> Underfloor heating, is it Green?

What is underfloor heating?

Simply put, underfloor heating is a when a heating element in embedded within the floor structure itself. Given the element will heat what surrounds it, this will then result in the floor acting as one big 'radiator'. Given cold air in a room sinks to the floor, this means the coldest air in the room is heated, which then rises to heat the rest of the air - generally raising the temperature and hence comfort level within the room so heated.

The big win for most people with underfloor heating is that the means of heating the room is essentially 'invisible' - no vents in the walls or floor, no free standing gas or electric heater. The other win is that given the floor itself is being heated its warm to walk on - something if importance in a tiled bathroom.

How does underfloor heating work?

Basically during construction a heating element is built into the floor just below the main top surface of the floor (i.e. right below the tiles or wood flooring). This element can be one of two types:

• Electrical - basically electricity passed through the element is converted into heat.
• Water - in this hot water is passed through pipes in the floor.

The electrical type is usually the easiest and cheapest to install - as the cable either comes on a preformed roll set at the right distances (like a continuing S wave) or the cable just comes on a straight roll and is laid out by the installer at the right distances. The first form is usually for DIYers, the second for contracted installers.

The water based type is very much a professional installation - as often the pipes need to be set into a rigid 'patterned' layer made out of stiff insulation with the pipe pathways preformed into them.

So which is best?

Depends on what you want, the electrical based form is great for small installs as it just needs to be wired in. The water based form often needs additional plumbing back to some form of on demand water heater. The electrical form is basically 'ready to go' by just switching on, although could take quite a time to get to temperature. The water based form has the advantage of the insulation behind it, so the heat should come up quicker; but due to it not interacting with the mass below it, it will also cool down quicker.

For ourselves, we went electric, as we were building on raised concrete slab. In this way we could run the underfloor heating at night on off peak electricity and use the slab as a form of 'storage heater' to then keep us warm the following day. This seems to work rather well, but you need to make sure you all the passive solar and thermal elements of your property set up correctly first (see the other articles in this site on how to do this). Performance to date has been rather good and the cost much lower than normal on demand heating; people keep being surprised how low our electricity bills are.

A possible enhancement for us it to add some insulation under the slab to reduce downward thermal loss in places like bathrooms.

So is it Green?

I think a conservative yes; as compared to other methods of heating a property it can be rather efficient and finely controlled to provide heat exactly where needed. Although a badly configured system will be very wasteful.