If it is a one-off or DIY project, it would be hard to know. If it is one of the following, you might find instructions for it.
http://www.baxi.co.uk/products/gas/back_boilers/bermuda_concept.html
http://www.baxi.co.uk/products/gas/back_boilers/
The UK's largest manufacturer of domestic space heating products, including Valor, Wonderfire and Baxi fires and Morso stoves.