Quick Answer
Yes, 60-70% of UK homes can keep their existing radiators when switching to a heat pump. Modern heat pumps work at 45-55°C flow temperature (vs 70-80°C for gas boilers), so radiators need to be larger or more numerous. Well-insulated homes (EPC B-C) with oversized radiators usually need zero changes. Poorly insulated homes (EPC D-E) may need 2-4 radiators upsized. A heat loss survey (required for BUS grant anyway) tells you exactly what's needed.
Most likely scenario: Keep 100% of radiators. Why?
Typical scenario: Keep 70-80% of radiators, upsize 2-4.
Challenge scenario: May need 50%+ radiators replaced OR insulation upgrade first.
| Home Type | EPC Rating | Radiators Kept | Typical Upgrades |
|---|---|---|---|
| Modern 3-bed (post-2000) | B-C | 95-100% | Usually none |
| 1990s 3-bed semi | C-D | 70-85% | 2-3 radiators upsized |
| 1970s-80s detached | D-E | 60-75% | 3-5 radiators OR insulation first |
| Victorian terrace (insulated) | C-D | 65-80% | High-ceilinged rooms need larger rads |
| Victorian terrace (uninsulated) | E-F | 40-60% | Insulate first (loft + walls) critical |
| Bungalow (cavity walls) | C-D | 80-90% | 1-2 radiators (single-storey = easy) |
Accuracy: 100% (required for BUS grant)
Accuracy: 70-80% (rough estimate)
💡 Heat Loss Survey Is Required Anyway
The £7,500 BUS grant mandates a heat loss survey. Your installer will calculate radiator compatibility as part of this process. Don't pay separately for a "radiator assessment" — it's included in the grant application.
| Flow Temperature | System Type | Radiator Size Needed |
|---|---|---|
| 70-80°C | Gas/oil boiler | Standard size (100% output) |
| 55°C | Heat pump (moderate weather) | 1.3x larger (30% bigger) |
| 45°C | Heat pump (mild weather) | 1.6x larger (60% bigger) |
| 35°C | Underfloor heating | N/A (whole floor is radiator) |
Key insight: Heat pumps are most efficient at 45-50°C. Radiators need to be larger at lower temps, but heat pump COP (efficiency) is 30-50% better. It's a worthwhile trade-off.
Heat pump compatibility: Excellent
Two panels + convector fins = high output at low temps. Most efficient for heat pumps. Common in UK homes built 2000+.
Heat pump compatibility: Good
One panel + convector fins. Adequate for well-insulated rooms. May need upsizing in larger/colder rooms.
Heat pump compatibility: Poor
Flat panel only, no convector fins. Low output at heat pump temps. Usually needs replacing with Type 22 or larger Type 11.
Heat pump compatibility: Variable
Large Victorian cast-iron radiators work great (high thermal mass, huge surface area). Small decorative column rads may need upgrading.
Heat pump compatibility: Check output rating
Vertical rads can be excellent (large surface area) or terrible (low BTU output). Check manufacturer's rating at 50°C ΔT.
| Upgrade Type | Cost Per Radiator | Typical Scenario |
|---|---|---|
| Type 11 → Type 22 (same size) | £150-250 | Upsize output without bigger radiator |
| Larger Type 22 (e.g. 600mm → 800mm high) | £200-350 | Bedrooms/living rooms needing more heat |
| Add second radiator to room | £300-500 | Large living rooms, conservatories |
| Designer/column radiator | £400-1,200 | Aesthetic upgrade in visible areas |
Typical total cost for radiator upgrades: £600-£2,000 (2-6 radiators). This is in addition to heat pump installation cost, but many installers include necessary radiator upgrades in their quote.
Cost: £1,500-£3,000 | Benefit: Permanent heat loss reduction
Cost: £0 | Benefit: Works with existing radiators
⚖️ Flow Temperature Trade-Off
Running at 55°C (COP 3.2) costs ~15% more than 45°C (COP 4.0), but it's still 50% cheaper than gas. For homes that can't easily upgrade radiators, this is a pragmatic middle ground.
🚩 "You'll definitely need to replace all radiators"
Reality: Very rare. Even poorly insulated homes typically keep 50-70% of radiators. Installer may be inflating quote or hasn't done proper heat loss survey.
🚩 "We don't need a heat loss survey"
Reality: Heat loss survey is mandatory for BUS grant. Installer skipping this is not MCS-compliant and you won't get £7,500 grant.
🚩 "Heat pumps only work with underfloor heating"
Reality: Myth. 80%+ of UK heat pump installations use radiators. Underfloor is nice-to-have, not essential.
🚩 "We'll run it at 70°C so radiators work"
Reality: Defeats the purpose. Heat pump COP at 70°C is ~2.0 (gas boiler efficiency). You'd pay more than gas for heating. Proper design runs 45-55°C.
Scenario: Built 2005, cavity walls, 270mm loft insulation, double glazing
Heat loss survey result: Heat loss 6.8kW at -3°C outside
Radiators: 8 radiators, all Type 22, slightly oversized from original install
Recommendation: Keep all 8 radiators, run at 48°C flow temp
Radiator upgrade cost: £0
Scenario: Cavity walls (no insulation), 150mm loft insulation, mix of single/double glazing
Heat loss survey result: Heat loss 13.2kW at -3°C outside
Radiators: 11 radiators, mix of Type 11 and Type 21
Recommendation: Replace 4 radiators (master bedroom, living room, dining room, office) with larger Type 22. Keep other 7 radiators.
Radiator upgrade cost: £850 (4 radiators × £210 average)
Scenario: Solid brick walls, 100mm loft insulation, single glazing, high ceilings
Heat loss survey result: Heat loss 16.4kW at -3°C outside (very high)
Initial radiators: 9 radiators, all Type 11 (inadequate)
Recommendation: Insulate first (cavity wall insulation + loft top-up to 300mm) for £1,800. Then heat loss drops to 11.2kW. Replace 5 radiators, keep 4.
Radiator upgrade cost: £1,100 (5 radiators) AFTER insulation
Alternative: Replace 8 radiators without insulation = £2,400 + higher running costs forever
Q: Can I mix radiators and underfloor heating?
A: Yes! Common setup: underfloor heating downstairs (35-40°C), radiators upstairs (45-50°C). Heat pump runs at higher temp for radiators, underfloor just gets less hot water (still works fine).
Q: Do towel radiators work with heat pumps?
A: Yes, but they won't get as hot (45-50°C vs 70°C). Most people add electric towel rail boost (£2-3/month electricity) for proper drying. Or use heat pump in summer for DHW only.
Q: Can I upsize radiators later if needed?
A: Yes. Some people install heat pump with existing radiators, run first winter, identify cold rooms, then upgrade just those radiators. Costs £150-300 per radiator.
Q: Will larger radiators look ugly?
A: Not necessarily. Type 22 radiators are only 20-30mm deeper than Type 11 (same height/width). Or you can go taller/wider with same depth. Column radiators are stylish alternatives with high output.
💡 Bottom Line on Radiators
Most UK homes (60-70%) can keep their existing radiators with little to no changes. The heat loss survey (required for BUS grant) tells you exactly what's needed. Budget £0-£1,500 for radiator upgrades as a contingency, but don't assume you'll need new radiators until the survey is done.
Our MCS-certified installers include a professional heat loss survey with every quote. You'll get: