Do Heat Pumps Work with Existing Radiators? A Cornwall Homeowner's Guide
One of the most common concerns about switching to a heat pump is whether existing radiators will work. The short answer is: often yes, but sometimes they need upgrading. This guide explains the flow temperature requirements, when radiators need replacing, and what it costs in practice for Cornwall properties.
Flow Temperature Explained
A gas boiler typically runs at 70–80°C. A heat pump is most efficient when running at 35–50°C. The lower the flow temperature, the higher the efficiency (COP). A radiator designed for 70°C water will output significantly less heat when running at 45°C — potentially only 60–70% of its rated output. This is why radiator upgrades are sometimes — but not always — necessary.
When Do Radiators Need Upgrading?
Radiators need upgrading when the existing radiator is undersized relative to the room's heat loss at 45°C flow temperature. They don't need upgrading when originally oversized for the room, when the room has good insulation and low heat loss, or when the heat pump can run at 55°C without significant efficiency loss.
In our experience with Cornwall properties: a typical Victorian terrace needs 2–4 radiators upgraded; a modern semi-detached needs 0–2; a well-insulated bungalow often needs none.
Sizing Radiators for Heat Pump Operation
Heat pump radiators need sizing for the room's heat loss at the heat pump's design flow temperature (typically 45°C for Cornwall's climate). As a rule of thumb, replacing a standard double panel convector radiator (K2) with a double panel double convector (K22 or P+) of the same physical size increases output by approximately 50% — often enough to compensate for the lower flow temperature without changing the footprint.
Cost of Radiator Upgrades
- Standard K22 double panel radiator (600x1200mm): £150–250 supplied and fitted
- Designer flat panel radiator: £200–400
- Towel rail (bathroom): £180–350
A typical 3-bedroom property needing 3 radiator upgrades will add £500–800 to the installation cost — a small proportion of the total and more than offset by the BUS grant.
Underfloor Heating: The Ideal Partner
Underfloor heating runs at 30–40°C — even lower than radiators — which maximises heat pump efficiency. A heat pump running a UFH system typically achieves COP 4.0–5.0 versus COP 3.0–3.5 with radiators. See our underfloor heating service page and guide: Underfloor Heating with a Heat Pump.
Book a Free Survey
During our free survey, we carry out a room-by-room radiator assessment alongside the heat loss calculation. You'll know exactly which radiators (if any) need upgrading and the associated cost. Book your free survey today.
Need personalised advice?
Our MCS certified engineers can answer your questions and provide a free, no-obligation assessment for your property.