Air to Water Heat Pumps
Air to Water Heat Pumps are ideal for retrofits or indeed where vertical/horizontal collector systems are not suitable. They can collect heat from the air in temperatures as low as -7 degrees.
This system will have to be fitted with a small supplementary back up system for when there is no heat in the temperature outside for the heat pump to draw from.
Can be installed with existing oil/gas heating system in place, and use them as the supplementary back up system.