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Underfloor Heating + Heat Pump Calculator
Design underfloor heating for heat pump operation at low flow temperatures. Calculate pipe lengths, circuit counts, heat output and compatibility with ASHP/GSHP systems.
Total UFH area
35°C for best COP
From heat loss calculation
Materials supply cost
Closer spacing lifts W/m²: heat pumps typically use 100-150mm
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How We Calculate This
This calculator designs UFH systems optimised for heat pump operation at low flow temperatures.
The formula
Heat output (W/m²) = Base output at flow temp × Floor finish factor × Pipe-spacing factor
Indicative base output for a tile/screed floor at the reference 200mm pipe spacing (wet UFH delivers 50–100 W/m² per BS EN 1264-2 / Warmup; flow temperature sits a few °C above the floor and differs from the mean water temperature, so treat these as design estimates):
- 35°C flow: ~55 W/m² base (tile, 200mm)
- 40°C flow: ~70 W/m² base
- 45°C flow: ~85 W/m² base
- BS EN 1264-2 caps occupied-zone output near 100 W/m² (29°C floor surface, ~9°C floor-to-room difference)
Closer pipe spacing concentrates the pipe and raises output: at ~45°C mean water temperature on tile, output runs roughly 100 W/m² at 100mm, 85 at 150mm, 75 at 200mm and 55 at 300mm — which is why heat pumps typically use 100–150mm centres. Floor-finish factors are indicative deratings (tile 1.0, engineered wood 0.9, laminate 0.88, carpet 0.7); a carpet-plus-underlay build often exceeds the EN 1264 0.15 m²K/W covering limit and should follow the manufacturer’s derating table.
- Pipe length = (Area ÷ Spacing) × 1.1 (approximate bend + manifold-tail wastage)
- Max circuit length: 100m for 16mm pipe (including tails)
Frequently Asked Questions
Underfloor heating operates at lower flow temperatures (30-45°C) compared to radiators (55-75°C). Heat pumps are most efficient at low flow temperatures, with COP improving by approximately 3% for every 1°C reduction. UFH at 35°C can achieve COP of 3.5-4.5, compared to 2.5-3.0 with radiators at 55°C.
Aim for 30-40°C flow temperature for maximum heat pump efficiency. At 35°C, well-insulated homes typically achieve 50-60 W/m² output which is sufficient. Poorly insulated homes may need 40-45°C flow temperature, which reduces COP but may be necessary.
Screed (wet) UFH systems cost £40-£70/m² for materials, plus £20-£40/m² for screeding. Overlay (retrofit) systems cost £50-£80/m². Manifolds add £250-£500. A typical 80m² installation costs £4,000-£8,000 excluding the heat pump.
Closer pipe spacing (150-200mm) is recommended for heat pump operation at low flow temperatures to maximise heat output. Standard spacing (200-250mm) may not deliver sufficient output at 35°C flow in less well-insulated rooms. 150mm spacing increases pipe use by 33% but improves output significantly.
Yes, significantly. Tiles and stone are best conductors giving 100% rated output. Engineered wood gives about 90%. Laminate gives 85-90%. Carpet with thick underlay can reduce output by 30% or more. With heat pumps at low flow temperatures, carpet may not deliver adequate heat.
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Last updated: March 2026
Verified against UK standards · estimates only, confirm with your supplier.