Heat pump in a 1970s bungalow
Aware that our ageing gas boiler would inevitably fail during the winter (in the summer it’s never on, as spare solar PV heats the water though our solar immersion diverter), taking advantage of the Government’s Boiler Upgrade Scheme (BUS) to replace it with a heat pump seemed the logical thing to do. Also we was inspired by a friend’s detailed blog about his experience of fitting an air source heat pump https://transitionsouthampton.org/2022/10/07/from-gas-boiler-to-air-source-heat-pump/.
Our 2 bedroom bungalow already met the insulation requirements for the BUS grant, and with the heat loss just below 5kW it met the requirements for a 6kW Grant Aerona air source heat pump. This is one of the smallest devices on the market, which was important to us as the only sensible location was the patio, and anything physically larger wouldn’t have left room for the bench seating we use extensively in the summer.
Grant manufacture in the UK and also had a good rating in Ethical Consumer https://www.ethicalconsumer.org/energy/shopping-guide/eco-heat-pumps. We found an installer and began the process. The only glitch was the EPC. Generally a heat pump supplier will arrange the EPC if it’s needed, however our installer is based in Andover and uses an external assessor, so they asked us to arrange it with someone local. We made the mistake of using an ‘EPC’ company found on the internet. They were slow to respond and eventually sent round an inexperienced assessor who took a week to upload the EPC, made major errors, and stopped responding when we tried to get them corrected. Despite being shown the loft the assessor “assumed” no loft insulation – without which we weren’t eligible for the grant! Eventually we did what we should have done in the first place and used the government EPC site https://www.gov.uk/get-new-energy-certificate to find someone else, a lovely lady assessor whose professionalism, efficiency and accuracy showed how poor the previous assessor had been.
The whole installation cost more than it normally would have because we wanted some bespoke elements. Chief of these was to retain our cold water tank and gravity-fed (vented) hot water cylinder, whereas the installer was expecting to dispense with this and fit a mains pressure cylinder in the loft. The reason we wanted this was that a few weeks previously our water had been cut off for 12 hours after a burst main – unlike our neighbours whose mains pressure systems delivered no water at all, we still had a hot water supply! However, our airing cupboard was sized for the old 90L cylinder and we needed a 150L one because of the larger heat pump coils. In the end the installer had a bespoke cylinder made just 1cm narrower than the cupboard and about 30cm taller than the old cylinder. This meant rebuilding the airing cupboard shelving, but because the pipework was neater and the old gas boiler pump was removed we ended up with the same amount of storage space as before.
Fitting the larger tank in the airing cupboard resulted in additional electrical work to move our iBoost solar immersion diverter. We also wanted the new radiators (5 of our 8 radiators were changed from singles to doubles) to match the existing ones, including two imperial (rather than metric) ones to fit better under the windows. We would be living with the new system for 20 years and it felt important to get it right. The work also included some loft boarding for easier access to the electronics and pipework in the loft. Installation took 7 days.
The pump is very quiet (unlike our old gas boiler), and when inside the house we can’t tell if it’s on without looking at the display. We have a Grant remote controller (which turns it on and off and allows access to various parameters such as weather compensation) and a separate thermostat. We chose a programmable thermostat rather than a ‘smart’ one, but can upgrade later if necessary. The thermostat allows up to 6 timeslots, although we generally run it on just 2 (18°C at night and 20°C in the day) and up to 3 hot water timeslots, although we find 30-50 mins in the early hours quite sufficient.
The system is designed for a flow temperature of 50°C, but in practice with weather compensation on it usually runs at between 30-40°C and the radiators feel warm(ish) rather than hot.
We have now been through a whole year. The heat pump’s energy consumption has been massively below the prediction, at 1400kWh instead of 4000kWh/year. Our total utility bill for the year was under £1000, fractionally lower than 2022-23 would have been at last winter’s prices. Even without a battery our solar panels have provided on average 10% of the heat pump’s electricity consumption, helping keep costs down,
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