Gravity Furnace

I got a call from agentleman who has a “Gravity feed furnace”. In 10 years of being a contractor, I’ve never seen one. Anyone have any info on them and how to inspect it? I have a heating contractor who will look at it with me, but I hate to have to pay him for it.


You’re going to run into an ancient furnace that looks similar to this…

“Click to Enlarge”

Gravity furnaces are only found in much older homes. They are usually covered in asbestos and are generally in a basement.

The term gravity refers to the fact that the furnace doesn’t have a blower fan to move the heated air around a room. They rely on the fact that heated (less dense) air rises and the cooler (more dense) air falls to circulate the heat.

When I inspect gravity furnaces (which a few and far between) with no obvious defects, I always annotate the following, in my report…

The heating system was paced through it’s normal sequence of operating modes, with no obvious defects noted at time of inspection. However, due to systems age,it is clearly beyond it’s life expectancy, and replacement should be considered. Until then, I recommend annual maintenance from a licensed HVAC contractor.

David, I live in Illinois and we have a lot of older homes here. I run into these monsters more times than I care to. I think the reply on your report is spot on and do you mind if I use it?

Many people affectionately referr to them as the “Octopus”.

You should also see floor grates throughout the house. This allows the heated air to rise through to the second floor from the first and also cool air to fall to the basement (or wherever the furnace is).

Not very efficient! Suggest upgrading, expensive due to having to install ductwork also. The home is also usually of an age where it would have been balloon style framed and most likely has no insulation in the wall cavities. Unless windows have been replaced they also may only be single pane glass.

Very good chance house has mixed galvanized/ copper plumbing. Look for di-electric unions.

Go right ahead.

Happy inspecting.

David’s reply is similar mine, I’ve seen many of these in older homes they seem to run forever with little repairs. With the cost of fuel these days an upgrade should be considered. Also many have been converted from coal to gas or oil.

Thanks guys. Suprisingly, the house was built in '51. I refered the inspection to an HVAC contractor due to age, and reccomended upgrading.

Not many left around here but most all have asbestos covering on everything which makes replacement cost sky high.

There was no asbestos on it anywhere.

The buyer called and left a message on my VM yesterday. The HVAC contractor recommended upgrading to save money, but said the thing was working as good as it could.

Not to quibble, but:

“no obvious defects noted”

Were there glaring defects? Subtle defects?

Seem to me it was visually observed during its normal operating cycle, and either it operated properly, or did not…

I come across a lot of them in Detroit. Being simple units, they’re actually easy to inspect. The most important thing to check for is carbon monoxide in the supply air, which can be the result of openings in the seams of the burner chamber.

As the guys said, these can last for a very, very long time, as long as the burner chamber remains free of leaks. I’ve seen a unit from the 1920s that was operating just fine. I report them as above, noting the high cost as a reason to consider upgrading. But some people with dust sensitivity do like them.