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    Furnace Buyer's Guide


    While many of our products offer supplemental or zone heating, the most important heat source is the one that supplies heat to your entire home. Often called a heater or boiler, the wall furnace is the main component for central heating and it makes a huge difference in the cost and efficiency of your heat.

    There are several different fuel options including gas, electric, and wood, but we will focus on gas furnaces in this article. These furnaces are fueled by either natural gas or liquid propane. Read on for more information on the different types of gas furnaces, configurations, things to consider before you buy, installation, and more.

    What is a Furnace?

    A wall furnace or floor furnace is a heating appliance designed to be the main heat source of a home or commercial building. Unlike zone heaters that only heat a room or section of the home, furnaces heat the entire home. Gas furnaces heat air by igniting the gas and then distribute the heated air through an HVAC system.

    Empire framed wall furnace

    Since both natural gas and propane units hook up to gas lines, the furnaces do not need to store the fuel like a wood stove.

    Gas models heat faster than electric models and are better for colder climates because they produce higher temperatures than electric furnaces. Natural gas is also cheaper to use than electricity.

    Installation and maintenance of gas furnaces are relatively easy. They also tend to have minimal issues or breakdowns and last around 10-20 years.

    One of the disadvantages is that you need to have access to natural gas or install a propane source. The installation also includes the cost of running new gas lines to your furnace if you don't already have a hookup in place. Gas units also release low levels of carbon monoxide. For safety, you should install carbon monoxide detectors in case there would be an unexpected build-up of carbon monoxide.

    Four Categories of Furnaces

    Furnace models differ in how they distribute the heated air. The four main categories of furnace models are natural draft, forced-air, forced draft, and condensing. Here's an overview of each of the categories and how they direct heat throughout your home.

    Natural Draft

    Natural draft furnaces rely on the fact that hot air rises. They don't require a fan to create a draft; instead, the exhaust gases from the combustion of the fuel rise naturally up through the vent system. These models are also known as gravity vented furnaces. This natural rising can also be used to distribute the warm air in the home.

    While many furnaces have blowers to help distribute the warm air, some natural draft furnaces rely solely on the rising warm air to drift upward through the pipes and vents in the home. An accessory blower can be added to natural draft furnaces to help improve circulation, but it won't be as effective as a forced-air furnace.


    Empire surface mount wall heater

    Forced-air furnaces use a blower or fan to force air through the furnace and distribute it through the HVAC system. There are many types of forced air furnaces, but the ones we carry are called downdraft or counterflow furnaces.

    The difference between natural draft and forced-air furnaces can get a little confusing. It helps to break down the venting into two parts: the exhaust from the burn that needs to be vented outside and the warm air heated by the burn that is distributed to the house.

    Technically, if the exhaust air is vented through the natural rising of the exhaust up a vertical vent, it falls under the category of a natural vent or gravity vent.

    Forced-air furnaces have built-in blowers to distribute the warm air heated by the burn throughout the house. However, forced-air furnaces can also fall under the category of a natural vent or natural draft furnace because even though they use fans to distribute the "home air," they use natural vent to release the exhaust.

    For example, this unit has a powerful air distribution blower, so it is classified as a forced-air furnace. However, it also uses a natural draft to vent the exhaust, so it also classifies as a natural draft furnace.

    On the other hand, this forced-air furnace trades using room air for combustion. Instead, it draws in combustion air from outside and vents the exhaust outside like a direct vent model. On our website, you would find these types of furnaces under the direct vent category even though the process of venting the exhaust doesn't rely on fans.

    Forced Draft

    Forced draft furnaces use a draft induction fan to make sure no combustion vapors "spillover." It essentially vacuums the vapors up the vent pipe and outside. The majority of forced draft furnaces are also forced air types that use a blower to distribute the warm air throughout the different rooms.

    Diagram of forced air furnace

    Here is an example of a high-efficiency forced-air model that is also a forced draft furnace. It uses a direct vent system and a draft induction fan to remove exhaust gases and draw in the fresh air from outdoors, creating excellent fuel efficiency.


