Older furnaces

The oldest furnaces in the city had no blower at all. Steam energy from coal and industrial mass production made early central heating possible, sending heated air or steam through metal ducts or pipes. If your bungalow has no radiators and never had them, it started life with a coal furnace feeding a network of ducts. Lacking electricity and fans to move air, these early furnaces moved heat by natural convection, with heated air rising through ducts to the rooms above. A technician can tell you whether your furnace began life this way.

Source: National Park Service · Historic Chicago Bungalow Association

When a furnace is changed over from coal or oil to gas, the chimney deserves attention. Chimney inspections are especially important where oil or coal heating systems have been converted to gas. After the conversion, built-up soot and debris in the chimney could block the escape of carbon monoxide and send the gases into the home. Chimneys should be checked and cleaned every year until no more soot is found. If you convert from oil to gas, have the chimney inspected at the time of the conversion, then every year after.

Keeping the chimney clear is the point of all this. Chimneys and flues should be clear at all times to let toxic flue gases out, especially carbon monoxide. If the fall inspection finds soot built up on the chimney walls, the CPSC says a chimney sweep should clean the chimney. The venting and chimneys page explains more about how chimneys work with furnaces.

Source: U.S. Consumer Product Safety Commission

Efficiency standards help you place an older gas furnace in time. The first federal standard, enacted by Congress in 1987 and in effect from 1992, set the minimum at 78 AFUE, meaning 78 units of heat out for every 100 units of energy in. AFUE is, in general, the percentage of the heat in the fuel that becomes space heat instead of being lost. So a furnace built before the standard took effect in 1992 was not held to that floor. For comparison, ENERGY STAR gas furnaces for the northern states, including Illinois, are rated 97% AFUE or greater.

How a furnace vents matters as much as its efficiency. Category 1 appliances are the oldest, least efficient type of combustion appliance: their flue gases are over 140°F and the flue pipe is under negative pressure compared with the room. Because they take their burning air from the room around them, they are open to backdrafting. Backdrafting is when the products of burning, including carbon monoxide, are drawn back into the house by negative pressure. The main concern is furnaces, boilers and water heaters whose venting can let combustion gases spill out through their vent hoods. The CPSC estimated 57 carbon monoxide deaths in 1986 from gas-fired furnaces and 14 involving oil-fueled ones.

Source: U.S. Energy Information Administration · ENERGY STAR · U.S. Department of Energy · U.S. Consumer Product Safety Commission

Age alone does not mean a furnace has to go, but it changes the questions worth asking. ENERGY STAR lists a furnace or boiler more than 15 years old as one sign it may be time to consider replacing it. Equipment more than 10 years old, or that needs frequent repairs while your energy bills climb, is another sign it names. The EPA recommends having HVAC equipment more than 10 years old, or that is not keeping your house comfortable, evaluated by a professional HVAC contractor. If you are not sure how old your furnace is, a technician can help you find out.

Source: ENERGY STAR · U.S. EPA

Old furnaces and their ducts can sit beside materials from an earlier era. Asbestos was commonly used in home building materials before the mid-1970s, and occasionally until the late 1980s, because it is strong, resists fire and corrosion, and insulates well. Materials with more than one percent asbestos count as asbestos-containing materials. Once inhaled, asbestos fibers can stay lodged in tissue for a long time and can cause cancer. If such material is in good condition and left in place, it should not present health risks.

Ask before anyone disturbs it. The EPA says to inspect a heating and cooling system before cleaning it, to be sure there is no asbestos in parts such as insulation or register boots. If you are not sure asbestos is present, people who often work around it, such as heating specialists, can help, or you can hire an asbestos inspector. The asbestos and lead page explains the rest.

Source: Illinois EPA · U.S. EPA

An older furnace needs yearly care like any other. The CPSC says a qualified heating contractor should inspect the home heating system every year. Worn or poorly kept furnaces can be significant sources of carbon monoxide, as can a flue that is wrongly sized, blocked, disconnected or leaking. Carbon monoxide is a colorless, practically odorless and tasteless gas. With an old furnace, the yearly check is worth keeping, and the safety steps are at the end of this page.

Source: U.S. Consumer Product Safety Commission · U.S. EPA