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Cross-market term

Underfloor heating

Heating delivered through the floor surface rather than from an emitter on the wall. Runs at a much lower temperature than a radiator because the emitting area is the whole room.
  • 4Markets
  • NoSame thing everywhere
  • 3Calculators

What it is called, by market

One concept, four markets. Where a name means something else locally, the card says so rather than leaving you to find out on site.

  • United Kingdom

    Close, not identical

    underfloor heating

    also UFH, wet underfloor, electric underfloor, manifold

    Usually WET — a pipe circuit fed from a manifold and mixed down from the boiler flow temperature. Electric mats exist and are normally a single-room retrofit rather than a whole-house system.

  • Australia

    Close, not identical

    in-slab heating

    also hydronic floor heating, underfloor heating, slab heating

    In-slab names where it sits, and the thermal mass of a heated slab is the defining design issue in a climate with large day-night swings.

  • United Statesyours

    Same word, different thing

    radiant floor

    also radiant heat, hydronic radiant, electric radiant, PEX

    RADIANT is the standard word and is partly a misnomer — a heated floor delivers a large share by convection. Electric radiant under a bathroom tile is far more common than a whole-house hydronic system.

  • Canada

    Close, not identical

    radiant floor

    also in-floor heating, hydronic radiant, PEX

    As the United States, with hydronic whole-house systems more common given the heating season.

The governing standard, by market

  • United Kingdom

    BS EN 1264 / BS 8204-1

    Water-based surface embedded heating: design, installation and heat output, and screeds receiving floor heating.

  • United States

    ASHRAE Handbook — HVAC Systems / RPA guidelines

    Panel heating and cooling design, and radiant panel installation practice.

Calculators for this

Each works in either measurement system, and the terminology on the page follows whichever market you have selected.

Radiant Floor PEX Tubing Calculator →Heated Screed Volume Calculator →Radiant Floor Heating Cable Spacing Calculator →

Frequently asked questions

Why does underfloor heating run so much cooler than a radiator?
Because the emitting area is the entire floor rather than a panel on a wall, so the same heat output needs a far smaller temperature difference. A radiator might run at 60 or 70 degrees; a floor runs at 35 to 45 in the pipe and its SURFACE is limited to around 27 to 29 degrees in an occupied room — not by the equipment but by comfort, because a floor warmer than that is unpleasant to stand on and causes complaints. That low flow temperature is also why underfloor heating pairs so well with a heat pump: a heat pump's efficiency falls steeply as its output temperature rises, and a system asking for 40 degrees rather than 70 is asking for its best operating point. It is the single strongest argument for the technology beyond comfort.
Why does it respond so slowly, and what follows from that?
Because the floor is a large mass that has to be warmed before the room feels it, and cooled before the room stops feeling it. A screed-embedded system can take hours to respond and continues emitting for hours after it is switched off — which makes the room-thermostat behaviour people are used to actively wrong. Turning it down at night and up in the morning means the floor is cold when the house is occupied and warm when it is not. The correct control strategy is a flatter one: leave it running and let weather compensation adjust the flow temperature, or set back by a small amount rather than switching off. A thin electric mat under a tile is at the other extreme, responding in minutes, which is why the same control advice does not apply to both.
What does it do to the floor covering above it?
It constrains it, and this is the part most often discovered too late. Every covering has a maximum surface temperature and a thermal resistance, and a covering that insulates well throttles the whole system: a thick carpet with underlay can halve the output of the floor beneath it, so the system either cannot meet the heat loss or has to run hotter than it should. Timber and engineered boards have a maximum permitted surface temperature and a moisture content they must arrive at, because a heated floor dries them further and they shrink. Tile and stone are the natural partners — low resistance, high tolerance — which is why they dominate. The screed's own commissioning matters too: it has to be brought up to temperature gradually over days before a covering goes down, and doing that after the tiles are laid cracks them.