THE REAL COST Is electric underfloor heating expensive to run? ThermoSphere discusses.
Whenever you read articles about electric underfloor heating, the majority discuss the features and benefits of different types of systems but very little is mentioned about the cost to run it. With the rapid rise of energy prices, running costs have been catapulted further into the limelight and become an even greater concern for house builders and homeowners alike.
WHAT DRIVES RUNNING COSTS UP? Time
Unlike other heating sources, electric underfloor heating gets to the desired comfort temperature very fast – often within 20-30 minutes. However, there is a misconception that homeowners must have their heating switched on for 90 minutes before needing to use the room. This can be the case for some central heating, but not for electric underfloor heating.
Nowadays, many thermostats, thanks to LOT 20, have an ‘Adaptive Start’ function where the thermostat learns how long the electric underfloor heating system needs to heat up, and then sets the right length of ‘heat-up time’. This can often save three hours of running time in an average property per day.
Insulation
The heat generated by the electric heating cable travels in all directions equally, until it encounters a layer that is more insulative. For example, in the build-up for a tiled floor finish, you have the substrate below the heating cable and flexible tile adhesive with tiles above. Installing without insulation board, the heating cable will warm the layer below and the layer above at the same rate and it will take twice as long for the floor to heat up to the right temperature.
By including insulation board, you’ll significantly reduce heat being lost downwards. Instead, the majority of the heat is heating the floor above which means the system is on for less time to reach optimum temperature which saves money on the overall running costs. In fact, installing insulation board can improve the efficiency of an electric underfloor heating system by 50% or more.
28 | UNDERFLOOR HEATING
TYPES OF INSULATION Uncoated insulation boards
A cost-effective thermal insulation for concrete and screed substrates. They are manufactured from a high-density extruded polystyrene and can be installed using a flexible cement-based tile adhesive.
Coated insulation boards
Manufactured from a high-density extruded polystyrene core with a fibreglass reinforced cement coating on both sides which adds rigidity, strength and thermal insulation to a timber substrate. These boards are water resistant and rot proof which makes them a great choice for wet environments such as bathrooms and wet rooms.
The standard thickness of insulation board is 10mm. If there are restrictions to floor height, 6mm insulation boards are better than nothing.
CALCULATING RUNNING COSTS Here’s a simple calculation to use: 1.8p x m² x hours.
Here’s an example for a 3m² bathroom where the system is on for two hours in the morning and two hours in the evening: 1.8p x 3 x 4 = 21p per day or £1.51 per week.
Depending on location, the cost per kWh can vary.
Do running costs vary depending on what type of system you use?
No. If you are moving a floor temperature from 160C to 210C, it will use the same amount of energy to do so, regardless of what system you choose.
If a 3m2 bathroom with a 150W/m2 system takes 30 minutes
to heat up, it will use 225W to get to temperature. If the same bathroom is installed with 200W/m2
www.thermosphere.com , it will still
use only 225W to get to temperature, but will do so in 22 minutes instead.
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