A guide to underfloor heating in old homes

Discreet, effective and comfortable underfoot, warm water pipes and electric mats hidden beneath the floor can be an ideal solution for period properties. Roger Hunt offers a guide to the different systems

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Underfloor heating could be the best possible solution in an old house. Hidden away beneath the surface of the floor, it is energy efficient and unobtrusive, so does not upset the interior aesthetics and allows furniture to be arranged at will. Because it has to be laid into the fabric of the floor, however, its installation is invasive, so it is not a suitable option where historic floors would be damaged or the house’s foundations undermined.

Both electric and wet (hydronic) underfloor heating systems are available and are suitable for most types of floor construction. They distribute predominantly radiant heat evenly across the floor, which produces gentle, constant warmth without the draughts that result from the convection currents associated with radiators or open fires.

Related articles: The ultimate guide to heating your home | The beginner’s guide to central heating

Underfloor heating tips

  • Underfloor heating works best with a programmable thermostat, automating downtime and imporoving energy efficiency.
  • Check that the floor covering is compatible with UFH, especially if it is wooden.
  • Choose a system that has an insurance-backed warranty of at least 10 years. Controls tend to carry a two to five year warranty, and pipes, a 50-year manufacturer’s warranty.
  • Remember that concrete floors and damp-proof membranes may upset the equilibrium of the structure, causing damp problems.
  • Don’t undermine the foundations of the building when excavating a floor to install UFH, and beware of vibrations that may cause damage when drilling out an old concrete slab.
  • Get a full room heat loss calculation from the manufacturer or installer, to help you decide exactly what system you require.

Manufacturers of both electric and wet systems offer options for either solid or suspended timber flooring. The heat output achieved when underfloor heating is installed into suspended timber floors is likely to be lower than with solid floors. To work effectively and save on long term running costs, it must be installed above a sufficiently thick layer of insulation for the heat to be directed upwards.

Electric underfloor heating

Electric UFH is easy to install, requires little maintenance and is ideal for occasional use over smaller areas. A continuous cable is employed, either laid into the floor or on the surface as a mat.

Where full-room heating is required, cables laid into the floor are the best solution. These are generally fixed to the insulation layer within the floor and then a screed laid over before the final floor finish is applied. Cables are also suitable for suspended timber floors.

Left: This wide board Oak Classic engineered flooring from Junckers is suitable for use over UFH; it costs from £84 per sq m; Right: Electric UFH is ideal for rooms where you don’t want radiators, such as the kitchen. Pictured is the easy-to-install Heat Mat

For small areas, such as bathrooms or where the chill needs to be taken off cold floors, electric heating mats are a good solution. They are laid directly over existing floors below the final floor covering. The great advantage of mats is that they are generally only about 4mm thick and therefore do not have much impact on the height of the finished floor. Mats are useful where “instant” heat is required, as they tend to offer the advantage of a much shorter reaction time than UFH systems set into a screed.

When buying heating cables or mats, check that the system you buy is the correct size, as UFH cables cannot be cut down to fit. The system must also have the correct rating depending on the floor covering and heating level required.

Water system underfloor heating

Wet underfloor heating systems circulate heated water through loops of pipe laid into the screed of solid floors, or between the joists of suspended timber floors. Each loop of pipe is connected, via a manifold, to a boiler, heat pump or other source of hot water. It is worth remembering that these units take up space, require regular maintenance and involve an added capital cost.

Left: UFH pipes can be run through and between the joists of suspended timber floors where access is available, such as via a cellar; Right: A manifold is used to control the flow of water through the UFH system

When installing wet underfloor heating systems into suspended timber floors in older buildings, particular thought must be given to the harm that might be done to the historic fabric. To fit the pipes will require floorboards to be lifted or ceilings to be removed, both of which can be destructive and may require consent in a listed building.

Systems can be installed into a suspended floor in a number of ways. To achieve maximum performance, the pipes are laid on to insulated boards fixed between the joists and are then embedded in a sand-and-cement screed, which is poured over them.

Make sure floors can breathe

Modern concrete floor slabs installed into old buildings frequently cause damp. An alternative, breathable option is Limecrete. This works particularly well with underfloor heating and includes a compatible layer of insulation. The pipes or cables are laid on to the Limecrete slab using stainless steel or plastic mesh, clip rails or mechanical fixings – avoid plastic tray or other systems that cover the entire floor and would trap moisture. The pipes or cables are then covered with a vapour-permeable screed and an appropriate floor covering laid over the top.