Underfloor heating in open-plan living spaces and rooms with feature fireplaces or glazing

Open-plan rooms are where underfloor heating earns its keep. A kitchen-diner with an island, a sofa area and a wall of glass has no good place for radiators, and radiators in one corner leave the far end cool. A heated floor spreads warmth across the whole space and keeps the walls and the view clear.

It still needs design. One large room can lose a lot of heat through glazing, gain a lot from the sun or a wood burner, and hold areas that want different temperatures. This guide covers how to zone an open-plan space, how to handle bifolds and floor-to-ceiling glass, how to work around kitchens and fireplaces, and where to put the thermostats. To check the floor can meet the room's heat loss, use our guide to heat loss and UFH output.

Is underfloor heating good for open-plan living?

Yes. It heats from the whole floor area, so the temperature is even across a large room, and it needs no wall space. That is why it is a common choice for kitchen-diners and extensions with large glazing.

The limit is output. BS EN 1264 caps the floor surface at 29°C in areas where people sit and stand, which gives about 100W/m² in a 20°C room. In most modern open-plan rooms that is plenty. If a room has very high heat loss, the floor may not cover it all, and you need more insulation, better glazing or extra heat near the glass.

Area	Max floor surface	Approx max output
Occupied area	29°C	100W/m²
Edge zone by glazing, up to 1m wide	35°C	175W/m²
Under tiles (industry guidance)	27°C	Lower

How should you zone an open-plan room?

Zone by use and by heat gain. Kitchen, dining and living areas are often used at different times and want different temperatures, and a sunny glazed end behaves differently from a shaded one.

• One loop does not cover a big room. Keep each 16mm loop to about 100m. A 50m² space at 150mm centres needs about 335m of pipe in the floor, so four loops or more.
• Loops can share a zone. Two or three loops in the living area can all open together from one thermostat, through a wiring centre.
• Separate the kitchen. Cooking, appliances and people add heat, so the kitchen end often needs less.
• Separate a sunroom or glazed end where solar gain can overheat it on a bright day.

Part L normally asks for thermostatic control in each room. It allows one zone where a single-storey open-plan home has a living area of more than 70% of the floor area, or where two adjacent rooms have a similar use and heating need. Even where one zone is allowed, more zones usually give better comfort. Our guide to how many manifold ports you need shows how loops and zones add up, and UFH zoning and wiring covers the controls. The Heatmiser UH8 wiring centre handles up to 8 zones.

How do you heat an open-plan room with bifolds or floor-to-ceiling glass?

Lay a perimeter band of tighter pipe along the glazing, start the loop there so the warmest water reaches it first, and check whether the glass is tall enough to need extra heat.

1. Mark the cold edges: bifolds, sliding doors, glazed gables and roof glazing.
2. Lay a band up to 1m deep at closer centres, such as 100mm, where BS EN 1264 allows the floor surface to reach 35°C.
3. Run the rest of the zone at 150mm in the same loop.
4. Keep the loop within length, because the band adds pipe.

Very tall glass is harder. Cold glass cools the air next to it, which sinks and runs across the floor as a cold draught. Research on large glazed facades found that triple glazing with a U-value of about 1.0 W/m²K prevents draught discomfort for windows up to normal room height, while older double glazing at about 3.0 W/m²K caused it for a good part of the winter, more so for windows over 1m tall. For glazing taller than normal room height, the glass alone cannot prevent it, and an active measure near the glass, such as a convector or trench heater, is the usual answer. The research did not test floor heating, so do not rely on a floor band alone for a double-height glazed gable.

Our guide to UFH pipe centres shows how much pipe a band adds.

Can you have underfloor heating with a wood burner or fireplace?

Yes, but leave the hearth out of the pipe layout, and plan for the extra heat the stove gives. A wood burner can heat its end of an open-plan room well past the thermostat setting.

