The Monster in Your Basement – the Gravity Furnace

The gravity furnace is also commonly called the Octopus furnace because it has long ducts coming out of the central unit. It can be quite a sight to behold and even scares some buyers the first time they see it. These types of units were installed in homes built in the late 1800’s and early 1900’s. There are still many homes in Minneapolis and Saint Paul which have this furnace as their heat source. Slowly, home owners are replacing them with more efficient HVAC units, as well as replacing the duct-work throughout the home.

The concept of the Octopus Furnace is that heat rises and cold air falls. Heated air rises through the heat ducts and then the cold air sinks, entering the return air ducts, where it is reheated again. The original fuel source for early models was coal, but many since then have been converted to natural gas or oil. The above diagram is a great example of how it works.

Reasons you might want to replace your Gravity Furnace:
  • energy efficiency – gravity fed furnaces are 50% less efficient than a conventional heating system
  • most gravity furnaces contain asbestos. Asbestos is not harmful if left untouched, but if you do plan on replacing your gravity furnace, a licensed abatement contractor will most likely seal off the basement and safely remove any hazardous material.
  • they take up an enormous amount of space in the basement
  • you cannot install a whole house air conditioning system with this type of furnace

I have shown homes to buyers with Gravity Furnaces and many are shocked to see one for the first time. Some even fear purchasing the home, but they are easy to get along with. If you plan on purchasing a home with a Gravity furnace, DO think about replacing one in the near future. It will save you money in the long run.

10 Responses to “The Monster in Your Basement – the Gravity Furnace”

  1. Kassie says:

    We have one and until we get the $15,000+ to get it replaced, it is staying.

    Two more reasons to get rid of it:

    1) Asbestos (or however you spell it)
    2) Scares small children.

  2. Kassie – I had not thought about it scaring young children, but I can see how it would. Thanks for letting us know what the cost is to replace one! Wow, I really didn’t know it got that high!

  3. DethWench says:

    Scares young children?? I am from Minneapolis, and one of my scariest memories from college was going into my friend’s grandma’s basement with a candle and discovering an octopus furnace!

  4. stewart says:

    Do not replace that furnace. Great antique value,re-wrap pipes,no fans to repair and no power to operate and quite, not to mention other positives. More heat/cooling, just insulate home. Attic, windows and such. I have the same furnace (PG&E) friends say they are awesome and they do not break at all.. 1918 is my model, as is still going strong. Including my wedgewood gas stove(both have not been replaced). total for a 2300 SQ ft home is less than 60.00$ per month.. If it does not break, do not replace. Those home improvement guys do not always give you the truth.. Stu

    • Heather says:

      I have one in this old house I recently bought. This is my first winter in the house and I love it. I think I will keep it for as long as it works. Its quiet, heats well, and I think it looks cool it matches everything else original to the house. I think my house is about 2300 sq feet as well and my first full gas bill was $100 not to bad. I might get the asbestos removed I havent made up my mind on that one yet.

  5. Joan says:

    I owned an 1896 home in Kenwood for 26 years. It had a gravity-system furnace converted from coal to gas in the 1920s. It cost me 59 cents in repairs in all that time—a switch wore out. It was the most comfortable heat I’ve ever experienced, the heat flowing gently upward from the cast-iron floor vents, the air circulating via cold air returns made of beautiful hardwood grids in the floor. A few years ago I had an energy-efficient Bryant furnace and central air conditioner installed in the house I now own, and I hate it. No matter where I sit, the forced air streaks across the floor and hits me. I actually have to put boxes a few feet in front of the wall vents to deflect the air current—a low-tech answer to a high-tech problem. I can’t remember what the gravity furnace cost in heat, but I’d pay it happily to have that comfortable system now.

    My children were not afraid of the octopus. They spent many hours under its tentacles, building ships that did not float, Star Trek models that did not fly and tall Lego towers that crashed to whoops of joy. But of course, they, like the children of Lake Wobegon, were above average. 🙂

  6. Trisha says:

    Hi we had one in our basement it always scared me when I went down to the basement, but what I don’t understand was how did the heat get in to my third floor bedroom. There were no registers on the floor but there was this scary looking square hole in the wall with a cement patch in the middle, I always put things in there as it was big enough to store books! Is that where the heat came from? I have asked a million people and no one seems to know what I am talking about

  7. Scharlene Torres says:

    I’m house hunting in Connecticut and today i saw a house built 1813…GORGEOUS.. And in the cellar lived the Octopus furnace.. my partner was the one to find this monster and came up with the WHAT IS THAT FACE. I instantly fell in love with this house as I see nothing but character and beauty in the homes off old…

  8. john says:

    To all who think it is scary, they work well, are the quietest and a lot more efficient than the hvac industry would have you believe. As for the fear factor? DEAL with it, or are you afraid of the dark too? Stop watching Home Alone!

  9. Katelyn says:

    I have a octopus furnace unhooked in my basement and looking to see what they are worth.

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