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Furnace Guide

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A Comprehensive Overview of Furnaces

Furnaces are devices that provide heat for your home, by creating the heat through burning oil, natural gas, or propane. The heat generated by the combustion warms a metal component in the furnace called the heat exchanger. Air is circulated over the heat exchanger by the furnace blower mechanism, then the warmed air is circulated throughout your home by your ductwork. There are air handlers that have electric heat strips that produce the heat, and these are sometimes called electric furnaces, although most manufacturers will call these all electric devices air handlers or fan coils. For our purposes in this overview of furnaces, we will not be talking about the all electric air handlers. No matter which fuel source is used, a furnace is a vital part of every home's HVAC system in the cooler climate regions of our country.

Different types of Furnaces

The earliest furnaces had cast iron or steel heat exchangers that would get hot from the combustion of various types of fuels - coal, oil, natural gas, propane, etc. These early types of furnaces relied on a natural draft that took advantage of hot air rising. This warm air was circulated throughout the home in large metal pipes, which delivered the warm air to the living spaces through floor or wall vents.

Furnaces can be classified into four categories based on their efficiency and design: natural draft, forced-air, forced draft, and condensing furnaces. Each type has its unique features.

One of the earliest types of furnaces developed were natural draft furnaces, which featured cast iron or steel heat exchangers that were housed within a shell made of brick, steel or masonry. Gas and oil furnaces were usually controlled by thermostats, while furnaces that burned wood or coal were just controlled by adjusting dampers.


In the 1950s and 60s, forced-air furnaces became a popular replacement for the old natural draft furnaces. These furnaces had more efficient heat exchangers and had blowers to move the air over the heat exchangers, and then distribute the warmed air throughout the duct work of the home. These were a huge improvement over their natural draft predecessors. After the forced-air furnaces became very popular, air conditioners were developed, which would utilize the furnace blowers to distribute the cooled air throughout the home.


As technology advanced, forced draft furnaces were developed which further enhanced the efficiency, and allowed for smaller furnaces. These furnaces featured steel heat exchangers and multi-speed blowers, reducing fuel consumption. Due to their smaller size, forced draft furnaces offered greater options for installation, and their popularity quickly increased.


The invention of condensing furnaces enabled furnaces to obtain much higher levels of efficiency. These high-efficiency gas furnaces are able to achieve impressive Annual Fuel Utilization Efficiency (AFUE) ratings of 90% to 98%. A condensing furnace incorporates a sealed combustion area, a combustion draft inducer, and a secondary heat exchanger, to optimize the amount of heat produced from the fuel source.


The primary advantage of a condensing gas furnace is its ability to capture heat from exhaust gasses by utilizing a secondary heat exchanger. By condensing water vapor, these furnaces extract additional heat from the exhaust gasses, which significantly improves fuel efficiency. The vent pipes used in condensing furnaces are made of PVC to prevent corrosion. Many different types of PVC were originally used for the venting of these furnaces, but over time, the cellular or foam core PVC has shown to be not as stable as solid core PVC. It is now standard practice to only install solid core PVC for the venting of condensing gas furnaces.


Various Fuel Sources for Furnaces

The choice of fuel source for a furnace depends on regional availability, cost, and environmental considerations. The most common fuel sources for furnaces are natural gas and propane. There are still a few oil furnaces, but due to the fact that the oil has to be stored and does not burn as efficiently or cleanly, most people are choosing to switch to either a natural gas or propane furnace. Natural gas is the most preferred fuel source for furnaces. It is a readily available and cost-effective fuel for furnaces. Propane furnaces are a good alternative for areas without a natural gas pipeline. Propane gas is stored in tanks, and homeowners can take advantage of price drops to top off their tanks.

Some Key Factors in Selecting a New Furnace

Here are some things to consider when selecting which type of furnace will best suit your needs:


The climate in the area where you live plays a major role in determining your heating needs. Colder climates require more powerful furnaces to keep your home comfortable when it is very cold outside. Since colder climates require more fuel, efficiency ratings are an important consideration in keeping your heating cost as low as possible. A furnace's efficiency is measured by its AFUE rating. The AFUE rating indicates how effectively the furnace converts fuel into heat. A higher AFUE rating translates to lower energy bills.


The availability of fuel sources in the area where you live are an important consideration when selecting your new furnace. If natural gas is easily accessible, it is usually the most cost-effective choice. However, in areas without a natural gas pipeline, propane furnaces may be the best alternative. Electric furnaces (air handlers or fan coils) are good options for homes without access to gas or propane, but heating with these alone is a very expensive option. These units are best when used with a heat pump, which extracts heat out of the outside air, even in cold weather. Technology with heat pumps is rapidly progressing and will be discussed in our heat pump section.


Natural gas furnaces are the most popular heating source in the United States. Approximately half of all US homes use natural gas for their heating source. The latest advancements in technology have enabled some of the top end furnaces to have AFUE ratings as high as 98%.


Modulating furnaces are the most efficient gas furnaces available. They obtain this efficiency by utilizing a modulating gas valve, which provides a continuous flow of gas to the burners based on the differences between the thermostat temperature setting and the actual temperature of the home. Furnaces with a modulating gas valve tend to provide enhanced comfort in your home by reducing the hot and cold spots, which are mostly due to short cycling of the furnace.


Selecting the Best Furnace for your Home

When you are in the market for a new furnace, you need to consider many various factors. These include the climate in the area you live in, the energy efficiency of the furnace, the type of fuel that is readily available, and your budget for a new furnace. Consulting with knowledgeable HVAC professionals can provide you with valuable information and help you make your final decision on which make, model, and efficiency rating is best for your home.


Once you have made your furnace selection, be sure to give adequate consideration to which HVAC professional to use for your installation. Look for HVAC professionals that have high ratings, good customer reviews, and highly trained technicians. By selecting a company with these characteristics to install your new furnace, you are ensuring optimal performance and safety. Improper installation can lead to a myriad of problems such as high energy consumption, and safety hazards. Westin Air's professional installers have the necessary expertise and knowledge to correctly install your new furnace, so that you will enjoy maximum energy savings and comfort. Most furnace manufacturer warranties are only valid when the furnace is installed by a qualified heating and cooling professional.


Getting educated on the different furnaces and fuel sources available in your area, will enable you to make a good decision on this major purchase. If you are in the Central Ohio area, consider calling Westin Air to have one of their home comfort consultants come to your home to answer all your questions and help you select the best furnace to keep your home warm and comfortable for many years to come.


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