• Gas boilers are one of the most energy efficient heating options available.Comstock/Comstock/Getty Images
  
  Gas boilers offer the most energy efficient heating options for residential, commercial and industrial use. The American Council for an Energy Efficient Economy reports the annual fuel utilization efficiency (AFUE) ratings of gas boilers range is 80 to 99 percent. Gas boilers heat by burning gas and boiling water that is then circulated through pipes in radiators throughout the building. Add an indirect water heater to your gas water boiler to further increase your home or building's overall energy efficiency.
  
  

Weil McLain Ultra Series 3-UE

• Weil McLain manufactures the most energy efficient gas boilers available on the market. The Ultra Series 3 boilers boast an average AFUE of above 95 percent. The burner is made from stainless steel with an aluminum heat exchanger, which facilitates extremely low operating noise. The McLain Ultra Series 3 gas boilers offer a substantial increase in energy efficiency and savings compared to electrical heaters of similar heat output. It features six independent energy efficiency certifications, including the Energy Star and the Department of Energy. This series of boilers ranges from $3200 to $6233 as of November 2010 and qualifies for a tax credit of one-third of the price.
  
  

Lennox GWB9-IH

• The GWB9-IH is the most energy efficient model in the Dave Lennox Signature Collection of gas boilers. The boiler features Energy Star and Good Housekeeping certifications. It comes with a cast-aluminum heat exchanger for greater heat transfer efficiency. The GWB9 boiler is built with the combustion chamber sealed inside the unit for quick operation and no fumes escaping into your home. The shell of the boiler is made of thick, durable steel. Lennox provides a 15-year warranty on the heat exchanger and a 10-year warranty on the remaining parts. The boiler also qualifies for a tax credit.
  
  

Embassy Ambassador Onex OX-160C

• The Embassy Ambassador Onex OX-160C condensing boiler puts out 160,000 BTUs with natural gas or propane at 93 percent energy efficiency. The wall-hung boiler comes fit with a domestic hot water unit that produces more than 4 gallons per minute instantly. Adjust the heat level and hot water temperature with an electronic control panel on the boiler cabinet. The stainless steel heat exchanger add to its efficiency and durability. The OX-160C is Energy Star certified and qualifies for a tax credit. The unit sells for about $3600 as of November 2010 and comes with a five-year limited warranty on the heat exchanger and a one-year warranty on all other parts.