Forums DIY Ground Source Heat Pumps Reply To: Ground Source Heat Pumps October 25, 2018 at 2:43 pm #443 housemouse 10 Posts Have you considered air source heat pumps. Mitsubishi are claiming to have a new range of co2 refrigerant based ones offering CoPs of up to 4 whilst producing DHW. They sound too good to be true and they might be. I’ve not checked to deeply yet. https://www.ecodan.de/en/heat-pumps/co2-hot-water-heat-pumps/