Mechanical Systems: Indoor

The last thing residents need is a sudden shutdown of heat on a cold January night. Address the condition of your boiler and heating-system mechanisms well before cold weather sets in.

Boilers. As part of your maintenance contract with a heating contractor, have the boiler's flue checked to make sure it is clean and not blocked or partially collapsed. If the boiler's combustion gases cannot freely exit through the top of the flue, they may diffuse to apartments or other building spaces, creating a hazardous condition. Check flue tubes, over which hot water or steam passes, to ensure they are not leaking or clogged, as well as the insulation around the boiler piping.

Most boilers require some type of chemical treatment to inhibit rust and corrosion, Your heating contractor will add the chemicals before the heating season and then continue the procedure once every month or two thereafter.

Burners. Your heating contractor should also conduct a test to determine the burner's combustion efficiency. Maximum efficiency for common Scotch-marine boilers is roughly 85 percent; 80 percent or less is too low and will burn more fuel. The oil-transfer and oil-preheating systems are also part of the contractor's checklist.

Radiators. A common resident complaint about these is the loud banging. This noise is caused by steam coming in contact with cooler water (condensate), creating a rapid expansion of the condensate water in the pipes. Radiators in prewar buildings typically have just one pipe shared by both the steam and condensate. Single-pipe systems rely on the pipe's downward slope to return water back to the boiler for heating it back into steam, but, in aging pipes, the condensate can get trapped. Steam hitting this trapped condensate creates that hammering sound. The pipe may have to be repositioned or replaced to eliminate the banging.

In a two-pipe system, one pipe is used for steam supply and another for condensate return. A steam trap at the bottom of the radiator expands when steam comes in contact with it, blocking the steam from exiting the return pipe. Operating like a diaphragm, steam traps expand and release thousands of times in a heating season, so the element will eventually fail. When a radiator remains cold even as steam is flowing to it, it could mean the steam trap is no longer working and needs replacement. You should also check the air-release valves on the side of the radiator (they should hiss as steam enters the radiator) and replace as necessary.

Mechanical Systems: Outdoor

Cooling towers. Buildings with central chillers, heat pumps or fan-coil units use rooftop cooling towers to reduce the temperature of the condenser water circulating through the system. Many properties shut down their cooling systems around October 1, at which time New York City buildings are required by law to provide heat. Supply valves are closed off and drain valves opened to remove any leftover water in pipes to prevent freezing.

Some heating and cooling systems, however, operate year-round. For these systems, water in the cooling tower must be kept from freezing either by adding a glycol-based fluid (antifreeze) or using immersion coils that heat the water. Wood tanks used only as a fire-standpipe supply also need immersion coils to keep the water from freezing.

Brick vents. These vents on the façade of the building bring in fresh air from the outside for fan-coil units used to cool apartments in summer. During the winter, when the fan-coil units are being used for heating, drafts can enter if the dampers to the vents are not shut or sealed. The dampers, however, can be tricky to access: the cover may have to be removed, and a hard-to-reach lever pushed or pulled. For dampers that are stuck or do not close all the way, removable foam insulation can be inserted around the edges of the unit as a temporary measure.

Outdoor piping. Cold water pipes running to and from a rooftop water tank or cooling tower are often heated using an electric coil, known as heat tracing, wrapped around the pipe to keep the water inside from freezing and the pipe from bursting. A layer of insulation is wrapped around the heat tracing, which is plugged into a ground-fault circuit-interrupter on the roof. A routine roof check should include making sure the heat tracing is plugged in and none of it is exposed by insulation that is worn away or missing.

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