for lights and appliances.

Controls: Electric floor heating systems should always be used with a controller that senses floor temperature. This way the system will not "run away" and dump heat into the floor.

• Kitchens and Baths can be controlled with thermostats that switch 120 VAC or 240 VAC at up to 15 amps of service. These thermostats should be connected to a floor sensor so that the thermostat will not allow the floor to go over a high limit temperature. If more that 15 amps of service are needed sub-relays or additional thermostats can be used.
• Thermostats can also be Wi-Fi enabled to allow the user to monitor and control the temperature using an app on their phone.
• Snow Melting systems usually require higher loads than room heating systems. The power can sometimes be switched with the thermostat or snow sensor but when higher loads are control with a contactor. The contactor has high power relays that can switch 50, 100 and 200 amps. These contactors can be connected to snow melting sensors that measure moisture, outdoor temperature and slab temperature. The controls can also be attached to Wi-Fi controls that can be turned on and off remotely as well as download weather data and turn on automatically.