Your furnace is one of the hardest working appliances in your home. Although you may not think much about it, you most certainly are aware of the warmth and comfort it provides. Whether you are in the market for a new furnace or just want to become more familiar with the furnace you have, knowledge of some common furnace terms is always helpful. 

Common Furnace Terminology 

Annual Fuel Utilization Efficiency (AFUE) 

AFUE ratings determine the efficiency of heating systems. The ratio is determined by the percent of heat produced for every dollar of fuel consumed. The higher the AFUE, the more efficient the furnace. A high-efficiency heating system has an AFUE ratio of more than 90%.

British Thermal Unit (BTU) 

One BTU is the amount of heat required to raise one pound of water by one degree Fahrenheit. Furnaces with higher BTUs have higher heating capacities. The amount of BTUs your home requires is dependent on numerous factors.  Your HVAC contractor can do a load calculation to determine the appropriate size.

Downflow Furnace 

A downflow furnace is a unit that takes cool air in from the top and blows warm air from the bottom, typically installed when the ductwork is located below the furnace. 

Dual Fuel 

A dual fuel heating system uses two sources to heat the home. An electric heat pump is paired with a gas furnace, and the two sources alternate to maximize efficiency. Heat pumps are efficient so long as the temperature stays above freezing. However, once the temperature dips below 32 degrees, it’s more efficient to switch to a gas-powered furnace. 


A system of ducts runs most commonly inside walls and ceilings. It’s responsible for transporting air from the HVAC (heating, ventilation, and air conditioning) unit throughout your home. Most homes have ducts, although ductless HVAC systems are available. They use individual air handlers in each room to provide heating and cooling without the need for ducts. 

Heat Pump Unit 

Heat pumps are different from traditional HVAC systems because they provide both heating and cooling for year-round comfort. Depending on the season, the heat pump will either draw heat from outdoors to circulate throughout the home or remove heat from the home and release it outside. 

Horizontal Furnace 

Lying on its side and pulling cool air in from one side and pushing warm air out the other, horizontal furnaces are used in areas where space is limited, such as a crawl space. 

HVAC Zoning System 

Using dampers in the ductwork to redirect air to specific areas of the home, a zoned HVAC system allows heating customization in different areas of the home. HVAC zoning can help homeowners reduce energy consumption and save money. 

MERV Rating 

MERV stands for minimum efficiency reporting value and is used to measure the efficiency of air filters. A higher MERV rating indicates smaller holes in the air filter, which allows fewer particles to pass through, making the air filter more efficient.

Upflow Furnace 

An upflow furnace circulates the air through the sides or the bottom of the HVAC unit, and then out through the top. An upflow furnace is primarily used in basements, closets, or attic installations. 

Contact Ravinia Plumbing, Sewer, Heating & Electric for Reliable Heating Services 

Now that you know more about the components and types of furnaces, you can power through the remainder of the winter staying warm and comfortable. For all your home’s heating needs, reach out to the heating, air conditioning and indoor air quality professionals at Ravinia Plumbing to schedule service.