Gravity furnace? What is that???

Not long ago I showed a buyer a house with a gravity furnace and got the response I often get… what is that???

Gravity furnace

Often nicknamed an 'octopus' furnace because of its multiple 'arms' they date back to the late 1800's and early 1900's. They were originally designed to burn coal, but later switched to burn oil or natural gas. There aren't too many left but you still sometimes find them in older homes, especially ones where the owners have lived there for many decades.

Although they are only about 50% energy efficient and take up huge amounts of space older homeowners often don't replace them because, like the Energizer Bunny, they just keep going and going and going… with few moving parts, there isn't much that can break down.

As its name implies, air circulation in a gravity furnace relies on gravity… the principle that warm air rises and cool air falls. There typically is no fan on a gravity furnace… that is why there are so many 'arms' and why they are so large. Since no fan is pushing the air, the air pressure is lower as the warm air gently enters the room and there tend to be fewer hot spots. However, there is no way to provide central air conditioning or warm air to the basement with this type of furnace… and there is no filter since that obstructs air movement.

When a home has a gravity furnace, the new homeowners will usually choose to replace it with a new energy-efficient forced air furnace and air conditioning system… which requires all new ductwork. Additionally, almost all gravity furnace systems are insulated with asbestos… ok as long as it remains sealed, but needs asbestos abatement if removed because of the health hazard.

Sharlene Hensrud, RE/MAX Results – EmailMinneapolis Realtor



Written By

I love what I do! Highly insightful, analytical and creative, there is nothing I love more than helping you find the right solution for your real estate transition. My mission is to serve my clients with honesty and integrity, exceeding their expectations in service and support… and to help others by donating a portion of every transaction to Habitat for Humanity.

Related Posts

Are gravity furnaces still around? Do they need to be replaced?

đź–¨ Print Article It has been so long since I saw a gravity furnace in a property that I was shocked when I saw not one, but two in a...

Subscribe to Our Newsletter for Market Updates & Mid-Century Modern Listings

Our weekly HomesMSP Update includes current local market information and a curated list of mid-century modern properties for sale, plus posts from an inspector, a lender, a stager, info about neighborhoods, life in the Twin Cities… even recipes!


Blog Categories


Sharon and John Hensrud

About Us

The HomesMSP Team is committed to meeting you where you are and listening… really listening to understand you so we can use our extensive knowledge of the market and local neighborhoods to give you personalized service.