Do I Need New Radiators for a Heat Pump?

Usually not all of them — and often none at all. The idea that a heat pump means ripping out every radiator is one of the most persistent myths in the industry, and it is rarely true when the system is designed well.

Whether any radiators need changing comes down to one number: your flow temperature. Get that right and most homes keep the majority of their existing radiators.

A radiator emits more heat the hotter the water flowing through it. A gas boiler typically runs at 70–80°C, so your radiators were sized for very hot water.

Heat pumps are most efficient at lower flow temperatures, so a common approach is to run cooler water — which means each radiator emits less heat and may need to be larger to compensate. This is where the “bigger radiators” worry comes from. But it is a design choice, not an iron law: the higher the flow temperature your heat pump can sustain efficiently, the less you need to change.

The R290 (propane) units we install can sustain flow temperatures of 70–75°C — close to a gas boiler — while remaining efficient. That headroom means we can often design a system where your existing radiators stay exactly as they are.

We still aim for the lowest sensible flow temperature because it saves you money on running costs, but R290 lets us strike the balance between efficiency and keeping your install simple. Many of our customers are surprised how few (if any) radiators we recommend changing.

We never guess. During the survey we carry out a room-by-room heat-loss calculation: how much heat each room loses on a cold day, and how much your existing radiator in that room can deliver at the design flow temperature.

That tells us precisely which rooms (if any) need a larger emitter. Typically it is one or two rooms — often a large living room or a north-facing bedroom — not the whole house. You get a clear, itemised list before any work starts.

Underfloor heating (UFH) is a brilliant partner for a heat pump because it works at very low flow temperatures, squeezing out maximum efficiency. But it is not a requirement — retrofitting UFH throughout an existing home is disruptive and expensive.

For most retrofits, well-sized radiators are the pragmatic choice, sometimes with UFH in a new extension or a tiled kitchen. We design around what makes sense for your home and budget, not a one-size-fits-all rule.

The honest answer is “some, sometimes” — rarely all, rarely none. Because a heat pump runs at a lower flow temperature than a boiler (typically 45°C rather than 70°C), each radiator emits less heat, so some may need to be larger to deliver the same warmth. The way to know is the heat-loss survey, which calculates the output each room needs and checks whether the existing radiator can deliver it at the design flow temperature.

In our experience across typical UK homes, roughly 60–70% of existing radiators can stay, and 30–40% benefit from an upgrade — usually swapping a single panel for a double, or fitting a slightly larger size. Whole-house replacement is rare and usually a sign of poor design.

On cost, a radiator upgrade is modest — typically £150–£400 per radiator supplied and fitted — and any changes needed are included in our fixed-price quote, so there is no surprise mid-job. The alternative to upsizing a few radiators is running the whole system hotter, which quietly raises your running costs for 20 years; targeted radiator upgrades are almost always the cheaper choice over the life of the system. We identify exactly which rooms need attention at the survey, not by guesswork.