In many countries radiators have been the standard way to heat a home for generations, and underfloor heating was something you met in hotel bathrooms. Kitchen extensions, open-plan ground floors and heat pumps have since brought it into ordinary houses, and plenty of people renovating now have to choose between the two, or combine them.
Both systems do the same basic job: they take heat from hot water, or from an electric element, and pass it into a room. The difference lies in how much surface they use to do it, and that one fact explains almost everything else, from comfort and warm-up time to efficiency and running costs. The radiator cleaning and combi boiler care section has more on looking after a wet system once it is in.
How each one heats a room
Picture a bedroom with a single radiator under the window. The radiator is small and hot. Air touching it warms, rises up the wall, spreads across the ceiling, cools, sinks on the far side and drifts back across the floor to be heated again. That loop is convection, and it leaves the air near the ceiling warmer than the air at your ankles. A radiator gives off some radiant heat too, but most of its work is done by moving air.
Now picture the same room with underfloor heating. The whole floor becomes the emitter, and because the area is so large, the surface only needs to be a few degrees warmer than the room: warm to bare feet rather than hot. Heat leaves the floor mostly as radiant heat, warming people and furniture directly, with only a gentle upward drift of air. The temperature from floor to ceiling stays far more even, with no hot spot under the window and no cold corner by the door. As a bonus, every wall is free for furniture, shelving or glazing.
Wet and electric underfloor heating
Wet systems circulate warm water through loops of plastic pipe laid in the floor. Each loop runs back to a manifold, a row of valves usually in a cupboard, with its own pump and a mixing valve that blends the water down to a suitable temperature. Room thermostats open and close the loops through small electric actuators.
The pipes can be buried in screed, the classic new-build method, or laid in grooved insulation boards or aluminium spreader plates for lower-profile installations, including between the joists of timber floors.
Electric systems use thin heating mats, cables or foil elements under the floor finish. They are shallow, quick to fit and need no heating pipework, so they are mostly used for single rooms such as a bathroom or en-suite. Every unit of heat comes straight from a unit of electricity, which shapes running costs. The connection must be made by a qualified electrician, and bathroom wiring rules differ between countries.
Radiators: more variety than people expect
A steel panel radiator is described by its panels and layers of convector fins. A Type 11 has one panel and one set of fins, a Type 21 two panels and one set, and a Type 22 two panels and two sets. More panels and fins mean more heat from the same patch of wall, at the cost of depth.
Column radiators are the traditional look: vertical tubes in steel or cast iron. They hold more water and metal, so they heat up more slowly and keep giving off heat after the boiler stops; cast iron is also heavy, and the wall must carry it. Aluminium radiators sit at the other extreme, with low water content and a fast response.
One detail matters a great deal for this comparison. A radiator's quoted output is measured at a standard difference between the average water temperature inside it and the room's air temperature. Run the same radiator with cooler water and its output falls considerably, which is why a radiator sized for an old, hot system can feel inadequate when the water temperature is turned down.
Warm-up time and daily routine
A radiator heats a room in minutes, which suits rooms used for short periods and households that come and go at odd hours.
Underfloor heating in screed is slower, because the screed is a large thermal mass. From cold it can take hours to bring a room up to temperature, and it keeps releasing heat long after switching off, so the usual advice is to run it for long, steady periods with only a modest setback overnight. The same mass that makes it slow makes it steady. One known drawback: in a heavily glazed extension, a sunny afternoon can push a screed-heated room above comfortable, because the floor is still releasing stored heat.
Low-profile board systems respond faster, and electric mats under tile warm a bathroom floor relatively quickly, which is why they suit rooms used briefly in the morning.
Flow temperature, and why heat pumps prefer it low
Flow temperature is the temperature of the water leaving the boiler or heat pump. Older radiator systems were commonly designed to run hot, with flow temperatures in the 70s and up to around 80°C. Wet underfloor heating in screed typically runs somewhere in the 35–45°C range, because the floor area is so large.
This matters for two reasons. A heat pump becomes less efficient the hotter the water it has to produce, so a large emitter that works with cool water lets it run where it performs best. That is why the two are so often installed together.
Condensing gas boilers benefit too. They only condense, and so recover extra heat from their flue gases, when the water returning to them is cool enough, roughly below 55°C. A system running at lower temperatures lets them do that more of the time.
Radiators can work well with heat pumps, but they usually need to be larger than a hot boiler system would use. A room-by-room heat loss calculation shows which existing radiators are big enough.
