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Furnace Guide

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A Comprehensive Guide to Furnace Types and Details

Introduction to Furnaces

Furnaces provide warmth in residential and commercial buildings by heating the air that circulates through those buildings. They are essential to provide warmth in cold weather and are an essential component of a heating, ventilation, and air conditioning (HVAC) system.


In this guide, we will explain the different types of furnaces available. Whether you're considering a furnace upgrade or are simply interested in understanding more about furnaces, this guide will provide you with valuable information.

Understanding the Different Types of Furnaces

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

Natural Draft Furnaces

Natural draft furnaces were the earliest form of furnaces. These furnaces featured cast-iron or riveted-steel heat exchangers enclosed within a brick, masonry, or steel shell. The heat exchangers were typically vented through chimneys made of brick or masonry.


Air circulation in natural draft furnaces relied on large metal pipes which channeled warm air into floor or wall vents inside the home. This heating method took advantage of the fact that warm air rises. These furnaces could be adapted to burn various fuels, including wood, coal, and natural gas. As time went on, advancements were made and electric blowers were added to aid in air distribution, improving the efficiency of natural draft furnaces. Gas and oil-fired systems were controlled by thermostats, while wood and coal-fired furnaces were manually controlled by adjusting fuel levels and air dampers.

Forced-Air Furnaces

Forced-air furnaces, which were a popular replacement for natural draft furnaces, became popular during the 1950s and 1960s. These furnaces featured atmospheric burner styles and cast-iron or sectional steel heat exchangers. They were often installed on existing gravity ductwork.


Forced-air furnaces offered a wide range of airflow speeds by being equipped with blowers driven by belts. They were more compact than the old natural draft predecessors and had removable panels made of heavy steel. Forced-air furnaces were later designed to also accommodate central air conditioning systems, making them useful for both heating and cooling.

Forced Draft Furnaces

As technology advanced, forced draft furnaces further enhanced the efficiency and compactness of furnace designs. These furnaces featured steel heat exchangers and multi-speed blowers, reducing fuel consumption and allowing for compatibility with central air conditioning systems. Due to their smaller size, forced draft furnaces offered greater options for installation.

Condensing Furnaces

The invention of condensing furnaces represents the height of furnace 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.


The primary advantage of a condensing gas furnace is its ability to capture latent heat from exhaust gasses in the secondary heat exchanger. By condensing water vapor and other chemicals, these furnaces extract additional heat energy from the exhaust gasses, which significantly improves fuel efficiency. The vent pipes used in condensing furnaces are made of PVC to prevent corrosion.

Furnace Fuel Sources

The choice of fuel source for a furnace depends on regional availability, cost, and environmental considerations. The most common fuel sources for furnaces include natural gas, propane, oil, electricity, and in rare cases, coal.


Natural gas is the preferred and most commonly used fuel source for modern furnaces in North America and Europe due to its availability and cost-effectiveness. Propane furnaces are a good alternative for areas without a natural gas pipeline. Propane gas is stored in tanks. Oil furnaces are still prevalent in some regions.


Electric furnaces use electricity as their primary energy source, heating elements to generate heat. While they are less efficient than gas furnaces, electric furnaces are compact and suitable for smaller spaces. Coal furnaces are rare today but were historically used in areas with abundant coal resources.

Factors to Consider When Choosing a Furnace Type

Here are some key considerations when selecting which type of furnace would be best for your needs:

Climate Considerations

The climate in your region plays a significant role in determining the heating needs of your home. Colder climates may require more powerful furnaces to ensure adequate heating during extreme weather conditions. Understanding your climate will help you choose the right furnace size and efficiency rating.

Energy Efficiency

Energy efficiency is a crucial consideration when selecting a furnace. The efficiency of a furnace is measured by its AFUE rating, which indicates how effectively it converts fuel into heat. Higher AFUE ratings signify greater energy efficiency, resulting in lower energy bills.

Availability of Fuel Sources

The availability of fuel sources in your area will impact your furnace options. If natural gas is readily accessible, it is often the most cost-effective choice. In areas without a natural gas pipeline, propane or oil furnaces may be the primary alternatives. Electric furnaces are viable options for homes without access to gas or oil, but are best when used in conjunction with a heat pump.

Propane Furnaces: Efficient and Versatile Heating Options

Propane furnaces are a popular choice in areas where natural gas is not available. Propane offers similar efficiency and effectiveness as natural gas. Propane furnaces are often chosen for their lower upfront costs compared to other furnace types.

Electric Furnaces: Compact and Cost-Effective Solutions

Electric furnaces utilize electric heating elements to generate heat, making them suitable for homes without access to natural gas or propane.


While electric furnaces are less efficient than gas furnaces, they are often more affordable and easier to install.

Natural Gas Furnaces: Widely Used and Highly Efficient

Natural gas furnaces are the most widely used heating source in America, found in approximately half of all U.S. homes. These furnaces excel in providing even heating throughout the building. Natural gas is a cost-effective fuel source, resulting in lower utility bills compared to other options.


Modern natural gas furnaces can achieve impressive AFUE ratings of up to 98%, making them highly efficient and environmentally friendly. Older gas furnaces may have lower efficiency ratings, but still provide effective heating.

Modulating Furnaces: Optimal Efficiency and Precision Heating

Modulating furnaces combine the efficiency of natural gas with the cost-effectiveness of other furnace types. While the upfront investment is more, modulating furnaces offer significant energy savings in the long run.


Modulating furnaces operate by modulating a continuous flow of gas based on the temperature differential between the thermostat setting and the current home temperature. This design eliminates frequent on/off cycling, resulting in improved energy efficiency and enhanced comfort.

Determining the Right Furnace for Your Home

Choosing the right furnace for your home requires careful consideration of various factors, including climate, energy efficiency, fuel availability, and budget. Consulting with HVAC professionals can provide valuable insights and help you make an informed decision.


Professional installation ensures optimal furnace performance and safety. Improper installation can lead to inefficiency, increased energy consumption, and potential safety hazards. HVAC professionals have the necessary expertise to assess your heating needs and recommend the most suitable furnace for your home.

The Benefits of Professional Installation

While some homeowners may try to install a furnace themselves, professional installation offers several major benefits. HVAC professionals have the knowledge, skills, and experience to ensure proper installation, maximizing furnace performance, efficiency, and safe operation.


Most warranties provided by the manufacturers are only valid when the product is installed by a HVAC professional.


Professional installation also helps prevent safety issues and potential damage to the furnace or surrounding components. HVAC technicians can assess your home's specific requirements, recommend appropriate furnace models, and ensure proper ductwork and venting for optimal airflow and heating distribution.


Understanding the different types of furnaces, their features, and fuel sources is essential for making informed decisions about your home's heating system. Whether you choose a natural gas, propane, or electric furnace, each type has its own advantages and considerations.


Consider your climate, energy efficiency requirements, fuel availability, and budget when selecting a furnace. And remember, professional installation ensures optimal performance and safety.


By being well-informed about furnaces and their details, you can make the right choice for your home and enjoy reliable, efficient, and comfortable heating for years to come.

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