Hydronic boilers primarily burn fuels such as natural gas, oil, or electricity. The choice of fuel depends on availability, cost, and efficiency. Natural gas is the most common fuel for hydronic boilers in the United States due to its abundance and relatively low cost. Oil-fired boilers are also prevalent, particularly in areas where natural gas is not readily available. Electric hydronic boilers are less common but offer the advantage of being environmentally friendly and having no emissions.

The preference for natural gas over other fuels is driven by several factors. Firstly, natural gas is the cleanest-burning fossil fuel, producing fewer greenhouse gas emissions than oil or coal. According to the U.S. Energy Information Administration (EIA), natural gas emits about 55% less carbon dioxide per BTU than oil and 45% less than coal. This makes it an attractive option for reducing the environmental impact of heating systems.

Additionally, the cost of natural gas has been relatively stable and often lower than that of oil, making it an economical choice for boiler operation. The EIA reports that natural gas prices have been relatively low compared to other fuels over the past decade, which has further solidified its popularity in the residential and commercial heating markets.

Oil-fired boilers are still widely used, especially in regions where natural gas infrastructure is limited. While oil is less efficient and produces more emissions than natural gas, advancements in oil boiler technology have improved their efficiency and reduced emissions. However, the rising cost of oil and environmental concerns have led many consumers to seek alternative heating solutions.

Electric hydronic boilers are gaining traction, particularly in areas with high electricity prices or where renewable energy sources are abundant. These boilers can be powered by electricity from solar panels or wind turbines, making them a sustainable option. According to the EIA, the cost of electricity for heating is generally higher than that of natural gas or oil, but the overall environmental benefits can outweigh the higher operational costs.

In conclusion, the most common fuels for hydronic boilers in the United States are natural gas and oil, with electricity being a growing alternative. The choice of fuel is influenced by factors such as cost, availability, efficiency, and environmental impact.