What is the best method when sizing an oil fired hot water boiler? Is it best to go by the DOE rating or the IBR rating? In the past I have always used the IBR rating but I have read differnet arguemnets on this and was looking for your input. After doing a heat loss on a building if I find the heat loss is on the high side of a 3 section boiler I may recomend a 4 section and down fire the boiler to the lowest recomended rate for better efficiancy. Is this wrong?