HVAC Terms Glossary

A furnace is the appliance that creates heat for a building in a forced air system. The major components of a furnace are the thermostat (a separate device that regulates the temperature and initiates heating cycles), the burner, the gas valve, the heat exchanger, and the blower, plus the ductwork and vents used to distribute heated air throughout the building.

A forced air heating system takes air from inside the house, heats it with a furnace, and then uses a blower to circulate the air throughout the house via the ductwork and vents. You can also integrate a central air conditioner into a forced air system, and the A/C will use the furnace blower to circulate cool air in summer. This is in contrast to systems that use radiators, for example.

Upflow furnaces are among the most common in Canada. They draw air in from the bottom, heat it, and vent it upward into the ductwork, so they’re usually located in a basement, crawlspace, or other place near the bottom of the house.

Downflow furnaces have the opposite airflow compared to upflow furnaces. Downflow models draw in air from the top of the unit, heat it, and circulate it downward throughout the home. These units are typically found in upper-floor closets, attics, or other spaces near the top of the house.

A condensing furnace is a furnace that has a secondary heat exchanger. After the initial combustion process, the exhaust gasses enter the secondary heat exchanger, where additional heat energy is extracted from the flue gasses. Because condensing furnaces get more thermal energy from the same amount of fuel, they tend to be more efficient than non-condensing models.

An oil furnace is one that burns furnace oil instead of natural gas or propane to create heat. The burner in an oil furnace takes the oil, converts it into a spray, mixes it with air, and then ignites the mixture. Oil furnaces typically require large tanks on-site to hold the fuel supply.

A natural draft furnace is an older and less efficient type of furnace that uses natural atmospheric pressure to move exhaust gasses out of the ventilation system. As the hot air and exhaust gasses rise and leave the system, they’re naturally replaced by colder air, and this incoming draft keeps air flowing through the furnace.

A packaged unit is a single system that has two HVAC units in one, and all the components are inside the one system (as opposed to a split system, where there are indoor and outdoor components). It’s often a furnace and air conditioner in one system, but it can also be a heat pump, dual fuel, or gas/electric packaged system.

These units are often installed on the roof or side of a building, so they can be ideal for small homes that do not have enough space inside, or homes that were built on a crawl space and don’t have a large basement.

A rooftop unit, or RTU, is a large-capacity packaged system that offers heating and cooling for large spaces, such as commercial/industrial buildings or multi-family residential buildings. The units are quite large, so they’re installed on the roof of the structure.

A self-contained system is an HVAC system that has all the components in a single unit, unlike a split system. With a split system, usually an air conditioner or heat pump, there’s an indoor unit that houses the evaporator and an outdoor unit that houses the condenser and compressor. In a self-contained system, all those components are housed together. A package system is a type of self-contained HVAC unit.

A split system is a type of air conditioner or heat pump that has an outdoor unit and an indoor unit. The evaporator is part of the indoor unit while the compressor and condenser are part of the outdoor unit. With a heat pump that can heat and cool, the refrigerant flow can reverse so that the evaporator is outside and the condenser is inside.

The burner is an important component of furnaces and boilers. It’s where the fuel mixes with air and gets ignited, and the burning mixture produces the heat that’s distributed throughout the house. The type of fuel that’s mixed with air will depend on whether the furnace or boiler runs on natural gas, propane, or oil.

A heat exchanger is a device that transfers heat between two or more fluids within a contained system, and it’s a major component of furnaces and boilers.

The heat exchanger is a metal container, and inside is where the combustion process happens. The heat created during combustion is transferred to the air, which is circulated around the house. The heat exchanger is also a safety device that extracts the heat while preventing the fumes from mixing with the air you breathe.

A control board is often referred to as a system’s brain. It’s the circuit board that controls the gas valve, blower motor, flame sensor, and ignition process, and it tells the furnace what operations to perform and in what order during each heating cycle.

Furnaces and air conditioners have filters inside them that trap dirt and dust flowing through the system to improve the indoor air quality in your home. Some filters are more advanced than others, and you can buy special ones that also trap smaller particles and things like pollen, smoke, allergens, and pathogens.

