Underfloor heating installation: Everything you need to know

underfloor heating

As a professional architect, I would like to discuss the installation of underfloor heating in comparison to the traditional radiator heating system operated by a boiler.

When dealing with an underfloor heating installation, it is important to know all the peculiarities of this system since it has nothing to do with the classic boiler-radiator installation. We will explain everything you need to know before you decide to install one in your home..

 

Pipe installation
Pipe installation

 

The installation of underfloor heating is a more complex operation than the installation of radiators. It requires a comprehensive reform of the house, which may involve lifting up floor finishes, sometimes walls or ceilings. It is important to note that there are also electric radiant floors that are easier to install than radiant water floors but more expensive to run.

A radiant floor installation is based on the placement under the floor finish  a network of plastic pipes that circulates hot -or cold- water over the entire floor, which radiates heat or cold from the floor. The water that circulates through the underfloor heating pipes obtains its temperature from a heat generator: low-temperature boilers or heat pumps which are now the most common.

There are also electric underfloor heating installations in which an electric mesh is placed under the pavement that obtains energy directly from the electrical network, but in this article, we will focus on underfloor heating and cooling by water.

Features of underfloor heating

Its high thermal inertia: underfloor heating has to heat (or cool) the entire mass of the floor that covers it, so it has high thermal inertia. This means that it takes a long time to warm up, but in the same way, it continues to emit heat (or cold) for a long time after the system has been turned off. For this reason, its installation is convenient in those spaces where it is used continuously.

Low-temperature system: the water that circulates through the radiant floor circuit does so at a low temperature (30-45ºC) so it will require specific heat generation devices such as an aerothermal or geothermal heat pump or low-temperature boilers or condensing (gas or hybrid solar energy system).

These generators, in addition to using renewable energy sources (aerothermal, geothermal or solar energy) are highly efficient (they emit 100% of the energy they capture) and since they do not have to heat as much water as, for example, a traditional radiator circuit , they achieve great savings on their consumption.

Invisible comfort: as it is a pipe system installed underground, it can be said that it is an “invisible” system, with no visible thermal emitters. Only the placement of a cabinet for the hydraulic manifolds (similar to a light cabinet) on the wall should be taken into account.

The heat from the feet: The air temperature near the ground will be slightly higher than the air temperature at head height. The heat is distributed evenly throughout the house, without accumulating in specific areas such as radiators or on the ceiling in the case of air systems. It does not produce air currents, so it does not move dust and does not produce dryness.

 

Underfloor heating installation: Everything you need to know

Where is it advisable to install underfloor heating?

Due to its high thermal inertia, installing underfloor heating is not a good option for low-occupancy homes or premises where heating is only turned on for a few hours a day.

However, it is a good option for:

  • Individual and collective homes with continuous use of heating.
  • Teaching centres, nurseries, and nursing homes.
  • Indoor swimming pools, to heat the living and transit areas.
  • Hospital rooms and corridors.
  • Work centres and offices in general.
  • High-rise premises: churches, warehouses, industries, etc. In these premises, air heating systems cause enormous energy consumption.

 

The cost of the installation of a water-based underfloor heating is higher than the installation of traditional radiators. For a 100 square meter area, the cost of an electric radiant floor heating system can range between 6,000 and 8,000 Euros or more, while a radiator installation for the same area may cost between 5,000 and 6,000 Euros, depending on the brand, size of the boiler, and a number of radiators required. It should be noted that a new home may already have radiator heating installed.

 How is underfloor heating installed?

Before anything, you must prepare each of the components and kits necessary for the installation.

Floor preparation

The ground should be cleared and levelled. You should try to make the surface of the floor slab as smooth as possible, for the proper placement of the insulating panel, since these can break if they are placed on irregular surfaces. So, a finishing coat should be provided. On top of that, a dampproofed membrane film should be placed if necessary to prevent humidity from rising from the ground floor if no suspended slab is used.

A plastic perimeter band should be placed. When installing underfloor heating in humid areas, such as bathrooms and kitchens, care must be taken to surround the drain pipes with a perimeter band, to avoid the formation of thermal bridges and possible expansion absorption problems.

Distribution equipment

In general, they are always hidden in built-in cabinets, inside kitchen cabinets, in boiler rooms, under stairs, etc. at a medium height.

Placement of the insulating panel

The special boards that will serve to place the pipe are placed over the entire surface of the home or premises.

The union between panels is usually done by tongue and groove.

It is important to take into account that the installation of underfloor heating requires an extra space between the slab and the flooring (approximately 8 cm of additional height), so it must be foreseen from the beginning of the project.

Tube placement

The union of the ends of the tube to the distribution equipment is carried out by means of special tube union accessories.

The installation of the tube is carried out between two people: one holds and unrolls the tube coil and the second inserts the tube into the plates.

