When talking to my friend the other day about the death of her oil-fired boiler I was struck by the rapid change in attitude towards fossil fuels. Her plumber had told her that he wasn’t prepared to fit a new oil boiler because of its impact on the environment and that her best option was to consider a heat pump. Two years ago when we installed our ground source heat pump (GSHP) it felt like a scary and wacky thing to be doing. But the UK heat pump market has grown rapidly (18% in the last year) and is set to double by 2025.

Details on how air source and ground source heat pumps work can be found on the Energy Saving Trust website so I won’t repeat it here. This post is more about the  reasons why heat pumps should be seriously considered for space heating and hot water.

In the budget, Philip Hammond announced a proposal to ban fossil fuel heating systems in new homes from 2025. This means no more gas boilers and certainly no more oil boilers. Instead, new homes will either be heated by individual heat pumps or by shared ground loop systems powered by a centralised heat pump. The reason for this, as we’re all painfully aware, is the climate emergency requiring us to reach net zero emissions by 2050. 20 years ago no one would have suggested that we heat our homes using electricity because it’s so expensive. So what’s changed?

Heat pump improvements

The efficiency of heat pumps (what’s called the coefficient of performance or COP) has massively improved. This means that for every unit of electricity put into a heat pump you now get 3 or 4 units of heat out, often more. A well insulated home can be heated entirely by a heat pump for the same cost as heating it by gas.

Climate change strategy

In the UK we’ve made significant progress in decarbonising the national grid. Between 25-30% of our electricity is produced by renewables and this means that the amount of CO₂ emitted from producing grid electricity (0.233 kgCO₂/kWh) is very close to the amount emitted from burning gas (0.21 kgCO₂/kWh) in our homes. As more renewables feed into the grid then the carbon footprint of electricity will fall further, below that of gas.  As the climate emergency intensifies, carbon budgets will be squeezed further and electrifying our heating systems will be an important means of meeting them.

A GSHP system.

Benefits for home owners

Aside from the pressing and worthy cause of climate change mitigation, there are other reasons why heat pumps are an attractive proposition for our homes.

• They are clean at the point of delivery – they produce no exhaust fumes and no on-site CO₂.
• Up until 2021, maybe longer, there are government subsidies to install them. The Renewable Heat Incentive (RHI) pays a fixed amount over 7 years to homes with heat pumps installed by properly certified companies/individuals. The amount paid depends on the energy it takes to heat your home and, over the 7 year period, the subsidy can pay for between 60-80% of the heat pump installation costs.
• As electricity prices fall, which they are likely to do because of emission targets, then heat pumps will become the cheapest way to heat our homes. The development of battery storage at a national level, like the Oxford Energy Superhub, raises the potential for home owners to match their heat pump usage to time periods when electricity demand is low and prices cheaper. Heat pumps are also compatible with solar PV and can be programmed to heat hot water at times of peak solar generation thereby reducing running costs.
• A good quality, well installed heat pump should have a lifespan of between 20 and 30 years with low maintenance costs.

What if your house is poorly insulated?

Heat pumps work most efficiently when delivering low temperature heat. Ideally, homes should be as well-insulated as possible before installing a heat pump because otherwise they can end up costing a lot to run. In old houses the lack of insulation may not be a problem providing the walls are thick enough and there’s lots of thermal mass to store the constant, low temperature heat produced by the heat pump. In my own house, which has 50cm solid limestone walls and no wall insulation, the GSHP keeps us comfortably warm at a cost lower to when we were on gas.

For many homes, achieving high levels of insulation and airtightness is not feasible which is why hybrid (dual fuel) heat pumps are available. These have an air source heat pump (ASHP) component and a traditional gas component. Depending on the outside temperature, a smart control panel works out which component will deliver the required amount of heat for the cheapest price and/or lowest emissions. The ASHP runs for most of the time but when the outdoor conditions are too demanding  then the gas boiler kicks in. The Freedom Project has been monitoring hybrid systems in 75 homes in Wales and their initial findings are that they produce lower cost, lower carbon domestic heating than ASHPs working alone.

Heat pumps can also work well in conjunction with wood burners. On the coldest of days the wood burner can be used to relieve the load of the heat pump and reduce running costs.

A few tips if you are considering installing a heat pump

• Make sure the heat demand of your house is accurately calculated. Heat pump installers will do their own space and hot water demand calculations but it’s the EPC which determines your RHI payments. It is worth paying extra for good EPC assessor who will accurately assess the heat demand of your house.
• Look for a heat pump installer with experience and integrity. Make sure they provide you with payback calculations and estimates of your likely electricity consumption. Check their references, their guarantees and their service agreements.
• If you have underfloor heating or are installing it at the same time then check that the pipework is wide enough to give off enough heat at the lower temperatures (40-45^O) that heat pumps function most efficiently at. It’s far easier to replace a few radiators than it is dig up an underfloor heating system.
• Make sure that the heat pump can be programmed to heat hot water and space heating at different times. This is particularly important if you have solar PV and want to maximise your on-site consumption.
• Fitting a heat meter is a benefit although not essential. Most installers don’t fit them as standard but they do allow you to monitor the efficiency of your system.