Filter efficiency can be measured with something called minimum efficiency reporting values (MERV). The higher the MERV, the smaller the particles the filter can trap. The MERV scale is from 1 to 16.

A gas valve is a component of a furnace or boiler. It opens and closes to start, stop, and regulate the flow of natural gas or propane going to the burner.

An igniter is a component of a furnace or boiler. It ignites the fuel so that the combustion process can create heat. There are several types of igniters, including pilot lights, as well as more efficient direct spark ignition or hot surface ignition systems.

The pilot light is a visible blue flame that’s used to ignite gas. A pilot is a type of ignition system, and you can find them on some furnaces, boilers, and gas fireplaces. Older pilot lights are always burning, but there are more modern intermittent pilots that only come on when heat is called for.

The blower is the device that takes heated or cooled air from the heating/cooling system and blows it around the home.

In a ducted system, such as with forced air heating and central air conditioning, the blower blows the air from the furnace or air conditioner into the ductwork so that it can circulate around the house. With ductless systems, each indoor air handler will have a blower of its own to distribute heated or cooled air in the room.

A plenum is a special box that holds air, and it’s part of a forced air/central air system. Forced air HVAC systems usually have a supply and return plenum. Once air has been heated or cooled, it goes into the supply plenum, and from there the blower sends it into the ductwork for distribution. Stale air from the house then enters the return plenum, where it’s sent back through the furnace or air conditioner.

A thermostat is a device that controls the temperature in a building. It tracks the internal temperature of a space and initiates/ends heating and cooling cycles to maintain the set temperature.

The evaporator coil is the part of an air conditioner over which warm indoor air is circulated in order to cool it. In central air conditioners, it is affixed to the furnace during installation in order to use your home’s central ventilation ducts to circulate the cool air. In ductless units, the indoor wall-mounted unit contains the coil. The coil contains a network of tubing through which refrigerant is circulated and as air is passed over it, it absorbs heat from the air, cooling the air and causing the refrigerant to ‘evaporate’ from liquid form to gas form, before being cycled to the air conditioner’s outdoor condenser unit.

The condenser is the outdoor unit of a central or ductless air conditioner, and it’s the unit most people think of when referring to a central air conditioner. Its job is to release the heat extracted from inside your home by turning the refrigerant coming from the evaporator coil back into liquid form, releasing heat in the process. The refrigerant is then compressed and cycled back to the indoor evaporator coil to begin the process again.

ECM stands for electronically commutated motor, and it refers to the blower motor inside a furnace or air conditioner.

An ECM motor can regulate its own electrical consumption. This has two main benefits: ECM motors are more efficient, and they can also adjust the airflow. Many ECM motors are multi-speed, but they can be variable-speed as well.

A motor with more than one speed will tend to produce more even temperatures throughout the house, offer quieter operation, and manage humidity better.

An EC fan is another term you might hear, and this means the fan is powered by an electronically commutated motor.

The primary heat exchanger is the main heat exchanger in a furnace or boiler. The term “primary heat exchanger” is typically used when a furnace or boiler has two heat exchangers, a primary and secondary one.

A secondary heat exchanger is where the exhaust gasses go after they’ve been through the primary heat exchanger. Inside the secondary heat exchanger, additional thermal energy is extracted from the flue gasses. Furnaces and boilers with secondary heat exchangers are called condensing units.

A tubular heat exchanger is a type of heat exchanger that consists of a large cylinder filled with bundles of tubes. These heat exchangers are more resistant to pressure and temperature, so they can have longer lives and fewer maintenance requirements.

Single-stage means a furnace or air conditioner has only an ON and OFF setting, so when the unit is running, it always operates at 100 percent capacity. The unit will turn on and off as frequently as needed to maintain a comfortable indoor temperature.

These are typically the most basic and most affordable models. Higher-end units will often have more than one stage, allowing the unit to operate at different output levels to maintain a more consistent temperature and operate more efficiently.

A two-stage furnace has a gas valve with two output levels, and a two-stage air conditioner has a compressor with two settings. When running, a two-stage furnace or air conditioner can typically operate at either 60 or 100 percent capacity, which helps make it more efficient and better able to maintain a comfortable and consistent indoor temperature.

