Hot water coal boiler

It appears that Sears put that name in coal-fired furnaces and boilers for several years in the early to mid 20th century. I particularly like this article I found on the Famous Sears Indestricto. https://searshousesincincinnati.wordpress.com/2016/05/15/sears-indestructo-still-going-strong-after-92-years/
I believe that Sears would make deals with manufacturers to sell their products thru their retail stores and catalog. The catch is that they would "Rebrand" the product with a "Sears" registered trademark name. The popular Appliance brand name of Kenmore is another example. You can get a Whirpool washing machine from any appliance store, but you could only get a Kenmore from Sears. Even though they were the same exact product with a different label. (know this because I sold Heil furnaces and air conditioners for a Supply house. I had a box of Kenmore labels for the 3 "Sears Participating Contractors" we sold products to.)

I would guess that your Indistructo boiler is a boiler manufactured by a popular boiler company. I would not be surprised if it was installed in a Sears Home. Yes you could purchase a home from the Sears catalog . It was most likely installed as a gravity system. They like to use the scientific name for gravity system "Thermosiphoning." All this means is that hot water is lighter than cold water. So the boiler in the basement makes the water lighter so it floats to the top radiators thru the supply pipe(s) The heavier water in the radiators will, by gravity, fall to the basement thru the return pipe(s). This cycle continues to "circulate" as long as the boiler has a fire in it that will heat the water and make it lighter than the water in the radiators upstairs, where the water cools off by leaving the heat in the room to make it more comfortable in the winter.

Those old plumbers were pretty ingenious to get the heat to circulate without a circulator pump. But that is why the pipes are so big. Gravity is a powerful force but it can take its good old time in a heating system.

Fire door from a coal boiler or furnace


Steam boiler with Gas conversion burner


Water boiler

Here is an advertisement for the Sears Furnace with a 20-year guarantee. (they don't make 'em like they used to.

Yours Truly,
Mr.Ed

This is not a boiler story but @EdTheHeaterMan and anyone interested. Many years ago I went to a suit manufacturer to fix their boiler. The owner held up 2 suits and asked if I could tell him the difference between them. I looked at both but could not find any difference. He said that he could sell me the one on the left for $50.00 and the one on the right for $500.00. When I asked the difference he said that the one on the right had "Johnny Carsons" name sewed into it, but that they were the same suit. I bought 2 of them.

That gravity furnace looks a lot like this one I replaced a gas valve on.

I went to a house about 30 years ago, to look at a coal furnace in a home a few miles from my home. The first indication of problems with the furnace was that everything and I mean everything in the home was coated with soot. The walls were mostly black as were tables and every other surface. When I mentioned this to the homeowner he said that he knew of the problem but was not going to replace the furnace due to cost. I warned him about the problems of inhaling all this soot and was told by him that he, his wife, and kids sleep with "gas masks on". He did not replace the furnace but wanted to buy a can of furnace cement. (This is a true story)