Do You Need Bigger Radiators for a Heat Pump? A Bristol Guide

The short answer

Usually some, rarely all. Most Bristol homes switching from gas need two to five radiators replaced. Which ones depends on each room’s heat loss, worked out in the survey.

---

Why radiators give out less heat

A radiator’s output depends on how much hotter it is than the room. The figure on a radiator’s label assumes the water is about 50°C warmer than the air — roughly what a gas boiler at 70°C+ delivers.

A heat pump running at 45–50°C makes the radiator only around 20–27°C warmer than the room. At that gap, the radiator delivers roughly a third to a half of its labelled output:

Heat pump flow temperature	Share of label output (approx.)
45°C	about 33%
50°C	about 44%
55°C	about 55%

So a radiator that comfortably heated a room with a gas boiler may fall short with a heat pump, unless it was oversized to begin with. Many old radiators were, which is why not every one needs changing.

---

Which rooms in Bristol homes usually need upgrading

• Bay-fronted front rooms in Victorian terraces across Bishopston, Southville and Bedminster: big windows, outside walls and often a chimney breast.
• Tall-ceilinged rooms in Georgian and Regency townhouses in Clifton and Kingsdown, where there’s a lot of air to heat.
• Rear bedrooms above kitchen extensions, with three outside walls and often a flat roof.
• End-of-terrace rooms, which have an extra exposed wall.
• Basement rooms in older Clifton and Cotham houses, if they’re heated living space.

Mid-terrace middle rooms, sheltered by neighbours on both sides, often keep their radiators.

---

The options

Option	Good for	Notes
Larger single radiator	Most rooms	Same wall space if a taller or longer model fits
Double or triple panel	Limited wall space	More output from the same footprint
Column radiators	Period homes	Suit Georgian and Victorian interiors; good output
Fan-assisted radiators	Rooms with very little wall space	Small fans boost output; need a power supply
Underfloor heating	Extensions and renovations	Excellent at low temperatures, but disruptive to retrofit

In listed buildings, original cast-iron radiators can sometimes stay, with extra output added elsewhere in the room.

---

What it costs

Expect roughly £350–£600 per radiator, fitted, for a standard upgrade, and more for large column radiators or fan-assisted units. A typical Bristol terrace adds £1,200–£2,500 to the installation. It’s included in the installer’s quote, and the £7,500 grant covers the whole installation including radiators.

---

Pipework

Some homes had heating fitted in the 1970s or 80s with thin microbore pipes, which may not carry enough water at heat pump temperatures. Your surveyor should check, because replacing sections means lifting floors.

---

Why it’s worth doing properly

Larger radiators let the heat pump run at a lower flow temperature, which can save £150 or more a year in a typical Bristol home. See flow temperature. Skimping on radiators to cut the quote usually costs more over the life of the system.

Related: the heat loss survey · Victorian and Georgian homes