Bath Abbey restoration is part of the Heritage Lottery funded ‘Footprint project’, which highlighted a need to update the antiquated and inefficient heating system, to a new eco-friendly heating system.

Using a unique combination of Bath’s famous thermal springs, underfloor heating and ground source heat pumps, this project is one of the world’s first hot spring heating systems.

What did the project involve?

Bath Abbey has been used as a place of worship for over 1,000 years and has gone through several transformations during this time. Nothing has been as significant as this latest phase with floors being removed that have been undisturbed for centuries.

Many historical artefacts have been discovered and documented including a rare, complete medieval mosaic floor, two metres underneath the existing floor. The mosaic is considered a once-in-a-lifetime find by many archaeologists and has been a very exciting part of the overall project.

It is also estimated that the remains of up to 6,000 bodies were found within the floor, with many being carefully removed and replaced during the lengthy renovation process. Whilst the archaeological aspect of the renovation is unique, these findings have contributed to a challenging underfloor heating install, with many revisions to the design in order to remain sympathetic to the historical fabric of the building.

The innovation

Installing underfloor heating into a historic listed building must be undertaken with extreme care. In this case, we designed a bespoke clip-to-mesh system (MERCURY ARIAL) to ensure that no damage was caused to items of archaeological interest within the depths of the existing floor. It also enabled 20mm Grade-A PEX pipe to be installed beneath the screed, resulting in the original floor slabs of the Abbey being laid on top, retaining the look and feel of the Abbey from years gone by.

In addition to pipe positioning, the UFHN design had to make allowances for tombs. We also needed to consider how the system would be accessed and serviced. The solution was to horizontally set the MERCURY manifolds into trenches within the floor which can be accessed by a grille cover.

Our system design also had to be able to cope with 850,000 litres of 40° spring water that flows through the Abbey’s crypts and empties into the ground every day. Work has been carried out by others to divert the water through a network of underground pipes within Bath, contributing to the effective working of the carbon-friendly underfloor heating system. When harnessed and converted, the Abbey could potentially produce 1.5MW of continuous energy to support a 200kw Ecoforest ground source heat pumps, situated in a subterranean plant room that used to be the coal bunker for the original boilers at the east end of the Abbey.

The combination of using thermal springs and heat pumps alongside underfloor heating provides an environmentally friendly solution to heating Bath Abbey. Benefits include reducing electricity consumption, no harmful emissions and a significant saving on energy usage. The installation of ground source heat pumps in this project works by extracting heat from an underground source, reducing the reliance on fossil fuels.

Energy Savings

The heating bill for Bath Abbey has been astronomical as Victorian trench heating sends hot air upon a rapid trajectory into the high vaulted ceilings, stimulating down draughts from the windows that create cold spots at ground level. This has put Bath Abbey out of line with the Church of England’s ‘shrinking the footprint’ environmental campaign where the church of England as a whole is committed to an 80% carbon reduction by 2050.

By installing dispersed underfloor heating to create a low-level cushion of heat that does not rise so fast, powered by the geologically heated water passing through a Roman drain, this combination will enable Bath Abbey to contribute significantly to the Shrinking the Footprint target with projected savings of at least £30,000 per annum.

We designed the underfloor heating system to maximise the efficiency of the heat source, minimising running costs, whilst maintaining optimum comfort levels in 815m² of the worship environment. The initial investment, whilst high will not only future-proof the Abbey by utilising A-grade quality PEX pipework, but it will also have long-term financial benefit by reducing running costs and more importantly a reduced impact on the environment.

Heat pumps are generally well suited to historic buildings as they work efficiently when operated on a constant low temperature. The Abbey will heat up and cool down slowly, meaning there is less thermal movement within the building caused by expansion and contraction, thereby reducing potential damage such as shrinkage cracks.

We used a MERCURY underfloor heating system, manufactured in Europe using recyclable properties. The PEX pipework used in this project has been guaranteed for 50 accelerated tested to simulate 100+ years, ensuring Bath Abbey will benefit from an efficient and virtually maintenance-free heating system for years to come.