Wednesday , 22 November 2017

Underfloor Heating – A Brief Guide

What is Underfloor Heating?

Image courtesy of Warmup

 

Underfloor heating systems use a pipe network, of either electrical or water systems to heat the floor. Underfloor heating is considered to offer improved energy efficiency, improved comfort and better interior choices than a standard radiator system.

While a radiator will circulate heat, it is often inefficient, with the highest temperature being at the ceiling, and the cooler temperature being at the floor (closer to occupant level). The air circulation contributes to ventilation losses and results in higher fuel costs. Radiators require high temperature water flow due to the small surface available to be heated.

Underfloor heating creates a more stable and consistent temperature, with a lower energy consumption. Warm water is pumped through the underfloor heating tubes within the floor, and emits the heat across the whole surface heating the room effectively. A lower water temperature is required due to the higher surface area of the heating system.

Water vs Electric Underfloor Heating Systems

There are two types on underfloor heating system, wet and dry. The dry system is electric powered, and the wet system is heated water pumped through the pipes.

Water system – pros

  • Extremely efficient to run
  • Works at low temperatures
  • Work well with use alongside heat pumps

Water system – cons

  • Initial costs are high
  • Pipes are often difficult to reach if there are any problems

Electric systems – pros

  • Inexpensive to install
  • No pipework – east to install

Electric systems – cons

  • Expensive to run
  • Heavy items and furniture can damage the system

The electric system is more often seen in refurbishment or retrofit as it is a more slimline installation and has less effect on floor levels. It is possible to get low profile water systems for renovation projects however.

Wet systems are more often seen in new build scenarios, due to the increased floor thickness that is required for them. Water systems can also benefit from the varying renewable heat sources available such as air source heat pumps, ground source heat pump, biomass, and so on. The electric system is more limited.

Generally speaking, I would always go for a wet system incorporated into the build, suitably zoned, when working on a new build project. I feel that the electric systems, although they have a place in some retrofit situations, aren’t as efficient or as highly rated within the industry.

Why use underfloor heating?

Image courtesy of Warmup

Improved Indoor Air Quality

An underfloor heating system often encourages the use of perceived cold flooring materials such as slate, tiles, terrazzo and concrete. These surfaces have low VOC emissions compared to other flooring options. The temperature control of an underfloor heating system also provides improved conditions that prevent mould, bacteria and dust mites.

Energy

Underfloor heating systems require a lower temperature to operate which results in lower energy requirements for the system.

Control

Smart thermostat systems allow control over individual zones or spaces, meaning different zones can be set to different temperatures, or turned off completely when specific parts of the building are not in use.

Position of the system

For a solid concrete floor the insulation position is important, in terms of exposing thermal mass of the concrete to the heat from the pipes, or isolating the concrete/thermal mass from the heat.

For systems which require a 24 hour heating cycle, exposing the concrete slab to the heat from the heating system will allow for a more even heating regime. These systems present a slower response time to alteration requirements in temperature, due to the thermal mass of the concrete.

For an intermittent heating application, where a faster response time is required for temperature changes, it is more prudent to have less thermal mass available to absorb the heat, and instead place the insulation layer below the screed or timber floor, but above the concrete slab.

It is important the building type, client brief and heating requirements are thoroughly considered prior to selecting the underfloor heating system and flooring type in order to provide the best solution.

Floor Types

Underfloor heating can be installed in numerous types of flooring systems.

Floating

Not fixed directly to the floor deck.

 

Image courtesy of Nu Heat

 

A floating floor does not need to be fixed to the sub floor, and is usually supported on a continuous layer of insulation. This type of system can be suitable for new projects, extensions, over solid concrete slab, beam and block or over suspended timber joists.

A build up for this would usually consist of:

  • Subfloor
  • Floor insulation
  • UFH mat / tray
  • UFH tubes
  • Chipboard deck
  • Engineered timber flooring

This system is a dry floor construction giving a medium heat output and a medium response. It is lightweight and quick to install, and allows for floor coverings to be installed immediately. This is suited to an intermittent heating application.

Batten

Timber floor over a solid sub floor.

Image courtesy of OMNIE

 

When installing an underfloor heating system within a batten space the system must be in contact with the floor deck in order to provide good thermal performance.

