Case Study
Grant Solar Thermal system and thermal store partner up with VortexBlue oil boiler
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Grant Solar Thermal system and thermal store partner up with VortexBlue oil boiler
Credit: S Calvert Plumbing & Heating
The Grant Solar Thermal panels installed as part of the heating system upgrade for a large property renovation in Pembrokeshire.

In 2019, a large property in Llanfyrnach, Pembrokeshire underwent a complete refurbishment which included upgrading the heating system. Today, the home’s heating and hot water requirements are being met more sustainably by a bespoke hybrid system consisting of a Grant Solar Thermal system installed alongside a VortexBlue oil boiler.

Last summer, a large renovation project got underway in West Wales which involved completely clearing and redesigning the property’s interior, converting the attic into a bedroom, and building two extensions at either end of the property. The living quarters in the property now comprise over three floors which include six bedrooms, three bathrooms as well living space on the ground floor. With the size of the property increasing, a brand new heating system was required to meet the larger heating and hot water demand of the home.

Prior to the renovation, the property was heated by a non-condensing oil boiler so the homeowner wanted a direct boiler replacement which operated more efficiently and incorporated cleaner burning technology. After discussing the options available with the installing engineer, S Calvert Plumbing & Heating, a Grant VortexBlue Internal 26kW condensing oil boiler was selected for the installation. This utility model, which can achieve efficiencies of up to 91.71%, is white cased which makes it a sleek option to suit either a kitchen or utility room environment. For this installation, the boiler has been sited in the utility room.

In addition to the oil boiler, two other products from Grant’s product portfolio were installed. A Grant solar thermal system was fitted which comprises of two flat plate collectors. The collectors have been installed as part of an in-roof mounting arrangement allowing for a low-profile appearance. Grant’s in-roof mounting option comprises of the collectors being set into the roof tiles, naturally following the roof's angle to capture maximum energy from the sun.

The Solar Thermal system at this property has been connected to a Grant ThermaWave 400ltr thermal store. These hot water stores allow several heat sources to be connected on one system, in particular combining traditional heating systems (such as an oil boiler) with renewables (such as solar thermal). With this installation, the thermal gain from the solar panels heats the water which is then transferred to the ThermaWave store. Here the water is kept up to temperature and stored ready for when the property’s occupants demand water. By connecting multiple systems, the ThermaWave store has enabled this homeowner to utilise green energy alongside an oil boiler, reducing both their carbon footprint and energy bills.


This heating system upgrade was a large project for Steve Calvert, the G1 installing engineer. Steve designed the system himself to help maximise the benefits the system delivers, in particular setting the system up so that the thermal gain generated by solar thermal panels meets the majority of both the heating and hot water demand for the property. Consequently, Steve’s bespoke design has resulted in a unique hybrid system which requires the VortexBlue oil boiler to operate for a small proportion of the property’s heating demand.

We caught up with Steve to learn more about his innovative system design and how it operates. “The 400ltr thermal store is controlled by the solar controller with twin stats at the top and bottom of the store. The boiler is set to fire up when the top of the store is at 50°C and will remain running until the stat at the bottom of the store registers 65°C. This arrangement allows the boiler to run for 30 minutes, operating with optimal condensing and maximising efficiency with no cycling within the boiler.

“The energy produced by the solar thermal overrides the boiler input so that the solar gain delivers most of the heat needed for both the hot water and space heating. Two controllers are set up on the system which prioritise the energy from the sun over the boiler, thus reducing the demand on the boiler. Consequently, throughout the Spring, Summer and early Autumn, the solar thermal system should provide all of the property’s heating and hot water with the boiler required only during periods of extreme cold.

“To complement the store controls, the heating system is set to be low temperature at 45°C max. The heating lines are electronically mixed and, during periods of high solar gain, the circuit that the towel rails are set up on are able to be ‘heat dumps’ to ensure that no energy or heat is wasted. A hot water accumulator vessel is also installed to stabilise the system during peak periods of demand.

“I have designed this system in such a way so that the Grant Solar Thermal works the most to meet the heating requirements of this large property, rather than the boiler,” concludes Steve. “The system works on 10 hours of heating demand with the boiler only required for approximately 20% of this, unless of course solar gain is high in which case the VortexBlue boiler is not needed to kick in. This install demonstrates how solar thermal can play a dominant role in a heating system, not just as a supporting technology.”

Grant Solar Thermal system and thermal store partner up with VortexBlue oil boiler
Credit: S Calvert Plumbing & Heating
The Grant VortexBlue Internal oil-fired boiler installed in this heating system upgrade

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