A common saying in Ireland is that, if you don’t like the weather all you have to do is wait five minutes for it to change.

Underfloor heating in Ireland needs to be designed with this maxim in mind. With such variable weather, your heating system needs to be able to respond quickly, supplying heat when needed, then turning off rapidly as the temperature increases. Greentherm underfloor heating systems are designed first and foremost to be controllable. A dedicated thermal store and a lightweight floor screed gives a fast response to changing conditions, ensuring optimal comfort and efficiency.

Some installers like to replace the dedicated thermal store with a thick slab of concrete or heavy screed, especially when combined with a heat pump system. They justify this as ‘thermal mass’ doing the same job as a thermal store, saving on the cost of a large cylinder.

The effect of ‘thermal mass’ is to make the effective control of the heating system almost impossible.

A system with too much thermal mass will respond far too sluggishly to changes in temperature or demands for heat. The underfloor heating systems will only begin to supply heat to the room one the floor slab surface has exceeded room temperature. In some cases, with heavy concrete floors, this can take hours.

Heat will continue to soak up through the slab long after the thermostatic valves have closed, pushing the room temperature beyond that set on the thermostat until the air temperature matches the slab. With so much heat stored in the slab, it will take hours for the room to cool back down again unless a window is opened.

The graph below illustrates the effect. The low thermal mass system in blue has already reached a comfortable temperature, before the high mass system in red begins to respond. The high mass system also overshoots the set ‘comfortable’ temperature, continuing to radiate heat even after it is no longer required.

Effect of ‘Thermal Mass’ on underfloor heating response time.

The effect is similar to trying to push a heavy train with no brakes. It takes a lot of effort to start it moving slowly. And once it is finally moving, it takes so much effort to pull it to a stop again that the train overshoots the point where it was supposed to stop and must be pulled back again. It responds slowly to temperature changes and takes a long time to settle down afterwards.

Compared to this, controlling a Greentherm underfloor heating system is like pushing a lightweight car. It takes little effort to get it moving, and once you stop pushing it, it stops all on its own. The thermal store acts as a heat ‘battery’, charging up and then releasing energy exactly when and where it is needed.

Your own comfort is at your fingertips.

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