A modulating burner is an advanced burner for a furnace or boiler that can adjust the size of the flame in increments, allowing for more precise indoor temperature control and more energy-efficient operation. Most modulating burners can operate anywhere between 40 and 100 percent capacity, meaning they can maintain an accurate temperature no matter what the weather is doing or what the thermostat is set to.

A single-speed motor is a furnace or air conditioner blower motor that only has one speed to control airflow.

A two-speed blower motor has two settings for airflow output. These types of motors are quieter and more efficient than single-speed ones, and they provide a more consistent temperature throughout the house.

There are also multi-speed blower motors that typically have four speeds, and these are superior to single- and two-speed alternatives.

Variable-speed typically refers to a furnace or air conditioner’s blower motor. It means the motor can make incremental adjustments to the airflow, providing a more comfortable home with fewer hot and cold spots. Variable-speed blowers are among the quietest and most efficient, and they offer superior humidity control.

Variable-speed can also refer to an air conditioner with multiple compressor settings. Like a modulating burner, a variable-speed compressor can make incremental adjustments to the cooling output for more efficient operation and more consistent temperatures.

A self-diagnostic system is a special feature with some furnace and air conditioner control panels. The system tracks and monitors performance data regarding temperatures, power use, humidity, and more. It can also identify maintenance problems, thereby reducing service time and possibly increasing the life of the unit.

Powder coat paint is a special finish for furnace and air conditioner cabinets. It produces a hard finish that’s tougher and more durable than standard paint, so it protects the cabinet and internal components from the elements and wear.

The input of a furnace or air conditioner describes how much energy the device requires to operate or how much fuel it consumes. Input is measured in British thermal units (BTUs) per hour.

The input and output together indicate the size of the furnace or air conditioner, a variable that’s determined in part by the size and configuration of your home. Generally speaking, the larger the home, the larger the furnace/air conditioner.

The output of a furnace or air conditioner is the total amount of heat or cooling the system delivers to your home. Output is also measured in BTUs per hour. Air conditioner output can also be measured in tonnes.

The closer the input and output values are on a furnace or air conditioner, the more efficient the unit is.

Heating capacity is the amount of heat that a furnace, boiler, or heat pump can provide. Cooling capacity is the amount of cooling that an air conditioner or heat pump can provide. Both are measured in BTUs per hour.

An efficiency rating is a measure of how energy-efficient an HVAC appliance is. There are various measurements for the different types of HVAC equipment, but in general, the higher the efficiency rating, the more energy-efficient the unit will be and the cheaper it will be to operate.

Air conditioner efficiency is measured with seasonal energy efficiency ratio (SEER). The efficiency of a heat pump in the cooling mode is also measured with SEER, but in the heating mode it’s measured with heating seasonal performance factor (HSPF). Furnace and boiler efficiency is measured with annual fuel utilization efficiency (AFUE).

AFUE is a measure of how efficient your furnace or boiler is when it comes to using fuel versus producing heat. More specifically, it’s a ratio of the percentage of heat produced per dollar of fuel the unit consumes.

For example, a furnace with an AFUE of 98 percent will convert 98 percent of the fuel it uses into heat for your home. Here’s another way to look at it: $0.98 of every dollar you spend on heating fuel like natural gas gets converted into heat for your home.

The higher the AFUE, the more effectively a furnace or boiler will heat your home, and the cheaper it will be to operate.

In Canada, new furnaces must have an AFUE of at least 95 percent. There are models on the market with AFUEs as high as 99 percent.  

SEER is used for measuring air conditioner efficiency. It represents a ratio of the amount of cooling produced over a cooling season versus the energy the unit consumes. Air conditioner SEER ratings can run anywhere from 13 to 20-plus. In Canada, an A/C with a SEER between 16 and 18 typically provides an ideal balance of cost, cooling power, and efficiency.

The combined annual efficiency (CAE) measure lets you know how much heat is produced for every dollar that’s used on fuel, and it’s used specifically for appliances that provide both space heating and hot water, such as a combi boiler.

