Radiators for Air Source Heat Pumps: Do You Need to Upgrade?
Most homes need some changes, but very few need a full house swap. This guide explains how heat pump radiators work, how to size them correctly, and what it costs to upgrade.
Why Heat Pump Radiators Work Differently
A gas boiler heats water to 70–80°C and pumps it through your radiators quickly. Heat pumps operate at much lower flow temperatures — typically 35–55°C — and run for longer periods throughout the day.
This lower flow temperature is actually more efficient and cheaper to run, but it means radiators need to emit the same amount of heat at a lower temperature. To do that, they need more surface area. Learn more about how air source heat pumps work.
| System | Flow Temperature |
|---|---|
| Gas boiler | 70–80°C |
| Modern condensing boiler | 55–65°C |
| Air source heat pump (standard) | 45–55°C |
| Air source heat pump (low-temp optimised) | 35–45°C |
| Underfloor heating | 30–40°C |
A radiator that was perfectly sized for a boiler running at 75°C may only emit 50–60% of that heat output when connected to a heat pump running at 45°C. That shortfall has to be made up somewhere.
How to Tell If Your Radiators Are Adequate
Before installing a heat pump, a good installer will carry out a room-by-room heat loss survey. This calculates how much heat (in kW or BTU) each room needs to maintain a comfortable temperature on the coldest day of the year.
Your radiators are adequate if their rated output at the heat pump's flow temperature meets or exceeds each room's heat loss. Most radiator manufacturers publish 'correction factor' tables to help you calculate this.
The Correction Factor Calculation
Radiator output ratings are based on a standard ΔT of 50°C (mean water temperature of 70°C, room at 20°C). At lower heat pump temperatures the correction factor drops significantly:
| Flow Temp (°C) | Mean Water Temp (°C) | Correction Factor |
|---|---|---|
| 70 | 65 | 1.00 (rated output) |
| 60 | 55 | 0.77 |
| 50 | 45 | 0.55 |
| 45 | 40 | 0.46 |
| 40 | 35 | 0.38 |
| 35 | 30 | 0.30 |
Example: A 2kW radiator rated at ΔT50 will only output 0.92kW at a 45°C heat pump flow temperature (2kW × 0.46). If the room heat loss is 1.2kW, that radiator is undersized and will need upgrading.
Room-by-Room Radiator Sizing Guide
These figures are approximate guides for a well-insulated UK semi-detached home. Your actual heat loss will vary by insulation level, ceiling height, window size, and the number of external walls.
| Room | Typical Heat Loss | Recommended Output at 45°C | Typical Size |
|---|---|---|---|
| Small bedroom | 0.5–0.7 kW | 1.2–1.5 kW rated | 600 × 600mm double panel |
| Double bedroom | 0.7–1.0 kW | 1.6–2.2 kW rated | 600 × 900mm double panel |
| Master bedroom | 0.8–1.2 kW | 1.8–2.6 kW rated | 600 × 1000mm double panel |
| Living room | 1.2–1.8 kW | 2.7–4.0 kW rated | 600 × 1400mm double panel |
| Open-plan kitchen/diner | 1.5–2.5 kW | 3.3–5.5 kW rated | Multiple radiators or UFH |
| Bathroom | 0.4–0.6 kW | 0.9–1.3 kW rated | Towel rail + panel |
| Hallway/stairs | 0.4–0.8 kW | 0.9–1.8 kW rated | 600 × 600mm double panel |
A proper heat loss survey by a MCS-certified installer will give accurate figures for each room. These values are illustrative — do not use for installation specification.
Do You Need to Replace Your Radiators?
