Gas Furnace Types

Gas Fired Pool Heater

Gas Furnace Types come in a variety of sizes and can be used for different applications. Types of gas furnaces have different classifications. By and large, the most common gas furnaces use natural gas and utilize electronic ignition. Electronic ignition gas furnaces are slowly replacing the older style standing pilot furnaces where a pilot light remained lit all the time.

Now, with the newer modern electronic ignition, gas furnaces only use gas when there is an actual call for heat. That adds efficiency because, with the older standing pilot gas furnace, the pilot remained on even in the summer months. The heat produced by a standing pilot light is negligible. However, it is still added heat to the system in the summer.

The whole purpose of the AC in the summer is to remove the heat from the system. Rather than add heat like a standing pilot would do.


Gas Furnace Types | HVAC Heating

A gas furnace is rated for efficiency by AFUE or Annual Fuel Utilization Efficiency rating. Furnaces installed before the nineties have efficiency ratings down to 60 percent efficient (or less in some cases). AFUE ratings of gas furnaces are the amount of heat delivered by the furnace divided by the fuel used to make that heat. Another way to look at AFUE is to measure the amount of heat lost up the exhaust stack. If the furnace delivers 90 percent of the heat produced into the dwelling, then ten percent of the heat produced is lost up the stack.

Classification of Furnaces

Furnaces can be classified or categorized differently. It really depends on your perspective. Here are different to classify gas furnace types. There is an argument for having a standing pilot gas furnace versus an electronic ignition gas furnace.
Pilot Light with flame

  1. Standing pilot is a gas furnace type. These are slowly being replaced by electronic ignition gas furnaces. Standing pilot gas furnaces use older technology and are not as efficient as the newer more modern electronic ignition cousins.
  2. Electronic ignition is a gas furnace type. There further classifications of electronic ignition gas furnaces. One way to describe them is the type of electronic ignition they utilize. Among those furnaces, these can be classified as - Direct spark ignition, intermittent pilot, and hot surface ignition. Among these, there are direct-fired and indirect-fired furnaces. Direct fired happens when the ignition method directly lights the main burner. Indirect happens when a pilot light lights the main burners. The pilot light is lit by electronic ignition.

Further classification of gas furnace types are:

  1. Single Stage gas furnace
  2. Two-Stage gas furnace (there are some three-stage gas furnaces). For gas furnace types these can also be called condensing furnaces.
  3. Modulating gas furnace For gas furnace types these can also be called condensing furnaces that modulate.
Additional Classification

Among all furnaces, you can purchase there is an additional classification of gas furnace types. Or you could call it a subcategory of gas furnace types:

Energy Efficiency and Gas Furnace AFUE

Just because you spend extra money to buy a high AFUE gas furnace does not mean you will have true energy efficiency. There are many factors to getting true energy efficiency. Among these factors are:

  1. Proper installation of the gas furnace
  2. Ductwork Integrity
  3. Home Insulation including energy-efficient doors and windows
  4. Home humidity levels

For more information see our article on Gas Furnace Efficiency Factors

  1. Lowboy gas furnaces for installation tight spaces
  2. Upflow gas furnaces
  3. Downflow gas furnaces
  4. Horizontal flow gas furnaces
  5. Package unit gas furnaces
  6. Duct heater gas furnaces
  7. Pool heater gas furnaces
  8. Unit heaters
  9. Wall heater gas furnaces
  10. Floor heater gas furnaces
  11. Lastly, I have often heard people refer to their boiler as a furnace although technically it is a boiler. A boiler can either be a hot water boiler or a steam boiler within the gas-fired boilers. For a gas furnace type, a boiler could be technical because some use gas.

Efficiency and Gas Furnace Types

For gas furnace type efficiency is important. Even the highest AFUE-rated furnace is going to lose heat up the stack. It is nearly impossible to get 100 percent AFUE out of any gas or oil furnace. That is because all oil and gas delivered to a furnace have a small amount of moisture in them. You can also expect some jacket losses. Gas typically has a moisture content of 4 to 5 percent.

Oil depends on the quality of oil purchased, how many additives used in the oil, and the integrity of the oil tank and piping system. The end result of all this moisture and additives in the fuels affects the AFUE of the furnace and is the reason why no gas or oil furnace can achieve more than 96 percent efficiency.

The Standing Pilot Gas Furnace | Gas Furnace Types

The typical Standing Pilot Gas furnace uses a thermocouple. The thermocouple keeps a flame lit 24 hours a day, seven days a week. The pilot light is manually lit, and once lit, it should remain lit unless a draft blows it out or the thermocouple fails. Thermocouple failure is common but not as common as a draft blowing the pilot light out. Typically, whenever a high wind conditions, the wind could extinguish the pilot light. If this happens to you and you are not sure how to relight the pilot light call a professional.

Always follow the manufacturer’s safety guidelines. If you feel comfortable lighting the pilot, carefully do so at your own risk. Remember, both natural gas and propane are flammable and can be explosive, given the right conditions. By nature, natural gas is lighter than air, and propane is heavier than air. That means that propane will settle in the lowest parts of your dwelling. Natural gas will settle or get trapped in higher parts of the dwelling. Always keep this in mind, and if you smell a rotten egg smell, then do not light a match or lighter. At least not until the area is safely vented. Many gas-fired water heaters use the standing pilot system.

The Electronic Ignition Furnace

Electronic ignition gas furnaces are more commonly produced today than standing pilot gas furnaces. They offer added efficiency because these gas furnaces automatically light a pilot when the thermostat calls for heat. The standing pilot gas furnace requires a pilot light to be lit all the time. Most gas and oil furnaces are integrated with the air conditioning system. They make use of the same blower. Additionally, the electronic ignition keeps the heat out of the furnace even in the summer. Therefore, there is less heat to remove by the air conditioning system. The electronic ignition gas furnace is more efficient than standing pilot gas furnaces.

Gas Fired Unit Heaters

In some applications, it is necessary to use gas-fired unit heaters to heat a space. Gas-fired unit heaters can be found in garages, mechanical rooms, electrical closets, and large open spaces. Large spaces in large structures like warehouses, aircraft hangers, or vehicle garages. These gas-fired unit heaters are usually not ducted, but they can be adapted to ductwork.

High Performance HVAC

Gas Furnace Types

Use our handy calculator to see how many BTU's your natural gas appliances are producing: