Steam heat

A steam system is simple at heart: water, fire and pipes. A boiler heats water to provide hot water or steam for heating, which is then sent through a series of pipes. In a steam system the water is heated to its boiling point of 212 degrees Fahrenheit, and as it turns to steam the pressure in the boiler rises, pushing the steam through pipes to the radiators. Steam flows through the pipes under its own pressure, without a pump, and is far easier than hot water to spread through large homes or tall buildings.

Steam has a long history in the city. Coal-fired boilers used newly invented cast iron radiators to bring hot water or steam to every room. Steam and low pressure hot water radiator systems came into common use in offices and homes alike. Steam systems were usually put in larger houses of three stories or more and in commercial buildings. You can tell the radiators apart: steam radiators have connectors joining their sections across the bottom only, while hot water radiators join them at both top and bottom.

Source: U.S. Department of Energy · Historic Chicago Bungalow Association · National Park Service

Steam systems come in two main layouts, and the radiators show which you have. A steam radiator with one pipe has an air vent on the side opposite the pipe, about two-thirds of the way up. Steam radiators do not need bleeding: their automatic air vents let air escape on its own as steam comes in. Having a partly closed valve does not let condensed water drain out of the radiator properly, which keeps steam from getting in.

A two-pipe system has a second pipe that takes water away from each radiator. Two-pipe systems rely on steam traps to keep steam from passing through the radiator and out into the condensate return pipe. Some systems use condensate pumps, with steam traps and a condensate tank in the basement that feeds water back into the boiler. With two-pipe steam, a thermostatic radiator valve can sit at the radiator inlet and block steam from entering when it is closed. Two-pipe steam systems are common in larger buildings built after 1970.

Source: Historic Chicago Bungalow Association · U.S. Department of Energy

A steam system has to get air out of its pipes every time it starts. When the boiler starts again, the expanding steam must push the air out so that steam can reach the radiators. Air in the main and riser pipes blocks the passage of steam, and poor venting traps it in place. This trapped air is called air binding, and in the spots farthest from the boiler, such as top floors, it can leave rooms underheated. The farther a unit is from the boiler, the longer the air takes to vent and the longer steam is delayed.

Venting is often the fix. Most steam systems have vents that are too small, and many have none at all. The solution is very-high-capacity air vents at the ends of the mains and the tops of the risers. Radiator vents themselves should be slow models. Poor balance shows up as some areas too cold, others too hot, and open windows nearest the boiler during the heating season.

Source: U.S. Department of Energy

Steam heat makes sounds, and some of them are normal. Steam heat systems in particular can be noisy, and poorly kept radiators can damage wood floors. Hissing valves are a normal function, while faulty valves or sagging pipes can cause a knocking sound. When condensed water sits in the lines and fast steam is driven through them, the steam picks up the water and slams it into the end of the line; this is called water hammer.

Vents can be noisy for another reason. With a boiler of the proper size that is properly controlled, larger vents are silent. When the boiler is too large or poorly controlled, the vents can be very loud, and they can even squirt water if the boiler is making wet steam. If you hear banging or squirting, tell us what you see and hear.

Two simple checks are yours to make. If one of your radiators is not heating evenly, check whether the floor beneath it has settled; shims under the radiator will bring it back into line. Heated air must flow freely around each radiator, so a decorative cover should have plenty of openings.

Source: Historic Chicago Bungalow Association · U.S. Department of Energy

How much fresh water a steam boiler takes in matters to its life. Unlike steel, cast iron forms an oxide coating that stops further corrosion, but that layer cannot protect against too much makeup water, the fresh water added to replace losses. That makes it essential to watch water use and check for likely places of water loss, especially buried return pipes. If the daily makeup water exceeds 2% of a steam boiler's water content, the water loss should be fixed before switching to treatments such as anode bars.

Age and efficiency belong in the picture too. The efficiency of furnaces and boilers is measured by AFUE. ENERGY STAR lists a boiler more than 15 years old as one sign it may be time to consider replacing it. An ENERGY STAR boiler is 5% more efficient than a new standard model. Replacement parts and repair help for cast iron radiators may be hard to find.

Source: U.S. Department of Energy · ENERGY STAR · Historic Chicago Bungalow Association

Boilers are pressure equipment, so the law takes an interest in them. Boilers and pressure vessels are built in a similar way; essentially, a boiler is a pressure vessel. Boilers and pressure vessels can and sometimes do explode. Illinois law requires all boilers and pressure vessels to be registered and inspected unless exempted. Boilers in private homes, or in buildings with fewer than 6 dwelling units, are exempt from that state inspection.

Chicago has its own rules. The state act does not apply to boilers in cities of more than 500,000 people. In Chicago, the Boiler Inspection Bureau makes periodic inspections of boilers at apartment buildings where the boiler heats four or more apartments. Under Illinois rules, welded repairs to pressure equipment can only be done by a company licensed by the state's Division of Boiler and Pressure Vessel Safety. The heat and cooling rules page explains what landlords must provide.

Source: City of Chicago · Illinois State Fire Marshal · Illinois General Assembly