Since the end of January 2013, we have been keeping a record of the internal & external temperatures. The thermometer keeps a record of the daily minimum & maximum temperatures and has a wireless sensor that is mounted outside in the shade.
We also record the number of hours the immersion heater is on and the number of fires lit . This all gives a good indication of the energy performance of the house.
The only item not included is the amount of time the underfloor heating is on, there are 3 x 200W elements in the house (utility, bathroom & en-suite). This is reflected in the energy use which currently stands at 20.92kWh per day on average (since electricity connected). This will go down as we get into the summer.