A condensing hot water boiler heats homes and conserves the energy that, in other types of boilers, would escape out the chimney. When the boiler burns gas to produce water vapor, the vapor condenses into a liquid again, releasing latent heat, which boosts efficiency ratings as high as 98 percent.
The latent heat in the water gives condensing hot water boilers one of the top AFUEs (Annual Fuel Utilization Efficiency) ratings. Some manufacturers, such as Rinnai, produce models that combine to heat entire dwellings as well as domestic hot water, so that people can get hot water on demand, rather than having to wait.
Some characteristics to look for in a condensing hot water boiler include a heat exchanger made of stainless steel to resist corrosion; OSS, or one-side sealed construction, to provide stability through the cycles of contraction and expansion that accompany temperature changes; and an integrated boiler pump to increase overall efficiency and ease of installation. It is also important to choose a model that is compatible with the current ventilation ability in the building and the space requirements.
One of the largest monthly expenses associated with home ownership comes from climate control, and a condensing hot water boiler can cut that expense in the colder months significantly.