Gas Furnaces – What You Need To Know

January 30, 2018

A gas furnace is the important appliance that keeps your home warm. It can be confusing to shop for such an important piece of equipment. Let’s review some factors to consider when shopping for a new furnace.

Efficiency: Gas furnace efficiency is measured by Annual Fuel Utilization Efficiency (AFUE), which is also used to rate the efficiency of boilers and heaters. AFUE is the ratio of fuel that is transformed into heat to the fuel that goes into the furnace. For example, an 80 percent AFUE furnace will return 0.80 cents worth of heat for every dollar spent on natural gas.

Types: Gas furnaces are divided into three types: condensing furnace, induced draft furnace, and conventional warm air furnaces. These furnaces burn natural gas to produce heat. The heat is transferred to the various parts of the home through ducts and fans. More air can be pulled from the cool air coming from the house to the furnace to be reheated, or used to expel the flue gases through an exhaust. A conventional warm air furnace uses natural draft, which is air pulled through the gap at the flue and at the front of the furnace.

Using a fan is more efficient, which is what an induced draft furnace uses. Some of the natural or induced draft is mixed with exhaust gases and then expelled through a chimney. Chimneys also expel heat with flue gases, reducing efficiency. The condensing furnace is designed to make use of the escaping heat by condensing the flue gases with an additional heat exchanger. This adds heat to the house and is far more efficient than the other two types of furnaces. These units typically have a 97 percent AUFE rating.

Gas Furnaces

A chimney is not needed because escaping heated gases are condensed. The flue gases have a relatively low temperature, which makes them easy to release outside the house through a small PVC pipe. The conventional warm air furnace is the least efficient. Its efficiency drops way below the minimum AFUE rating of 78 percent as it ages. Old conventional warm air furnaces have only 55 percent AFUE. They also use a standing pilot, which is constantly burning fuel. Both the induced draft furnace and condensed furnace use an electronic ignition system and intermittent pilot that can be electronically controlled, is cheaper, and more dependable. The induced draft furnace has 20 percent higher AFUE than the conventional warm air furnace.

You should always have your gas furnace unit installed by a qualified HVAC professional. This ensures your unit will operate safely, effectively, and retain its full warranty. An HVAC installer will also have the know-how and tools to properly install your unit and calibrate it to the needs of your home. Unfortunately, many companies require that you purchase your HVAC equipment through them, preventing you from taking advantage of competitive pricing online or through a wholesaler. Some companies will install your equipment, but they will quote you for the labor and parts as if it were their unit, then subtract the price you paid for yours. This completely negates any financial benefit to buying the unit yourself.

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