If you are my age you will have good or bad memories of coal furnaces or maybe both. We had a coal furnace in our home and in the one room school I attended. At one time in my life I was responsible for the operation of both furnaces. There are many stories about our one room country school and they will be told later.
The basic principle of a coal furnace is you put coal into the firebox, it burns and heats the air in the plenum surrounding the fire box and that air moves into the spaces you want to heat. The earliest coal furnaces relied on natural convection to move the warm air up into the space to be heated. Later models had fans to move the air and some even had “stokers” you could fill with coal and it automatically fed the fuel to the fire.
In a typical cold day the furnace was heating the house. We didn’t have thermostats to control the heat however so as the house got colder you needed to increase the draft (air supply) on the fire to burn hotter and produce more heat. There was another control for the chimney damper which regulated the draft on the fire by adjusting the size of the opening to the chimney. We kids never messed with the damper, which was only to be adjusted by dad. He was the only one that knew how to do that properly. These were controlled by chains on a dial in our dinning room. Turn the dial to move the chain and adjust the damper or draft.
When the fire burnt hotter it consumed more coal which meant you had to add more fuel to the fire. Coal is a black soft rock. Small chunks of coal burn faster than large chunks. You wanted large chunks for the fire so you didn’t have to feed it as often. However, the size of the door on the fire box limited the size of the chunk you could put into the furnace. If your coal was too large there was a sledge hammer in the coal bin to break it into smaller chunks.
The smaller the person feeding the fire was the less weight they could lift so they tended to add small chunks in smaller quantities. Coal was fed into the fire box with a coal shovel. We had a large shovel for dad and a smaller shovel for mom and us kids.
Just before we all went to bed we would reduce the damper so there was less air to the fire and we would add the largest chunk of coal we could fit through the door in the fire box. In theory, we then had a lot of fuel and less air so the fire would still be burning when we arose in the morning. If the fire went out, we had to start it again.
Starting a coal fire is more of an art than science. First you shook the grate lever back and forth which controlled the grate the fire sits on in the fire box. This would drop the ash from the fire box into the ash pit. That makes it easier for the air from below to feed the fire and makes more room for coal. (We can discuss taking the ash out later.) Next we wad up old newsprint and put it into the fire box. If we were lucky we had a bucket of corn cobs nearby and added a few of them. They have sugar in them and burn hot once started. If there were no corn cobs we had to find some wood kindling.
We were doing all this in the dark as there are no lights in the firebox and no flames yet to light it up. Next add a can of kerosene to the corn cobs and paper and throw in a lit match. It would land on the kerosene soaked paper and start the fire. Once the fire was burning bright we would add the coal and get it started. All pretty simple.
The risk of starting the fire was the lack of light in the fire box. If there were a few glowing embers left from the fire you thought was out, they would heat and vaporize the kerosene. But you couldn’t see those wispy white kerosene vapors in the dark. Now when you throw in the lit match, there is a small explosion with a small fire ball coming out of the furnace headed for you. You could always spot the person caught in this trap because they singed their eyebrows and the hair on the front of their head. When you arrived at school or work everyone knew who had started the fire in the furnace that morning.
You may remember in the winter mom would hang the clean laundry in the basement to dry. Well, just try to walk through lines of white sheets hanging to dry and not touch them with the hands you had just used to pick up black coal. Believe me it is impossible and you will never convince mom you didn’t do it so just march upstairs right away and confess.