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Questions about underfloor heating

POLYPIPE WIRSBO UNIPIPE

Underfloor Heating Products and Information

 
The Questions
What is UFH? How does it work? Benefits of UFH

Where it can be used

Frequent Questions
 
The Products
UNIPIPE WIRSBO Considerations The Manifold Small Area Solutions
 
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)

 

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

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