underfloor heating - faq

Q. What is underfloor heating?
Q. What are the advantages of underfloor heating?
Q. Does every room have a room stat or sensor?
Q. Does it take long for underfloor heating to get to temperature?
Q. Timber floors with underfloor heating
Q. What floor finishes are suitable for underfloor heating?
Q. Will underfloor heating with high ceilings provide adequate heat?
Q. What type of boiler is suitable with underfloor heating?
Q. What happens if the pipes are damaged during installation?
Q. What guarantees are in place?
Q. Underfloor heating in renovation projects
Q. What is screed?

Q. What is underfloor heating?
There are two types of underfloor heating - Wet systems where warm water circulates around within polyethylene pipes and Electric systems which is electric matting.  Both methods are installed within the floor or wall structure.

You may not want a complete underfloor heating system but simply want to install it in your kitchen, conservatory or extension.  In this case, we offer pre-made Add-On kits specially designed for smaller areas.

The heat produced from underfloor or wall heating comprises 70% radiant heat and 30% convection heat. Floor heating is as close as you can get to the ideal heating curve.

• Clean and hygienic
• One of the main advantages of underfloor heating is the even warmth and comfort it gives throughout your home or workplace ensuring a pleasant living or working environment.  Due to the even heat distribution, temperatures are slightly lower than you would have with a conventional heating system.  The actual air temperature can be reduced by 1ºC to 2ºC compared to conventional systems. This adds to the overall comfort level and gives energy savings of between 15% and 50% depending on ceiling height.  The higher the ceiling, the more energy is saved.
• No dust circulation - excellent for people who suffer from asthma or allergies
• Environmentally friendly especially when used with ground source heat pumps, solar panels and condensing boilers
• Vandal proof
• Complete freedom for innovative interior design - no unsightly radiators
• Complete wiring and plumbing schematics
• Ease and speed of installation
• Easy to regulate due to compact manifolds
• Little or no maintenance

Q. Does every room have a room stat or sensor?
All main rooms have controls - a room stat or sensor that controls the thermal actuator on the manifold.  This allows hot water heating to the desired room and also switches on the pump and boiler as required.

Q. Does it take long for underfloor heating to get to temperature?
Underfloor heating runs completely differently to a radiator system.

If you've installed the system into slab or screed, it will take longer to heat up.  It takes from four to six hours for the real effect to be felt; after that, floor makeup will always retain heat and the setback function ensures that the room temperature never gets too low.   

The entire thermal mass or fabric of the building is heated up after the system has initally started running, so it won't take too much to bring it up to temperature at set times.

Q. Timber floors with underfloor heating
Wood is a natural material; it will expand and shrink as the moisture content varies.  In order to avoid substantial shrinkage in the wood, its mosture content should be between 6 and 10%.  It's important you take careful note of your floor suppliers' instructions regarding drying out or acclimatising the timber before you commence installation.

IHS recommends the use of hardwood in planks no wider than 80mm and no longer than 1.2 meters.  A number of our customers have however, by their own choice, used boards of 130mm wide and 2.5 meters long and this has been successful.  We think that this is the way the wood was cut and subjected to a slow acclimatisation process.

A good quality damp-proof membrane should be installed below the screed or concrete.  This will stop any new moisture being drawn up from lower layers.  The floor heating should be running for at least ten days to ensure the screed or concrete is dry.  If the concrete/screeded floor is not properly dried out, a high damp tension will occur and condensation will form against the coldest outside layer ie. the wood floor.  This can cause considerable expansion and capping of the wooden floor.

The glue we recommend for this process is Lekol 5500.  This glue contains no water and has a fifteen minute application time depending on temperature.  The heating should be switched off the night before the wood is to be applied, then switched on again twenty four hours after the wooden floor is glued down.    Starting with low temperatures, increase the temperature through the floor over a period of a week, allowing the wood to further acclimatise.  This can be done very easily using the regulating valve on the underfloor heating manifold.  Tongue and groove joints between the boards should not be glued to allow shrinkage and expansion to take place.

Please note that IHS do not supply glue or timber flooring.

Q. What floor finishes are suitable for underfloor heating?
To ensure and achieve optimal heat output and temperatures, you require good contact between the floor structure and floor covering with no air gaps.

Generally, thick cork and soft woods are not suitable for floor heating.  Watch out for some of the new laminate boards and how they're fixed to the floor.  If the underlay is too thick, it will insulate your floor and block heat output.  Underlay should not exceed 2mm.

