No new pipes, big savings: Vitocal 151-A saves retiree over £900 in first four months

Overview

Although the electric boiler in Anthony Brooks’ three-bedroom 1950s semi was 100% efficient, the eye-watering expense of running it was preventing him from retiring. An 8kW Vitocal 151-A air source heat pump from Viessmann combined with the OVO Heat Pump Plus electricity tariff proved the perfect solution, saving almost £1,000 on heating bills in the first four months of operation.

Cost vs efficiency

When Anthony Brooks bought an electric boiler to replace an old oil-fired system at his home near Stowmarket, Suffolk, it was sold to him as being 100% efficient. There is no gas connection to his rural property, so an equivalent gas-fired combi model wasn’t an option. However, a gas boiler could only ever reach around 94% efficiency anyway, so it didn’t seem a problem. 

What was not explained, however, was that the new electric boiler’s high performance would not translate into lower energy bills. In fact, because of the high price of electricity compared to gas, running Anthony’s central heating was so expensive that he was forced to replace the boiler after just a few years of use. 

“I had been planning to retire,” he recalls. “But the electric bills were so high, that it was starting to look untenable unless something changed.” He approached Suffolk-based VIPartner and renewable energy specialist Sun-Lite Group for advice, as Jon Miles of Sun-Lite had installed another heating system at the property before joining Sun-Lite. (That installation involved underfloor heating powered by a Viessmann Vitodens 100-W combi boiler running on LPG, in a garden annexe that Anthony built as a home for his elderly mother.) 

Jon takes up the story: “I knew Anthony was interested in the idea of a heat pump, as he’d wanted to use one for his mother’s place. Ironically, the amount of power needed to run the electric boiler in the main house ruled that out, and instead we went with an efficient Viessmann combi. This time round, I advised him a heat pump would be the best solution for the main house, and that, in turn, led us back to Viessmann.”

Doing the maths

Says Jon, “This job is an unusual one, because the focus was purely on getting running costs down. Generally, we’re really into efficiency in the heat pump world and that’s good on paper. But you always need to weigh up what it costs to chase that higher efficiency and performance. As installers, it’s our job to find the sweet spot for each individual customer. 

“For Anthony, I knew we would be hitting a SCOP of at least 3.1 with the Viessmann Vitocal 151-A without changing any pipework or radiators. They would simply need to be run at a slightly higher temperature than we would normally design to. Although the alternative solution predicted a higher SCOP of around 4 once the radiators and pipes were replaced, overall, it would still have ended up costing more over the lifetime of the system, so it simply wasn’t worth it. And that’s before you factor in Heat Pump Plus.”

Thanks to Viessmann’s partnership with OVO, Anthony could sign up to the OVO Heat Pump Plus tariff which caps the cost of his electricity at 15p/kW - at least 5p/kW lower than the price he was paying with his electric boiler. And, with the new set-up being at least 310% efficient, that would bring the real-terms cost to under 5p/kW, making the Vitocal around 1.5-2p/kW cheaper to run as well as being cheaper to instal than the alternative brand of heat pump. “When we did the sums, it was clear it had to be the Viessmann model,” says Jon.

A £7,500 grant from the Boiler Upgrade Scheme also helped to cover the cost of the new system.

Exeeding expectations

Since going live in November 2024, due to the Vitocal’s excellent weather compensation, combined with an adjustment to the heating strategy for the property, Anthony’s new open-loop system has in fact been averaging an impressive 4.2 SCOP, instead of the predicted 3.1. That means his heating bills are actually below 3.5p/kW, saving him over £900 in the heat pump’s first four months of operation. He’s also reduced his carbon emissions by around 77%, saving 850kg/year, which is equivalent to driving a mid-sized petrol car for around 2,500 miles. 

The heat pump’s compressor cycles are at the route of its better-than-expected performance. “We normally aim for a maximum of three compression cycles an hour, and even then, we wouldn’t be happy,” explains Jon. “But on this project, the compressor is kicking in and staying on for an incredible 22-23 hours at a time. That’s where the extra efficiency comes from – fewer starts. It’s a bit a bit like cruising up a motorway instead of taking your car on lots of short journeys.”

Jon has also worked with Anthony to change the hot water programming, with different approaches for winter and summer. “When you have a Viessmann heat pump on weather comp, as soon as you put your heating on in September, the circulator pump is running and ticking over continuously until it goes off in the spring,” Jon continues. “So, rather than having hot water cycles in winter, we’re running the cylinder so that it stores water at a slightly lower temp of 45o, with a range of -5 and +2. In other words, if the temperature dips to 40 o, it heats up to take it to 47o. Any residual energy is dumped into the house.

“In the summer, we’re probably going to change that to one or possibly two heat cycles, predominantly around 3pm when the air temperature is higher. As we’re firing it up specifically to do hot water, efficiency will be slightly impacted by storing the hot water, but overall, it will likely be the most cost-effective approach. And that’s the key thing. Efficiency is important, but at the end of the day, what most customers care about is what things cost. The difference the lower bills have made to Anthony’s life is huge. It just goes to show, when a system is used effectively with correctly selected equipment, the payback can be rapid.”

System specifications

• 8kW Vitocal 151-A

• Weather compensation (no room influence)

• Open-loop system

• Nine legacy radiators