Short answer: From cold, a screeded water underfloor heating floor typically takes 2 to 3 hours to warm up, and longer if the screed is thick or the room poorly insulated. Overlay systems on boards can respond in around 30 minutes, and electric systems in roughly 30 to 90 minutes depending on wattage. Don't switch a screed floor off and on like a radiator. Leave it running with a modest setback temperature overnight and when you're out, and let an optimum start thermostat decide when to bring it up. Heat pumps work best running steadily at a low flow temperature. Overlay and electric floors can be timed more like conventional heating.
Underfloor heating (UFH) feels different from radiators. A radiator gets very hot and heats the air quickly. A heated floor runs only a little warmer than the room, over a much bigger area, and it has to warm itself before it can warm the room. How long that takes depends mostly on how much material sits above and around the heating.
This guide compares warm-up times for screed, overlay and electric systems, explains setbacks versus switching off, and covers heat pumps, optimum start and insulation.
How long does each type of underfloor heating take to warm up?
The main factor is thermal mass, meaning how much heavy material the system has to heat before the floor surface gets warm. A screed floor has a lot. An overlay board or an electric mat under tile has very little.
| System | Typical warm-up from cold | Best way to run it |
|---|---|---|
| Water UFH in screed | 2 to 3 hours, often more | Steady, with a setback |
| Water UFH on overlay boards | From about 30 minutes | Timed or with a setback |
| Water UFH in joisted floors | Between the two | Timed or with a setback |
| Electric mat or cable in tile adhesive | About 30 to 90 minutes | Timed to when you use the room |
These ranges come from UFH makers and are a guide only. A badly insulated floor, a thick screed, a carpet or a very cold start can all stretch them. Our guide to floor systems explained covers each build-up.
Screed floors
A typical sand and cement screed is 65mm or more thick, so there is a lot of mass to warm. The pay-off is that the floor stores heat and stays warm long after the heating goes off, which suits steady running. Liquid screeds can be thinner, so they respond a bit faster. See screed for underfloor heating.
Overlay boards
Overlay systems put 12mm or 16mm pipe in grooved boards, usually with an aluminium or cement-faced surface, directly under the floor finish. With little mass to heat they respond quickly, which suits rooms used at set times and retrofits where height is tight.
Electric
Electric mats and loose cable sit in the tile adhesive just below the tile, so they warm the surface quickly. Higher wattage warms faster. Insulation boards underneath make a big difference to electric warm-up, especially over a concrete slab. See how to install an electric underfloor heating mat.
Why does underfloor heating take longer than radiators?
Because it works at a much lower temperature, on purpose. BS EN 1264 limits the floor surface to 29°C in areas people stand on, and a heated floor gives off roughly 11W/m² for each degree it is above the room. So the floor can't simply be made hotter to heat faster.
Turning the thermostat up doesn't speed things up either. The floor warms at the same rate, and the room just overshoots once it gets there. UFH makers advise against using a high setting to make up for a slow start, because it isn't sustainable or affordable.
Should I leave underfloor heating on all the time?
For screed floors, mostly yes, but not at full comfort temperature all day. The usual approach is:
- Comfort temperature when the room is in use, for example 20 or 21°C.
- Setback temperature, a few degrees lower, overnight and when you are out.
- Frost protection only when the home is empty for days.
A setback keeps the screed partly warm, so it gets back to comfort temperature quickly. Switching a screed floor off completely lets all that stored heat go, and you then wait hours and use extra energy to warm the mass up again.
The Heatmiser neoStat guide suggests a setback around 4 to 6°C below comfort temperature in new builds as a starting point, a smaller gap on screed floors more than 65mm thick so they recover in time, and a deeper setback in older homes where the heating should mostly be off outside comfort periods. Its frost setting can be set from 7 to 17°C. Try a setting for a week or two and adjust.
Overlay and electric floors respond quickly enough to treat more like conventional heating. Use a timed schedule, with a setback if the room still feels slow in the morning.
For what each approach costs, see underfloor heating running costs.
How should I run underfloor heating with a heat pump?
Steadily. A heat pump is most efficient at a low flow temperature, and it can only hold that low temperature if it isn't trying to recover a cold house in a hurry. Turn a heat pump off for the day and it may have to run harder and hotter later to catch up, which cuts its efficiency.
