When it comes to heat pumps, one of the most common misconceptions we hear is that they “don’t work in cold weather” or “they are only suitable for new, well-insulated homes”. This case study proves otherwise.
In December 2024, we installed a 5kW Vaillant Arotherm Plus air source heat pump and a 250L Vaillant Unistor hot water cylinder in a 1987 ex-council house – not your typical ultra-modern new build. With no cavity wall insulation, minimal thermal bridging, and only 25mm polyurethane board insulation, the home’s thermal envelope is far from cutting edge.
Property Overview:
– House Type: 1987 ex-council home
– Size: 137 m2
– Fabric Heat Loss: 5,394 (5.4kW)
– Insulation: 25mm polyurethane board, no cavity wall insulation
We removed the existing 30kW gas combi boiler and gas hob, replacing the latter with an induction hob, allowing the homeowners to remove the gas meter entirely. This not only eliminated their reliance on fossil fuels but also removed the daily standing charge of 32.76p, saving them around £110 per year.
Performance Monitoring
Since installation, we’ve been data logging the system’s performance over a 7-month period – including the coldest days of winter – using a MID-certified (Measuring Instruments Directive) meter. This allows us to track consumption, yield and overall system efficiency with high accuracy.
Energy Savings: Before vs After
Prior to the heat pump install, the household’s combined gas and electricity bills averaged £280 per month.
After switching to an all electric setup powered by the heat pump system, their average monthly bill dropped to £130.
That’s a daily cost reduction from £10 down to £4.64 – a 53.3% drop in energy costs while maintaining full comfort.
System Efficiency
The heat pump system has delivered some incredible efficiency results:
– Central heating efficiency: 440%
– Domestic hot water efficiency: 350%
In comparison, a typical gas boiler runs at around 80% efficiency. That means;
– For every 1 unit of gas, a boiler gives you just 0.8 units of heat
– For every 1 unit of electricity, the heat pump is giving back 3.5 to 5 units of heat.
Final Thoughts
This case study clearly shows that, with the right system design, installation, and commissioning, heat pumps can be a highly effective solution even in older, modestly insulated homes – and not just in ideal new-build scenarios.
Heat pumps do work in cold weather. They are efficient. And they can significantly cut your energy bills – even in real-world, everyday homes.
If you are considering a move toward low-carbon heating, this is proof that it is possible, practical and financially worthwhile.