The answer depends on three things: your current radiator sizes, your home's insulation level, and the flow temperature your heat pump will run at. Check whether your home is suitable for a heat pump.
| Scenario | Likely Outcome |
|---|---|
| Modern double-panel radiators + well-insulated home | Mostly adequate — minor upgrades in 1–2 rooms |
| Old single-panel radiators throughout | Significant upgrades likely in most rooms |
| Mix of old and new radiators | Survey needed room by room |
| Open-plan spaces or large living rooms | Almost always need larger radiators or UFH |
| Underfloor heating on ground floor | Ideal for heat pumps — rarely needs changes |
| Period property with poor insulation | Improve insulation first; radiator changes follow |
On average, Greentech finds that homes switching from a gas boiler need radiator upgrades in 2–4 rooms out of a typical 4-bedroom house. Very few homes need every radiator replaced.
How Much Does It Cost to Upgrade Radiators?
Radiator upgrade costs vary by size, type, and how many rooms are involved. Here are typical installed prices for a straightforward swap. See our full guide to air source heat pump installation costs.
| Radiator Type | Supply Cost | Installed Cost |
|---|---|---|
| Standard double-panel (600×600mm) | £80–£120 | £200–£350 |
| Standard double-panel (600×900mm) | £110–£160 | £250–£400 |
| Large double-panel (600×1400mm+) | £160–£250 | £320–£500 |
| Low surface temp (LST) radiator | £180–£300 | £350–£550 |
| Bathroom towel rail (HP compatible) | £120–£200 | £250–£400 |
| Underfloor heating (per m², wet system) | £45–£75/m² | £90–£130/m² |
Typical whole-house radiator upgrade cost for a 3-bed semi: £1,500–£3,500 (2–4 rooms upgraded). This cost is usually included in a full heat pump installation quote from Greentech.
Radiator Types That Work Best with Heat Pumps
| Radiator Type | Heat Pump Compatibility |
|---|---|
| Double panel convector (Type 22) | Excellent — highest output per m² of all panel radiators |
| Single panel convector (Type 11) | Poor at low temps — usually needs replacement |
| Fan-assisted radiators | Excellent — built-in fan boosts output significantly |
| Underfloor heating (wet/screed) | Ideal — designed for low-temp operation (30–40°C) |
| Underfloor heating (overlay/foil) | Good — lower output but faster response |
| Towel rails | Compatible if correctly sized; most need supplementary panel |
| Cast iron radiators | Can work but very high water volume — slow to heat up |
Heat Pump Brands We Install
Greentech installs leading heat pump brands, all optimised for UK homes and designed to run efficiently at the lower flow temperatures that make radiator upgrades less disruptive. View our full air source heat pump installation in Manchester page.
| Brand | Why We Recommend It |
|---|---|
| Vaillant aroTHERM plus | Industry-leading COP at low temps; pairs with aroCOLLECT for minimal radiator changes |
| Mitsubishi Ecodan | Proven UK track record; quiet outdoor unit; wide capacity range |
| Daikin Altherma | R-32 refrigerant; excellent efficiency down to -25°C; compact indoor unit |
| Samsung Gen 6 | Latest monoblock design; good low-temp performance; strong warranty |
| LG ThermaV | Competitive pricing; reliable in mild UK climates; good installer support |
Frequently Asked Questions
Looking for Manchester ASHP installation? Check your eligibility for the £7,500 Boiler Upgrade Scheme grant.
Related Guides & Resources
Heat Pump Systems
Samsung & Vaillant air source heat pump installation.
BUS Grant (£7,500)
How to claim your Boiler Upgrade Scheme grant.
How Heat Pumps Work
Understand the technology behind air source heat pumps.
Heat Pump Costs
Full pricing guide for heat pump installation.
Are Heat Pumps Worth It?
Honest analysis of heat pump value for UK homeowners.
ASHP Installation Manchester
MCS-certified heat pump installers serving Greater Manchester.
Solar Panels
Combine solar with a heat pump for maximum savings.
Government Grants
All available grants for renewable energy upgrades.
Get a Free Quote
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Get a Heat Pump Survey Including Radiator Assessment
Every Greentech heat pump installation begins with a detailed heat loss survey — room by room, radiator by radiator. We'll tell you exactly what needs changing and give you a full quote before you commit.
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