Low-Temperature Radiators and Heat Pumps: A Compatibility Guide
Air-to-water heat pumps have become the default choice for boiler replacement in Spain and much of Europe, driven by energy renovation programmes and the electrification of heating. The same question always comes up: can I keep radiators with a heat pump, or am I forced to install underfloor heating? The short answer: radiators work perfectly with a heat pump if they are sized for low temperature. The long answer follows.
Why heat pumps change the rules
A gas boiler is comfortable running water at 70–80 °C. An air-to-water heat pump reaches its best efficiency at 35–45 °C flow: for every degree the flow temperature drops, COP improves by roughly 2–3%. Running a heat pump at 60 °C is possible, but it penalises electricity consumption precisely on the coldest days. That is why the emitters — the radiators — must be able to deliver the required heat with much cooler water.
What ΔT30 is and why it matters
Radiator output is tested under EN 442 at ΔT50: mean water temperature 50 °C above room air (75/65/20 regime). With a heat pump, water circulates at about 40–45 °C mean in a 20 °C room — a ΔT of roughly 25–30 K. Output does not fall proportionally but exponentially: by the radiator characteristic equation, with n ≈ 1.3 for steel emitters, at ΔT30 a radiator delivers about 51% of its nominal ΔT50 output. A radiator rated 2000 W nominal provides about 1030 W with a heat pump.
Do steel radiators work with heat pumps?
Yes — with a specific advantage: steel allows large-surface emitters — type 22 and 33 panels, multi-column tubulars, vertical models up to 1800–2000 mm — that compensate the smaller temperature difference with more emission area. The installer's rule of thumb: to switch from boiler to heat pump without touching the pipework, installed radiator surface should roughly double compared with classic ΔT50 sizing. In renovations it is often enough to replace the most marginal radiators with deeper models (a type 22 instead of a type 11) in the same wall space.
Sizing step by step
First, calculate each room's heat load (in an average Spanish dwelling, 60–110 W/m² depending on climate zone and insulation). Second, choose the heat pump's design flow temperature: the lower, the better the COP. Third, select each radiator by its ΔT30 output, not ΔT50. To make this easier, JIUDING product pages show output at both regimes, ΔT50 and ΔT30, calculated with the characteristic exponent n = 1.3 — installers can compare directly without redoing the conversion.
Radiators vs underfloor heating in renovation
Underfloor heating is an excellent emitter for new builds, but in renovation it means lifting floors, several centimetres of screed and weeks of work. Replacing radiators takes hours per room, with no impact on ceiling height or flooring. With radiators correctly sized for low temperature, a heat pump reaches comparable seasonal efficiency in most existing homes — and the system keeps one advantage: low thermal inertia and fast response to setpoint changes.
What to ask the manufacturer
Before specifying, request three things: the EN 442 output declaration with the model's Km and n values, the ΔT30 output alongside the nominal figure, and the working pressure (JIUDING steel radiators operate at 1.0 MPa / 10 bar, with every unit factory-tested at 1.5× working pressure). Test reports and CE certificates are available in our documentation centre, and common questions about orders and lead times are answered in the FAQ.