When the outdoor temperature begins to drop in the fall and winter, a furnace provides welcome warmth and cozy indoor comfort. Before selecting a furnace, it is important to understand the technology behind the appliance as well as the available efficiency and fuel options.
Gas furnaces are manufactured to burn either propane or natural gas. Older models were relatively easy to convert, but modern gas furnaces are designed to burn a specific fuel. Natural gas is usually provided by a pipeline that runs through large neighborhoods, and propane is transported by truck and stored on site in steel tanks. When considering the amount of heat generated, natural gas is generally less expensive than propane, but propane provides a cleaner burn.
Gas furnaces are characterized by the inclusion of the following common components:
- Heat Exchanger: A stainless steel or aluminum device consisting of engineered hollow chambers that accommodate heat transfer between the burner and air handler.
- Burner: A specially designed assembly used for the controlled combustion of gas and air to generate heat.
- Venting: A double-wall piping system used to draw fresh air into the furnace for combustion while exhausting waste gas outdoors.
- Ignition System: Modern furnaces do not use a standing pilot. Intermittent pilot or direct spark ignition systems are safer and more reliable.
The heating cycle in a gas furnace is started through a relay that activates an inducer fan. When the air flow reaches a preset threshold, a valve opens and releases a specific amount of gas, which is subsequently ignited. The gas warms the heat exchanger until the blower is activated, drawing heated air across the surface and pushing it through the building’s ductwork.
In terms of the burn process, an oil furnace is similar to its gas counterpart in many respects. While both systems include a heat exchanger, blower, igniter, and burner, the process used to generate heat is substantially different.
Since oil is a liquid, it is pumped from a storage tank into the furnace where it is turned into a fine mist by a high-pressure spray system. As the oil enters a specially designed combustion chamber, it mixes with air and is ignited by an electric spark. The chamber continues to heat up and the energy is absorbed by the heat exchanger while waste gas is exhausted through the flue pipe. The blower forces the warm air through the distribution system until the thermostat call is satisfied.
Which Furnace is Right for Me?
The decision to purchase a fuel-specific furnace should be based on the design that reflects the buyer’s budget, comfort and efficiency expectations. When evaluating oil and gas furnaces, it is important to compare their respective features and benefits.
Efficiency Ratings: All furnaces are rated according to the Annual Fuel Utilization Efficiency standard, which was designed to help consumers compare different brands and models of furnaces. In essence, an AFUE rating conveys the percentage of fuel that is delivered in the form of useable heat. Gas furnaces like the Trane 95 series include a variable speed motor and a modulating gas valve to achieve efficiencies up to 97.3 AFUE.
An oil furnace like the Regal ECM uses a variable speed motor to provide an AFUE rating of 85.9. In general, a gas furnace is more efficient when compared with a comparably priced oil furnace, primarily due to the superior rate of energy transfer in the heat exchanger. However, it is important to check local fuel prices to make a direct operational cost comparison. While natural gas and propane are usually cheaper than heating oil, some areas of the country with high fuel oil demand enjoy much lower prices.
Maintenance: All HVAC equipment should be regularly serviced to ensure continued operational integrity, but oil furnaces are especially maintenance intensive. The buildup of heating oil residue can clog atomizer jets and severely reduce efficiency. Gas furnaces also need annual maintenance, but the service requirement is not as extensive. Parts for both systems are readily available and cost competitive, but the burner assembly on an oil furnace is more expensive to replace than a gas furnace with a similar capacity.
Safety: Both oil and gas furnaces are very safe and include a number of redundant mechanisms to avert a catastrophic failure. Areas with an operating furnace should always be well ventilated and the appliance must be periodically inspected for leaks. Regardless of the fuel choice, every building should be equipped with a carbon monoxide detector.
Choosing the Right Furnace
Modern central furnaces offer exceptional comfort, quiet operation, and maximum efficiency. Griffith Energy Services offers a complete line of Trane gas furnaces and Regal oil furnaces designed for every budget and heating requirement.