FAQ CHECK: BOILER BASICS

Q. What provides a building with heat and hot water?

A. Most apartment buildings each use a steam-heat system consisting of: fuel, whether it's oil stored in an oil tank or natural gas that comes through a pipe called a gas train that runs from the utility's gas main (the line coming into the building); a burner, which  turns fuel into heat; a boiler, in which water is heated; and a heat-distribution system, which is the collective name for the risers, branch lines, heating units (radiators, baseboard heaters, etc.) and air-release valves that together distribute heat through a building

Q. What types of boilers are used?

A. The vast majority of midsize to large apartment buildings each use a steel Scotch marine boiler, which is a type of fire-tube boiler. Heat passes from the burner through sections of tubing before being emitted out a chimney stack. Water in the boiler is heated by the tubes, producing steam, which is piped throughout the building to heating units such as radiators or baseboards in individual apartments.

The building's domestic (potable) hot water runs on a separate line from the water used for heating. It can also, however, use the heat produced from the boiler, via an integral hot-water coil, to heat the water that supplies kitchen and bathroom faucets, toilets, dishwashers, washing machines and the like.

They're called "marine" boilers since they were originally used on ships

Two other types — sectional cast-iron and modular cast-iron — are more common than steel boilers in new construction and low-rise developments. Iron boilers are much heavier and more difficult and expensive to replace. In addition, iron boilers usually have a lifespan of less than 25 years (as opposed to 30 for steel Scotch-marine) and are typically limited to smaller buildings because of their limited power generation (175 horsepower, compared to up to 700 HP). On the plus side, cast-iron boilers do not require as much space as steel boilers and therefore are frequently found in buildings with small basement areas.

Q. What are their useful lifespans?

Scotch marine boilers have a lifespan of roughly 30 years. Iron boilers usually have a lifespan of less than 25. Burners typically last 15 to 20 years, and oil tanks 35 to 40.

Q. Is there any advantage or disadvantage to having a single boiler for both heat and hot water, rather than a separate boiler for each?

A. While it's less expensive to install one large boiler equipped with an integral coil for hot-water production, this setup leaves the building vulnerable to a complete loss of heat and hot water if the boiler breaks down. Ideally, rather than one large boiler (even if equipped with a separate hot water heater for use during warm-weather months), it's recommended to have instead two slightly smaller boilers (say, 75 percent capacity each). With this configuration, your building can alternate between the two boilers, which improves heating efficiency and extends the life of the boilers in addition to providing redundancy protection.

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