Hi I am working at a manufacturing plant and we are applying a second layer of glass fibre/alumnium foil insulation to an industrial cylindrical boiler, on top of a previous layer. I need to calculate the approximate savings to be able to give a ROI figure. The surface temp of the current boiler insulation is 90c under average load (i am going to assume average load as a constant as it is fairly stable) and the thermal conductivity of the new layer of insulation is 0.033 W/mk at 10c The surface area of the boiler is 19m2 around the length of the boiler. (the ends are being insulated by other means). I take it once i have calculated a new surface temp i can work that out as equivelant energy from the calorific value of the gas against the internal temp of the boiler? This is all the information i have at the moment but i am a bit stuck, obviusly the figures are fairly loose but i have to justify expenditure where possible. this is a cheap saving but it would be useful to know the approximate annual savings. if any other figures are needed please let me know. thanks in advance.