ENERGY STAR is a program that was created by the United States Environmental Protection Agency and Department of Energy. The ENERGY STAR mark on an HVAC appliance means that it’s an efficient product that meets the energy and performance standards required by the EPA. ENERGY STAR models can save you money and help to protect the environment.

The Canadian Standards Association (CSA) is a standards organization that creates technical guidelines that are designed to ensure the quality and safety of electrical and mechanical products.

Air conditioners, heat pumps, furnaces, and other HVAC appliances with CSA certification have met their standards for safety and reliability.

ISO stands for International Organization for Standardization, and ISO 9000 is a set of international standards for managing quality assurance. Following the standards helps companies to manufacture quality products that meet any necessary regulations. HVAC appliances that bear the ISO 9000 mark were manufactured using a proven process and meet customer satisfaction standards.

Manufacturer approved typically refers to replacement parts for a furnace or air conditioner, for example. When you need to replace a part on your HVAC appliance, it’s important to get parts that have been approved by the manufacturer, otherwise you could void the warranty.

Natural Resources Canada is the department of the federal government that’s responsible for things like energy, forests, and natural resources.

Natural Resources Canada administers the ENERGY STAR program in Canada. They also run the EnerGuide labelling program, which helps consumers to understand efficiency ratings on things like energy-using products, including HVAC appliances.

The Air Conditioning, Heating, and Refrigeration Institute (AHRI) is a North American trade association for the manufacturers of HVAC and refrigeration appliances. As far as consumers are concerned, one of the most important things they do is create performance standards for equipment like furnaces and air conditioners.

The Kyoto Protocol was an international agreement among industrialized countries to reduce greenhouse gas emissions and combat climate change. The first commitment period lasted from 2005 to 2012, after which time several countries—including Canada—withdrew from the Protocol.

HVAC stands for heating, ventilation and air conditioning, and it has to do with the equipment and systems that increase comfort and air quality in buildings. Furnaces, boilers, air conditioners, ventilation systems, heat pumps, and humidifiers can all be considered appliances under the HVAC umbrella.

Relative humidity is the density of water vapor in the air relative to the temperature. This is different from absolute humidity, which just measures the amount of water vapour in the air. Relative humidity is an important measurement to consider because warm air holds more moisture, so the relative humidity will change with the temperature, even if the absolute humidity remains the same.

A load calculation is used to determine the proper size for HVAC equipment in a space. The calculation takes into account things like square footage, number of windows, and number of exterior doors to give you a BTU input/output range for things like furnaces and air conditioners.

A heat loss calculation is a way to determine how much heat will be lost from a building. It is measured in BTUs or kilowatts, and it’s based on factors like how well insulated and air-tight your home is.

A duct is a channel that moves air through a building as part of the HVAC system. Ducts can deliver heated/cooled air to different parts of a building or bring air from the building back to the heating/cooling system. Ductwork is a network of interconnected ducts.

A return air duct is part of the ductwork system in a forced air system. It takes air from the house and draws it back to the furnace or air conditioner to be heated or cooled again so it can be re-circulated throughout your home.

The air change rate (ACH), or air changes per hour (ACPH), measures how many times per hour the air in a space is replaced. A higher air change rate means better ventilation because stale air is removed more frequently and replaced with fresh air. To calculate ACPH, you need to know the airflow rate and the volume of the room.

Fresh air intake (FAI) is a connection from the inside of a building to the outside, and it allows a furnace to draw in fresh air for use in the combustion and heating process. Furnaces with a fresh air intake tend to operate more efficiently and improve indoor air quality compared to less-efficient models that draw air from inside the house.

Gas supply refers to the supply of available natural gas or propane that’s required for the combustion process in a furnace or boiler. For example, if you have a furnace that runs on natural gas, then the furnace will be connected to a gas supply line that runs outside to the meter and then connects with the utility’s gas lines.

A register is a cover that goes over the hole where a duct connects with a room. It has slats to allow heated or cooled air to flow into the room, and will typically have a damper that enables you to open or close the register to start or stop the flow of air.

Polyvinyl chloride (PVC), also known as vinyl, is a type of plastic. It’s often used to make pipes because it creates leak-free seals, it’s corrosion resistant, and it’s durable.

