3-Bedroom Semi-Detached House | 71m² | Epsom, Surrey
The Challenge
The homeowner contacted EVO Heating & Renewables through Heat Geek while undertaking a complete renovation of their property. Their goal was to replace an ageing gas heating system with a modern, energy-efficient solution that would deliver exceptional comfort, low running costs and long-term reliability.
The existing system consisted of a 25-year-old non-condensing gas boiler, a gravity-fed copper hot water cylinder, ageing plumbing and an original lead incoming water main. Rather than simply replacing the heat source, we designed and installed a completely new low-temperature heating system engineered specifically for this home.
BEFORE: 25-Year-Old Boiler & Lead Main
AFTER: Precision-Engineered ASHP
Every Great Heat Pump Installation Starts with Design
Before selecting any equipment, we carried out a detailed room-by-room heat loss calculation, taking into account the customer’s planned insulation improvements as part of the renovation. The result surprised the homeowner. The property’s total design heat loss was calculated at just: 3.4kW.
For this 71m² semi-detached home, the correct solution was a Vaillant aroTHERM Plus 5kW Air Source Heat Pump. What made this project particularly interesting was that another installer had previously recommended a 12kW heat pump—over three times larger than the property’s actual heating requirement.
Why Oversizing Matters:
Installing an oversized heat pump would have resulted in significantly higher installation costs, increased electricity consumption, lower seasonal efficiency, and a reduced equipment lifespan due to excessive compressor cycling. This project perfectly demonstrates why heat pumps should never be selected based on guesswork—they should always be selected through engineering calculations.
A Complete Low-Temperature Heating System
Once the design was complete, we removed the existing heating system and installed a Vaillant aroTHERM Plus 5kW Air Source Heat Pump and a Vaillant uniSTOR 200L Heat Pump Cylinder. The entire heating system was designed to operate at just 38°C flow temperature, allowing the heat pump to run at maximum efficiency while maintaining excellent comfort throughout the property.
Rather than installing a heat pump onto an outdated heating system, we built an entirely new low-temperature system designed to work as one.
The new Vaillant uniSTOR 200L cylinder perfectly integrated into the property loft space.
Whole-House Underfloor Heating
Instead of retaining conventional radiators, we installed wet underfloor heating throughout the entire property. Underfloor heating is perfectly suited to modern heat pumps because it delivers the required heat output at much lower water temperatures.
The benefits include: Even heat distribution, superior thermal comfort, lower running costs, higher seasonal efficiency, and clean interior spaces without radiators. Combined with a 38°C design flow temperature, this creates one of the most efficient heating solutions available for modern homes.
Complete Plumbing & Drainage Installation
As part of the renovation, we carried out extensive plumbing works throughout the property, including complete new heating pipework, new kitchen, bathroom and cloakroom plumbing, and a new above-ground drainage system. We also replaced the original lead incoming water main with modern MDPE pipework—improving water quality and future-proofing the connection for decades to come.
Premium Water Quality Protection
A modern heat pump is only as reliable as the water circulating through it. Before commissioning, we carried out a full system power flush and fully demineralised the heating water to comply with VDI 2035 standards using an IONIX MiniView 360 filling valve.
We also installed an Inta magnetic filter for continuous protection and a whole-house water softener to protect all taps, showers, and appliances in this hard water area.
External Detail & Intelligent Control
External primary pipework was insulated using 19mm Primary Pro insulation, and condensate pipework used Condense Pro insulation to prevent freezing. Rather than connecting into the house consumer unit, we installed a dedicated unit exclusively for the heating system for simpler diagnostics and servicing.
The entire system is controlled using Vaillant weather compensation, automatically adjusting output based on outdoor temperatures to deliver lower running costs and higher seasonal efficiency.
Heat Geek Performance Promise
This installation is supported by the Heat Geek Performance Promise. If the completed system does not achieve its agreed design performance because of the heating system itself, we will investigate the cause and carry out the necessary remedial work. This gives our customers confidence that performance matters just as much as the installation itself.
Project Summary
Property: 71m² 3-Bed Semi-Detached | Epsom, Surrey
New System: Vaillant aroTHERM Plus 5kW & uniSTOR 200L Cylinder
Design Flow Temperature: 38°C
Grant: £7,500 Boiler Upgrade Scheme (BUS)
Warranty: 7-Year Vaillant Manufacturer’s Warranty
Stop Guessing. Start Engineering.
At EVO Heating & Renewables, we believe in designing the right heating system—one that’s engineered to deliver exceptional comfort for decades to come.
Engineering First. Equipment Second.
This project demonstrates exactly what separates a designed heating system from a boiler replacement. Instead of an oversized 12kW unit, we engineered a complete 5kW low-temperature system around the property’s actual 3.4kW heat loss.
