Underfloor heating expert at Polypipe Home Solutions, Martin Dootson, explains the advantages of water based underfloor heating systems and discusses which system is best for self build and renovation projects.

What are the benefits of underfloor heating compared to radiators?

There are lots of benefits to installing underfloor heating over radiators:

  • Unlike radiator-based systems, underfloor heating ensures an even dispersion of heat across an entire room, delivering a comfortable environment with no cold spots or draughts. In general we all feel more comfortable when we are in an environment where our feet are warmer than our heads (there’s nothing worse than cold feet!).
  • Removing radiators from the walls gives self builders design freedom and flexibility in each room.
  • Radiators can reach a heat of around 80°C and often present sharp metal edges, making them a real risk to small children and the elderly. Underfloor heating removes this risk.
  • An underfloor heating system is far more controllable than radiator based equivalents and heat is only delivered where and when it is required.
  • Self builders may want to consider if, when selling a property, an underfloor heating system makes the home more desirable to that of the competition.

What are the benefits of water based underfloor heating versus electric underfloor heating?

  • Underfloor heating systems that use warm water emit heat across the entire floor surface, providing an even and comfortable heat throughout the room. As they are connected to the existing heating, they are more economical to run than electric systems.
  • While electric underfloor heating is cheaper to install than a wet system, it’s more expensive to run – particularly as it’s not conducive to use in combination with an off-peak electricity tariff such as Economy 7, for example (unless you only want to run underfloor heating at night).
  • For that reason, the Energy Saving Trust doesn’t recommend electric underfloor heating for large areas.

Can underfloor heating be used on any type of floor substrate? What are the considerations?

Underfloor heating, both wet and electric, can be installed on most floor constructions as long as there is enough space to build up the floor, taking into account doors and stairs, and the floor can take the weight. The key to success is to choose the right floor-heating system for the construction.

In new build projects, most manufacturers will have systems for solid, suspended and floating floor types. For upper floors, including those with difficult access or engineered joists, Modular Heating Panels are the best solution.

I have started my project and laid the floor. Is it too late for me to consider underfloor heating?

No, underfloor heating can still be installed. Look for brands such as Overlay™ or Overlay™ Lite. Overlay™ is a unique low profile underfloor heating system ideal for both renovation and new build projects. Installed over the existing floor and only 18mm in depth, these systems allow underfloor heating to be installed where traditional underfloor systems would either require expensive excavation or would require the floor to be raised to an unacceptable level.

Due to ease of handling and cutting these systems are more suitable for larger areas and multiple room installations.

How do I connect underfloor heating to an existing heat source?

When connecting to any heat source it is essential that the underfloor heating manifold(s) are fed directly from the heat source with a dedicated set of flow and return primaries, to enable total hydraulic control of the underfloor heating system. Under no circumstances should this primary feed be connected into any other heating pipework, such as radiator or domestic hot water primary circuits.

To provide independent hydraulic control of the entire system, it is important that the installation is designed as an ‘S Plan’ or ‘S Plan Plus’ configuration which allows for a two port zone valve to be fitted to all primary circuits and at each underfloor heating manifold.

It is the responsibility of the system designer/installer to ensure that the boiler/heat pump are capable of providing sufficient outputs in order to meet the requirements of the primary pipework, the underfloor heating system and any other equipment installed in the system.

Under no circumstances should an underfloor heating system be connected directly to a solid fuel or wood burner. Instead, the burner should be used to provide indirect heat via a thermal store or similar neutraliser. The low temperature feed from this store can then be pumped to the underfloor heating manifold, as with a heat pump installation. Specialist advice from the heat source supplier or manufacturer should be sought before commencing the installation.

How will underfloor heating affect my energy bills?

A water based underfloor heating system should affect your bills for the better – in the long run it can be more economical to run than a radiator based system, as the water is kept at a lower temperature to produce the equivalent heat output. As floor heating demands a low temperature rise output from the boiler, this form of heating is ideally suited to achieving maximum economy from a condensing boiler or heat pump.

I remember old underfloor heating systems making people’s feet ache. Is this true of new systems? How has underfloor heating advanced?

No. This was a genuine problem with older electric systems, where electric elements were embedded in a concrete slab with no insulation. As the majority of the heat was escaping, the systems had to work harder and at higher temperatures to keep the room at a comfortable level which led to people suffering from achy feet. However water based systems allow the temperature to be controlled much more easily, and houses are fully insulated underneath, meaning that there is no excessive heat loss.

One of the biggest advancements in underfloor heating is the floating floor system. It is designed for use in applications where solid floor insulation is not suitable due to structural weight limitations or where a ‘dry build’ floor option is required. Suitable for use in either new build or existing properties, the floating floor panels can be installed directly on top of both solid and timber floors.

What flooring is best for underfloor? Are there any special laying requirements?

Underfloor heating systems will work efficiently with any floor covering, as long as it is well insulated underneath. However, each floor covering has different thermal conduction properties, and harder surfaces offer better conductivity and, therefore, better heat output rates.

Carpet and underlay can be used with good underfloor heating systems. The nature and the thickness of the carpet underlay is fundamental in determining good heat transfer. The most popular underlay type is sponge with a waffle pattern moulded into the underside. These allow good heat transfer. Felt and rubber crumb underlay should be avoided. These products can seriously reduce the effectiveness of an underfloor heating system, as they insulate the floor surface and prevent heat transfer. The TOG value of carpet and underlay should be available from the respective manufacturer. For optimal system performance choose an underlay with a maximum TOG value of approximately 0.5. The maximum TOG value of carpet should be approximately 1.0 to 1.5.

Stone and ceramic tiles, marble or flagstones are usually cold underfoot. However with floor heating they are transformed into warm, comfortable surfaces. Each of these finishes is essentially brittle and it is imperative that the design of the supporting floor structure is stable and rigid to prevent cracking. It is recommended that flexible adhesives and grout should be used.

Sheet vinyl is suitable for use with all underfloor heating systems. However it is sensitive to long term exposure to heat. There are two categories of vinyl; one is limited to constant temperatures of around 26C and the other to 30C. Check the floor surface temperature indicated by the vinyl supplier for compatibility with underfloor heating. Laminate flooring should be laid on a roll type floor leveller, rather than the rigid panel type. Movement that occurs must be accommodated by an expansion gap around the floor deck.

Is it possible to install underfloor heating in unusual shaped rooms or split level properties?

Yes. Underfloor heating can be fitted into split level homes or into a room with an unusual shape or proportion as the panels can be cut to size. As the piping used in Polypipe systems is flexible polybutylene it is possible to bend the pipes to the angles required by a property – even to 90 degrees for a property with split levels. Using plastic pipes is a good solution to this situation, because of the pipe’s flexibility in comparison to traditional copper piping.

I may want to extend my underfloor heating system in the future. What should I do at this early stage to enable this?

It’s always easier to factor any planned extension into the original installation by allowing for future feed pipes and the extra ports on the manifold (the main distribution).

However, the key consideration is the placement of the manifold at the outset – this will negate the need to tear up the screed to re-lay pipe work travelling to any future extension.

For further information about Polypipe Underfloor Heating and to receive free advice from an expert, call the helpline and discuss your project with a designer.

Martin Dootson is the market development manager at Polypipe Home Solutions, which specialises in bringing together a selection of proven technologies to provide new build and renovation projects with systems that enhance comfort, reduce energy bills, and lower carbon emissions. For more information call 01709 770000 or visit http://homesolutions.polypipe.com/

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