The Evolution of Central Heating: Part 2

Chimneys became more sophisticated. People added doors that could be opened to add more fuel and closed to contain the fire. People found that if they sealed the box too tightly, the fire would go out. They had to find ways to allow enough air in to keep the fire going. They found that if holes were near the bottom, air would be drawn in, and smoke wouldn’t come out.

People also built flat surfaces onto their boxes so that they could use it as a cooking surface. This functioned like a rudimentary wood stove.

Through this transition, we have moved from direct combustion heating where we could reach out and touch the flame to indirect heating, where the walls of the fire box heat up the air and living space. This transition adds great safety and contributed to a much healthier environment, since people were not as exposed to the products of combustion.

At some point, people found coal was, in some ways, a better fuel than wood. It delivered more BTUs per pound and burned more evenly and predictably. As heating systems were becoming more sophisticated, so were homes. Homes grew from being one room, to having one main room with peripheral rooms for sleeping. Adding these rooms created a heating problem. The heating source was located in the central room and the other rooms would be cold. Sometimes the other rooms were given their own heating system, but that meant several fires to tend.

The first crude duct system was developed to transfer the firebox heat from the central room into the areas without a heat source. The first duct systems operated by convection, but the advent of the electric fan made it possible to move warm air through the duct system and warm air could be pushed to any room as desired.

While some people were excited about moving warm air around through ducts, others realized that you could also pass water around or through the box, heat the water and move the heat by moving the water. If the water was piped to another room, and the heat was released through large cast-iron pans (eventually radiators and convectors), we could move the heat from our fire into the other rooms quite nicely.

As was true with the duct system, the early piping systems worked on gravity (or convection). The warm water would flow out to the radiators and the cold water would flow back. The water would move in a loop, heated by the firebox every time it passed through the boiler. Just as fans helped move air through the duct systems, pumps were added to hot water systems to make the water move more uniformly through all parts of the system, which improved the evenness of heating.

The wood and coal heating systems still required manual stroking and tending of fires. When people realized they could use a liquid fuel like oil, the homeowners life became much easier. The basic oil burner is nothing more than a brick firebox with an oil based flame shooting into it. The oil could be stored in drums or tanks and a pump could be used to pipe it to the burner. The pump sprayed the oil through a nozzle in a fine mist into the burner chamber. An electric fan blew air into the burner chamber to mix with the oil (fire needs oxygen), and an ignition source would light the oil. Once the flame was established, it was easy to maintain by controlling the flow of air and oil. The dawn of the thermostat meant that the temperatures could be maintained easily and effectively throughout the home and at minimal burden to the homeowner.

Shortly thereafter, people started to think about using natural gas as a fuel in much the same way as oil. Gas can be delivered through pipes much the same way water is delivered- you simply open the tap and allow the gas to enter the burner chamber. While spark ignition is effective, today we typically see pilot lights that keep a constant flame going and responds to demands from the thermostat.

This brings us up to current day. A number of safety devices and some convenience items have been added to improve the comfort and quality of life, such as high temperature limits, thermocouples, filters in the duct system, humidifiers, and electronic air cleaners are examples of these. Efficiency improvements are also common on modern systems.

As homeowners, we are thankful for the innovations that keep us comfortable today. As inspectors, we recognize that central heating is a critical component of your home inspection. We carefully evaluate the system for proper operation and check registers throughout the home for even heating. We look forward to working with you!

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