If you have an old gravity furnace or steam boiler, it’s time to replace these energy guzzlers.

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If you have an old monster-sized furnace in the basement with huge ducts that snake off in various directions, your home may be heated by a gravity furnace. Gravity furnaces were installed in homes at the turn of the 20th century and well into the 1940s. Depending upon locally available fuels, they may burn coal, wood, oil, or natural gas.

An old gravity system is different than a forced-air system precisely because it doesn’t “force” air. Instead of utilizing a blower to push heated air into rooms, a gravity furnace allows the heated air to rise by natural convection through large ducts into rooms.


Because it doesn’t have a blower, a gravity furnace is quieter than a forced-air furnace and doesn’t stir up dust and allergens by blowing air—but that’s where the benefits end. Though these big monstrosities do a pretty good job of heating, they waste a tremendous amount of energy compared to today’s high-efficiency furnaces. Not only do they send about 50 percent of the heat straight up their flues, but the heated air also takes longer to reach distant rooms.

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Because asbestos was commonly used for fireproofing and insulating these furnaces and their ducts, the chances are good that an old gravity system presents an asbestos hazard. This white, fibrous wrap is a known carcinogen that can cause asbestosis when airborne. It should not be disturbed other than by a certified asbestos abatement company.

If you intend to be in your home for more than a couple of years and your budget will allow, it would likely pay to replace your outdated gravity furnace with a new, high-efficiency furnace. Doing so will probably reduce your heating bills by half. But be advised that this is a big job that requires complete removal and replacement of the old system, usually including the duct work, patching floors, installing new registers, and more.

Perhaps even more antiquated than gravity heaters are steam boiler heating systems. Steam boiler systems utilize radiators to heat air and provide radiant warmth. A steam-rated gas or oil boiler produces steam, which moves through insulated pipes to room radiators. As the steam gives off its heat, it vaporizes and drains back to the boiler, where it’s reheated, and the cycle begins all over again.

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Again, if you intend on staying in your home for at least a couple of years, replacing your steam boiler heating system with a high-efficiency furnace is a wise investment.

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About Don Vandervort
Don Vandervort has developed his expertise for more than 30 years as a remodeler and builder, Building Editor for Sunset Books, Senior Editor at Home Magazine, author of more than 30 home improvement books, and writer of countless magazine articles. He appeared for 3 seasons on HGTV’s “The Fix,” served as MSN’s home expert for several years, and is featured as Yelp's home improvement expert. Don founded HomeTips in 1996. Read more about Don Vandervort