    The final category is condensing furnaces. These furnaces are so efficient that the flue gas condenses on the wall of the vent pipe. Because of the condensing, the vent pipes need to be PVC, aluminum, or stainless steel.

    High-efficiency condensing furnace

    They also require gasketed or glued joints so the condensation can't leak out. Instead, the droplets run back down into the heat exchanger where they evaporate.

    In terms of venting exhaust, these condensing models can be either a direct vent or natural vent.

    Before You Buy

    In the market for a new gas furnace? Here are some things to consider before you make a purchase. We've broken it down into BTU output, budget, maintenance, and efficiency. A good starting point is to calculate the square footage of your home as a way of ballparking how much heat you will need.

    Cottage home in wintry weather

    The heat requirements of your home are determined not only by the square footage, but also by the layout, insulation, and climate.

    The layout also makes a difference. Compact two-story homes are easier to heat than sprawling ranch homes because the hot air rises to the second floor. Furnace heat output is measured in BTU so you can compare the heat output between different models.

    Another important step is to establish a budget. This includes not only the price of the furnace itself, but also the cost of installation, maintenance, and the fuel costs of operating the unit.

    Speaking of maintenance, as a general rule of thumb, the more expensive the furnace, the more costly the maintenance. Gas furnaces tend to be low maintenance, but it's helpful to do some research on the models you are comparing so you know what maintenance to expect and how much it might cost.

    Finally, there is the consideration of efficiency. You can use AFUE (Annual Fuel Utilization Efficiency) ratings to help you compare between models.

    Know the Efficiency Rating

    High-efficiency furnaces have sealed combustion chambers and condense the flue gases. They have AFUE ratings between 90% and 98.5%. Although they have excellent efficiency, the purchase price of the units is more expensive.

    Mid-efficiency models use exhaust fans to control the flow of combustion air. They are more compact and lighter than the low-efficiency models and have an AFUE of around 80% to 83%. These models also use electronic ignition instead of a pilot light.

    Low-efficiency models use a natural draft for the flow of combustion exhaust. They also have a pilot light instead of electronic ignition and range from 56% to 70% AFUE rating.

    How to Boost the Efficiency of Your Furnace?

    The AFUE rating is not the only thing that determines the cost-savings and efficiency of your furnace. There are also things that you can do to maximize the heater's performance and keep it in good working order. Here are some tips to get you started.

    The first and most important advice is to read and follow all of the manufacturer's guidelines for your specific unit. Those instructions will be tailored to your particular heater and are the best place to start. Typical maintenance includes things like dusting the blowers or replacing the filters.

    Again, it's important to follow the manual for your specific model. Some maintenance may require you to shut off the unit as well as the circuit breaker for the unit.

    Framing for an installation

    Another thing that helps with efficiency is to think through how the hot air is traveling through your home. Do you have curtains or furniture blocking air vents? Does the ductwork have leaky joints? All of these factors could be making the furnace work harder (and use more fuel) than it has to.

    What Are The Parts of a Gas Furnace?

    Furnaces have come a long way from the old-fashioned wood stoves that used to heat homes. Here is a quick overview of the different parts of a gas furnace and how it works. Note that this list might be slightly different depending on what model of gas furnace you have.

    Let's start with the burners. When the thermostat senses that it's getting too cold, it signals the gas valve to open and allow gas to run through the burners. The burners have tiny holes that allow the gas to come out and ignite in the combustion chamber.

    If you have a model with a draft fan, this will work to draw combustion air in and exhaust out. The exhaust is carried away by the flue. The burners heat up their surroundings and this heat is transferred to the clean air with the heat exchanger. (The clean air is inside metal tubes which are heated by the burner.)

    Finally, the heated air is sent by blowers through your HVAC system. Colder air is directed back to the furnace by return vents. Many models are also equipped with a filter to filter the air before it is distributed throughout the home.

