What is a Gravity Furnace?

Malcolm Tatum

Gravity furnaces are heating equipment that employ the use of gravity to conduct warm air to various parts of the structure. At one time, this type of furnace was a common means of providing heat in homes and apartment buildings. While this type of furnace has been replaced in many case by devices such as the heat pump, there are still many homes that continue to make use of a gravity furnace.

Gravity furnaces were a common means of providing heat in homes at one time.
Gravity furnaces were a common means of providing heat in homes at one time.

The function of a gravity furnace is relatively simple. Typically, the furnace proper is usually housed in the basement area of the home or building. Different types of heating fuels may be used, such as electricity, coal, oil or gas. When active, the furnace distributes the produced heat into the upper levels of the dwelling by the means of ductwork that is ran throughout the walls and floors of the building. Vents that are strategically attached to the ductwork allow the hot air to escape into the rooms of the home. This design is sometimes referred to as an octopus furnace.

It is the basic gravity principle that hot air rises and cold air sinks that allows a gravity furnace to function. As hot air is generated, it moves through the ductwork at a slow but steady pace. Upon entering the room, the warm air continues to move upward to the ceiling. Along the way, the warm air emerging from the vents helps to make the overall temperature in the room more pleasant.

While there are other heating options available today, many people choose to continue using a gravity furnace. While not necessarily considered the most efficient of heating equipment, gravity or octopus furnaces do have a few advantages. First, furnaces of this type have few moving parts; this translates into less components that can break down. Second, air pressure is usually lower. This means the flow of warm air into a room is likely to be less obvious and will tend to create fewer hot spots in the area of the vent.

Malcolm Tatum
Malcolm Tatum

After many years in the teleconferencing industry, Michael decided to embrace his passion for trivia, research, and writing by becoming a full-time freelance writer. Since then, he has contributed articles to a variety of print and online publications, including EasyTechJunkie, and his work has also appeared in poetry collections, devotional anthologies, and several newspapers. Malcolm’s other interests include collecting vinyl records, minor league baseball, and cycling.

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Discussion Comments


I dug my basement out and noticed an 18 inch wide rectangular trough that ran from the side wall to the center of the house. The trough had ashes in it. The trough led the center of the home to a brick well looking structure.

I stuck my shovel down the middle of the well like structure and I pulled out this ash like material on my shovel. My house was built in 1900 and I can see two 1 ft/1.5 ft rectangular holes in the floors. Looks like an old vent or duct was there.

The same situation with the room above. In the basement I noticed there was sheet metal stuck on my floor joist beams that looked like they were there to protect from getting burned.

Did I have a gravity furnace at one point? What was the trough used for? I noticed ashes inside of it and they lead to the well like structure.

This is important because I would like to take the trough out and cement my basement.


Do you know how I can find parts for a gravity flow furnace (model # GR-105)? I have a client that is willing to pay up to $1,000 for parts.

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