How does underfloor heating work? Your questions answered
Posted by NicoleYouGen on 24 May 2013 at 9:52 am
What is underfloor heating?
Underfloor heating can be either a system that pumps warm water through piping under the floor (a ‘wet’ system) or electric coils placed under the floor (a ‘dry’ system). Taking advantage of the basic principle that heat rises, warmth from under the floor is radiated into the room.
Underfloor heating is the oldest form of central heating – the Romans used a form of underfloor heating called hypocausts, which heated buildings and baths. Today’s form of underfloor heating is common in Northern Europe, and gaining popularity in the UK.
Will underfloor heating save energy?
This depends on how well insulated the building is, the efficiency of the boiler, and what kind of heating needs your system will be meeting.
High occupany commericlal buildings are more likely to see efficiency gains from underfloor heating because it is most effective for periods of continual occpupancy, and because for larger heating needs the capital costs of an underfloor heating system become relatively smaller.
According to the Energy Saving Trust:
In an existing home with average insulation, for an air to water heat pump system, an underfloor heating under insulated timber will save 20% of energy costs over a radiator system (£500/year vs £400 average).
In an existing home with average insulation, with a gas or oil-fired boiler, the energy savings are smaller (about £10/year average).
In new and well-insulated homes, underfloor heating with a heat pump will save (£190 vs £230 average) over radiators
In a new and well-insulated homes, underfloorfloor heating will save negligably over a radiator system.
How much does it cost?
A wet underfloor heating system will cost about a third more than a radiator system, on average. This includes the fact that more insulation is likely to be added below the pipework. If the system is installed at the time of building or renovation, its installation costs will be minimized.
Electric, or ‘dry’ underfloor heating generally costs less to install, but is more expensive to run. Dual storage underfloor heaters involve two sets of pipes and extra thick screed, so they can gain most of their running energy from cheaper nighttime tariffs. This is not a cost-effective form of heating.
Is underfloor heating suitable for my building?
A wet underfloor heating system is best suited to buildings that are well insulated. Underfloor systems operate at a lower temperature than most radiator systems (35-45 degrees C). This makes underfloor heating ideal for heating from heat pumps. As a low temperature form of heating, underfloor heating is most effective when kept on continuously. It is slower to respond than traditional radiators, so is not suitable for intermittent heating. Some homes have underfloor heating in a main ground floor room and smaller intermitent heaters in other rooms.
Commercial buildings might see more efficiency gains than homes, because of having a larger volume of continual occupancy.
What is it like to live with underfloor heating?
Underfloor heating is not very responsive, so after you turn it on, you will have to wait longer to feel warm. It’s most effectively used where it can be left on continuously. Electric systems are more responsive, but are more expensive to run.
Underfloor heating delivers a more consistent temperature, with heat distributed more from the bottom of the room. Whereas radiators will send warm air through the room, but less at the bottom of the room, the underfloor heating will send an even warmth, and will heat more at the bottom and top of the room than in the middle.
Not having radiators gives you more space. But you will need to consider that furniture items such as cupboards and wardrobes should not sit above the heat coils, as they can be damaged. Bathrooms are harder to heat because the bath takes up a lot of floor space, but if you have a claw-foot tub this will be less of an issue.
Is underfloor heating suitable for a retrofit?
It is possible to retrofit underfloor heating. You will probably have to raise the floor (and adjust doors accordingly). Concrete floors are generally harder to retrofit, and suspended timber floors tend to be easier to retrofit. Electric systems are usually thinner and easier to install in a retrofit where there isn’t space to raise the floor.
Will I need a new boiler?
For a gas powered system, it’s best to have a condensing boiler, which is most effective for low-temperature heating such as underfloor heating. Most new boilers are condensing. Underfloor heating can also be connected to a thermal store, and works well with heat pumps.
What type of flooring can I install with underfloor heating?
Underfloor heating is commonly installed with stone, ceramic or terracotta tile floors, but can also be installed with wood, linoleum or carpet.
When installing with wood, you will need to keep in mind that wood will natural expand and contract with changes in heat and moisture more than stone or ceramic tiles will. This is commonly addressed by floating wood boards on a layer of polythene foam that allows subtle movement. Depending on the type of wood floor, it can also be a less effective heat conductor. That said, timber floors are more responsive, so can be more ideal where there are more sporadic heating needs.
Carpet insulates, which is good for stopping heat loss from the floor, but bad for letting heat from underfloor heating in. But underfloor heating can work effectively with carpet. You need to know the combined tog value of the carpet and underlay, which should be a maximum of 2.5 and ideally lower.
Do I need a professional to install underfloor heating?
For a wet underfloor heating system, unless you’re very handy with DIY, you will probably want a professional with experience to do the installation. You can expect to pay more for the installation than you would for new radiators.
Installation should take a couple of days, depending on the floor space, but screed can take up to three weeks to dry.
Do I have to install the system with screed?
Wet underfloor heating systems are commonly installed with a layer of screed on top to create a level surface which the floor is laid onto. Suspended floors can have underfloor heating added without screed. And even without suspended floors, it is possible to install without screed (a ‘dry’ installation, not to be confused with a ‘dry’, or electric, system) using screed replacement tiles, which are fixed together in order to make a level, floating floor. This might be preferable if you want to avoid brininging extra moisture into the building, and also means less wait time before you can walk on the floor.
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