Air Source vs Ground Source: Which Heat Pump is Right for You?
A detailed comparison of air source and ground source heat pumps covering costs, efficiency, and suitability.
Choosing between air source and ground source heat pumps is one of the biggest decisions you'll make. Here's everything you need to know.
Quick Comparison
| Factor | Air Source | Ground Source |
|---|---|---|
| Installation cost | £10,000 - £18,000 | £20,000 - £35,000 |
| Cost after grant | £2,500 - £10,500 | £12,500 - £27,500 |
| Efficiency (COP) | 3.0 - 4.0 | 3.5 - 4.5 |
| Running costs | £900 - £1,400/year | £700 - £1,100/year |
| Lifespan | 15-20 years | 20-25 years |
| Space required | Small outdoor unit | Large garden (100m²+) |
| Installation time | 2-3 days | 5-10 days |
Air Source Heat Pumps
How They Work
Air source heat pumps extract heat from the outside air (yes, even when it's cold) and transfer it indoors. They look like a large air conditioning unit mounted on a wall or placed on the ground.
Advantages
- Lower upfront cost: Half the price of ground source systems
- Fast installation: Usually completed in 2-3 days
- Works anywhere: No garden space needed, just wall or ground mounting
- Easier maintenance: Outdoor unit is accessible
- Cooling option: Many models can reverse to provide air conditioning in summer
Disadvantages
- ✗Lower efficiency: COP drops in very cold weather (though still works fine)
- ✗Noise: Outdoor unit produces 40-60dB (similar to a fridge hum)
- ✗Visual impact: Outdoor unit is visible on your property
- ✗Higher running costs: Slightly more expensive to run than ground source
Ground Source Heat Pumps
How They Work
Ground source systems extract heat from the ground via pipes buried either in horizontal trenches (1.5m deep) or vertical boreholes (50-150m deep). The ground stays at a constant 10-15°C year-round.
Advantages
- Higher efficiency: More consistent performance, 10-20% more efficient than air source
- Lower running costs: £200-300/year less than air source
- Silent operation: No outdoor unit, all components indoors or underground
- No visual impact: Invisible once installed (pipes buried, unit in plant room)
- Longer lifespan: Ground loops can last 50-100 years
Disadvantages
- ✗High upfront cost: £20k-35k even with the grant
- ✗Requires large garden: Horizontal: 100-200m² of garden. Vertical: Less space but drilling needed
- ✗Disruptive installation: 5-10 days with garden excavation or drilling
- ✗Complex planning: May need environmental permits, especially for boreholes near water sources
Which Should You Choose?
Choose Air Source if:
- ✓ You want lower upfront costs (£2,500-10,500 after grant)
- ✓ You have limited or no garden space
- ✓ You want fast installation (2-3 days)
- ✓ You're on a tighter budget
- ✓ You might want cooling in summer
Choose Ground Source if:
- ✓ You have a large garden (100m²+ of lawn/planting area)
- ✓ You want the absolute best efficiency and lowest running costs
- ✓ Noise is a concern (neighbors close by)
- ✓ You want an invisible system
- ✓ You're planning to stay long-term (better ROI over 15+ years)
- ✓ You can afford the higher upfront investment
Real-World Payback
Let's look at a realistic 15-year comparison for a typical 4-bedroom home:
Air Source
Ground Source
Over 15 years, air source is £7,250 cheaper. Ground source only catches up if you stay 25+ years or running costs increase dramatically.
The Verdict
For most UK homes, air source makes more sense. It's affordable, practical, and perfectly adequate for our mild climate. You get 90% of the benefits for 40% of the cost.
Ground source is worth it if you have the space, budget, and plan to stay long-term. The superior efficiency and silent operation justify the premium for some homeowners—especially rural properties with large gardens.