types of furnaces

It is important to help your customers better understand the need for a reliable furnace and all the options available. The furnace is at the heart of a building’s HVAC system, as furnace blowers are responsible for circulating cool air in the summer months as well as heating the space comfortably. 

Below is a breakdown of some of the types of furnaces that are commonly found in most buildings.

Single Stage Furnace 

Of all the different furnace types, the single stage is the simplest and one of the most common. Like the name suggests, the single stage furnace is a one-trick pony, with two settings: On or Off, with a single fan speed. 

The upside of a single stage furnace is its front-end costs; thanks to its simple design, they’re the least expensive to buy. The downside is that, especially in colder climates, there likely will be cold spots from one room to the next. That might seem like a minor concern until your customer walks into a room that’s three degrees colder, because that’s enough of a drop in temperature that you’ll definitely notice it. 

Operating costs can be higher as the single stage furnace cycles on and off more frequently during the course of the day. The more the furnace cycles on and off, the more wear on the furnace blower motor and the higher start up amperage draws more electricity. There is also greater heat exchange expansion and contraction, lessening the furnace life cycle.

Two Stage Furnace

The two stage furnace offers the option of two stage firing. Comparing a one-stage vs two-stage furnace, the chief advantage here is that you get more flexibility and efficiency in keeping your customers’ space warm, making it easier to keep a consistent temperature. 

A two stage furnace is much quieter since it operates on low fire most of the time.  And two stage furnaces create less carbon dioxide emissions for the environment. Two stage furnaces also help to increase energy efficiency on moderate-temperature days since it will, in most cases, remain on low stage. They also provide a higher level of comfort due to the steady flow of warm air on the colder days.

Variable Speed Furnace

Think about setting the AC or heat in a car . You get to choose not only the temperature setting, but the fan setting as well. That’s what you get with a variable speed furnace, and homeowners can fine-tune the temperature to a degree or even a fraction of a degree. With that kind of flexibility, your customers can keep the temperature where they want it. 

Since these types of furnaces can be more complex, they’re more expensive on the front end but they are much more efficient. You also have the option of letting the fan run continuously, circulating (and filtering) air throughout the property, improving indoor air quality by a great extent. 

Furnaces by Fuel Type 

The other way to think about different furnace types is by the kind of fuel that they use. Most residential furnaces run on fuel oil, natural gas or electricity, although there are some that use wood, propane, biomass or coal. 

Gas Furnace

gas furnace type


Gas heat is by far the most common in the United States. Municipalities or gas companies route a network of gas lines underground, with service for each home or building. The gas that’s piped into the home is then directed across the furnace’s burner and ignited. The gas furnace includes a heat exchanger, and as the air in the heat exchanger is warmed up, it’s distributed throughout the building by the blower fan. 

Especially when comparing an electric furnace vs gas furnace, many people find the heat from a gas furnace to be less dry and more comfortable overall. Natural gas is reliable and cheap, and a modern gas furnace can operate at up to 98% efficiency. That’s why high efficient condensing furnaces must be vented in PVC.  The flue gas temperatures are so low typically below 120 degrees which can cause the flue gases to condensate. 

Efficiency Ratings and Types of Gas Furnaces

Gas furnaces are categorized by their Annual Fuel Utilization Efficiency (AFUE) rating; a furnace with an 80% AFUE rating means that it can turn 80% of the fuel it consumes into heat. Obviously, the higher the AFUE number, the more efficient the furnace is in its operation. The different types of gas furnaces are: 

  • 80% single stage
  • 80% two-stage
  • 80% two-stage with variable speed blower
  • 92% single stage
  • 95% single stage
  • 96% two-stage
  • 96% two-stage with variable speed blower
  • 97% modulating gas furnace with variable speed blower
  • 98% modulating gas furnace with variable speed blower

A two-stage furnace can run at 65% or 100% capacity. Most two-stage furnaces run over 90% of the time on the first stage. It’s a longer, slower heat cycle that’s quieter and distributes heat more evenly through the building, without the blast of hot air that many customers find uncomfortable. Two-stage furnaces also can mean better air filtration and enhanced air quality, as air is circulating through the building more regularly. 