A smart home is used to describe a home that’s outfitted with Wi-Fi enabled devices and appliances, including heating and cooling systems, that can be controlled remotely with a smartphone, computer, or tablet.  

An HVAC zoning system allows you to control the temperature in different zones or areas of your home separately. Zoned HVAC is great for larger homes, families who have different ideas of what a comfortable temperature is, and rooms with unique heating/cooling needs, such as a sunroom.

To winterize something means to prepare it for winter, and that involves protecting against the cold, snow, ice, and wind. For example, you might winterize the outdoor component of a central air conditioner by putting a protective cover over it.

Black ABS piping is used for plumbing these days, but it was once used for some HVAC applications as well. Over time, however, the black ABS pipe would crack and potentially cause carbon monoxide leaks, so codes were amended to recommend white PVC pipes instead. Although new HVAC equipment won’t be installed with black ABS pipe, you don’t have to replace black ABS pipe in an older HVAC setup unless it’s cracked, damaged, or otherwise compromised.

HVAC stands for heating, ventilation and air conditioning, and it has to do with the equipment and systems that increase comfort and air quality in buildings. Furnaces, boilers, air conditioners, ventilation systems, heat pumps, and humidifiers can all be considered appliances under the HVAC umbrella.

A carbon monoxide leak can happen when fuel doesn’t burn properly. It often happens when a furnace’s or boiler’s heat exchanger is cracked. The crack prevents the fuel from burning fully, and this produces carbon monoxide that can escape into the air.

Carbon monoxide prevents your blood cells from carrying oxygen, so high enough concentrations can potentially be fatal after just five minutes.

Carbon monoxide leaks can be very dangerous, but you can keep yourself and your family safe by having your fuel-burning appliances inspected and serviced regularly, and by installing carbon monoxide detectors in your home.

A fossil fuel is a material that contains hydrocarbons, and that was created over millions of years from decomposed animals and plants. Fossil fuels include natural gas, oil, and coal, and they can be extracted from the ground and burned for heat and energy.

Natural gas is a hydrocarbon gas, usually from a fossil fuel source, that contains methane and ethane primarily. It can also contain nitrogen, carbon dioxide, hydrogen sulfide, and other gasses. In HVAC, natural gas is often used as a fuel for furnaces and boilers.

Direct current (DC) refers to an electrical current that will only flow in one direction. DC current is very efficient, and is often used in things like blower motors.

Alternating current (AC) refers to an electrical current that reverses direction periodically.

HEPA stands for high efficiency particulate air, and a HEPA filter is an example of a more advanced filter. These filters can eliminate up to 99.97 percent of contaminants as small as 0.3 microns from the air. They remove pollen, dust, mold, bacteria, viruses, and more.

HEPA filters don’t have a MERV rating because they exceed the parameters of the scale, meaning they would have a MERV of 17 or higher.

They’re often used in commercial and industrial applications, such as hospitals, medical facilities, schools, and dental offices, but they can also be great in homes where people have allergies, asthma, and similar medical conditions.

A media filter is a type of HVAC air filter that’s more effective than a standard air filter. Media filters are made of pleated material, such as polyester or fiberglass, and the pleats enable them to trap more dust and other particles.

An electronic air cleaner (EAC) uses an electrically charged filter to trap particles from the air passing through an HVAC system. Electronic air cleaners are more effective than standard filters and remove more mold, bacteria, allergens, and other contaminants from the air.

An air purifier is a device that uses a filter and fan to remove contaminants from the air. This is particularly useful for people that suffer from allergies and asthma. There are room air purifiers as well as whole-home systems that integrate with your HVAC system.

A heat recovery ventilator (HRV) is a device that brings in fresh air to the home, but it also transfers heat between the incoming and outgoing air. That way, you have a constant supply of fresh air coming in, and your HVAC system doesn’t have to work harder to maintain the temperature.

An energy recovery ventilator (ERV) is a device that brings in fresh air to the home, but it also transfers heat and moisture between the incoming and outgoing air. That way, you have a constant supply of fresh air coming in, and your HVAC system doesn’t have to work harder and the humidity level remains constant.

