Wet Underfloor Heating

Wet underfloor heating is a type of heating system which involves laying a network of pipes under, or into, the flooring. Warm water is circulated through these pipes from a boiler or separate heat source, and heat is transmitted into the floor.

Underfloor water pipes being installed on site.

The entire surface of the floor emits heat into the room, much of it via radiation rather than convection.

It is similar to a typical radiator circuit, except the pipe work is all concealed within the floor.

How does it work?

There are several different ways of laying out the pipe work, and the style will depend very much on the room or property to be heated

Essentially, they all operate in the same manner by pumping warm water through the circuit and then back to the heat source to be re-heated.

Insulation is laid underneath the pipes to reduce downward heat loss, and around the perimeter of the room to prevent heat loss into the walls.

Heat is transmitted into the concrete or timber of the flooring, from which it radiates into the room.

This type of heating is more efficient than convection heating as much of it is absorbed by furnishings and objects in the room, which in turn become heat emitting surfaces.

This creates a much more even spread of heat from floor to ceiling, and reduces heat loss from the building as less heat is able to escape.

Where can it be installed?

Water based underfloor heating systems can be installed in any building, although there are various considerations if it is being retrofitted.

It is particularly suited to new builds as the flooring can be designed to accommodate the pipe work, and it can be fitted when the property is being built.

When it is being retrofitted, it will require a lot of extra work. Floors may need to be dug up for the piping to be laid and the entire floor level may need to be raised to fit it in.

This could mean expensive alterations to doors and skirting boards to allow for the raised floor. It will also need to be connected to the existing plumbing and to the boiler or heat source.

Again, when installing into a new building, this is something that can be planned from the outset.

Typical Layout of water pipes for wet underfloor heating.

It can be used with most types of flooring, with vinyl and stone flooring providing the best performance.

Timber flooring has a certain heat tolerance depending on the type of wood, and it is usually recommended that it should only be fitted with timber which has a moisture content of 10% or less to avoid drying out and shrinkage or warping.

Heavy carpets will act as an insulator and stop heat from getting into the room, so it is advisable to use a carpet which has a TOG rating of less than 1.5.

What are the costs?

Cost of installation will vary greatly depending on the size of the property and whether it is a new build or a retrofit.

Due to the nature of installation, a wet system is likely to be more expensive than a ‘dry’ (electric) system, as there is more work involved with plumbing, which must be done by a qualified person.

The price of the products, however, is a little easier to gauge. Prices taken from one supplier, UK Underfloor Heating, range from:

• £395+VAT for underfloor heating for floor areas up to 20m², to £665+VAT for underfloor heating for floor areas up to 60 m².
• Both prices include delivery, but not installation.

Independent research from checkyourprice.co.uk shows the cost of the install on average to be £18 per square metre for the laying of the system, and £240 per zone for the electrical and plumbing work.

Running costs can only really be assessed when the heating is installed and in use.

Gas fired boilers are cheaper per KWh than using the electricity supply to heat underfloor heating, the rate of difference will vary with the price of gas and electricity.

Estimates suggest that underfloor heating could reduce heating bills by around 10-15% when compared with conventional heating methods.

Although savings of anything up to 50% could be realized in the right circumstances.

What are the disadvantages?

One of the biggest problems with wet underfloor heating is the cost of installation. They may be more energy efficient and save money on energy bills.

However if they cost thousands of pounds to install in the first place it will be a long payback period before any real savings materialise.

Another common complaint about underfloor heating is the slower heat up time compared with other heating systems.

A large room could take up to 2-3 hours to heat up, but it is worth remembering it will also take longer to cool down.

Some of the more sophisticated systems also incorporate a ‘setback’ system, whereby the water temperature will drop overnight to a lower set point rather than completely cooling; this allows a quicker re-heat when the heating comes back on.

Not all systems can completely heat a room; some may only heat the floor, or simply not have enough surface area to fully heat the space.

This may mean that you end up with a combination of radiators and underfloor heating, with both bills.

Underfloor heating is not suitable to be fitted directly beneath floor mounted units such as kitchen cupboards, as it may cause the units to sweat and eventually damage them.

The layout of pipes can be designed to avoid any fixed fittings, but they may need to be re-laid in the future if you wish to change the layout of the room, or change furnishings and fittings.

Summary

Wet underfloor heating systems are becoming more popular, particularly in the new build sector, as they offer improved efficiency over more traditional heating systems.

Although they are unlikely to be the first choice when refurbishing a property, they are excellent when fitted into a new building as the system can be integrated into the design and fitted during construction.

Running costs are generally cheaper than both conventional systems and electric underfloor systems.

In the long term they will provide savings on energy bills, as well as reducing the buildings carbon footprint.

Although it is possible to install a wet underfloor heating system almost anywhere, with any type of floor; serious consideration should be given to whether it is the right heating system for the type of flooring you are using, and the type of property you intend to install it in.