The basics of furnaces
A furnace is a system that distributes heated air throughout your house. It's usually made up of a heat source called a burner, a heat exchanger that transfers this heat to your household air, and some fans that move the air to where you want it.
The burner ignites the fuel to create heat. Fuels are heating oil, propane or natural gas, and for older furnaces, kerosene, coal, wood or anything else that burns. All fuel systems require a ventilation system to remove the exhaust gases. The burning of the fuel requires oxygen, so ensuring a fresh supply of clean air to the burner is important. The furnace's burning efficiency can be maintained by periodically replacing air filters. The household air ducts also need regular filter changes to keep the air clean and healthy.
The burning fuel's heat typically flows through a series of heat exchanger tubes. These sealed tubes pass through part of the duct system for the household air. The fuel exhaust is kept separate from the household air, and the heat is transferred from one to the other - hence the term heat exchanger. Over time, the heat exchanger will develop cracks and it'll usually have to be replaced long before other parts.
Another process, known as hot water heating, heats water instead of household air and sends it to the radiators in your household, as well as to your sinks, tubs and showers. Steam generators, which can be added to showers and tubs to create steambaths, heat the water further to generate steam.
Some fuel furnaces don't have a heat exchanger. They heat the household air directly. Likewise, electric furnaces directly heat the air that flows through their electrical heating elements, and because they don't have any exhaust gases, they don't require a ventilation system. Their most common problems are electrical in nature, such as blown circuit boards, fuses and breakers. It's an efficient process, but not necessarily cheaper, because electricity can sometimes cost more than other fuels.
Once the air is heated in these kinds of furnaces, it gets circulated by a fan. A hot water heater would move the hot water to radiators by using a pump instead of a fan.
The settings on the thermostat control the system's flow of heated air into your house by regulating and monitoring the flow of fuel, the pilot light or igniter, the fans and various heat sensors and switches.
Regular cleaning and repair should maintain your furnace's efficiency, but if your heating bills are getting worse, you should consider replacing your furnace.
A high efficiency furnace costs up to a $1000 more than other furnaces, but it can reduce your heating bill by up to 25 percent. For example, if your original monthly bill was $100, you'd save $25, or, only have to pay $75 a month. For a $1000 investment, you'd break even in 40 months - after that, you'd be making money.
You could also consider an integrated system for both your air and water supply. There's a higher investment cost, but the payoff would be in 5 to 10 years. If you can afford it and aren't moving for several years, it may be worthwhile.
By Jeff Parsons