Underfloor heating in a barn conversion

Barns are tall, open and full of character: exposed trusses, big cart-door openings and long runs of wall with no natural place for a radiator. Planners often want those features kept, and that makes radiators awkward. Underfloor heating hides the heating in the floor and leaves the building's structure on show.

This guide explains why underfloor heating suits barns, how to deal with high ceilings and large glazing, which floor build-up to use, how to zone open-plan spaces, how to pair it with a heat pump, and what Building Regulations and grants to check. It applies to timber-framed, stone and brick barns.

Is underfloor heating good for a barn conversion?

Yes. It is the most common choice for barns, for practical and planning reasons. One council's design guidance for barn conversions puts it simply: "an underfloor heating system is less visually obtrusive," with low-level radiators at plinth level as the alternative.

• Exposed structure stays clear. Planning guidance often asks for internal framing to stay exposed and for large open volumes to be kept. Underfloor heating needs no wall space at all.
• Heat where people are. In a double-height space a radiator's warm air rises to the roof. A heated floor warms the people and surfaces at the bottom of the room first.
• Big, open rooms heat evenly. The whole floor gives out heat, so there is no hot wall and cold far end.
• Suits traditional floors. Stone, quarry tiles and reclaimed boards all work over underfloor heating, within their temperature limits.

Check your own council's conversion guidance and any listed building conditions. Our period and listed property guide covers consent issues.

Can underfloor heating cope with high ceilings and big glazing?

Yes, if it is designed for the heat loss. Underfloor heating's output is limited by floor surface temperature, not by the room height, so a tall space needs its fabric to be well insulated rather than more heating.

BS EN 1264 limits the floor surface to 29°C in occupied areas and 35°C in edge zones. Those edge zones are useful in barns: run the pipe closer, in a band along the big cart-door glazing and outside walls, so the floor there gives more heat and counters the cold glass.

Pipe centres	Output at 50°C mean water temperature	Typical use in a barn
100mm	91W/m²	Edge band by glazing; high heat loss rooms
150mm	Between the two	Most rooms
200mm	76W/m²	Well-insulated bedrooms

Figures are one maker's published outputs for a screeded system. Start with a room-by-room heat loss calculation, then choose the spacing. If a space still needs more heat than the floor can give, improve the glazing or insulation, or add a supplementary heat source. For more on glazing, see underfloor heating with open plans and glazing.

What floor build-up do I need in a barn conversion?

Usually a new insulated ground floor with the pipe in screed. Many barns have earth, brick or broken concrete floors with little or no insulation, so the floor is dug out and rebuilt anyway.

1. Sub-base and slab as specified by your designer or structural engineer.
2. Damp-proof membrane where the design calls for it.
3. Floor insulation to the U-value your building control body accepts. Approved Document L gives 0.18W/m²K for a new floor in an existing dwelling and 0.25W/m²K as the improved value for a renovated floor.
4. Edge insulation strip round every wall.
5. Pipe fixed with clip rail, tacker clips or castellated floor panels.
6. Screed: at least 65mm of sand and cement over the pipe for domestic use (BS 8204-1), or a liquid screed to the supplier's depth.
7. Floor finish: stone, tile, engineered wood or reclaimed boards.

The insulation under the pipe matters. BS EN 1264 expects enough insulation below the heating that downward heat loss does not exceed 10W/m². Use a 16mm oxygen barrier pipe such as our PERT-EVOH pipe, keep each loop to 100m or less, and keep the pipe under pressure (6 bar in one maker's guide) while the screed is laid. Do not use the heating to dry the screed. Our guide to screed depth and drying time has the detail.

If the barn has a timber upper floor or mezzanine, use a board or spreader plate system there, the same as any joisted timber floor.

Do barn conversions have to meet Building Regulations for heating?

Yes. Approved Document L has a section on material change of use and change to energy status, and your building control body will confirm which fabric standards apply to your conversion. For the heating system itself, the guidance in Approved Document L includes:

• Flow temperature. A new or fully replaced wet heating system should be designed to run at a maximum flow temperature of 55°C or lower. Underfloor heating meets this easily.
• Room controls. Each room should have thermostatic room controls. Zone control is allowed in some cases, including a single-storey open-plan dwelling where the living area is more than 70% of the floor area, which can be treated as one zone.

Open-plan barn layouts often fall between these cases, so agree the zoning with your building control body early.

How should I zone an open-plan barn?

Split the floor into zones by use, not by walls. A big open barn might have a kitchen, dining and living area under one roof, plus bedrooms and bathrooms off it.

• Large open space: several loops on one or two thermostats, so the whole area heats evenly.
• Bedrooms and bathrooms: a thermostat each, so they can run at different temperatures.
• Glazed edges: part of the same loop as the room, at closer centres.
• Two wings or two floors: often a manifold for each, which shortens the pipe runs back to the manifold.

Big barns can need many loops. An auto-balancing manifold (2 to 12 ports) makes balancing a large number of loops easier.

Should I use a heat pump with underfloor heating in a barn?

It is often the best match, especially where there is no mains gas. Underfloor heating gives a large heated area, so it can run at low flow temperatures, which is where heat pumps work most efficiently. See our guide to underfloor heating with a heat pump for flow temperatures and pump sets.

The Boiler Upgrade Scheme gives £7500 towards an air source or ground source heat pump, with an extra £1500 available until March 2027 for properties heated by oil or LPG with no mains gas connection. An MCS certified installer applies for the grant on your behalf. Check eligibility on GOV.UK before you commit.

On VAT: MaxHeatUFH charges 20% VAT on all products. HMRC's energy-saving materials relief gives 0% VAT until 31 March 2027, but only where a qualifying installer supplies and installs a qualifying measure, such as a heat pump, insulation or heating controls. Buying underfloor heating kit supply-only from a merchant, including MaxHeatUFH, includes 20% VAT. Check HMRC VAT Notice 708/6 for the current rules.

Frequently asked questions

Can I lay underfloor heating under a stone or flagstone floor?

Yes. Stone passes heat well. Lay it on the screed over the pipe, with an adhesive suitable for heated floors, and follow the stone supplier's guidance on movement joints.

Can I keep the original barn floor and still have underfloor heating?

Sometimes. Reclaimed boards or stone can be lifted, a new insulated floor with underfloor heating built, and the original finish relaid on top. Agree this with your conservation officer if the barn is listed.

How many loops will a barn conversion need?

It depends on the floor area, pipe spacing and room layout. Each 16mm loop should be no longer than 100m. ProLoop gives a quick estimate of circuits and manifold size for your rooms.

Is underfloor heating enough on its own in a barn?

In a well-insulated barn, usually yes. If the heat loss calculation shows a space needs more heat than the floor can give, improve the fabric first, then consider a supplementary heat source.

How long does a screed floor take to warm up in a barn?

Several hours from cold, because the screed is heavy. Barn screed floors are best run on a steady schedule, which also suits a heat pump.

Can I get a grant for underfloor heating in a barn?

There is no grant for the underfloor heating itself, but the Boiler Upgrade Scheme gives £7500 towards an air or ground source heat pump through an MCS certified installer.

Does MaxHeatUFH install barn conversion heating?

MaxHeatUFH supplies the kit and passes installs to vetted, approved installers. Ask for an installation quote through our website, or email sales@maxheatufh.com.

Sources: Reigate and Banstead Council: barn and farm conversions SPD, Approved Document L volume 1 (2021, 2023 amendments), GOV.UK: Boiler Upgrade Scheme, HMRC VAT Notice 708/6, and manufacturers' installation guidance to BS EN 1264