Christ Church Unitarian Chapel
Bridgwater  Somerset

Christ Church Unitarian Chapel is the oldest non-conformist Chapel in Bridgwater there being a building on this site since 1662. This first meeting house was demolished in 1683 and its contents destroyed.

The meeting house as presently built was erected in 1688 with an extensive restoration
carried out in 1788.

The engineering services comprising gas lighting and central heating were installed
during the Victorian period.

The building was Listed Grade II* in 1950.

The Heritage Group was notified that the heating system in this Chapel was thought to have a saddle type wrot iron boiler still in situ. As saddle boilers can date back to the early Victorian era every one now discovered has historic and engineering heritage importance. 

A site visit March 2013 by the Heritage Group was arranged for an inspection of the Chapel and its heating system. This wet system had remained unchanged since its installation in the mid-Victorian period circa.1860 and was thought to have a most unusual water circulation system. What was found became an exciting discovery.

The Chapel Interior

The Chapel has four aisles forming a rectangle around the building that allows access to the box pews on either side. In the centre of the floor of each aisle are laid decorative cast iron floor plates with small openings along either edge. The floor plates are laid in sections each approx 400mm wide by 1500 mm length.

The Saddle Boiler

The boiler for the heating system sited in a small semi-basement room is a saddle pattern set into brickwork, with flow and return cast iron (CI) pipework laid within the brickwork enclosing the boiler.

There was no name inscribed on the boiler, but the decorative floor plates in the aisles of the Chapel bore the name Garton & King Manuft’s Exeter. This engineering firm was well known in south west England and had been in existence since the 17th century with their own ironfoundry operating since the 19th century.

The flow and return CI pipework (approx 3” dia.) from the boiler then entered into a small under floor duct. What then made this heating system different and possibly unique was that these two pipes appeared to connect directly to a metal trough.

The Distribution System

Examination of the floor plates showed that there was a cast iron metal trough sited underneath. The trough was fitted tight to the underside of the floor covers and secured to it by screws. Each length of trough was constructed with one end socket into which the spigot of the next section was jointed by using caulking hemp/rope soaked in black mastic. Both sides of the trough had flanged tops with a slight grove into which was laid a hemp rope soaked in black mastic. This sealed the top of the trough when screwed to the underside of the plate making the trough watertight. 

The metal trough (internal dimensions of 81/2 ins wide by 5 ins deep) would have been filled with water that circulated by gravity circulation. The heating system water circuit was arranged as a simple single loop around the four aisles from and returning back to the boiler.

The floor surface of the four aisles is flat and level with no steps, so the water could only have circulated due to the circulating pressure created by the small height difference of approx 900 mm between the flow and return pipes connecting to the saddle boiler.

The Air Venting 
Another strange feature of this heating installation is that no obvious cold feed or air vent pipework could be found. However upon inspection, the two far corners of the floor trough are each fitted with a small lead pipe having an open end, placed into the top of the trough. These lead pipes then rise up inside the end corner of the adjacent box Pew, which has a series of small holes drilled into the box pew corner. This appears to be the means by which the sealed water trough was air vented.

Filling the Water Trough

Another query was deciding what method could have been used for filling the water trough. Inspection of the decorative floor plates found a number of small circular holes drilled in the centre of the plate that could have been used as filling positions. The holes are located in one aisle at the start of the trough on the flow side, with similar openings at the end of the trough on the return. These circular holes could have held a funnel through which the water was poured. Dip-sticks would have been used to measure the correct depth of water. Removable plugs could then be fitted in the holes.

Where did the water come from that was needed to originally fill the system. In the semi-basement room close to the boiler is an open Well full of water. This Well must have provided the water used to fill the whole system, most probably by bucket. The quantity of water calculated to fill the trough would have taken approx 100 normal size buckets.

Design Considerations
To have had any positive effect in raising the space temperature of the Chapel would have required the circulating water to have been very hot to maximize the radiant and convective output. The high surface temperature of the floor plates may have been capable of causing a skin burn if touched.    

The saddle boiler was solid fuel fired with no safety or temperature controls fitted, so the overall control of boiler temperature and its output was at the discretion of the person acting as the stoker fireman. To start the water contents of the system moving and achieve an initial gravity circulation must have required the boiler flow temperature to be very high close to boiling point. Otherwise there would not have been sufficient temperature difference between flow and return pipes to “kick start’ the circulation.    

Whether this new method of circulating hot water was capable of providing sufficient heat to raise the air temperature in the Chapel to an acceptable comfort level is questionable. The water circulating in the trough could only transfer its heat to the occupied space above firstly, by conduction and radiation from the warm surface of the floor plates, and secondly by convection through the small openings in the sides of each section of floor plate.

As the building would have had intermittent usage, the length of pre-heat time would have been disproportionate to achieve the required space temperature. Most likely the boiler when started at the commencement of the heating season would have remained alight and only banked down during the period when the Chapel was not in use. This method would have kept the large quantity of water in the trough always warm never allowing it to become cold.

The success of this method of circulating hot water around the building is highly debatable. So the search must continue to discover other Garton & King heating systems from the Victorian period having a similar water circulatory system. Until another system is found then the assumption must be that this new method was most likely a one-off that proved to be unsuccessful.  

Finally the cost of the Installation

APRIL  2013