Lower installation costs
System can be installed outside or inside
No need for expensive (and messy) boreholes
Easier for retro fit
Good coefficient of performance in UK due to high air temperatures
Higher noise levels
Lower coefficient of performance (varies)
Larger in size
Higher/constant coefficient of performance
Lower running costs
Quieter system (no fans)
Generally smaller in size (easier to locate in a property)
Higher installation costs
Large area needed to support horizontal ground loop
Installation of boreholes can cause major disruption
Critical to size ground collector correctly (no second chance if you get it wrong)