Underfloor heating vs radiators: an honest comparison

The physics that drives everything

A radiator is a small, hot surface – a square metre or two at a high temperature. Underfloor heating is a very large warm one – the whole floor, at a temperature you can comfortably stand on.

Because output depends on both area and temperature, a much larger area can deliver the same heat at a much lower temperature. That single fact drives every difference between them.

Where underfloor clearly wins

• New build and extensions, where the floor is being constructed anyway and the additional cost over radiators is modest.
• Full renovations where the floor is coming up regardless.
• Heat pump installations, where the low flow temperature is exactly what the heat pump wants.
• Rooms where wall space is precious – kitchens with units on every wall, bathrooms, small rooms.
• Large open-plan spaces, where sizing radiators to heat a big volume evenly is difficult.
• Hard floor finishes – tile, stone, polished concrete – which conduct well and are otherwise cold underfoot.
• Properties heated continuously, where slow response is not a disadvantage.
• Where comfort is the priority. The even temperature profile is genuinely better and people who have lived with it rarely want to go back.

Where radiators clearly win

• Retrofit into an unaltered house, where lifting floors is the whole cost.
• Intermittently occupied rooms, where you want heat quickly – a spare bedroom, a home office used two days a week.
• Properties heated intermittently, because thermal mass works against you if you want heat now and none later.
• Thick carpet and heavy underlay, which substantially reduces underfloor output and can defeat it entirely.
• Buildings with limited floor build-up height, where raising the floor affects doors, thresholds and stair bottoms.
• Budget-constrained projects, where the difference is substantial.
• Listed and period interiors, where lifting original floors is not acceptable.
• Where flexibility matters. Moving or adding a radiator is straightforward; altering underfloor heating is not.

Response time, which is the practical difference

This is the thing people notice most after moving to underfloor heating, and it is worth understanding before rather than after.

A screed floor holds a great deal of heat. Once warm, it stays warm for hours; once cool, it takes hours to warm up. That means:

1. Timer schedules designed for radiators do not work. Switching on at seven and off at nine leaves the floor still warming when it turns off, then still emitting for hours afterwards.
2. Underfloor should be run steadily, ideally with weather compensation adjusting the flow temperature to the outside conditions, holding the house at temperature rather than chasing it.
3. Setback should be modest – a degree or two overnight, not a full shutdown.
4. It is forgiving of a mild day and unforgiving of a sudden cold snap, because it cannot respond quickly.
5. Low-profile and overlay systems respond faster than screed, because there is less mass. That is an argument for them in retrofit beyond just the build-up height.

For a household that is out all day and wants the house warm at six, radiators – or a hybrid – frequently suit better. For a household that is in most of the time, or a well-insulated house that holds its heat, steady underfloor running is both comfortable and efficient.

The hybrid answer, which is common and sensible

A great many British houses end up with underfloor downstairs and radiators upstairs, and that is not a compromise – it is frequently the right answer.

• Downstairs typically has hard floors, open-plan spaces, and continuous occupancy. Underfloor suits it.
• Upstairs has carpets, bedrooms used intermittently, and the heat rising from below anyway. Radiators suit it, and bedrooms benefit from being able to be cooler.
• The systems need separate control, because they want completely different flow temperatures. A mixing manifold blends the radiator flow temperature down for the floor.
• A towel rail in the bathroom alongside underfloor is normal – the floor heats the room, the rail dries towels.

The mistake to avoid is running both from one flow temperature. Either the radiators are inefficient because the temperature is too low for them, or the floor is uncomfortably hot. Separate control is not optional in a hybrid system – see underfloor heating.

Cost, honestly

We do not publish figures – see what things cost – but the relative picture is worth setting out.

The honest conclusion for a lot of unaltered Norfolk housing: retrofitting wet underfloor heating rarely justifies itself against simply fitting larger radiators and running the system at a lower flow temperature, which achieves most of the efficiency benefit for a fraction of the disruption.