How does underfloor heating affect the energy bill in the long term?

Underfloor heating is a popular heating system, and one of the first questions people ask about it is how it affects energy consumption and the energy bill. The answer depends on several factors, but in a well-insulated home it is usually a fairly economical way to heat.

How underfloor heating works

Underfloor heating can be electric or water-circulated. Electric underfloor heating uses electric cables or heating mats installed under the floor and consumes electricity directly. A water-circulation system pumps heated water through pipes in the floor, and that water can be heated with electricity, district heating, a heat pump or another energy source. In both systems, heat spreads evenly across the whole floor, so the room can feel warm at a lower air temperature than with radiators.

What affects the bill

Several factors determine how much underfloor heating adds to your energy bill:

• Type of system: Electric underfloor heating draws electricity directly, so its cost tracks the electricity price closely. A water-circulation system's cost depends instead on the price of whatever energy source heats the water; combined with a heat pump it is usually the more economical option.
• Insulation: A well-insulated floor and building lose less heat, so the system does not need to run as hard or as long to keep the room warm. Poor insulation increases consumption regardless of the heating system.
• Room temperature and usage time: The higher the target temperature and the longer the system runs, the more energy it uses.
• Thermostats and timers: Smart thermostats and timers let you lower the temperature when a room is not in use, which reduces unnecessary consumption.

Roughly how much energy does it use?

Electric underfloor heating cables and mats are typically rated at around 100–150 watts per square metre. That is the system's maximum draw, not its average consumption: a thermostat cycles the heating on and off to hold the set temperature, so actual use over a day is well below what the rated power would suggest if it ran constantly. The real figure for any home depends on insulation, room temperature and how often the system needs to run.

Estimating your own consumption and cost

You can get a rough estimate of consumption and cost with the following steps:

1. Total power (W) = power per square metre (W/m²) × heated area (m²)
2. Power in kilowatts (kW) = power (W) ÷ 1000
3. Daily consumption (kWh) = power (kW) × hours the system actually runs per day
4. Annual consumption (kWh) = daily consumption (kWh) × days of use per year
5. Annual cost (€) = annual consumption (kWh) × electricity price (€/kWh)

Example: a 50 m² system rated at 100 W/m² has a total power of 5000 W, or 5 kW. If it effectively runs for 8 hours a day on average (accounting for the thermostat cycling on and off) over 200 heating days a year, that is 5 kW × 8 h = 40 kWh per day and 40 kWh × 200 = 8000 kWh per year. At an electricity price of €0.15/kWh, that works out to roughly €1200 for the year. Your own numbers for area, running hours, heating days and electricity price will differ, so use this only as a template for the calculation.

Advantages and disadvantages for your bill

• Lower operating temperature: Even heat distribution means underfloor heating can keep a room comfortable at a lower air temperature than radiators, which tends to save energy.
• Higher installation cost: Installing underfloor heating, especially retrofitting it into an existing building, costs more up front than a radiator system, which lengthens the payback time.
• Slower response: Underfloor heating reacts more slowly to temperature changes than radiators, so poor scheduling can waste energy by heating rooms that are not in use.
• Lower maintenance: A correctly installed system is generally durable and needs little maintenance, which helps keep long-term costs down.

Tips for keeping the bill down

• Make sure the floor and the building are well insulated.
• Use thermostats and timers so the system is not heating rooms that are empty or already warm enough.
• Keep the room temperature at a reasonable, not excessive, level.
• If you use electric underfloor heating, following the electricity price can help you shift heavier use to cheaper hours.
• Have the system serviced and checked periodically so it keeps running efficiently.

Summary

Underfloor heating's effect on your energy bill depends mainly on the type of system, the building's insulation and how you use thermostats and timers. Installed correctly in a well-insulated home, it is usually an efficient way to heat, even though it costs more to install than radiators. You can find more information on underfloor heating and energy efficiency on Motiva's website.