Warm floors are pleasant and it may be nice not to have visible radiators, but would underfloor heating be of interest to anyone who is also concerned about energy consumption?
The amount of insulation you have under the heating coils and the flooring material you intend to use are the most important factors that determine whether or not underfloor heating will be efficient.
Air-based, water-based or electric coils
Underfloor heating may be air-based, water-based or may consist of electric coils. If you have a water-based heating system in the house, it would be wise to decide on water-based underfloor heating. If you install underfloor heating in part of the house, a separate shunt is often required for controlling the temperature of the water flowing under the floor.
Comfort underfloor heating
Electric coils can be installed as underfloor heating even if the remainder of the house has water-based underfloor heating. This is generally known as comfort underfloor heating, since the electrically heated floor gives a more distinct warm feeling. If you install underfloor heating as comfort heating, the energy consumption will often be higher, since the underfloor heating is likely to be left on in the summer in order to avoid cold floors.
If you have underfloor heating in the floor structure of the ground floor, more heat will leak into the ground than if you use radiators. However, you can minimize the leakage by insulating properly under the coils. The rule of thumb is that at least 300 mm of insulation should be provided under the coils in the foundation slab or the basement.
Effect of floor material
Another factor that affects the heat loss is the floor material used. Parquet flooring, for instance, increases the heat losses to the ground, since the parquet restricts the heat flow through the floor. Clinker brick and PVC flooring are good materials that conduct the heat from the underfloor coils to the indoor air.
Underfloor heating and energy consumption
The energy consumption can theoretically be cut by underfloor heating, since you can lower the indoor temperature while retaining the sense of comfort. The floor temperature need to be only 22 – 24 degrees C to achieve a room temperature of 20 degrees C. But a floor at 22 degrees C does not feel particularly warm to the soles of the feet. The number of months of the year that you use underfloor heating is also of major importance to the energy consumption. If you have clinker brick flooring, for instance, this could feel cold, which may lead to the heating being left on throughout the summer.
Risk of moisture damage and cold down-draughts
If you intend to install underfloor heating in an existing house, it is always wise to entrust the work to a tradesman. Underfloor heating could lead to moisture migration and damage to parts of the building.
If your windows are not well insulated, there is risk of cold down-draughts if you install underfloor heating to replace radiators. The windows should have a U value (thermal conductivity) of 1.2 W/m²K to perform well with underfloor heating.
Another disadvantage of underfloor heating is that it has high inertia, so that it adjusts itself slowly to temperature changes. If the day is sunny after a cold night, the system may find it difficult to adjust itself in time, and will over-compensates for the cold of the night. The result will be that the room will be too warm and heat will thus be wasted.
Life of underfloor heating
The pipes used for water-based underfloor heating have a life of 40 – 50 years. Electric coils have a shorter life, but at least 20 – 25 years. If the underfloor heating needs to be repaired or changed, the floor will have to be removed. If the coils are cast into the foundation, both the foundation and the floor will have to be broken up when the time comes for repairs to be done.