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1950’s Retrofit:

Heating system overhaul, Solar PV and battery storage.
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Age/Period: 1950s
Type: 2 storeys semi detached
Years in residence: 10
No. Bedrooms: 4
Wall type: Bath faced block cavity wall
Area: Larkhall

Key Features

Solar PV
Battery Storage
Condensing boiler
Wastewater heat exchanger
Under floor heating
Solar-thermal hot water
Energy efficient lighting
Double glazed windows and doors


Toby and family moved into their home in 2013, built in the late 1950’s and in need of restoration the house lacked the warmth and feel of a modern home. Keen to implement established green technologies Toby and Sarah embarked on a long journey to reduce the energy demand of their family home and improve thermal comfort.


Heating system overhaul

The construction of a new rear facing kitchen dinner extension in 2013, provided the ideal opportunity to overhaul the existing heating system. Investment in a high efficiency Viessmann Vitoden 242 floor-standing gas condensing combination boiler with built in storage tank, allowed for further energy saving additions to be made.

The existing pipework and radiators from the ground floor were replaced with an underfloor heating system. Complete removal of the original suspended timber floor, and installation of an insulated concrete ground-slab provided, a new level of thermal comfort throughout the ground floor of their home.

As part of the heating system overhaul, Toby and Sarah opted to install a solar-thermal water heater on the south-west facing roof at the front of the property. Difficulties in sourcing a MSC certified installer, meant the homeowners were unable to take advantage of the renewable heat incentive on offer at the time. In-service, the experience of living with a combined solar-thermal and condensing boiler system was less than perfect. The solar-thermal hot water system caused several reoccurring faults and errors to be generated with the boiler controls, it was eventually removed and resold.

The installation of a wastewater heat exchanger finalised the heating system overhaul. Utilising the heat within the wastewater from the upstairs bathroom to preheat the incoming water, reduces energy demand from the boiler.

Solar PV

In 2020, motivated by the need to convert their loft space, the homeowners invested in an array of 10 solar panel PVs on the southwest facing roof at the front of the property. Combing installation of the panels with the loft conversion helped to reduce installation costs and need for extra scaffolding.

Capable of providing 3kW peak and power late into the afternoon, the panels costing approximately £5000 will have paid for themselves in approximately 8-10 years. The power supplied by the set-up is enough to partially offset their electricity consumption over the course of the year and is estimated to save approximately 565Kg CO2/Year.

Following a shift to electric vehicles, a 10-kWh bank of Gro-Watt batteries was installed in 2022 for about £5000, significantly enhancing the utilisation of the electricity produced by the solar PV array. Excess solar PV output can now be stored and then either sold to the grid or used, to help charge the electric vehicles overnight. The batteries may also be charged via the grid at lower prices in off-peak hours. The installation of the battery storage after the solar PV required a second invertor, which increased costs and results in extra losses.

Current monthly electricity costs for the household are as low as £30 per month in summer (using about 350kWh of grid power), or £100 in the winter (using about 600kWh of grid power), including charging for 2 electric cars. Toby commented that, to make the most of the off-peak charging you really need the right tariff.

The performance of the solar PV and battery storage is directly accessible through a mobile App, ensuring that monitoring and any adjustments to the battery charging cycle is easy to make.

Lighting & appliances

Alongside the significant investments in heating PV systems, several small-scale interventions to further reduce the energy demand have been thoughtfully implemented further enhancing the comfort within the family home.

Programmable dimmer switches and LED lighting provide controllable light levels throughout house, while motion sensitive stairway lighting ensure safe access to the stairs for the children without Toby and Sarah having to worry about leaving the lights on.

Reflective blinds fitted in the sky lights of the rear facing extension help reduce overheating from overhead sunlight in summer, whilst internal louvres reduce solar gains at the front of house.

Future plans: Air source heat pump

Toby and Sarah are keen to investigate the installation of an air source heat pump (ASHP), to replace the gas-powered condensing boiler. During the overhaul of the original heating system, pipework was arranged to allow for easy connection to an external ASHP situated at the rear of the property. ASHPs can be up to 500% efficient at extracting ambient heat from the outside air when used with underfloor heating, compared with a gas boiler’s 80% efficiency. The heat pump could reduce the home’s carbon emissions from heating and hot water by up to 85%.


GroWatt :