Beyond Net Zero: walking the walk - personal experiences of installing heat pumps

Four years ago, I installed a heat pump in my terraced home in London, supported by the government-funded Microgeneration Certification Scheme (MCS). I’d just joined Max Fordham as an engineer without much experience in heating systems, so with hindsight, I might have approached the design slightly differently. I found a heat pump installer from a contact, who was able to guide me through the process.

I was aware that oversizing the heat pump could mean the system would be inefficient, so I’d anticipated a small unit would be suitable for my small house which I intended to insulate and make more airtight. However, the main problem with this approach is that to get government funding for the heat pump, the MCS requires the system to supply all the heat for the building in its present state which meant a much larger heat pump had to be used. The installation was reasonably efficient over the course of two days by the installers, and I spent some time tinkering with the settings to optimise it for efficiency. 

I’ve had no problems with the heat pump itself, although at one point a valve in the pipework stopped working, which led to an error code on the heat pump controller. Another time, there was an electric fault in the hot water cylinder which caused the back-up heater to fail, but with some research I was able to locate these problems and fix them myself.

I’m incredibly glad that I opted for a heat pump instead of a new gas boiler, and I’d struggle to go back to a house which was cold and required blasting the boiler to rapidly warm it up. After living in the house for four years with my wife and rapidly growing son, I’m pleased to say that we have always found it warm. The heat pump delivers heat at a lower temperature, so the best and cheapest strategy is to leave the heating constantly on, so our bills are very manageable. When we get back in from taking our son to the playground there is a lovely warm feeling as we walk through the front door. 

I have long been concerned about climate change, and in late 2022 I started considering what adaptations I could make to my own house to reduce its impact on the local and global environment. I’ve also tried to make lifestyle changes, such as cutting out meat and reducing dairy consumption. A significant impact can also be made by stopping the use of fossil and solid fuels (i.e. gas, oil, liquefied petroleum gas (LPG), coal and wood) for heating, hot water and cooking. I chose to do this by installing a heat pump using the government Boiler Upgrade Scheme and replacing my gas stove with an induction hob. I have also installed solar panels, to generate renewable electricity to run my heat pump and new hob.

I live in a draughty Victorian mid-terraced house in Bristol, with solid uninsulated walls and 30-year-old double-glazing. The received wisdom is that this kind of house isn’t suitable for a heat pump. When we bought the house in 2017, the combi boiler was already old and did not even have a room thermostat – it was effectively on or off. It struggled to produce a continuous stream of hot water, resulting in an unpleasant showering experience. I hated using it to keep the house warm because of the emissions it generated and the house was generally uncomfortable in winter. 

I've worked at Max Fordham since 2015, helping design low energy buildings as a mechanical and electrical engineer. My budget could support either insulating the house and getting a new gas boiler or not insulating the house and installing a heat pump. I opted for a heat pump, knowing it would deliver the significant short-timescale carbon reductions needed to mitigate the worst effects of climate change.

After an initial struggle to find an installer, the works were planned for autumn 2023. However, in October 2023, a few days before my installation was due, the government increased the grant available via the Boiler Upgrade Scheme from £5k to £7.5, which resulted in further delays as my installer (very kindly) reapplied for the increased grant. Work finally began in November 2023. Over the course of approximately two weeks, my boiler was removed, the heat pump and hot water cylinder installed, new pipework installed and all radiators replaced with larger ones. In addition, I had my gas stove replaced with an induction hob.

There were a few teething problems, including a seized circulation pump which the manufacturer replaced under warranty. However, everything has been resolvable by myself or by the installer returning to tweak the system. 

In February 2024, I installed third party monitoring of the heat pump, to provide accurate readings of the electricity it was using and the heat it was generating. With over a year of data my heat pump is proving to be very efficient, with a seasonal coefficient of performance (SCOP) of over 4.3. That means that for every unit of electricity used, it has generated 4.3 kWh of heat for space heating and hot water. All this in an uninsulated house! The third party monitoring data is available here.

Furthermore, in June 2024, I installed a 2 kWp solar photovoltaic array (the largest that could fit on my roof) and 9 kWh battery system. This has resulted in a significant reduction in my reliance on the electricity grid, particularly in summer, when I often have days of not using any grid electricity. In addition, it allows me to make use of a “time of use” electricity tariff, so I can charge the battery when grid electricity is cheap and low carbon, and discharge the battery when grid electricity is expensive and high carbon. Having the solar panels has changed the way I use electricity – I now try to stagger using high power items (e.g. kettles/hob/oven etc) to maximise the ability for this energy to be delivered from the solar and battery through the inverter.

Following the heat pump installation the house is the most comfortable it has ever been, and my energy bills, including VAT and electricity standing charge have been halved. Overall, the energy use intensity of my house is less than 35 kWh/m² which is the target for new housing to be net zero carbon compatible, and I’ve saved nearly 1.5 tonnes of carbon in a year through zero gas use, heat pump efficiency savings, solar generation and solar export to the grid. If it’s achievable in a 100-year-old, uninsulated Victorian terrace, it’s achievable anywhere.

In September 2024, I held an open house for neighbours to come and see the various systems which have been installed. All were surprised at how quiet the outdoor unit is and how straightforward it could be to install both heat pumps and a PV array in a house typically considered unsuitable. In future, I plan to start replacing windows and possibly consider external wall insulation, however those changes will make a fairly negligible impact to the carbon emissions, relative to having the heat pump installed.