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Understanding Underfloor Heating
Popular questions about underfloor heating

FAQs about Underfloor Heating

 

Frequently asked questions about wet underfloor heating

(If you question is not covered here, please don't hesitate to contact us. The answer to your question may be of interest to others and may subsequently be added to this list of FAQ's)

  1. What is underfloor heating?

  2. How does underfloor heating work?

  3. How do you regulate the temperature of living space with underfloor heating?

  4. What if I have a leak in the underfloor pipework?

  5. Underfloor heating looks complicated. Is it ?

  6. How can water in and underfloor heating system work at a cooler temperature than the radiators in the rest of the house in a mixed wet system?

  7. Is it difficult to install underfloor heating?

  8. it is more expensive to install compared with a conventional wet radiator system.

  9. Are there any drawbacks to underfoor heating systems?

  10. I've heard about 'night set-back'. What is it?

  11. But what about electric (DRY) underfloor heating?

  12. How should I lay out my underfloor heating pipe?

  13. What is an underfloor heating  manifold?

  14. Can I get somebody to quote for materials? (FREE QUOTE)

  15. My project is relatively small. Can I buy a kit for a small area?

  16. Can I discuss my underfloor heating project with somebody?

 

 

Q. What is underfloor heating?

A. As the name infers, heat for the living space emanates from below or within the floor. By heating the floor and using it as a giant radiator a lower temperature can achieve the same resultant warming effect over the larger surface area of the floor (when compared to the higher temperature needed in more traditional radiator systems to heat a room of the same volume).

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Q. How does underfloor heating work?

A. Heat is imparted to the floor which in turn warms the room. It's as simple as that. The floor in effect becomes a giant wall to wall radiator.

How the floor is warmed is a little more complicated, but the most common methods include a 'wet system' that involves circulating water that is warmed remotely through a run of pipe secreted under or within the floor (timber floor or solid floor  respectively), or an electric cable run under or in the floor that warms up as current is passed through - each warming the floor and in turn - the room.

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Q. How do you regulate the temperature of living space with underfloor heating?

A. By regulating the amount of warmed water passing through the pipework of a 'wet system' the amount of heat percolating into the floor and subsequently into the room can be controlled.

By the same token, by regulating the current either by amount or by switching that passes through an electrical underfloor heating cable (a 'dry' system) the temperature derived within the room can be controlled.

Regulating the amount of warmed water or the electrical current (depending on which type of system you have) is done by utilising a room thermostat (also known as a 'room stat'). The room stat (positioned at about shoulder height on a wall within the room) feeds temperature data back to a wiring centre, which in turn issues commands to allow/disallow the flow of water or electrical current (depending on type of system) so as to maintain the temperature set on/by the room stat.

Very large rooms or spaces may have more than one stat controlling different zones within that space - enabling for example a room to be set hotter at one end or place than another if so desired.

In underfloor heating terminology, an area controlled by a particular stat (room stat) is referred to as a zone. Whilst a area may be split into multiple zones, a zone may contain and control several heating coils (wet or dry) working together to heat the space. The setup and layout of zones being dependent on size and desired control.

For example: An relatively small dining room on a wet system may only need a small amount of heat to sufficiently warm the area with the minimal amount of control. Therefore, a single room stat communicating with the control (wiring) centre and single coil of UFH pipe bring heat into the zone would suffice. A very large lounge however may require more than one coil (or loop) of UFH pipe to bring in sufficient heat to warm the area. Multiple loops of pipework could be configured to work with one room stat (and therefore as a single zone) or configured to work with more than one room stat, giving the area more than one zone to be controlled. In reality, the large lounge would need to be very very large to reap the benefits of multiple zone control (i.e. the potential to be hotter in one place than in another).

The amount of heat imparted to the floor in any one place may also be 'affected' by the design of the loops on a wet system. Bearing in mind that the water travelling around the loop is constantly loosing heat, the water in the early part of a loop is logically hotter than it will be at the end. By concentrating early loops in a wet system close together an 'uneven distribution' of heat can be achieved. This for example can be useful if one wall of a room is totally glass or has a much higher heat loss than other areas. By running more early coils within that area more heat can be directed to colder areas - giving a means of balancing heat against loss at the design stage. (Please refer to pipe designs for examples)

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Q. What if I have a leak in the underfloor pipework?

