Roman Great Drain + Bath water + modern technology = heating medieval Abbey

Background to Footprint

Shock, horror!  Bath Abbey's magnificent floor is collapsing!  However, what at first seemed a total disaster for a centuries old, iconic building has become a once-in-a-lifetime opportunity - and probably the most important church project in the country today - the Footprint project.Whilst lifting the 800+ enormous memorial stones to repair the floor, we can install an innovative, eco-friendly underfloor heating system that will harness excess energy from Bath's natural hot spring waters to heat the Abbey. 

Footprint will lead the way: there is no known precedent for a heat recovery system using natural hot spring waters in a medieval building - and Footprint will encourage other historic buildings to seek innovative ways of adapting and using modern technology to reduce their impact. Using the constantly available natural hot spring waters will significantly reduce the Abbey's massive carbon footprint in a particularly sensitive location (UNESCO World Heritage Site and conservation area) and will sustain it for many generations to come.


Bath's famous hot spring waters rise naturally to the surface at a temperature of around 45 degrees and a total flow rate of 14-15 litres/second throughout the city. These natural springs feed both the historic Roman Baths and the modern Thermae Bath Spa - but so much of the 1.2million litres of water that is available each and every day is simply wasted.

Via the subterranean Roman Great Drain, vast amounts of unused hot water flows past the Abbey and out into the River Avon.  The Romans knew what they were doing - the drain is still in excellent condition and perfectly placed to provide the solution to the Abbey's inefficient, fuel-hungry Victorian heating system. As part Footprint, 'Energy Blade' type 'closed loop' heat exchangers will be submerged in the Roman Great Drain to harness the excess energy in the unused water which will then heat the Abbey.

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Research, Investigations &Approvals

Extensive research and consultation has taken place over a number of years; numerous trials and tests have been carried out to establish acceptable water levels in the Great Drain and the impact of heat extraction on water temperatures and drain stability.  A quality analysis of the hot spring water has been carried out by Wessex Water and liaison undertaken with numerous specialists to scope out the specification and costs for a tailor-made heating system.  Investigations in the Great Drain confirmed it would be possible to raise the water depth to 600mm so that an Energy Blade of maximum 3000mm x 450mm could be installed. Trials also established dirt/silt build-up, temperature changes and fortuitously covered different weather periods, including one of heavy rain and the River Avon flooding. Whilst conducting a trial repair of the Abbey's collapsing floor in 2013, new pipes were laid to test the effectiveness of underfloor heating.


Hot Spring Water Heat Pump Specialist Package

Advice received from the engineering firm carrying out tests and investigations stressed the importance of the complete hot spring water recovery system (including heat exchangers, heat pumps and associated items) being provided by one specialist contractor.  A 'Design & Build' package and an outline budget for the supply and installation of the system has therefore been sought and provided.

Pipework will be required to connect the heat exchangers in the Great Drain and the heat pumps in the Abbey boiler plantroom, and this will be pre-insulated to minimise heat loss. The existing boiler room is below ground with limited access, so thge new heat pumps will be located in an adjacent disused coal vault and the existing boilers will also replaced. New boilers will provide back-up for the hot spring water heat pumps.  Once complete, boilers and hot spring water heat pumps will be connected to the underground pipework to heat the Abbey.

Designed to meet a 200kW heating load, the system comprises:

  • 125mm flow and return pipework
  • 2 x 500lt cooling buffer tanks
  • 2 x 1000lt heating buffer tanks
  • Air and dirt separators on both heating and brine pipework
  • Pressurisation unit and expansion vessel on heating pipework
  • Suitably sized expansion vessels
  • 9 x 2 panel 316 Stainless Steel Energy Blades
  • 25mm Gantry above Energy Blades

with either:

  1. A pair of 66kW Stiebel Eltron heat pumps and controller putting out 194kW at the specified conditions, or
  2. A Dimplex S175TU 75kW Heat Pump and a Dinplex S150TU 50kW heat pump with a controller putting out 183kW at the specified conditions

The total costs are:

Option 1: £211,315.00

Option 2: £209,225.00

The prices include installation and pressure testing of all plant room pipework to suitable standards, including provision of all necessary control wiring to enable correct operation of the heat pump system, plus full installation and commissioning of the system, but do not include VAT.  For an additional £4,100 there is the option to include a metering package if the Abbey decides to go down the Renewable Heat Incentive route.