A modulating furnace can run almost constantly (depending on thermostat setting), but at a very low level. Modulating furnaces are usually calibrated to about 40% capacity and can increase by increments of .5% at a time. This can help the temperature in each room stay a lot more consistent, as the furnace is running at a steady state rather than blasting, settling for a while and then blasting again. As sophisticated and efficient as these systems are, they also tend to be some of the most expensive heating setups on the market.

Ruud Furnaces

For a number of years, Ruud furnaces have been rated by Consumer Reports as the #1 furnace in terms of reliability. Ruud units have some definite advantages in terms of design and quality: 

  • Most units use a hot surface ignition system, which can become fragile and crack or break over time. Ruud furnaces are designed with a direct spark ignition system, which is more expensive on the front end but has a longer service life. DSI is nine times more reliable than HSI.
  • Ruud’s seven-segment LED control board is designed to make troubleshooting and servicing much simpler and more streamlined for the technician. 
  • Ruud high-efficiency furnaces (90% or more) include a patented condensate management system. 
  • The heavy-gauge sheet metal on Ruud furnace housings and doors is safer; their hemmed edges prevent workman’s comp claims from cuts on the sharp sheet metal edges on cheaper units. 
  • Ruud’s 97% and 98% modulating furnaces won a Best Product award from ASHRAE at the time of their introduction. 
  • Ruud holds more patents than any other natural gas furnace manufacturer on the market.

Types of Blower Motors     

Modern furnace designs can have more than one type of blower motor: 

hvac furnace motor

  • Permanent split capacitor (PSC) motors are the oldest design and no longer manufactured due to the new FER ratings. A PSC blower motor is either on or off. The output and speed of a PSC blower isn’t adjustable, and either blows at full force or is not blowing at all. 
  • Electronically commutated motors (ECM) are a more energy-efficient design; developed by General Electric, ECM motors are brushless. They are activated by signals from a controller and ramp up through a range of speeds each time the furnace cycles on. ECM motors are lower-maintenance and can typically last 90k hours/10 years, vs 50k hours/8 years for a PSC motor.
  • Variable speed blower motor furnaces precisely control airflow to better temperature control, humidity control and air distribution. A higher degree of precision means a higher degree of comfort. Compared to single speed PSC motors, a variable speed performs better and uses about 2/3 less electricity! During the cooling mode, variable speed systems typically result in an efficiency gain of about 1 SEER. The higher SEER rating will save your customer hundreds of dollars annually. Variable speed furnaces ensure quieter operations.
  • Variable speed furnaces slowly ramp up to speed, so there’s no sudden kick or blast of air at startup. A variable speed motor can also better help clean the air. When the fan is in constant operation the motor will continue to slowly circulate the air, allowing the filter to capture more contaminants.

Electric Furnace

Electric furnace setups are another option if your area has never been set up with gas service. With an electric furnace, the heater is supplied by an electric element, and then the hot air is forced through the ducts via a blower. Electric furnaces tend to be more compact than gas or oil units, as well as usually being fairly affordable. The distinct downside of an electric furnace is that it is not as cost efficient operationally as gas, and that wintertime electric bill can come as a rude surprise especially if your home’s windows and attic insulation are subpar. In general, electric heat is as much as 2.5 times as expensive as gas heat, but it’s sometimes the only choice when there’s no way to vent the combustion exhaust from a gas furnace (such as in many multi-story, multi-family buildings).

Things To Consider When Recommending A Furnace

  • Think about what your customer’s needs are.
  • What are the structure’s heating needs? This involves manual J load calculation, the size of each room, the number of windows and doors should be measured, the R values of the walls, windows, doors, ceilings, floors, infiltration, existing ductwork, registers and insulation as well as other factors like people and appliances should be considered when properly sizing a structure for its heat loss. It’s not good to have a furnace that’s either oversized which is more typical or undersized for the space it needs to heat. 
  • Be sure and check the ductwork sizing with a duct calculator and measure and count out all the supply and return registers and grilles. Most homes do not have adequate return air. 
  • Remember there has to be as much air coming back in the return as was distributed in the supply duct. It’s recommended to take a static pressure reading to properly access the ducted air distribution system.  The furnace is only as good as the systems proper sizing, design and installation.  
  • Help your customers make an informed decision, by relaying the pros and cons of each furnace option. 

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