Bamboo is suitable for use with underfloor heating.

All stone, concrete, screeds, slate, ceramic and quarry tiles allow excellent heat transfer and output.

All carpets are suitable, however, the total carpet thickness should not exceed 12mm. If the carpet has a foam backing it should be no more than 3mm thick.  The function of underlay is to prevent wear and tear on the underside of the carpet.  A thinner type of no more than 3mm should be used with no air pockets being allowed to develop.  The carpet can be laid loose, tensioned or glued to the floor - if glued, the heat output is higher.

Hardwood flooring: wood should have a moisture content of no higher than 10%.  The total wood thickness should not exceed 22mm.  Ensure the concrete or biscuit is dry and all moisture is eliminated prior to applying ANY wood finish.  Start up the heating to dry out the concrete or screed. You should refer to floor suppliers' guidelines for advice on applying adhesive.

Q. Will underfloor heating with high ceilings provide adequate heat?
One of the main benefits of underfloor heating is the even warmth and comfort it gives throughout your home or workplace ensuring a pleasant living or working environment.  Due to the even heat distribution, temperatures are slightly lower than you would have with a conventional heating system.  The actual air temperature can be reduced by 1ºC to 2ºC compared with conventional systems. This enhances the overall comfort level and gives energy savings of between 15% and 50% depending on ceiling height.

Q. What type of boiler is suitable with underfloor heating?
You can use any boiler or heat source that can produce heat from 40ºC to 90ºC.  We're happy to give you advice but your personal preference is what matters.

Examples include, ground source heat pumps, solar panels, district source, wood chip burners, wood burning stoves, back boilers, condensing boilers, combi or system boilers with hot water cylinder, oil or gas fired boilers, Agas, Rayburns.

Q. What happens if the pipes are damaged during installation?
During system installation, when wooden floors are being installed or when the pipes are exposed, the pipes are vulnerable.  Accidents do happen but don't worry – we supply special pipe connectors.  Refer to the Installation Manual for repair guidelines or contact us for further information.

Q. What guarantees are in place?
Both standard and HD pipes have a 50-year guarantee.  Ensure you have a written insurance-backed guarantee for the first ten years.

ALL IHS pipe has an oxygen diffusion barrier.

All our designs carry heat loss calculations and design guarantees that are not subject to a time limit.  Most UK companies do not have this - ask for a written copy of ours.

Q. Underfloor heating in renovation projects
It's possible to install underfloor heating in any building but cost is a major factor in determinging whether it's practical to install underfloor heating in an older property.  It will involve pulling out older floors and, sometimes, considering whether to the existing floor covering can be utilised again.  

It is possible to install underfloor heating into a building with existing solid floors. The most important question to initially consider is whether your U-values are up to current building regulations. For optimum efficiency, it’s imperative that the heat generated by the system is captured and not lost through cracks or open fireplaces.

When installing underfloor heating pipe, ceiling height will determine whether it's necessary to dig up floors.  In most cases, it will be necessary to raise floor level by a minimum of 75mm.  Please see Floor Constructions in our underfloor heating section for illustrative drawings.

Floor Construction 30F requires a minimum floor height of 75mm; Floor Construction 6F requires a minimum floor height of 95mm (minimum insulation level is 25mm).  Another possibility is to lay wooden joists on top of the existing floor which require a minimum height of 75mm.

If you need advice specific to your project, please don't hesitate to contact us and we'll advise you on correct methods and give you a clear idea of what costs you will incur.

Q. What is screed?
Screeding is the process of laying the cement floor layer above the floor insulation and below the floor finished (rather than using a suspended timber floor).  It is usually a job for either a specialist floor screeding firm or your plasterer.  As a general guide, expect a floor screed to take around 30 mins per metre square to lay - so a 100m2 floor area should take about six man-days to screed.  The overall time taken is also affected by whether it's a large space or lots of small rooms. 

Screeding needs to be planned carefully into your schedule.  For standard screeds, allow setting time of two days; however some fast-set mixes can set in less than 12 hours.  Most applications will take up to three weeks to dry out completely.

BS EN 1264 recommends that you limit the area to be screeded to 40m2, or 8m lengths in any one direction.  If you exceed this, you should separate the floors into bays divided by some flexible expansion material.  You can generally stop cracking by using mesh or adding fibres to the mix but on very large areas you may find that the screed has a tendency to lift up due to expansion.

Expect to pay in the region of £15/m2 including labour and materials.