Air Source vs Ground Source Heat Pump UK — 2026
Which heat pump suits your UK home — air source or ground source? Real cost comparison, SCOP performance, install practicalities, and the 25-year total cost picture from an MCS engineer.
The 30-second decision
If you're a UK homeowner with a typical 3-bed semi, modest garden, and a 10-year time horizon — get an air source heat pump. The cost-vs-benefit doesn't favour ground source for you.
Consider ground source only if any of these apply:
- Property is 200+ m² (large 5-bed detached or period country house)
- You have a large garden (700+ m² for trenches) OR budget for a borehole (£8-15k extra)
- Insulation is poor and won't be upgraded (high heat demand favours GSHP efficiency)
- You're planning to stay 15+ years to recoup the cost premium
- You have a long-term focus on energy independence vs payback
Cost comparison — installed and net
| Property type | ASHP installed | ASHP net (BUS) | GSHP installed | GSHP net (BUS) |
|---|---|---|---|---|
| 2-bed (70 m²) | £11,500 | £4,000 | £22,000 | £14,500 |
| 3-bed (95 m²) | £13,500 | £6,000 | £26,000 | £18,500 |
| 4-bed (140 m²) | £16,500 | £9,000 | £30,000 | £22,500 |
| 5-bed (200 m²) | £20,000 | £12,500 | £35,000 | £27,500 |
The £12,500 cost premium for GSHP (3-bed) needs to be recouped through running cost savings — usually 12-18 years depending on energy prices.
Performance — SCOP makes the difference
| Metric | ASHP | GSHP |
|---|---|---|
| SCOP (average UK) | 2.8-3.4 | 4.0-4.5 |
| Performance in -5°C | Drops to ~2.0-2.4 | Stays at ~3.8-4.2 |
| Hot water (60°C) | Less efficient | Comfortable |
| Noise (outdoor) | 35-48 dB | 0 (no outdoor unit) |
| System lifespan | 15-20 years | 20-25 years (above ground); 50+ years (ground loop) |
GSHP's better SCOP comes from the stable ground temperature (~10°C year-round in UK soil) vs ASHP which extracts heat from variable air temperature.
Annual running cost comparison (typical 3-bed)
| Scenario | ASHP/year | GSHP/year | Annual saving (GSHP) |
|---|---|---|---|
| Standard Ofgem cap | £985 | £720 | £265 |
| Octopus Cosy | £695 | £500 | £195 |
| Octopus Go | £780 | £565 | £215 |
GSHP saves about £200-£265 per year — but you paid £12,500 extra for it. Simple payback: 47-63 years. That's why ASHP wins for most homes.
25-year total cost of ownership
| Component | ASHP | GSHP |
|---|---|---|
| Install (net of BUS) | £6,000 | £18,500 |
| Fuel × 25 yrs (Cosy) | £17,375 | £12,500 |
| Annual service × 25 | £2,000 | £2,500 |
| Replacement at year 17 (ASHP only) | £8,500 | £0 |
| 25-year TOTAL | £33,875 | £33,500 |
The 25-year picture is genuinely close (£375 difference) — but only because ASHP needs one replacement at year 17 vs GSHP lasting the full 25 years. If you go 15 years without ASHP replacement, ASHP wins by ~£8k. If you go 20 years with GSHP and budget for a compressor refresh, the maths swings again.
Install practicalities
Air source
- Outdoor unit goes against an external wall (no boundary distance rule since May 2025)
- Install: 2-4 days
- Indoor: hot water cylinder (typically 180-250 L) + buffer tank if needed
- Pipework: refrigerant lines from outdoor unit to indoor system
- Planning: permitted development in most cases (Article 4 zones need permission)
Ground source
- Slinky trench array: requires 700+ m² garden, dug to 1.2m depth, ~£8,000 extra
- Borehole: 100-150m deep, no garden space needed but drilling cost £10-15k extra
- Install: 1-2 weeks on site (longer for borehole)
- Indoor: compressor unit (inside, no outdoor unit), hot water cylinder, controls
- Planning: trench arrays usually permitted development; boreholes may need permission
Which heat pump for typical UK homes?
| Home type | Recommendation | Why |
|---|---|---|
| 3-bed semi, average garden | ASHP | Cost-effectiveness, fast install |
| 4-bed detached, large garden, 20+ yrs stay | GSHP (or ASHP) | GSHP starts to make sense |
| 5-bed period country house | GSHP | High heat demand favours efficiency |
| Modern flat | ASHP | Small heat load, GSHP overkill |
| Listed building, no outdoor unit allowed | GSHP | No external unit visible |
| Off-gas-grid rural home | Either | Both replace oil/LPG well |