It is necessary to provide expansion joints for areas greater than 40 m2 or when the length of the room is equal to or greater than twice the width.

Filling of the installation and pressure test

The system must be filled slowly, circuit by circuit, to minimize the entry of air.

The standard requires for underfloor heating installations that the tubes be tested at a test pressure of 6 bars for 24 hours before being covered.

Underfloor heating installation: Everything you need to know

Pouring of mortar and installing the floor finish

The temperature of the mortar and the floor in the room should not drop below 5ºC and should be kept like this minimum for 3 days.

The placement of the floor finish will be carried out 28 days after the pouring of the concrete.

The type of floor finish that can be used with radiant heating is limited. It is not recommended to use wood or cork floor finishes, although special compressed timber boards can be used for underfloor heating in the UK. In Spain, where most buildings have terrazzo floors, marble, or granite, the use of selective floor finishes is advised.

The thickness of the floor finish may increase due to the thermal

insulation required under the heating elements. This can be problematic if there is limited head height.

Obtaining a comfortable temperature with electric radiant floors can take up to 5 hours for hydraulic floor finishes. Cooling down may take another

5 hours or more, which should be taken into account when using this heating system.

The selection of the floor finish and installation firm is crucial. For wood floors, ceramics, and materials of a screed type, high thermal transmittance is required, i.e., they should transmit heat even at temperatures from 20 degrees onwards. The installation of electric radiant floors should be carried out by specialized personnel with previous experience in the installation of radiant floors. Plumbing should be done by qualified personnel,

and it is recommended to obtain an extended warranty from the installer.

Not every type of floor may be used

Radial heating limits the type of floor finish to be installed in the house. It is recommended not to put any type of wood or cork floor finish although I have seen in UK underfloor heating with special compressed timber boards. Here in Spain as we all know most buildings have terrazzo floors, marble or granite as a more selective floor finish.

The thickness of the floor finish

There is an increase in the thickness of the pavement due to the thermal insulation under the heating elements which may turn out to be a problem if we have a limited head height.

Hydraulic balancing of the installation

With underfloor heating, a uniform temperature is achieved throughout the area to be heated. The regulations impose the condition that the resulting temperature in the premises, measured in its centre and at 1.50m from the ground, is between 18ºC and 22ºC. For reasons of comfort, they should not exceed a maximum temperature of 29ºC.

Hydraulic balancing allows constant maintain the water temperature at all points of consumption.

A correct balance is achieved when the return temperature is the same in all the circuits and the thermal difference between flow and return does not exceed 10ºC.

Note about moisture in cooling floors

All underfloor heating systems could also operate to cool a space. when operating in cool (refreshing) mode, must operate above the dew point of the air. The capacity is defined by the thermal difference between the ambient temperature and the average surface temperature of the floor construction (Driving Temperature Difference DTD). In rest environments, such as apartments or offices, the cooling capacity of the floor is limited for reasons of comfort, from 30 to 40 W/m2.

 

Underfloor heating installation: Everything you need to know

The price of the installation.

It is a more expensive system than heating using vertical radiators. 100 square meters of radiant floor heating system can range between 6,000 and 8,000 Euros or more. On this same floor area heating system, a radiator installation involves a cost of between 4,000 and 6,000 Euros, depending on the brand and size of the boiler and the number of radiators to install, naturally in new homes heating using radiators may already come installed.

It takes too long….

To my mind, the main disadvantage of this system is that obtaining a comfortable temperature may take up to 5 hours, in the case of a hydraulic floor finish and it will take another 5 hours or so to cool down which could be a good or bad thing. In any case, this period should be taken into account when using this heating system

Careful selection of floor finish and of the installation firm.

For wood floors, ceramic and materials of a screed type, they should have a high thermal transmittance, i.e., that they transmit heat, even at temperatures from 20 degrees onwards.

The job needs to be carried out by specialised personnel

It isn’t as simple as installing radiators, it is a more complicated task and plumbing should be done by qualified personnel with previous experience in the installation of the radiant floor. It is appropriate to mention that correcting the defects of installation will be to raise the floor so it will be better to hire a good installer to avoid greater evils. It is recommended to obtain an extended warranty from the installer.

But remember, the first action to gain health, comfort, safety and sustainability is to insulate the house the best you can. It is no good having energy efficient systems if our house is not well insulated and we throw the energy out through badly insulated roofs, windows or walls.

So before an investment in underfloor heating is thought of, we must plan good insulation around the shell of the building and I can assure you that no money will be better spent, or shall I say better invested.

But remember, the first action to gain health, comfort, safety and sustainability is to insulate the house the best you can. It is no good having energy efficient systems if our house is not well insulated and we throw the energy out through badly insulated roofs, windows or walls.

So before an investment in underfloor heating is thought of, we must plan good insulation around the shell of the building and I can assure you that no money will be better spent, or shall I say better invested.

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