Floor finishes and tog ratings
Whatever sits on top of underfloor heating either lets the heat through or holds it back. Stone and ceramic tiles conduct heat well and are the easiest partners. Engineered wood generally works within its manufacturer's limits, while solid timber moves more and needs more care. Laminate and vinyl are often suitable, but many carry a maximum surface temperature, so check before ordering.
Carpets and underlays are rated in tog, the same unit used for duvets: the higher the tog, the more insulating. A commonly quoted ceiling for carpet and underlay combined over underfloor heating is 2.5 tog. Thick foam or rubber underlays can use up most of that on their own, so choose one sold for use with underfloor heating. Large rugs, beds without legs and built-in furniture act as blankets too, which is why loops are normally left out from under fitted kitchen units.
Retrofit disruption
Swapping a radiator for a larger one is usually a day's work or less, sometimes with short pipe alterations to move the valves.
Fitting wet underfloor heating to an existing ground floor is a different scale of job. A screed system needs the old floor taken up, insulation laid so the heat goes up rather than into the ground, then pipes and screed, with drying time before any finish. Floor levels rise, which affects thresholds, skirting and kitchen plinths. Low-profile overlay systems add less height and far less disruption, though some give less output per square metre.
Upstairs timber floors can usually take pipes between the joists, from above with the boards up or from below with the ceiling down. Anything that involves notching or drilling joists is structural and should be designed by someone qualified to do so; building rules on this vary by country.
Electric mats are the least disruptive option and fit naturally into a bathroom refit. The bathroom renovation plumbing checklist covers the order of work if you are planning one.
Running costs: the logic rather than the numbers
Energy prices vary too much between countries, and over time, for a fixed figure to mean anything here. The logic holds anywhere.
First, a house needs a certain amount of heat to stay warm, set by how fast it loses heat through its walls, windows, roof and floor, not by the emitter. Underfloor heating does not change that, although many people find a warm-floored room comfortable at a slightly lower thermostat setting.
Second, the cost of each unit of heat depends on the heat source and its efficiency. Lower flow temperatures make heat pumps and condensing boilers more efficient, which favours large emitters, whether a heated floor or generously sized radiators.
Third, electric underfloor heating converts electricity to heat one for one. For a small bathroom used briefly each morning that may be modest. As the main heating for a whole house it is, in many countries, an expensive way to buy heat compared with a heat pump, which delivers several units of heat per unit of electricity.
Finally, insulation beneath a heated floor is not optional. Without it, a share of the heat goes into the ground or the ceiling below.
Maintenance compared
A wet underfloor system keeps its moving parts at the manifold: the pump, the mixing valve and the actuators. Actuators wear out eventually, and a single cold zone is the usual symptom; the head often just clips on and off, but the wiring centre behind it is electrical work. The buried pipes are very long-lived. The main risk is someone drilling through them later, so photograph the loops before the screed goes down.
Water quality still matters. Oxygen getting in, for instance through older plastic pipe made without an oxygen barrier, can produce sludge that slows the loops, so inhibitor and a filter protect underfloor heating just as they protect radiators.
Radiators need bleeding, occasional balancing, and attention to thermostatic valve pins that stick after a summer off. When sludge builds up they can be cleaned individually or as a system, as the guide to what radiator flushing involves explains.
Questions people ask
Can underfloor heating and radiators run on the same system?
Yes, and it is a common arrangement: underfloor heating downstairs, radiators upstairs. The underfloor circuit gets its own mixing valve so it receives cooler water, while the radiators take water at the boiler's flow temperature. With a heat pump, the whole system is usually designed around a single low flow temperature instead, with the radiators sized to suit.
Will underfloor heating heat a room on its own in winter?
Usually, in a reasonably insulated room. The limit is how much heat a floor can give off per square metre at a comfortable surface temperature, so heavily glazed or poorly insulated rooms may need a supplementary radiator. A heat loss calculation answers this before installation rather than in January.
What happens if an underfloor pipe leaks?
It is uncommon, because each loop is a continuous length with joints only at the manifold, and systems should be pressure tested before screeding. If a leak does happen, a technician can often find it without lifting the whole floor, typically with thermal imaging while the loop runs warm. Electronic leak detection describes the methods.
Selin Aydemir
Selin writes about central heating – combi boilers, radiators, underfloor loops and the small habits that keep a sealed system running quietly. She likes explaining why a fault happens before saying what to do about it.
General guidance only. Gas, electrical and structural work must be done by a suitably qualified person, and rules differ from country to country.
