Air source vs Ground source
Both air source and ground source heat pumps use the same basic refrigeration technology, but they extract heat from different environments. Understanding these differences will help you decide which is right for your property.
Air Source Heat Pumps (ASHP)
The most common type of heat pump in the UK. They consist of an outdoor unit (resembling an AC unit) and an indoor controller or cylinder.
- How they work: They extract heat from the outside air, even when temperatures are as low as -20°C.
- Efficiency: Typically achieve a Seasonal Coefficient of Performance (SCOP) of 2.8 to 3.5.
- Installation: Usually takes 2-4 days. Minimal disruption to the property.
- Cost: Total installation typically costs £8,000 to £14,000 (before grants).
Ground Source Heat Pumps (GSHP)
GSHPs use the solar energy stored in the ground. They require either horizontal trenches or vertical boreholes.
- How they work: They circulate a water/antifreeze mix through buried pipes. The ground temperature stays a constant 10-12°C year-round.
- Efficiency: More efficient than ASHPs, with an SCOP of 3.5 to 4.5.
- Installation: Significant excavation or drilling is required. Can take several weeks.
- Cost: Total installation typically costs £18,000 to £35,000 (before grants).
Comparison at a glance
| Feature | Air Source (ASHP) | Ground Source (GSHP) |
|---|---|---|
| Efficiency | Good (300%) | Excellent (400%+) |
| Upfront Cost | Lower | Higher |
| Outdoor Space | Small area for fan unit | Large area or borehole access |
| Disruption | Low | High (excavation) |
| Visual Impact | Visible unit on wall/ground | Mostly hidden underground |
| Lifespan | 15-20 years | 20-25 years (50+ for pipes) |
Which should you choose?
Choose Air Source if:
- You have a standard-sized garden or limited outdoor space.
- You want the lowest upfront cost and fastest installation.
- You are looking for a straightforward replacement for a gas boiler.
Choose Ground Source if:
- You have a very large garden or are building a new home.
- You want the highest possible efficiency and lowest running costs.
- You have the budget for a larger upfront investment.
- You want a system that is entirely hidden from view.
Note: Both types are eligible for the £7,500 Boiler Upgrade Scheme grant, making the price gap between them narrower than it first appears.