Combi boilers are tanks or vessels used primarily to transfer thermal energy from a heat source to water or a stream in accordance with the demand for hot water. Combi, or combination, boilers are different from conventional models because they do not store hot water but rather heat it rapidly on demand.
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Combi boilers have a second heating element to speed the heating process and maintain a steady supply for as long as the boiler runs. Boilers produced for commercial or industrial uses are much larger in size and capacity compared to residential units. Industrial boilers either use electricity or a fuel such as wood, coal or natural gas to operate. In the most basic definition, boilers apply heat to water, which, as it boils (hence the name), circulates through the system in the form of steam. Boilers are usually rectangular with the heating source and components housed in a cast iron, copper or steel enclosure. Most boilers are housed in a fireproof, well-ventilated, stable-air environment within the building that they are heating. Combi boilers are used to heat air for schools, offices, factories, manufacturing plants and virtually any other building that requires warmth. Mobile units are used to provide temporary hot water or steam power in emergency or military situations. Hot water is also a necessary component in many manufacturing processes.
There are two main ways boilers use to generate heat: fire-tube and water-tube. The first operates by directing heat through a heat exchanger, often metal rods or tubes, that is centrally located in a vessel immersed in water. To maximize efficiency, heat can pass through the rods or tubes many times before leaving through the flue. Fire-tube systems also have good surface area heat transfer. In a water-tube boiler, heat is directed through metal rods or tubes that are themselves filled with water. These boilers are vertically oriented and are able to generate more steam, though they can store less water. In a combi boiler, either one of these methods may be used but they are usually both the same method. Though a combi boiler is able to provide an endless source of hot water or air when provided with a steady supply, some models are not able suitable for use by multiple users. In cold weather, the water may take longer to heat, even though there are two heating elements in the boiler. Combi boilers may also be a type of condensing boiler, which captures the steam and condenses it back into water to be used again, thus increasing its efficiency. Combi boilers are smaller than most other boilers because they do not require a water tank for storage.
