Once early man had discovered fire and learned how to start his own, the outdoor fire became a common source of heat. As people started living in caves, or variations thereof, they thought it would be a good idea to bring the fire in. This had several advantages: rain wouldn’t put out the fire, and the space was warmer. It also had disadvantages, such as requiring constant maintenance, and the risk of dying from the products of combustion.
One of the biggest problems turned out to be the smoke that filled the living space. Sometimes the fire was the only thing that stayed in the living space and the people had to move outside until the smoke went away.
While a hole in the roof is usually a problem, people discovered that if they put the fire under the hole in the roof, most of the smoke would go out through the hole most of the time. A cave with a skylight was a luxury, not so much because it let light in, but because it let the smoke out.
As things evolved, homes were built with this in mind. If you look at some of the teepees of the Native Americans, you can see that excellent use is made of the hole in the roof. Even the shape of the teepee tended to funnel the products of combustion up and out through the opening in the roof. This opening was often adjustable. There were still some disadvantages though, including constant maintenance, rain and wind, and uneven heat distribution.
People started to build boxes to contain the fire. These were often made of stones and located int he center of the home. This provided a well defined area for the fire and restless sleepers weren’t so likely to roll into the fire. Some of the boxes were shaped to help carry the exhaust products up towards the hole in the roof. People noticed they were getting warmth from the walls of the box even if they weren’t seeing the fire directly. This was an important realization.
Somebody decided that if you were going to build a box to contain the fire, why not extend it all the way up to the hole in the roof? This was particularly significant because the smoke was finally contained. It also reduced the problem of letting in rain, birds, and other animals. Having a fire in a contained box, with the box extending up to form a chimney through the roof was a great innovation. Be sure to look for Part 2 of our series The Evolution of Central Heating next week!