- Use the heat pump's weather compensation, which sets the flow temperature from the outdoor temperature, so it runs as cool as the weather allows.
- Prefer a small overnight setback to switching off. One heat pump supplier suggests around 13 to 15°C may suit many homes during longer winter absences.
- Keep room thermostats working as limits, so rooms that gain sun or have a fire don't overheat.
- Use a non-mixing pump set on the manifold, so the floor gets the heat pump's flow temperature directly.
Our guide to underfloor heating with a heat pump covers flow temperatures and pipe spacing for heat pumps. With a boiler, see underfloor heating with a boiler.
What is optimum start, and does it help?
Optimum start is a smart thermostat feature that learns how long each room takes to warm up, then switches the heating on early enough to reach the set temperature at the time you ask for it. You set "21°C at 7am", not "heating on at 4am".
It suits UFH well because warm-up varies so much with the floor, the weather and how cold the room got overnight. On the Heatmiser neoStat, optimum start is off by default and you set the longest it may start early, from 0 to 5 hours. It then starts as late as it can within that window, so it avoids heating an empty room for longer than needed.
- Give screed floors a longer window and overlay or electric floors a shorter one.
- Combine optimum start with a setback. The setback keeps the floor partly warm, and optimum start judges the final lift.
- Smart thermostats with a neoHub also let you change schedules from your phone when plans change.
Our guide to underfloor heating thermostats compares the Heatmiser range.
How does insulation affect warm-up time?
Insulation under the heating decides where the heat goes. Without enough of it, a large share heats the slab or the void below instead of the room, so the floor warms slowly and costs more to run.
BS EN 1264 sets minimum thermal resistance under the heating layer, depending on what is below:
| Below the heated floor | Min resistance under heating |
|---|---|
| A heated room | 0.75m²K/W |
| Ground, an unheated room or a different use | 1.25m²K/W |
| Outside air | 2.00m²K/W |
Ground floors in new work usually need far more than this to meet Building Regulations. In practice:
- Screed floors: insulate fully below and fit edge insulation round the walls, so heat goes up, not down or sideways.
- Electric over concrete: lay insulation boards under the mat. Without them, much of the heat goes into the slab.
- Overlay over an uninsulated floor: the board's own insulation helps, but heat loss through the old floor still slows warm-up.
- Floor finish: thick carpet and underlay slows warm-up and cuts output. See UFH under wood, laminate, vinyl, tile and carpet.
If a floor is far slower than these ranges suggest, see underfloor heating not warm enough? Air in loops, low flow rates and a blending valve set too low are common causes.
Products for this job
- Heatmiser neoStat V3 Smart Thermostat
- Heatmiser neoAir Wireless Smart Thermostat
- Heatmiser neoHub G3
- Heatmiser neoStat-e for electric UFH
- UFH Non-Mixing Pump Set for heat pumps
- Overlay boards and insulation boards
- All thermostats and controls
Related guides: Is underfloor heating worth it?, Underfloor heating vs radiators and Water vs electric underfloor heating.
Frequently asked questions
Is it cheaper to leave underfloor heating on low?
For screed floors and heat pumps, a modest setback usually works better than switching off, because the floor doesn't lose all its stored heat. For overlay and electric floors, timing it to when you use the room is usually cheaper.
Why does my underfloor heating take so long to warm up?
Usually a thick screed, poor insulation below, a heavy carpet or switching it off completely. If it never gets warm, check the flow temperature, flow rates and air in the loops.
How long does electric underfloor heating take to warm up?
Typically around 30 to 90 minutes, depending on the wattage, the floor finish and whether there are insulation boards underneath.
Should I turn underfloor heating off at night?
For screed floors, set it back a few degrees rather than off. For electric and overlay floors, switching off overnight is usually fine.
Can I turn underfloor heating off in summer?
Yes. A thermostat won't call for heat when the room is warm anyway. Leave frost protection on if your system or heat source needs it.
Get a design that warms up when you need it with MaxHeatUFH ProLoop. Upload a floor plan and get a Quick Design and a fully priced kit in about 3 minutes. Start your design
Sources: Homebuilding & Renovating, UFH warm-up times, Heatmiser neoStat user guide (Nu-Heat), Heatmiser neoStat V8 user guide (Nu-Heat), Wunda, should you leave your heat pump on?, Kensa heat pump tips, Danfoss UFH handbook (EN 1264)