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How to retro-fit warm water underfloor heating

A recent two-year study has confirmed that warm water underfloor heating (UFH) really is more energy-efficient than radiators – something the industry has always maintained. The British Research Establishment’s revised version of the Standard Assessment Procedure (SAP), which becomes effective on 1st January 2008, is expected to show UFH in a more favourable light; for the first time buildings fitted with UFH are likely to get better SAP ratings than those with radiators.

Over the years, UFH has been perceived as an exclusive commodity, however recent technological advances have led to a steady increase in its availability and popularity in the UK, making it one of the fastest growing and most lucrative markets for heating engineers. 

Due to both a short-fall in available land and consumers’ increased environmental awareness, the most recent trend sweeping the industry is retro-fitting underfloor heating.

What to consider
In the first instance, installers should consult with their client to make sure the existing property will be brought in line with, or surpass, the requirements of Part L of the Building Regulations. In renovation and refurbishment projects, wall insulation should be present and double glazed windows and doors are usually essential. It is Nu-Heat policy not to recommend an underfloor heating system unless sufficient insulation can be provided to prevent wasteful downward heat losses.

Floor constructions
There are three standard floor constructions available: floating floor, suspended timber and screed. However, screed is generally deemed better suited to new-builds, extensions and conservatories as it will, on average, mean a 150mm floor height build-up.

Although suspended timber floors have very little impact on floor height build-up and can be retro-fitted, either ceilings or floors will have to be removed in order to lay the floor heating tube. This will not be a problem if they are being replaced anyway, but if they are to remain in-situ, a floating floor is more likely to be the best solution.

The floating floor construction is a popular option for retro-fitting as it benefits from minimal floor height build-up and is straightforward to install – see below.

Floating floor – as easy as 1, 2, 3
The general installation sequence is as follows:

  1. Lay additional insulation over, or within, the floor structure to meet current building regulations

    Lay additional insulation over, or within, the floor structure to meet current building regulations

  2. Lay Nu-Heat panel with diffuser plates

    Lay Nu-Heat panel with diffuser plates

  3. Walk in the floor heating tube

    Walk in the floor heating tube

Nu-Heat supplies a heat diffuser plate attached to an extra high density (EHD) polystyrene base layer that can be laid directly on the existing floor.  That said, in some circumstances, additional insulation such as Kingspan or Celotex will be required, especially on ground floors. The plates are then fitted to the base layer and Nu-Heat’s tubing is simply walked into them. 

The chipboard or final timber floor deck is laid directly on top of the panels making installation very straightforward.

Floor finishes

6mm ply should be laid across the entire floor before the fitting carpet. Carpet gripper can be used around the perimeter of the room and nailed in the conventional manner. But, whenever underfloor heating pipes pass under gripper (e.g. doorways); the gripper must be glued into position using Gripfill of equivalent.

Ceramic/natural tiles
Areas to be tiled must be covered by a 6-12mm plywood deck. Ceramic or natural tiles should be fixed with a flexible two-part adhesive and flexible grout following the manufacturer’s guidelines.

Engineered hardwood flooring
Engineered hardwood flooring (laminates) 16-22mm thick can be laid directly onto the OSB. The hardwood must be glued into position using SikaBond®TS2, or equivalent, using an applicator gun. Where boards are laid over 6mm ply they can either be glued directly to the plywood or glued and butt-jointed together as in a conventional floating floor with a maximum of 2mm foam sound-deadening layer.

Laminates less than 15mm thick
Fix to the 6mm plywood deck using the adhesive recommended by the manufacturer or float the floor in the conventional manner by gluing the tongue and groove with D3 quality PVA adhesive over a maximum 2mm foam layer.

Controls & Zoning
Discussing controls and zoning with your customer is particularly relevant in a refurbishment situation as the overall effectiveness of any heating system largely depends on how it is controlled.

Many customers will need guidance on which control system will best suit their needs and lifestyle – which is why it is so important for installers to have a clear idea of the options available.

For high efficiency gas and oil boilers, requirements typically include an electronic timer or programmer, a room thermostat, thermostatic radiator control valves and a separate thermostatic control on the hot water system. The same rules apply for underfloor heating (UFH): intelligent controls need to be fitted in conjunction with the system to optimise the performance and ensure the greatest environmental benefits.

Any competent UFH supplier should zone the property – comparable to setting radiator TRVs at different temperatures throughout a house; you wouldn’t have one light switch for a house, and therefore you should not have one temperature control for a whole-house UFH system. The only exception being open-flow systems, which will work in conjunction with the heat pump controls.

With the increasing use of renewable heat sources in conjunction with UFH, system control takes on even more importance as, typically, a variety of heat sources, (ie. heat pump, solar collector, cylinder), must be integrated. Although each different unit is likely to have a control panel, all must be coordinated to achieve optimum efficiency.

End-users must also understand how their UFH system works in order to get the best performance. For example, Nu-Heat recommends that its systems maintain a minimum background heat of 16˚C – should more heat be required, the UFH has less ground to make up in delivering the correct temperature.

Wireless thermostats are ideal for retro-fitting in renovations where channelling wiring into walls can be problematic as hard wiring is only necessary at the manifold and receiver – making installation quick and straightforward.

For more information about the integration of underfloor heating into new or existing property, call Nu-Heat on 0800 731 1976. Alternatively visit http://www.nu-heat.co.uk