Gas-fueled hot water boilers are the most popular choice in the United States in 2015, followed by oil-fueled hot water boilers. The technology used in these systems also makes them the most energy efficient for heating water for residential use.
When purchasing a boiler, homeowners must decide whether to purchase a model designed to provide hot water for in-home use or whether to purchase two standalone systems. While it might be tempting to purchase a cheaper boiler and an electrical water heater, the ongoing savings of integrated models saves money over time. Electrical water heaters are rated highly in terms of efficiency, but the cost of electricity makes them more expensive to operate. Although power plants are designed with efficiency in mind, they must convert generated energy into electricity, which always incurs a significant cost in terms of efficiency.
For combined systems, steam distribution tends to be less efficient than hot water distribution. Since steam boilers operate at higher temperatures, water from condensing their steam is too hot to meet most regulations, meaning it must be cooled down significantly. This cooling leads to wasted heat, driving the operational costs up significantly. As a result, many steam boilers lack the ability to provide residential hot water, which, combined with their less efficient operation, contributes to their falling popularity.