How Underfloor Heating (UFH) Works?
In its simplest term Underfloor heating or UFH is a method of warming the building by using the floor as a radiator.
However, unlike the radiators that you may be used to, the floor is operated at a much lower temperature. The reason for this is that the floor is a far larger area than a radiator and, therefore, does not need to run at such a high temperature to heat the room.
The Romans had a form of UFH that used warm air from a fire drawn through ducts in the floor. Today we use warm water through pipes in the floor to achieve the same result.
Vast improvements to the thermal insulation of our modern buildings makes UFH the best option for heating.
Heating Pipes are laid in the floor at the time of construction or during renovation work. Warm water is circulated through these underfloor heating pipes that are either embedded within a concrete screed or other floor types see floor types
The water is distributed to the pipes through manifolds at between 30-45°C and heats the floor surface to a temperature in the range of 22-29°C. Heat is emitted into the room as approximately 60% radiant heat, 20% convection, and 20% conduction.
Each room or area would have its own circuit and be individually controlled by a room thermostat.
When the room reaches its pre-set temperature the thermostat sends a signal to an electrically operated valve on the manifold, closing that particular circuit. The floor effectively becomes one large heat store giving off a gentle, even, radiant heat to the whole room.
Any type of boiler can be used to provide heat although the condensing boiler option or a heat pump offers far greater energy savings.
Can I fit Underfloor Heating (UFH) in to my building?
UFH can be used in any type of building and in most types of floor structures. Whether it is a new build or complete renovation, partial renovation, or retro-fit.
New Build & Complete Renovation, plan the use of UFH from the very start of the project. Decide what you are going to use to generate the heat because this can affect the way in which UFH is used and installed.
For instance, if you plan to use a heat pump then you will need to put in more pipe and also use one of the floor types that has good thermal mass.
This will ensure that the heat pump always works with a high level of efficiency.
For example it is also better to have all suspended floors in block and beam rather than timber.
Block and beam has a number of advantages over timber such as excellent sound suppression, improved fire prevention, good thermal mass and the ease of putting in UFH.
If you intend to use a conventional boiler (modern oil or gas condensing type) then you can use any of the floor types. The pipes can also be spaced a little further apart which will keep the installation cost down.
The building itself can be of conventional brick or stone, timber frame, structurally insulated panels (SIPS) or architectural glass and steel.
It is only the floor structure that needs to be carefully considered when deciding to use UFH.
Partial Renovation, this is similar to a Complete Renovation although the levels of insulation may not be able to be quite so high.
If the ground floors are to be removed and replaced to overcome damp or structural defect then UFH is the obvious choice in the new solid floor.
If the ground floor is the suspended timber type and is structurally sound, UFH can still be fitted. The floor boards can be lifted to expose the timber joists. The floor is then insulated between the joists and pipe fitted to this insulation (see floor types, suspended timber floors, thermal mass).
If the joists are strong enough to take a thin layer of screed then this should also be applied. Thin screed of around 20 – 25mm depth and adds an additional weight to the floor joists of around 25kg/m2.
The prime benefit of this is to add thermal mass to the floor which will give an improved performance for the UFH.
Lifting the floor boards is also an ideal opportunity to treat the joists with preserving agents to give long term protection. However an overlay system such a Variotherm can also be used.
For suspended first floors that are structurally sound the choice is quite limited. You either have to take up the floor boards, take down the ceiling or fit an overlay system with a new floor over the top.
The latter is more expensive and adds around 25–50mm extra height onto the existing floor. For reasons of cost you may therefore decide to use radiators instead of UFH.
Retro-fit, removing a radiator and fitting UFH in an existing solid ground floor room is never straightforward. The UFH pipes have to be placed in a new overlay floor (see floor types) and this requires a minimum space of 18mm plus the floor board.
This means the total floor build up is around 25-45mm over the existing floor. If this is not what you want then the existing floor will have to be taken up to gain enough space for the insulation, pipe and the finished floor.
