How to retro fit underfloor heating



You are probably already aware of the huge land shortfall in the UK and, as a result, may be considering an alternative to new build – refurbishing a property.

Environmental considerations are increasingly at the forefront of building specifications and energy saving products, such as warm water underfloor heating and heat pumps, can be seamlessly integrated into existing dwellings – as long as some simple guidelines are followed.

What to consider
In the first instance, the existing property must 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, give a 150mm floor height build-up. It is perfectly suitable for a renovation project where floors are being removed or sufficient height is available.

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 the floor structure to meet current building regulations


    Lay additional insulation over 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 which can be laid directly on the existing floor.  That said, in some circumstances, additional insulation such as Celotex or Kingspan 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.

Nu-Heat’s LH14 floor construction – another user-friendly solution
Nu-Heat’s LH14 is another option when retro-fitting underfloor heating as the floor construction causes negligible floor height build-up and is also relatively easy to install. 

The general installation sequence of LH14 is as follows:

  1. Remove floor boards and open joists

    Remove floor boards and open joists

    Floor preparation can either be completed by the builder or the heating engineer.


  2. Place foil and insulation between exposed joists


    Place foil and insulation between exposed joists

    Building Regulations recommended that on an existing suspended timber ground floor, there should be a minimum of 100mm mineral wool over heavy duty foil (2L2 or equivalent) stapled to joists, or 100mm Celotex board. For first floors, no insulation is required except over unheated areas. However, 100mm mineral wool will improve sound insulation.

  3. Evenly space the 135mm orientated strand board (OSB) over floor

    Start at the furthest point of the room from the manifold, place the first plate against the edge and push the second timber strip against it. Glue or nail each 135mm wide strip as you go.


  4. Lay heat transfer plates

    Lay heat transfer plates

    Clips are used to secure tube on turns or wherever necessary.


  5. Walk the floor heating tube into the heat transfer plates

  6. When all zones are completed, pressure test the system as described in Nu-Heat’s manual

  7. Screed gaps with self-levelling compound

    Screed gaps with self-levelling compound


It is now possible for your choice of floor covering to be fitted – see below.

Floor finishes

Carpet
Six-millimetre ply should be laid across the entire floor before fitting carpet. 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 and glued into position. 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.


Integrating UFH with renewable technology
Both ground source (GSHP) and air source heat pumps (ASHP) and solar thermal systems are ideally suited to work with underfloor heating and both can be used in renovation projects.

Air source heat pumps are the easiest heat pump to fit, either in a retro-fit or new-build situation, as they require no groundworks. The only space required is beside an outside wall, making them ideal for well-insulated houses and apartments.

There are two installation options for ground source heat pumps – either using horizontally-laid collector tubes (the amount of land needed is approximately double the floor area of the property to be heated) or, where insufficient land is available, the collector tube can be set into a vertical borehole.

Solar thermal technology can be fully integrated with both underfloor heating systems and heat pumps. Options include flat panel and evacuated tube collectors, available in a full range of sizes. Nu-Heat designers will advise on the correct system configuration to fully achieve optimum efficiency for domestic hot water, underfloor heating or both, depending on project requirements.


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

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 is open-flow systems that 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, (i.e. 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.

Homeowners must also understand how the 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