A heat pump was the obvious choice when Jonny and Caroline Murton-Lavelle’s gas boiler broke down – and award-winning heating engineer Nick Irlam, of Irlam UK, was the obvious choice to fit it.

As part of a long-term plan to retrofit their 1970s bungalow near Lancaster, they decided to make use of the £7,500 Boiler Upgrade Scheme (BUS) grant to help fund the works.

Jonny ran some initial MCS-approved heat loss calculations using software which suggested he needed a 16kW heat pump and new radiators in every room. However, Nick’s subsequent calculations – measuring all rooms, windows and radiators – discovered that the house had an 8kW heat loss, which meant only one radiator needed changing – and a much smaller and cheaper 8kW heat pump would suffice.

“Assuming a cost difference of £500 for each size of heat pump and £500 per radiator, my calculations amounted to an overspend of £6,000, not least for an oversized heat pump, but unnecessary costs for replacing radiators,”

says Jonny.

“Although the data was right, because I couldn’t change the air infiltration rate on the software, it spat out some spurious results. So much for trying to help. Perhaps I should have just left this bit to the professional!”

Minimised discomfort
Armed with all the necessary information, Nick applied for the BUS voucher and work started in November – not the best month to be without heating and hot water, but the couple still managed to work from home during the week-long installation, as Nick minimised discomfort by providing plug-in heaters.

The existing electrical installation was old and an electrical test highlighted that the house would benefit from a re-wire. The consumer unit was full and not to current Building Regulations, so this had to be replaced during the two-day wiring job, explains Nick.

“We always advise on carrying out an electrical test/survey to ensure an installation is compliant. Not everyone would consider that to be part of the heat pump installation process, and some firms would look to do a fit more cheaply and quickly, but that’s when you can get a bad result.”

As the old boiler and immersion cylinder were in a bathroom cupboard, this was adequate space to accommodate the new hot water cylinder and the pipework could connect to the air source heat pump (ASHP) by going under the floorboards without sacrificing any space. After a day of commissioning, the heat pump – installed outside the bathroom in the back garden – was ready to use. Since then, Nick has made a couple of follow-up visits to make sure it’s running smoothly. As part of the service plan, Irlam UK monitors the pump remotely and its reporting system means any fault is flagged.

“It’s not ‘fit and forget’,”

Nick says.

“If the heat pump goes off, we can reset it remotely.”

Huge saving
Perhaps the question many heat pump sceptics are asking is, have the couple seen any cost-savings? “The temperature in the radiators is 37°C, whereas a boiler would be pumping water out at 60°C or more to go around the pipes at 55°C or more, which is a huge saving in energy costs,” says Jonny. Nick has all the statistics to hand and reveals that in the last three months, their heat pump has already proven to be 367% more efficient than a gas boiler; for every kilowatt of energy, it’s producing 4.52 kilowatts of heat. As the house has PV panels and battery storage, Jonny and Caroline are getting even better returns by generating their own electricity and can access off-peak tariffs. By optimising the system, it will only use the necessary energy and can ramp up at night when electricity is cheaper.

Running the heat pump from a PV battery means it will be eight times cheaper than running a gas boiler, explains Nick.

“If you pay 7p a kilowatt for gas and 8p for electricity, your unit costs are the same, but because the heat pump is 400% more efficient, it works out at 2.5p per kilowatt.”

Switch tariffs

“We are currently on the Octopus Flexible Tariff which is 28.45p/kWh for electricity and 7.43p/kWh for gas,”

explains Jonny.

“We still have a gas fire in the living room which we will probably take out. We do need to switch our tariff to something more suitable for the heat pump and EV charger, like Octopus Intelligent, Cosy or Agile.”

Comfort and warmth in the house have also improved. That’s because a heat pump doesn’t overheat the air, adds Nick, who uses the analogy of driving a car at a steady 65 miles an hour instead of alternating between 50 and 100 miles an hour, which is how a boiler usually operates. Instead, the heat pump delivers a constant temperature throughout the house – apart from the living room which will have a new radiator when the room is remodelled. Another bonus is that clothes dry more quickly in the utility room.

At 23kW, the old gas boiler was too big for the house, and meant it was frequently being turned on and off, explains Jonny.

“With the boiler, the over-heated air meant I’d wake up feeling uncomfortable – that doesn’t happen now. Plus, Caroline and I no longer battle over the thermostat.”

Key statistics
Property: 1970s bungalow with cavity walls, insulated pitched roof and uninsulated, suspended timber floor

Previous heating system: 23kW Vaillant system boiler with a hot water cylinder

New heating system: Stiebel Eltron WPL A07 air source heat pump and a 225-trend hot water cylinder

Cost savings: The new air pump is 367% more efficient than the old gas boiler

EPC change:

  • C (69) before solar PV, battery and ASHP
  • C (72) with ASHP
  • B (86) with ASHP, solar PV and battery – EPC methodology doesn’t take account of the battery storage

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