How does underfloor heating work?

How does an Underfloor Heating System Work ?

These days, underfloor heating systems are in the main either warm water (wet) systems or electric (dry) systems.

Wet underfloor heating systems

In a 'wet' system pipework is laid in or under the floor. In the floor if the floor is solid (screed or concrete), under if the floor is suspended timber.

As warm water is passed through the pipework heat percolates into the floor and as a result the floor heats the room. In effect, the floor has become a gigantic radiator.

In the solid floor type, insulation should be installed under the slab to negate the cooling effect of the earth below thereby avoiding heatless through wastage by conductivity.

With suspended timber floors the pipework is installed between the joists. To avoid heat loss through convection to the void below a reflecting medium (quilt or tray) is installed beneath the pipework which insulates and also reflects heat upward.

Underfloor heating operates at lower temperatures

Unlike radiators, underfloor heating systems do not need to run at high temperatures. Heat imparted to the floor is gently released across a large area rather than the relatively small and focussed area of a radiator. As such,  UFH systems do not need to operate at such high temperatures. This of course has its advantages. Not only is UFH less expensive to operate, you also do away with the need for radiators and scalding that can occur. (You also get more choice when it comes to room layout because there are no rads!)

Dry underfloor heating systems

In a 'dry' or electric system the principle is the same. The difference is that instead of imparting heat from water passing through a pipe, you use the electric current passing through a special cable that heats up as the heat source.

Control systems for underfloor heating

Of the two types of system (wet and dry) the wet system control is far more interesting. Electric systems require fairly simple control (basically switching on and off as heat is called for). Wet systems certainly look complicated but in reality are quite logical once you understand why things do what they do.

Wet control systems invariably employ a manifold. This complex looking gadget is in fact just a means to connect multiple pipe runs to a common heat source. Each pipe run from a manifold is controlled by an electrically operated valve (an actuator head) which opens and closes as the controlling room stat commands. This way the pipe run (or zone) can put heat into a room or area as required.

In essence this is how it works....

Room gets cold > Room stat calls for heat > Control system commands actuator on manifold to open (letting hot water down pipe run > room reaches required temperature > room stat notifies control system that no more heat is required > control system instructs actuator head to close

This of course is a highly simplified account as there are other functions at work such as boiler control, temperature regulation, circulation etc. But it does at least give you an insight to the system control.