Underfloor heating under wood and stone: temperatures, commissioning, which floors suit

At a glance

Sources: a UK timber floor maker, a UK distributor, NWFA and the Tile Association (dates below). Other makers differ; the maker's instructions prevail.

The build-up: what sits where

A water-fed system in a screed is the usual arrangement under a wood or stone floor: slab, insulation, a screed that holds the pipes, then a primer or damp-proof membrane, a flexible adhesive and the finish. A floor probe sits in the build-up and cuts the heat if the surface climbs. Electric systems exist; one maker says to choose one with a cut-off that holds the surface to 27 °C, and the documents give system-specific rules that this sheet does not repeat.

How hot the floor can get

Three kinds of number get called ‘the maximum floor temperature’, and they are not the same thing.

• The comfort limit. The Tile Association's paper, drafted with support from the Underfloor Heating Manufacturers Association, tabulates the BS EN 1264 maximum floor surface temperatures: 29 °C in an occupied area with a 20 °C room (a heat emission of 100 W/m²), 35 °C in a peripheral area (175 W/m²) and 33 °C in a bathroom or similar with a 24 °C room (100 W/m²). An underfloor heating maker's training page gives the same occupied-area figure as 9 K above room temperature. We have not read the standard, and the two sources differ on bathrooms (see the unverified list).
• The timber maker's limit. A UK timber floor maker's guide (28 March 2024) says the system ‘must not generate temperatures above 27 °C in the timber floor surface’ and recommends probes in the build-up of each room or zone. A UK flooring distributor's installation guidelines (parquet, January 2024; engineered plank, 2024; end-grain, November 2022) give the same figure for each, with probes tied to a thermostat for each zone. 27 °C is 2 K under the occupied-area figure.
• A US association's limit. The National Wood Flooring Association's Appendix H (revised February 2016) gives 85 °F, 29.44 °C, as the maximum subfloor surface temperature for each method it lists. That is a subfloor figure, a different measuring point, and not a UK timber maker's number.

Two lower limits follow. The floor limit sets the heat output: the maker's training page gives about 10 W/m² for each degree the floor is warmer than the air, so a 27 °C surface in a 20 °C room is about 75 W/m² and in a 22 °C room about 50 W/m². And where the limit is measured matters: the same page says some timber makers apply the 27 °C to the underside of the floor, and that for a 14 mm, 1 tog board that cuts the output to about 35 W/m² in a 20 °C room. Ask the maker where its 27 °C is taken.

The water is limited as well. The timber maker's guide says the flow temperature at the manifold should generally not exceed 40 °C for a system embedded in a screed, or 35 °C for pipes in overlay panels or under a suspended deck, and that flows above 45 °C are normally not appropriate under timber. The Tile Association gives a maximum operating water temperature of 45 °C for calcium sulphate screeds. The heating engineer sets the real figure from the whole build-up.

Commissioning: four documents, four sequences

Heating a new screed does two jobs: it proves the system, and it takes moisture out of the screed before a floor that reacts to moisture goes on top. The documents agree that the heating should be commissioned and run before the floor is laid, and that the process should be recorded. They do not agree on the steps. The table sets four documents side by side, as written. None is a programme to copy: the system maker's own steps and the floor maker's instructions prevail, and BS EN 1264-4 (installation) is where the formal clauses sit. Its 2021 contents list ‘initial heating up of the emission system’ (4.2.4), ‘heating up for readiness for covering’ (4.2.5) and an informative heating-up protocol (Annex B). We could not read the text.

Water temperatures and floor temperatures are not the same quantity. The Tile Association and the timber maker give water-side figures; the distributor and the US association give floor-side ones. A specification should say which it means.

Which floors suit, and why

The table at the top of the page sets out what each document asks of each floor. Three points sit behind it.