A fan coil unit (FCU) is a stand-alone HVAC device that blows air over a heated or cooled coil and then blows the air into a room to heat it or cool it.

A garage heater is a space heating device for garages, workshops, and other open spaces that aren’t connected to a home’s main heating system. There are several different types, including portable and stationary ones, forced air, radiant, and convection models, and ones that run on natural gas, propane, electricity, or diesel.

A heat pump is a device that takes heat from one place and transfers it to another. All heat pumps can provide air conditioning by removing heat from a home and transferring it outside. Other heat pumps can also provide heat by taking heat from the air outside and transferring it inside.

A humidifier is a device that adds moisture to the air. Humidifiers can help to alleviate allergy symptoms and reduce dry skin, sore throats, static electricity, and other problems associated with dry air. There are room humidifiers that are designed to add moisture to small spaces as well as whole-home humidifiers that use the HVAC system to add moisture to the entire house.

A programmable thermostat is a thermostat that enables you to schedule changes to the temperature settings based on things like the time of day or the day of the week. For example, in winter, you might program the thermostat to automatically reduce the temperature during the day when everyone is out of the house to conserve energy.

A smart thermostat is a programmable thermostat that’s connected to the internet. As such, you can access and change the thermostat settings from anywhere using a smartphone or tablet, for instance. Many smart thermostats also have the ability to learn your behaviours and make automatic adjustments to the comfort settings based on your previous adjustments.

A British thermal unit (BTU) is a unit of measurement for the heat contained in an energy or fuel source. One BTU represents the amount of energy needed to increase the temperature of 1 pound of water by 1 degree Fahrenheit.

Celsius is a temperature scale that’s used all over the world, especially where the metric system is used, including Canada. The basis for the Celsius scale is the freezing and boiling point of water: water freezes at 0 degrees Celsius and boils at 100 degrees Celsius.

Fahrenheit is another temperature scale, and it’s used primarily in the United States. Like Celsius, Fahrenheit is also based on the freezing and boiling points of water. However, on the Fahrenheit scale, the freezing point of water is set at 32 degrees and the boiling point is at 212 degrees.

Cubic feet per minute (CFM) measures the volume of flow for gasses and liquids. In HVAC, one of the main uses of CFM is to determine airflow.

Decibel (dB) is a unit of measure for sound level. For example, the sound of breathing is around 10 decibels, whereas the sound of a thunderclap is around 120. Decibels are used in HVAC to demonstrate how quiet appliances are, especially air conditioners.

A kilowatt (kW) is equivalent to 1,000 watts, and a watt is an electrical unit that measures the rate at which energy is consumed or generated.

A kilowatt hour (kWh) is a unit of energy and a way to measure electricity use. One kWh represents 1,000 watts of power being used for an entire hour. As such, a kWh measures both the number of watts used by an appliance and the amount of time it was used.

The kilowatt-hour is a unit of energy equal to one kilowatt of power sustained for one hour or to 3600 kilojoules unit of energy and it will tell you how much gas and electricity that you are using. In other words, it is the watts that you use in one hour.

PSI stands for pounds per square inch. It’s a unit of measurement for pressure expressed as pounds of force per square inch of area. It can be used to measure the pressure of gasses and liquids, such as the pressure of air in a tire or the pressure of refrigerant in an air conditioning system.

A ton is a unit of measurement that’s typically used for weight. It’s equivalent to 2,000 pounds or about 907 kilograms.

Tonnage means weight in tonnes. In HVAC, tonnage is used to measure an air conditioner’s capacity, or the amount of cooling it can produce. In this respect, one ton is equal to 12,000 BTUs per hour.

In an electrical circuit, voltage is the pressure that forces the electrical current to move through a conducting loop. Voltage can also be thought of as potential energy, and it’s measured in volts.

Pascal (Pa) is a unit of measurement for pressure. It’s equivalent to one newton per square meter, which is roughly 0.000145 pounds per square inch.

Revolutions per minute (RPM) is used to describe the number of turns in one minute. It’s a unit of rotational speed that can also tell you how much energy a motor or engine is outputting.