A. In short, leaks are highly unlikely.

In smaller and domestic installations it is unlikely you will need to join pipes anywhere other than at the manifold. Pipes are normally supplied in various coiled lengths that will enable you to run a full continuous loop. If you have your layout calculated for you, it will become evident from the plan how long each loop will be. Pipe coils in lengths closest  to your requirement/s will therefore be supplied as part of the kit.

Should you need to join or repair pipes, special fittings designed for underfloor heating are available.

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Q. It looks complicated. Is it ?

A. At a glance, underfloor heating can look complicated. All those pipes converging on a manifold covered in actuators, cables, valves, pump and thermostatic controls might look frighteningly complicated, but the reality is somewhat more simple.

The manifold is only a simple way of connecting several coils of water pipe to a single regulated heat source. Manifolds are supplied in kit form and assemble easily to include all of the components required to make them function. Full instructions are supplied and technical support is available if required during the installation process.

Example: If you had a single pipe coil feeding to a single zone things would look somewhat more simple. As the room stat calls for heat, the actuator (an electrical solenoid valve) opens to allow water to flow around the loop. The temperature of the water being fed around the loop is regulated by a thermostatic valve so it does not get too hot. When the room stat is satisfied with the room temperature it instructs the actuator to close and flow stops. Simple - It just starts to look complicated when you have several loops and zones on one manifold, but each zone is simply opening and closing at the command of it's room stat whilst sourcing heat from a common supply.

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Q. How can water in an underfloor heating system work at a cooler temperature than the radiators in the rest of the house in a mixed wet system?

A. Wet underfloor heating systems actually use the boiler's return water. In a heating system, return water (water returning to the boiler having been around the system) is cooler than the flow (water from the boiler that has just been heated). Providing the temperature of the return water is adequate, this is adequate to heat your floor/s. Of course though, as water passes through or under your floor it will continue to give up heat to the floor and therefore cool. At this time, a sensor on the manifold detects this temperature drop and if necessary automatically adds water from the boiler flow (water that has just been heated) to ensure the required temperature is maintained in the underfloor loop.

A very simple way to extract as much heat from your system.

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Q. Is it difficult to install underfloor heating?

A. It would be fair to say more labour intensive, but not difficult. It's still two pipes (flow and return to the manifold) but you use the floor as the radiator instead of a wall mounted tin can.

Installing the manifold is actually fairly simple. This complicated looking component is only a convenient way of connecting several loops to a regulated hot water supply and presents no major problem.

Compared to hanging a radiator, which is fairly simple - only requiring a pipe to and a pipe from - underfloor heating takes a little longer, but still only requires two connections. You have a large coil of pipe that must be laid in or under the floor which of course takes time. However, there are many advantages (as described here) to an underfloor system - not least of all the savings that can be made in operating costs. So the time invested when installing your system is recovered many times and in many ways throughout the life of the building.

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Q. it is more expensive to install compared with a conventional wet radiator system.

A. Initially, underfloor heating is more expensive to install than a conventional wet radiator system. It takes longer and there are more components required. But it is a more efficient system to run, should not require maintenance as with radiators and produces a more controllable climate. So over a period of time will reduce running costs, maximise available wall space and remove potentially hazardous hot surfaces from your environment.

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Q. Are there any drawbacks to underfoor heating systems?

A. The most obvious difference between a conventional radiator system and underfloor heating system is the response time - both on heat up and cool down.

It takes longer to heat up a concrete slab for example using lower temperature water than it would to heat a small radiator with hot water. Similary, a concrete slab (when warm) will take a considerable time to cool down. This makes the response time to control input much slower. However, underfloor systems are not really designed to provide instant heat control, they focus more on providing a comfortable even  climate with no local 'hot spots'.

Point of interest: A feature becoming common on underfloor systems is 'night set-back'. This works in the following way -

Take a concrete slab for example. This takes a while to reach operating temperature so heating up every morning would also take a while. The room stat is set say to 20oC during the day so the system heats the floor to achieve an ambient temperature of 20oC. When you go to bed at night you may not want to maintain this temperature, but instead of simply switching your system off it enters 'night set-back mode'.

'Night Set-Back'  (when enabled) is a feature where the system allows the slab to cool down slightly - typically by about 4oC. So the slab temperature will only fall during the night to 16oC. Depending on conditions, this can take several hours. The system remains at rest until it reaches it's set-back temperature. When the morning comes the floor is not heating from cold, so it only has to raise it's temperature by 4oC to return to the daytime setting of 20oC. This of course does not take as long.