Timber moves with moisture, and heat dries it. That is why the documents favour engineered boards, narrow boards and quarter-sawn faces, and why they ask for the floor to be bonded and the screed to be dry: the maker's guide says the commonest problems are moisture rising from the substrate and excess heat. Our guide to wood flooring over underfloor heating covers the reasoning, and solid vs engineered wood flooring draws the movement. Pipes or cables should not touch the back of the board. The maker asks for a layer of at least 6 mm (plywood, particleboard, dry-screed board or levelling compound) between pipes in overlay panels and the floor, so the heat spreads evenly and hot spots do not form.

Stone passes heat easily but does not give. The Tile Association's table of thermal resistances lists 25 mm marble at 0.05 m²K/W, against 0.10 for 13 mm hardwood on an 8 mm underlay and 0.15 for wood blocks. The paper says stone is rigid and will not deform sideways when it is bonded to a heated screed, so movement joints are more important than under a soft covering.

Tile Association, Table 4, itself taken from an underfloor heating design guide. Values are rounded and indicative: ask the maker for the figure for the actual board and the heating engineer for the output. One tog is 0.1 m²K/W.

A thermal resistance limit is often quoted as 0.15 m²K/W. We could not confirm that figure as a limit. The contents of BS EN 1264-2:2021 show its output curves are stated for a reference covering of 0.15 m²K/W (‘R;B = 0,15’), which makes 0.15 the standard's reference value, not necessarily a maximum. Treat it as a question for the heating engineer: what resistance has the heat output been designed for, and does the chosen board and any underlay fit inside it?

Stone over heating: joints, adhesive and drying

The Tile Association gives these provisions for ceramic and natural stone floors over heated screeds. They are the practical difference from a timber floor.

• Perimeter. A compressible strip round the edge and round columns, kerbs and steps, allowing at least 6 mm of screed movement.
• Bays. Intermediate movement joints so that no bay exceeds 40 m² for ceramic and natural stone (25 m² for resin-agglomerated tiles), square to rectangular, no longer than 8 by 5 m.
• Other joints. Over structural joints, at doorway thresholds, at junctions of heated and unheated screed, between zones on separate controls, and at significant changes of width. A joint across heating pipes needs the pipes sleeved.
• Adhesive. Flexible, and the stone fixed in a solid bed with no voids. The paper asks for deformable adhesive to BS EN 12002 class S1 or S2 over comfort-heated timber bases, and describes a sand and cement bed for natural stone where flatness or thickness varies.
• Drying. For marble, agglomerated stone, limestone or travertine on a cement and sand screed, the paper asks for an extended drying time to reach no more than 75% relative humidity at 20 °C in the screed.

The paper adds that the expansion of the finish should not be too different from the base. Its sample indicative values, in millionths per degree Celsius, are: marble 3.5 to 7, slate 3 to 9, granite and basalt 6 to 9, limestone and dolomite 6 to 10, sandstone 11 to 12 and quartzite 11 to 13, against 11 to 13 for a cement and sand screed and 10 to 12 for a calcium sulphate screed. The movement is small for one slab (a 600 mm slab at 10 millionths per degree warming by 10 degrees grows 0.06 mm, our arithmetic) but it builds up across a bay if the slab is restrained, which is what the joints are for. Travertine and onyx are not in the paper's list. See also natural stone finishes and types of natural stone.

What to ask the heating contractor for

Most heated-floor failures turn on a gap between the heating contractor, the screeder and the floor contractor. Say in the specification who does each step, and ask for the records before the floor is delivered. The list is our suggestion, built from what the documents ask for.

• The system type, the screed type and thickness, and the dates the screed was laid.
• The pressure test report.
• The heat-up record: dates, temperatures and durations at each step, and the last day of running.
• The screed moisture readings taken after commissioning (the test and limit are in the subfloor requirements sheet).
• The maximum floor surface temperature the system will allow, where the probes are and what they are set to.
• Written approval from the floor maker, or the stone workshop, for the build-up and the heating system.
• The restart steps after fitting, and a note for the end user to raise the heat gradually after any period when it has been off.

The floor surface should be protected during the work, and one distributor adds: never have the heating on while the floor is protected. For the wider site conditions see timber floor acclimatisation and site conditions.

