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The Great Old Ones: Octopus Gravity Furnaces

Grendil the Octopus Gravity Furnace

The darkest days of winter seem to be behind us here at the Technocave, but for all of you who would like a little more warmth in your lives right now, we have an interesting heater to share.

Having just moved into our first house, we are very aware of the many quirks and discoveries that one finds out about during the home owning adventure. However, while reading the Yarn Harlot’s blog the other day, we were blown away by her description of her ancient furnace as an Octopus Gravity Furnace. For those readers like us asking what the hell an Octopus Gravity Furnace is (besides a great name for a band), she provided a helpful link to another blog with a more detailed description.

StuccoHouse has been renovating their 1924 farmhouse, which came with the aforementioned Octopus Gravity Furnace. They have named it Grendil (see the full pic here), which we feel is a very appropriate name for such a monstrosity (one of the commenters on the blog had named theirs Wolverine, also a good name).

Octopus Gravity Furnaces work on the principle that heat rises. The once coal-fed furnace is located in a basement, and the tentacle-like ducts (very possibly covered in a plaster made from our good friend Asbestos) carry the heat up to the registers on the upper floors of the house, with no fan needed to blow the hot air. The heat keeps rising, and the colder air sinks back through an air return vent on the ground floor to be reheated by the friendly Octopus in the basement.

From everything we’ve read about them, gravity furnaces are very quiet– no blowers to force the air around, and while they are not the most energy-efficient heating option, they seem to keep their owners toasty warm in some rather frigid climates. If you have one, it is also unlikely that you have to stoke it with coal multiple times a day, as most have been converted to run on gas. So bundle up out there, and for those like StuccoHouse and Yarn Harlot whose Great Old One is serving them well, we wish you many more toasty years with your tentacled friends.


  • Gravity furnace kinda scary looking,however as a kid my
    Neighbors had one it sure kept their home warm, didn’t
    Need a blower to wake you up., seems that today they could
    Come up with a high efficient type gravity furnace.