A typical build up for a batten floor underfloor heating system would be:

  • Subfloor
  • Floor insulation with pipe trenches, between battens
  • UFH tubes/pipes
  • Chipboard deck
  • Engineered timber flooring

This system is a dry floor construction giving a medium heat output and a medium response. It is lightweight and quick to install, and allows for floor coverings to be installed immediately. This is suited to an intermittent heating application.

Suspended

Timber suspended floor using joists to support the deck.

Image courtesy of OMNIE

 

The underfloor heating system to a suspended floor usually fits between or straddles the joists. This system is suitable for new projects, extensions, and also retrofit options.

A typical build up for a suspended floor:

  • Insulation between joists
  • Pipe mat with trenches
  • UFH pipes/tubes
  • Chipboard deck

This system is a dry floor construction giving a medium heat output and a medium response. It is lightweight and quick to install, and allows for floor coverings to be installed immediately. This is suited to an intermittent heating application.

Screed

Common underfloor heating construction filling with screed or concrete

Image courtesy of Nu Heat

 

Screed is frequently used in floor construction and particularly popular with underfloor heating systems. It is suitable for use in new builds, extensions, over solid slabs or beam and block. It does provide a deeper system and therefore a thicker floor build up than the dry systems mentioned previously.

A typical build up of a screed underfloor heating system where an intermittent heating application is required:

  • Concrete slab
  • Floor insulation
  • Protection layer
  • Clip track for pipes
  • UFH pipes / tubes
  • Sand and cement screed
  • Floor covering – usually tiles, ceramic etc

A typical build up of a screed underfloor heating system where 24 hour heating application is required:

  • Floor insulation
  • Concrete slab
  • Protection layer
  • Clip track for pipes
  • UFH pipes / tubes
  • Sand and cement screed
  • Floor covering – usually tiles, ceramic etc

Note that on the 24hr heating requirement, the floor insulation is under the concrete slab to allow the thermal mass of the concrete to absorb the heat.

This is a wet floor construction, gives a high heat output and works well with a longer heating cycle. Floor coverings must be fitted after the screed is dry.

There are also retrofit systems, and many acoustic options out there too. There are some great suppliers and manufacturers available that provide useful information, data, images and details. Some of my favourites include:

OMNIE

NU-HEAT

Warmup

Images courtesy of:

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6 comments

  1. Thanks Emma for your website’s cornucopia of excellent material.
    Your article regarding under floor insulation really interested me.
    We are still trying to educate clients to install timber subfloor insulation, and as regards conc slab on ground, very few actually insulate the slab..Aust Construction
    Code specifies slab edge insulation for hydronic or electrical heating for slab.
    Full slab insulation is almost unheard of.
    But from July 1 this year, our winter, power prices have risen dramatically and perhaps folk will think about floor insulation more intelligently within the Aust bldg environment.
    So thanks for your material which will help me as a designer to offset the large thermal draw that so often charactizes australian domestic architecture.
    As usual you’re doing a fine service for us all.

    Kind regards
    Gordon, shivering in a Victorian winter.We’re not that from the Australian Alps, so we do feel the breezy cold.

    • Hi Gordon, great to hear that the content is useful for you – thank you for your comments, I appreciate it. Keep warm 🙂
      Regards, Emma

  2. Hello. This is a great article. Can I add the article to my new blog? If so how do I do it?

    Spot the Newbie.

  3. Pipe network is very beneficial for the underfloor system. I was using last one year in the house and it’s working at low temperatures

  4. good day;
    being a home & building designer in Canada for the past 40 some years, i have used in floor heating constantly over the past 25 plus years. put it in my own home that i built in 1983. the tech knowledge was not great back then.
    we generally put tubing over an R- 16 or more for a poured concrete slam , as for a basement or as a frost wall & poured interior slab on grade.
    for wood framed floors, we prefer a 1 1/2″ concrete over pour on a sub floor with radiant tubing stapled to the subfloor. we have tried putting the tubing under the subfloor, with insulation below it,but find there is a greater loss of heat than with the over pour.
    a combination of inslab heat & ductless mini split heat pumps is the most common in our area at this time.

    david

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