The Beam Engine at Tees Cottage requires steam to generate power. This steam is produced in one of two, coal fired, Lancashire boilers dating from 1902. Currently only one boiler is used for this purpose.

The two boilers were constructed by Teasdale Brothers of Darlington in 1902, one operating and one on standby. Each contains 3,300 gallons of water and takes five days to warm up from cold. Gradual warming is necessary to reduce the thermal stress on the boiler so helping to preserve it for as long as possible. The energy required for steam generation is provided by the combustion of coal, up to four tons per day when working in anger. Today, half a ton of coal is consumed each day of an Open Weekend.

The fuel (waste wood and then coal) is ignited in each firebox and the resultant hot gases then pass through two tubes which run through the water contained in the boiler drum. These gases heat the water to boiling point, creating steam. The steam escapes through a pipe at the top of the boiler and is fed to the Beam Engine.