    Configuration Options

    There are two main configuration options when it comes to gas furnaces. The first is a floor furnace, designed to install in a floor cavity. The second option is a wall furnace that is either mounted on brackets or framed into the wall. As always, pay close attention to the clearance requirements your model needs.

    Empire floor furnace

    A model like this floor furnace installs in the floor cavity and heats without any electricity. It is equipped with a piezo matchless ignition and requires a vent system. Floor furnaces are not as easy to install as some of the wall-mounted ones and often require professional installation.

    In contrast, many of these wall furnaces mount on brackets and are easier to install. They are ideal for small spaces like apartments, mobile homes, or offices. Larger upright furnaces are often framed into a wall, or some may be installed in basements.

    Top Manufacturers

    Durability, longevity, and efficiency are some of the main priorities when it comes to finding a furnace for your home or business. Each of the manufacturers we recommend below has a long-standing reputation for building quality furnaces that last.

    • Empire — Empire has been making heaters since 1932. Their American-made gas heaters come in a wide range of options and are a quality choice for your home.
    • Ruud — Edwin Ruud patented the first automatic hot water heater in the mid-1880s. He went on to found a company that has continued to offer quality, innovative heating solutions. Ruud has a wide range of heating and cooling products including several gas furnaces.
    • Trane — Trane has been in business for over 100 years and is well-known in the heating and cooling industry. They also have a nice selection of durable gas heaters designed to heat your entire home. 
    • American Standard — American Standard is yet another company with over a century of experience in home comfort systems. Their gas furnaces come in a range of sizes so you can pick the size and features that fit your home.


    While some furnaces should be installed professionally, other models like the wall-mounted furnaces can be installed by homeowners who are experienced with appliance installation. We do recommend a professional for installing any new gas lines. Also, please note that these installation tips are general guidelines. It is very important to read and follow all of the instructions in the manual.

    Installing a high-efficiency furnace in the basement

    Start by planning out the gas line supply and the venting route that your furnace will require. Hire a professional to route any new gas lines and make sure that they are at the right pressure for your appliance.

    Many of the wall-mounted furnaces are direct-vent, so they need to be installed on an outside wall. The direct-vent pipe goes through the wall horizontally, so you don't need to worry about routing vent pipe up through the roof.

    The manual will outline instructions for assembling the mounting bracket and securing the unit. After you mount the unit, you can follow the steps for cutting the vent pipe and installing the vent assembly.

    Care and Maintenance

    When it comes to maintenance, the best advice is to set up a routine that covers all of the recommendations in the owner's manual. With a schedule, all the maintenance steps are completed on time and you will be helping to ensure the safety and longevity of your furnace.

    In addition to the more detailed instructions found in the owner's manual, here are some tips for caring for your furnace:

    • Check that all the wiring and venting are secure.
    • Smell along the gas line and the gas connections to see if you detect the "rotten egg" smell of propane or natural gas. This could indicate a leak.
    • If at any time you notice a strong gas smell, call 911.
    • Dust or vacuum the blowers and other components. Do this with both the furnace and the circuit breaker off.
    • If your furnace has a filter, be sure to replace it as recommended.
    • Also, if your furnace is equipped with a drain for the condensation, make sure it stays open and unplugged.


    Almost all furnaces will ship via LTL freight. Once you place your order, the shipping company will contact you to schedule a delivery. Inspect your furnace as soon as it arrives (and before you sign off on the delivery!) If you notice anything amiss, contact the manufacturer for assistance.


    Empire wall furnace in a small room

    Choosing the right furnace is a major investment in the comfort of your home. Gas fueled furnaces are popular due to their low maintenance and cost-effective heat. It's worth taking the time to plan carefully and find the unit that best suits your home and budget. Thankfully, there are many options and configurations to choose from!

    And if you have any further questions about furnaces, please reach out to us! Our NFI Certified Technicians would be glad to help.

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