Boilers designed to handle two types of fuel only save money if the cost of the fuels used fluctuate significantly. If the cost of natural gas is consistently lower than the cost of heating oil, for example, the dual-fuel burner does not save money.
New dual-fuel boilers are more expensive than their single-fuel counterparts. However, many dual-fuel boilers are converted units. Homeowners who wish to switch to natural gas, for example, may save money by converting their oil-burning unit into one that can handle both types of fuel. These boilers also provide heating backup if a gas line is broken and if heating oil is available.