Installing underfloor heating into an existing home need not be disruptive or expensive, says Natasha Brinsmead.
Which Floor Type are You?
The type of floor you have, and are planning to fit your new underfloor heating (UFH) pipes into, will have an effect on how disruptive the job will be. In new builds, pipes are usually fitted into screed floors which are being laid at the time anyway. But in old homes, unless you were planning on taking up the whole floor and starting again, the options are different. If you can add to your floor height without it causing too much of a problem – existing skirting boards will have to be removed and it will affect your doors, too, which may need to be re-hung to open smoothly over the new floor, or have some of their height taken off – it is generally best to lay a floating floor over your existing floor structure to accommodate the new UFH tubes.
Screed/Solid Floor: Screed floors are generally specified in new build homes and are sometimes not recommended in renovations, as they give a floor build-up of around 150mm — plus having them prepared and poured is more trouble than using an existing floor. However, if you are creating an extension or removing floors anyway, screed floors are a good option.
Suspended Timber Floor: If you are working with a suspended timber floor, and do not want to add to your floor height by adding a floating floor on top to conceal the underfloor heating, it will have to be removed and the tubes laid underneath, usually between joists on top of insulation, in order to lay the underfloor heating. Some systems can also be installed from below.
Floating Floor: A floating floor is the best type for retro-fitting underfloor heating, being easy to install and not adding much to the overall floor height. With a floating floor, additional insulation is added over the existing flooring to meet Building Regulations. Some companies such as Nu-Heat, for example, supply a heat-diffuser plate which is attached to a high- density polystyrene base layer that can be laid directly on the existing floor. Once a panel with diffuser plate is laid and the floor heating tube pressed in, chipboard or the final timber floor can be laid.
Which System to Choose?
There are now a number of companies offering systems specifically for retrofit situations. These are designed to be fitted with minimum disruption and to raise the existing floor height as little as possible, usually around 30mm. Take a look at Nu-Heat’s systems for floating floors and its LH14. Also Nu-Heat’s ONEZONE® is an underfloor heating pack which has been designed to integrate with existing radiator systems and to provide underfloor heating in single rooms, extensions and conservatories. Floor areas of up to 60m2 can be controlled by a single programmable thermostat, and packs start from £515. It can be installed on a DIY basis, too. Other systems designed for retrofit situations include Ippec’s Pexatherm thin system, the Schlüter-BEKOTEC-THERM, Polypipe’s OverlayTM Lite and Robbens Systems’ Single Room Underfloor Heating Pack, which is great for extensions. You should also take a look at systems from Warmafloor.
Upgrading Your Existing Heating System
Whilst you can connect a single zone of underfloor heating (UFH) to your existing heating system, this does not offer as much control over your heating — it will mean the UFH can only be on when the rest of the central heating is on. As UFH takes longer to warm up than radiators, the area with UFH will stay cold whilst the rest of the house warms up. In retrofit situations, UFH will ideally operate on a separate zone system with direct boiler control. One way of doing this is to ‘tee-off’ from your boiler primaries so that one set of flow and return goes towards your radiators whilst the other goes to your UFH system. Alternatively, systems such as ONEZONE® from Nu-Heat (0800 731 1976) can be individually controlled and can call for heat independently from the boiler.
Electric underfloor heating – also known as a dry system – was previously the first option renovators wishing to install underfloor heating thought of. Electric systems come in a number of forms. Some consist of a series of loose-fit flexible wiring which is ideal for small or awkward spaces, whilst others are made up of heating mats which can be rolled out to cover larger areas. The flexible wiring systems are a great idea if you are creating a new en suite or refurbishing a bathroom, for example. Electric systems are cheaper to buy and install than wet systems. Prices for roll-out mats start from around £75/m2, whilst loose-fit kits can be bought for around £100/m2. However, from a longer-term point of view, the systems are more expensive to run and are not recommended by the Energy Saving Trust for heating large areas.
You should run your underfloor heating on a separate heating zone system to your radiators, which will heat up far quicker than underfloor heating.
Insulation: you’ll need to insulate below the underfloor heating pipes in order to ensure the heat rises up rather than falls into the subfloor. aim for a minimum 100mm mineral wool over heavy-duty foil stapled to joists, or 100mm of rigid pur or pir insulation board (e.g. celotex).