I have just built a house of 3000 square foot. It has concrete floors, insulated walls and roof, double glazing etc. We had underfloor heating installed with a 10kw PZP Air Source Heat Pump for the central heating and hot water with a 200 litre buffer tank - this was specified by the supplier who had a copy of our building plans and our SAP report. We moved in last November and have used over 31,500 kW/h of electricity at a cost of £3,500 - £500 to £600 per month during winter. The system does not cope with drops in temperature, during winter the water produced was not hot enough to have a bath in. The unit was supposedly sized for the property using the SAP calcs and it is is an HP1AW 10SE-2AG, the power input is listed as (A2/W35) - 2.5kW, the Ph is 8.9kW the COP is 3.6, Max Power Input 8kW, Max Total Power Input 11.8kW. The heating elements were on most of the time during winter and we werer struggling to keep the house warm, 21C in living areas 18 in beds. We have the CH output at 35C, the spacing of the underfloor heating pipes is 100mm to allow for lower output temperature. The supplier/installer now wants to install a gas boiler as a back up heat source rather than using the systems own electric elements. We have asked for our money back - no joy. Has anyone else had problems with these systems?