Underfloor heating vs radiators for heat pumps in 2026: what to choose

Why flow temperature matters

A heat pump’s efficiency (SCOP) depends heavily on how much it has to lift the refrigerant temperature. At a flow temperature of 35°C, a typical air-source heat pump runs at SCOP 4.8–5.0. At 55°C the same unit drops to 3.8–4.2. The physics is unavoidable: the bigger the temperature delta the compressor has to span, the more electricity it uses per kWh of heat delivered.

Underfloor heating works at 35–40°C because it spreads heat across the entire floor — a 16 m² living-room floor at 38°C delivers more warming power than a 1.5 m² radiator at 55°C, even though the radiator is hotter per square metre. Radiators concentrate the heat, so they need to be hotter (or much bigger) to deliver equivalent room warming.

Upgrading radiators to oversized “low-temperature” versions (typically 30–50% larger surface area than gas-boiler-era rads) closes most of the efficiency gap. A properly-sized radiator system runs at 45–50°C with the heat pump at SCOP 4.2–4.5 — close to but not matching UFH’s 4.8–5.0.

The retrofit cost story

Where UFH and radiators diverge sharply is install cost in existing homes. A typical 3-bed UK semi:

• Radiator upgrades: £1,500–£5,500 to swap 4–8 rads for low-temperature versions, plus any pipework if existing 10mm microbore needs upsizing to 15mm. Disruption is minimal — installer in for 1–3 days, minor decorating where rads are replaced.
• Full wet UFH retrofit:£6,000–£15,000 depending on floor construction. Suspended timber floors mean lifting boards + insulating beneath + laying pipe; solid concrete means either chasing in or building up (with the screed / new floor finish that implies). 1–3 weeks of disruption per area; you typically can’t live in the room while UFH is being installed.
• Low-profile retrofit UFH: £4,000–£10,000. 15–25mm panels laid on top of existing floors then covered by new flooring. Less efficient than embedded UFH (less thermal mass) but much less disruptive. Doorways often need rehanging.

The £6,000–£15,000 cost gap means UFH retrofit needs to recover ~£300–£700/year of running-cost saving to pay back in 20 years. In practice the SCOP advantage delivers £80–£200/year. UFH retrofit doesn’t pay back on running cost alone — it pays back on comfort, resale value, and the absence of visible radiators.

When UFH is the right call

Three scenarios where UFH makes sense even with the cost premium:

• New builds and major renovations. If the floors are coming up anyway (renovation, extension, new build), the incremental UFH cost shrinks dramatically — typically £40–£70/m² vs £150–£250/m² for retrofit on existing floors. The SCOP advantage compounds over 20 years.
• Solid floors with no thermal break. Some older ground-floor concrete slabs benefit from the insulation work that UFH retrofit includes. The fabric improvement is real even before accounting for the heating efficiency.
• Comfort priority.Underfloor heat delivers an even, draught-free warmth that radiators can’t match. For owner-occupiers with long-term comfort priorities (children playing on floors, bare feet, large open-plan spaces), the cost premium maps to a lived-experience improvement.

When upgraded radiators are the right call

• Most existing-home retrofits.The cost-per-comfort calculation usually favours rads in a property where you don’t need to disturb floors. The 0.3–0.5 SCOP advantage of UFH translates to £80–£200/year on a typical home — slow payback against the £4,500+ incremental cost.
• Older properties with sensitive floors. Original Victorian / Edwardian floor tiling, parquet, or listed-building heritage flooring often can’t be disturbed. Radiator upgrade keeps the floor intact.
• Phased retrofit.Some homeowners install a heat pump now with existing radiators and upgrade rooms-by-room over time as decoration cycles allow. That’s a sensible spread-the-cost strategy.

The hybrid approach (UFH downstairs, rads upstairs)

A common UK heat-pump install pattern: UFH on the ground floor (where floors are easier to lift, especially in properties already getting solid-floor work), upgraded radiators on the first floor and above. The heat pump runs at the lower of the two zone setpoints, blending toward UFH’s 35–40°C in mild weather and stepping up toward 50°C for the radiator circuit only on cold days.

Cost typically lands between full UFH and full rads — £4,500–£10,000 for a 3-bed UK semi depending on ground-floor size. SCOP lands at 4.2–4.7, capturing most of UFH’s efficiency advantage without the upstairs retrofit cost. Probably the best practical answer for most retrofitters in 2026 if they have the budget headroom for a partial UFH install.

What to ask your installer

1. What flow temperature have you sized for, and what SCOP does that imply? Anything above 50°C should prompt a discussion about rad upgrades.
2. Which rooms can keep existing radiators? Which need upgrades? Get the heat-loss survey breakdown per room.
3. What does a UFH option for the ground floor add to the quote, and how does that change the projected SCOP?
4. Will rad upgrades or UFH be funded within the BUS scope, or quoted separately?

Switching pathway

1. Run a free pre-survey at propertoasty.com/check to get the BUS-eligibility verdict + indicative system size for your property.
2. When briefing installers, ask for three options: heat pump alone (with existing emitters), heat pump + rad upgrades, heat pump + ground-floor UFH. The incremental cost-per-SCOP-point is what to compare.
3. If you’re doing any flooring work in the next 2–3 years anyway (kitchen refurb, extension, new build), time the UFH install to coincide. The incremental cost drops by 50–70% when the floor is already up.

The takeaway

Heat pumps work efficiently with both UFH and properly-sized radiators. UFH delivers a real but modest SCOP advantage (~£80–£200/year on a typical home). Retrofit UFH costs £6,000–£15,000 on existing floors — the cost gap means UFH retrofit doesn’t pay back on running-cost alone; it pays back on comfort and resale. For new builds and major renovations, UFH is usually the right call. For most retrofits, radiator upgrades are the cheaper, faster path. The hybrid approach (UFH on ground floor, rads upstairs) is the practical middle ground.