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Q. But what about electric (DRY) underfloor heating?

A. In a DRY system an electric heating element replaces the pipes associated with WET systems. The principle however remains the same, the floor becomes a huge radiator.

There is one subtle difference. The electric heating element looks a bit like a cable but is in fact a flexible heating element shrouded with insulation and mechanical protection. Due to the properties of the heating element wire, heat is generated as current is passed through it. The length of an electric heating element has a design calculation to provide a specific number of Watts over a given area when installed to a layout plan. An electric programmable controller energises and de-energises the heating element/s in conjunction with a room stat or temperature probe installed in the floor between elements (according to application) - this allows you to regulate the floor/room temperature.

A common application for electrically heated floors is 'Undertile Heating'. This is slightly different and should not be confused with 'underfloor heating'.

Ceramic tiles are becoming popular in homes, especially in bathrooms and kitchens. A ceramic tile is however cold to the touch - an unpleasant experience when walking around in bare feet, showering in a tiled area or when climbing out of the bath. Undertile heating is designed to warm the tile to a comfortable temperature and provide a cosy sensation to the touch. Whilst it will have a warming effect on the room, it is not the same as true underfloor heating and should not be relied upon to heat the living space.

Undertile heating is often no more powerful than the Wattage from an electric light bulb, so whilst very cheap to run it should be used in conjunction with a supplementary heat source.

Advantageous points to Undertile Heating:

  1. Relatively cheap to buy.
  2. Relatively simple to install*.
  3. Cheap to run.
  4. Wet floors dry much quicker.
  5. Very thin element (2-3mm thick) means there is no significant increase in floor level.
  6. Installs within the layer of floor adhesive directly under the tile.
  7. Suitable for 'new-build', refurbishments and wet room showers.
  8. Programmable to provide several 'on' and 'set-back**' times throughout the day.
  9. Transforms cold tiles to a warm and cosy experience.
  10. Temperature of floor is selectable with suitable programmer.
  11. Available in different sizes to suit the area to be heated.
  12. Available as single strand or pre-formed mats for ease of installation.

* An RCCD protected supply is required for reasons of safety. All wiring must conform with IEE Regulations and Building Regulations, and be installed and commissioned by a competent person.

** The 'Set Back' feature maintains a lower temperature in the floor surface during 'off peak' periods of the day (periods when the living space may not be used - when you're at work for instance, or throughout the night) so the floor doesn't fully cool and warm-up times are shorter.

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Q. How should I lay out my underfloor heating pipework?

A. The installation of an underfloor heating pipe can be determined by the type of floor into which you plan to install.

There is often less flexibility with how you run a pipe in a timber floor due to the direction in which the joists run and their proximity to each other. In timber floors pipes are run between joists - passing through notches from one void to the next.

There is a degree more flexibility when installing to a screed floor. Pipework in a solid floor can be laid in loops or coils (or a combination of both) prior to screeding. A pipework layout can be supplied if you have had a quotation once an order has been received. However, the final layout can often depart from a suggested plan due to various factors that require a different logic.

You should remember that the water leaving the manifold is warmer than that returning. Therefore the water in the earlier part of the run will be hotter than that at the end. This fact can be used to great advantage if you carefully consider which parts of your room will be colder than others. For example, if you happen to have patio doors or large windows in a room it is likely that the area adjacent will be generally colder in winter than say an inside wall. It therefore follows that concentrating loops in the early part of the pipework run (with the warmer water) in the colder zone may help to defeat the cold air causing the localised cold spot. Having done so the loops can then change pattern to however else logic might dictate - leaving the final part of the pipe run (containing the cooler water) for the naturally warmer areas. There are various different opinions and layout patterns on this subject, but here are some of the more common solutions - example layouts

 

Q. What is an underfloor heating manifold?

A. The term 'manifold' refers to bringing several into one. In an UFH system there are often many loops of pipes carry warm water from or cool water back to the start. This is achieved by using a manifold. The many loops of pipe terminate at the manifold. The manifold is equipped with valves that allow or disallow water to flow through each loop. The valves open and shut in response to signals received from the wiring centre as the room stats call for heat.

 

 

Things to know about underfloor heating

 

Considerations The Manifold Small Area Solutions
 

 


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