The normal depth of existing screed is typically 50mm and this can often be very easy to break up and remove.
If the floor already has insulation below the floor slab (oversite concrete) then Radiant has a special 4mm thick insulation foil to lay over the exposed slab. This foil reflects the heat from the pipes up into the new screed. A reinforced screed of 46mm can then be applied to bring the floor back to the same level. See floor types for other alternatives and if in doubt, contact us.
The method for suspended timber floors is the same as described in Partial Renovation.
Hardwood flooring and wood laminates, are ideal finished floor coverings as they allow heat to transfer easily through the floor giving an even surface temperature that will not damage the floor.
It is good practice to lay the natural wood flooring out loose to allow it to acclimatise to the room in which it is to be finally laid.
This acclimatisation should be for a minimum period of ten days but only once all moisture is removed from the building.
Don’t forget, building, plastering and screeding introduces lots of water into the fabric (walls and floors etc) of the building. This water has to dry naturally so that the internal humidity of the building is reduced to a normal level.
You don’t want your beautiful new wood floor to absorb all this moisture as it will warp and be permanently damaged.
You can have natural hardwood rather than engineered, if you wish, but the surface temperature will need to be limited to around 27°C.
If the floor is too warm, then damage to the wood may occur once the heating comes on. Close control of floor temperature is achieved by fitting a floor sensor.
Before laying a wood floor the concrete must be thoroughly dried out. As a rule of thumb a concrete screed dries at approximately one day per 1mm thickness.
There are various ways to lay hardwood but in every instance you should follow the manufacturer's guidelines.
Some woods require a nail fixing, and for this it would be necessary to fit battens into the screed to facilitate this, or fix directly into the joists, depending on the floor construction.
Most hardwoods are either glued directly to the dried screed with (flexible) mastic adhesive or floated over it.
If floating, the wood is clipped or glued together and it then lays over a proprietary hardwood underlay. This allows the entire floor to expand and move as all natural materials do.
Carpet The carpet and underlay should not have a combined tog rating greater than 1.5. (a resistance of 0.15m2 K/W)
Radiant’s Radfloor underfloor heating can be used in conjunction with most types of carpet although natural fibres are best.
Carpets will act as an insulator so the output from the floor will be slightly reduced. Most reputable carpet manufacturers have approved carpets and underlays for underfloor heating.
If you are in any doubt, please contact us with your questions.
Stone or Tiles Any type of hard stone or ceramic tile is an excellent floor covering for Radiant’s Radfloor underfloor heating.
The thermal resistance of a hard material (concrete, stone, clay, rock or ceramic) is extremely low. Heat therefore passes through with virtually no losses at all.
This makes a hard floor finish perform better than any other type of floor finish. It is therefore the ideal choice when using low temperature heat sources such as a heat pump.
It should be noted that it is not the only choice.
Are there any drawbacks to Underfloor Heating?
Some consideration should be given to the type of carpet to be used. Natural fibre carpets give a better performance than man-made fibre.
The type of underlay used should not be the closed cell foam type as this is an insulator, but crumb rubber based underlay.
Underfloor Heating can be much slower to warm up than radiators. It is, therefore, not practical to have the UFH on for short periods as you would with radiators. The UFH should be selected to run for between 4 to 12 hours a day. This may seem extravagant, but the reality is that once the fabric of the building has been heated the UFH system requires little energy to maintain an appropriate level of heat.
The possibility of putting a nail through the UFH pipe is no more likely than for any other type of pipe. Remember that Multi-Layer Pipe is a plastic/metal pipe and is easily detected with a metal detector.
If the UFH pipe is buried within screen, then there is at least 50mm of screed above the pipes. For a timber floor the pipes will be directly below the timber so great care should be taken. In the unlikely event that a continuous length of pipe is damaged, a simple connection piece is all that is required to make a permanent repair.