29 October 2024
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Insulation prevents heat loss and reduces energy costs, but is the additional cost worth it when installing a heat pump? Paul Spence, Technical Manager of Heatly explores the facts and stats, using data from Heatly to illustrate the benefits of the ‘fabric first’ approach and help homeowners make an informed decision about heat pump costs.
Heat pumps have been proven to work efficiently in all types of homes but horror stories about £700 a month running costs persist in the media, which understandably is off-putting for homeowners who might be considering low carbon heating.
I’m not saying these systems don’t exist – I’ve rectified enough of them myself – however, the belief that all heat pumps are expensive to run is a myth and there are lots of things that can be done to keep heat in and energy bills low.
Crucially, energy efficiency improvements should be undertaken alongside heat pump specification to achieve the best savings long-term. According to my own calculations (see below) using Heatly, a new app designed for heating engineers and their customers, the addition of basic loft and floor insulation reduced heat loss by as much as 45%, saving more than £1,000 a year in fuel costs.
Fabric first!
When preparing to install a heat pump, the ‘fabric first’ approach is the best way forward. It’s not the only way but preventing heat loss as much as possible before final calculations are made will reduce the cost of the equipment required (small heat pumps are usually cheaper) and ensure the system is designed for optimum efficiency.
Oversizing is a common problem that I see first-hand, through both my work as a heating engineer and my Facebook Group ‘Heat Pumps U.K.’ when heating systems are put before energy efficiency improvements. Once new windows or insulation have been installed, the heat pump can end up grossly oversized, leading to excessive energy consumption, high costs and poor performance.
Heat pumps maintain a constant low temperature throughout the day, keeping rooms warm without ever being hot. You might feel heat loss more keenly with a heat pump, and if you are used to blasting the gas central heating for two hours morning and night, it will require a change of mindset! But the point is, losing heat through walls, roofs, windows and doors is wasted energy and pounds down the drain – the same is true of any heating system.
Understanding heat pump efficiency
If you have an old gas boiler, somewhere between 60% and 85% of the gas it burns is converted into useable heat for your home, the rest is wasted in the process. With a heat pump, there is no waste, in fact, the system delivers more usable heat than the electricity it consumes because it transfers existing heat from the environment.
The relationship between power in and heat out at any one time is known as co-efficient of performance (COP). Research has shown that even on the coldest days, air source heat pumps are capable of delivering the required heat at 244% efficiency (COP 2.44) and most of the time COP will be much higher – up to 7 or 8, or even beyond.
There will of course be the odd expensive day but to get a true picture of heat pump costs, we must take the whole year into account. This average is known as the seasonal co-efficient of performance (SCOP) or seasonal performance factor (SPF).
A well-designed, installed and commissioned system could expect to see a SCOP of at least 4 or even 5. Open Energy Heat Pump Monitor is a good resource for homeowners who want to see real-time heat pump performance data, fabric improvements, and costs.
How much money does insulation save?
There is lots of information online about the costs and benefits of installing insulation. For example, according to the Energy Savings Trust, a detached house with an uninsulated loft could save at least £400 a year on energy bills by installing 270mm of roll insulation at a cost of around £1,000. But estimates like this are too generic and don’t give you any useful information.
Developments in technology, however, paint a much clearer picture of the savings of installing insulation and other draught-proofing measures. Heatly uses 2D/3D modeling and AR/VR to create an interactive virtual model of your home, incorporating detailed thermal efficiency data to generate accurate heat loss calculations. This allows virtual experimentation with different levels of insulation to see what delivers the best energy savings and value for money.
Basic insulation reduces heat loss by 45%
Using Heatly, I looked at the impact of various levels of insulation based on a 4-bedroom house with a total floor area of just over 200m2, assuming an outside temperature of -2.2°C and a ground temperature of 6°C. As a starting point, with no floor or roof insulation, Heatly calculated the heat loss as 16,420 W and annual energy consumption as 36,100 kWh. It also indicated that most of the heat loss was coming from the roof and windows and doors, with walls and floors also leaking heat.
The following equation reveals the running costs: Annual energy consumption (kWh) / efficiency (SCOP) x electricity unit price (£) = annual energy costs (£)
Assuming electricity costs 25p/kWh and a SCOP of 3.5 (or 350%) the annual energy costs would be less than £2,580. If I then add 150 mm of PIR floor insulation and 300mm of mineral wool loft insulation, the annual energy consumption comes down to 20,045 kWh, a reduction of 45% compared to no insulation at all. Based on this scenario, annual running costs would be less than £1,450.
We can compare the running costs of an old gas boiler using the same method. For our house, uninsulated, assuming an efficiency of 80% and a gas unit price of 7p, the running costs would be around £3,160 per year. Add the floor and roof insulation and the cost goes down to just over £1,750.
In switching to a heat pump you’d also benefit from losing the gas standing charge, which is usually around £115 per year – we all pay the electricity standing charge anyway. Heat pump tariffs are generally more competitive and you might get a unit price as low as 15p p/kWh – Heatly can also help homeowners access the best energy tariffs.
In our scenario, replacing an old gas boiler with a heat pump and insulation reduces running costs by well over 50%. While the addition of insulation would increase the initial spend – which I appreciate is usually already quite high, even with the Boiler Upgrade Scheme grant - it’s a one-off fee and the annual savings will accumulate for life.
What help is available?
There are several schemes and grants available for homeowners who want to make energy efficiency improvements and install a heat pump:
- Boiler Upgrade Scheme – get a grant of £7,500 towards heat pump installation. Ask your local heating installer for more information.
- The Great British Insulation Scheme – free or cheaper insulation
- ECO4 – energy company obligation to improve the energy efficiency of domestic buildings
- Warm Homes Plan – the Labour government has pledged to implement grants and low-interest loans to support homeowners to install insulation and low-carbon heating – watch this space.