Floor surface not to exceed [27] °C at any point, limited by floor probes in [each room or zone]. Flow temperature not above [40] °C. Heating contractor to pressure test (report issued), then commission and run the system before the floor is delivered, to [BS EN 1264-4 / the system maker's protocol]: up by no more than [5] °C a day to [the maximum operating water temperature, [ ] °C], held [3] days, then cooled. Record and issue the dates, temperatures and durations with the screed moisture readings.

[Engineered oak, [ ] mm], fully bonded with a flexible adhesive the maker approves for underfloor heating; maker to confirm in writing that floor, build-up and heating are approved together. Heating off during fitting and for [48] hours after, then up by no more than [2] °C in each 24 hours.

Stone [type, [20] mm, [600 x 600] mm] in a solid bed with a flexible adhesive [BS EN 12004; BS EN 12002 class [S1]] over a screed at no more than [75]% RH at 20 °C. Perimeter strip allowing [6] mm. Movement joints: bays no larger than [40] m² and no longer than [8 x 5] m, and at structural joints, thresholds and heating zone edges. Heating off for fixing; commission [7 / 14] days after fixing, then as the system maker's manual.

Standards and sources

• The Tile Association, Tiling to Heated Floors (2013, updated 16 July 2014): read in full 5 Nov 2026.
• BS EN 1264 (parts 1 to 5), BS 8201:2011, BS 8204, BS EN 12002 and 12004, BS 5385-4: named by the documents read; paywalled and not read (only the contents of EN 1264-2 and -4, 2021, were seen). Confirm against the current editions.
• A UK timber floor maker's guide (28 March 2024); a UK flooring distributor's guidelines (2022 to 2024); an underfloor heating maker's training page (undated): read 5 Nov 2026; not named. The distributor is not an independent trade body.
• National Wood Flooring Association, Installation Guidelines, Appendix H (rev. 2016): read 5 Nov 2026; US figures.

Questions we are asked

What is the maximum floor temperature for wood over underfloor heating?

UK timber floor makers and one flooring distributor quote 27 °C at the floor surface, held by probes in the build-up. BS EN 1264, as the Tile Association tabulates it, allows 29 °C in occupied areas, so the makers' figure is stricter. Ask the maker where its 27 °C is measured and use its own instructions.

Can solid wood go over underfloor heating?

Only where the maker approves it. One UK maker says its solid timber floors are not suitable unless specified otherwise, and the US association says engineered boards are more stable, with narrow and quarter-sawn boards moving least. Engineered, fully bonded floors are the usual choice.

How long must underfloor heating run before the floor goes down?

The documents differ. One distributor asks for a full cycle to 27 °C left running for 2 weeks; one maker asks for a heat-up over several days, 5 days of running and a cool-down; the Tile Association describes about a week of conditioning for a cement screed, with 3 days at the maximum. Ask the heating engineer and the floor maker, and write the one you want into the specification.

Is stone a good floor over underfloor heating?

Yes, in the sense that it passes heat easily: the Tile Association lists 25 mm marble at 0.05 m²K/W. But stone is rigid, so the floor needs a perimeter strip, bays of no more than 40 m² and a flexible adhesive, and marble, limestone and travertine need a drier screed.

Can herringbone or chevron go over underfloor heating?

Yes, bonded. One maker asks for chevron, Versailles and other parquet patterns to be bonded whatever the joint, and a distributor asks for parquet fully bonded. Click-joint herringbone may be floated or bonded on one maker's say-so. Get the choice approved in writing.

When can the heating be switched on after the floor is laid?

Not at once. One maker keeps the heating off at least 48 hours after a timber floor is fitted, then raises it by no more than 2 °C in each 24 hours. The Tile Association says commissioning after tiling is 7 days for rapid-setting adhesive and 14 for normal-setting, then as the system maker's manual says.

What thermal resistance can the floor have?

It depends on the heating design. Marble 25 mm is listed at 0.05 m²K/W and wood blocks at 0.15 in the Tile Association's table. The figure 0.15 is the reference covering in the contents of BS EN 1264-2:2021, but we could not confirm it as a maximum, so ask the heating engineer.