In the HVAC world, a boiler is a combustion appliance designed to heat water. While some boilers produce steam for heating or other purposes, those used in home heating systems today are likely to be the hot water type.
Most residential boilers are designed to burn oil, propane or natural gas.
Boilers are described by size, efficiency and combustion
Like furnaces, heat pumps and other HVAC components, boilers are described according to size, efficiency and the type of combustion or venting that is utilized.
Here’s a brief summary of these descriptive terms:
- BTU output denotes size. The amount of heat energy a boiler can produce is measured in BTUs (British Thermal Units). For example, a medium-size boiler might have an 80,000 BTU rating.
- AFUE defines efficiency. “Annual Fuel Utilization Efficiency” tells you the percentage of input energy (fuel) the boiler can convert to output energy. An old boiler is probably operating with an AFUE of 60%-75%. The most efficient new boilers are rated at 90% and above.
- “Direct-vent” boilers don’t require a chimney. Old-style boilers exhaust their combustion gasses through a chimney. “Direct-vent” boilers extract much more heat from fuel, so their combustion gasses are much cooler. Instead of venting through a chimney, a small fan blows the exhaust outside through a plastic pipe. A direct-vent boiler is sometimes referred to as “condensing” boiler because water condensation occurs in the boiler’s secondary combustion chamber.
- “Sealed-combustion” boilers get combustion air from outside. Some direct-vent boilers are also sealed-combustion models, which means that the air required for combustion comes from outside the house rather than from inside. These boilers are appropriate for houses that have been tightly air-sealed to limit air infiltration. By drawing air from outside for combustion instead of from the inside, it doesn’t create a vacuum inside the house, causing outside air to leak into the house. By drawing air from outside for combustion instead of from the inside, it doesn’t create a vacuum inside the house, causing outside air to leak into the house.
Combi-boilers supply hot water for heating and washing
Boiler repair and installations in West Virginia. Regardless of the fuel used, a boiler can supply hot water for heating alone or for heating and washing. A boiler that does both jobs is often referred to as a “combi-boiler.” With a combi system, no separate hot water heater is necessary. In fact, when the boiler is running to provide water for whole-house heating, hot water for washing is heated for free.
Boilers supply hot water for different “hydronic” heating systems
“Hydronic” is a term used to describe any HVAC system that uses water or fluid. There are several different types of hydronic heating systems that utilize boilers. Hot water can be pumped to baseboard and other types of radiators located throughout the living space. It can also be circulated through plastic tubing that has been installed beneath finished floor surfaces. In this type of “hydronic radiant floor” heating system, the flooring becomes a giant radiator to provide home heat.
A third type of hydronic heating system, called “hydro-air,” circulates hot water from the boiler to a heating coil in a duct system, where a fan circulates the heat to the rooms in your house.