• Hearth: a stove that can heat the floor beneath it above 100°C needs a constructional hearth at least 125mm thick, usually masonry or concrete. A stove tested not to do so can sit on a non-combustible sheet hearth at least 12mm thick. Either way, the hearth is not a place for UFH pipe.
• Hearth zone: for a closed stove or open fire, keep combustible finishes back at least 150mm at the sides and rear and 225mm at the front.
• Zone it separately: put the stove end on its own zone so the floor there can turn down when the fire is lit.
• Thermostat: do not fit a room thermostat near the stove, or the rest of the room will go cold while the fire is burning.

Check the stove maker's instructions and Approved Document J with your HETAS installer before you finalise the floor layout.

Should underfloor heating go under kitchen units and islands?

Generally not under fixed units. Heat under cabinets is trapped and wasted, and it can warm food in base units. Keep pipe away from fridges, freezers and other large appliances too, which have to work harder over a heated floor.

• Heat the open floor where people stand, in front of worktops, around the island and in the dining area.
• Leave the island footprint and fixed runs of units out of the loops, unless the units stand on legs.
• Do not screw fixed units down through the floor finish into the pipe zone.
• Count only the free floor when you size the system.

Where should the thermostat go in an open-plan room?

On an inside wall, at about 1.5m high, with free air around it, in the zone it controls. Keep it out of direct sun, away from the stove, cooker or TV, and away from doors that let in cold draughts.

• Avoid spots behind curtains or furniture, corners, and walls with cold air leaking behind them.
• Use a wireless sensor where there is no good wall. The Heatmiser wireless air sensor can sit where the room is used.
• Add a floor probe under tiles or wood, so the floor stays within its surface limit. A 10K floor probe comes with a 3m lead.

See floor probes and air sensing for how to set the limits.

Which floor finish is best for open-plan UFH?

Tiles and stone give the most heat, then thin wood, LVT and laminate. Carpet gives the least. Many open-plan spaces mix tiles in the kitchen with wood or carpet in the living area, and each finish changes the output.

BS EN 1264 design assumes a floor covering of about 0.10 m²K/W in living rooms, which is 1 tog. Higher values need agreeing at design stage. If the living end will be carpeted, design that zone for it rather than for the tiles. Our guide to UFH floor coverings compares them.

Frequently asked questions

Can one thermostat control a whole open-plan room?

It can, and Part L allows one zone in some open-plan layouts. Separate zones for kitchen, dining and living usually give better comfort, because each area gains and loses heat differently.

Does underfloor heating stop condensation on bifold doors?

It helps keep the floor and air near the glass warm, but condensation also depends on the glazing and the humidity. Good ventilation and low U-value glazing matter more.

How many UFH loops does a large kitchen-diner need?

About one loop per 13 to 14m² of free floor at 150mm centres, keeping each 16mm loop to 100m. A 50m² heated area needs four or more.

Can I put underfloor heating under a kitchen island?

Leave fixed islands out of the loop layout. Heat under a fixed island is trapped. Islands on legs can have pipe under them.

Is UFH enough for a room with a glazed gable?

Often not on its own. For glass taller than normal room height, research shows an active heater near the glass is usually needed to stop cold draughts.

Do I need a separate zone for the wood burner area?

It helps. A separate zone lets the floor near the stove turn down when the fire is lit, while the rest of the room stays warm.

Can open-plan UFH run from a heat pump?

Yes, and it suits it well, because a large floor area gives the heat out at a low water temperature. See UFH with a heat pump.

Sources: Approved Document L Volume 1 (paras 5.20 and 5.21), Aalborg University: measures to avoid downdraught from large glazed facades, HETAS answers your hearth questions (Professional Builder), Homebuilding & Renovating: UFH under kitchen cabinets, Ideal Home: where not to fit UFH, BEAMA: room thermostat siting, PBC Today: UFH in floor screeds (27°C under tiles), and manufacturers' installation guidance to BS EN 1264