HVAC Speak: A Glossary of Common HVAC Terms

Carrier term referring to a feature on some of their thermostats in which the thermostat will determine the most energy-efficient number of degrees for your temperature to set back during off times.

Annual Fuel Utilization Efficiency is a thermal efficiency used to measure heating equipment such as furnaces, boilers, and space heaters. Similar to SEER, this is a seasonal efficiency measure. It is a good measure, but doesn’t fully address the efficiency gains when using staged burners and advanced, programmable thermostats.

This device removes heat energy from indoors to outside. In most homes, an air conditioner works with the furnace and ductwork to accomplish this task. It will also remove moisture during this process. Better A/Cs will remove more moisture allowing you to keep the indoor temperature higher and feel more comfortable.

This is possibly the best tool to clean indoor air. It is a hybrid of a media filter and electronic air cleaner on steroids. Essentially, the unit will kill and capture just about anything in the air. This is the best indoor air quality treatment.

This device has two purposes. One is to lower indoor pollutants through dilution. The second is to lower indoor humidity, in winter months, from today’s extremely tight and insulated homes. The unit will exchange indoor air for outdoor air through a heat exchanger that will save a good portion of the energy contained within the air being expelled from the home. These operate efficiently and are generally very durable with some semiannual maintenance. A healthier home is the result.

This is literally the amount of energy required to raise the temperature of one pound of water by one degree. We use this term to measure the amount of heating or cooling capacity needed for your home and the amount the equipment will provide.

This measures the amount of airflow through the furnace or air handler.

This word refers to how the thermostat participates in the operation of the HVAC system. Most thermostats are non-communicating. They simply send a signal to turn on or off to the furnace or air conditioner. A Carrier Infinity controller is a communicating thermostat. It sends and receives information to and from the equipment. It then processes this information and makes operational decisions for the system. This results in better comfort and efficiency.

The name of the device that controls humidity by removing it from spaces like basements. Cheap portable units from big box stores require low investment but are not efficient and have shorter life-spans. Professional quality dehumidifiers require a larger investment but return much better efficiency, longevity, moisture removal, and warranties than cheap portables.

A brushless DC electric motor, which is electrically efficient and reliable. Many of these motors will operate with some degree of variable speed or output. You will find these in higher quality furnaces and boiler pumps. Sometimes these will be called variable speed, ECM-PWM, X-13, or variable frequency drive. This type of motor technology will save you money and in many cases improve comfort levels.

Similar to SEER, this air conditioner ratio takes into account the air conditioner’s energy performance only at 95 degrees ambient temperature. This rating is more important in consistently hot climates such as Arizona.

A program created by the US Department of Energy and Environmental Protection Agency that creates efficiency standard levels and rewards those products that meet these efficiency levels. These products generally use 20 to 30 percent less energy than required by federal standards.

Equipment that is very similar to an air conditioner but works in two directions. In summer, it moves heat from inside to the outside. In winter, it moves heat from the outside to the inside. These units create very little heat and instead they move heat. We use these most often when we do not have access to natural gas or we are adding supplemental heat to an area.

Refers to a single-stage furnace that only operates at 100 percent capacity.

This is the efficiency rating used for heat pumps. Again this is a seasonal rating. The higher the number, the better. Anything over 10 is considered excellent, and anything over 8.2 usually meets ENERGY STAR requirements.

A device, typically attached to the ductwork of a home, which adds moisture to the air automatically.

This device measures and controls humidity. Some thermostats have a humidistat included as an extra feature.

In summer, we want to lower the amount of humidity in the air to improve comfort. We use air conditioners and dehumidifiers to accomplish this task. Lower summer humidity reduces odors and mildew in basements. Lower humidity will also allow us to feel more comfortable at higher temperatures. Humidifiers lower energy costs and stop the “cold clammy” feeling.

In many homes, winter humidity levels fall too low. This can cause health problems, static electricity, damage to furniture and possessions, and make us uncomfortable. Adding moisture can help protect ourselves and our possessions as well as save us money. Most people can lower their thermostats a degree or two when proper humidity levels are attained.

The acronym and industry term for the system (or package of services) used to provide heating, cooling and ventilation to buildings.

A Carrier term concerning the automatic switchover from heat pump function to furnace function, based on energy efficiency and comfort factors. This improves the function and performance of Carrier heat pump/furnace systems.

This industry term refers to the overall health and comfort of the air inside your home.

Another Carrier term used to describe how the Infinity Control will stage the furnace or air conditioning/heat pump equipment. The control uses real time information from the equipment and the environment (indoor and outdoor) to make staging decisions in order to maximize efficiency and/or comfort level.

This an industry term referring to how a piece of equipment (air conditioner or heat pump) is able to have variable output. You can equate the term with equipment having the highest levels of efficiency and comfort.

This is an air filter that is typically about 4 inches thick. It will be made with a long piece of filter material that is folded back and forth. The purpose is to do a better job of cleaning the air without adding too much restriction to the system. This provides more protection for the equipment lowering operating and repair costs while presenting cleaner air to breathe. We recommend a MERV rating of 8 to 10. A higher MERV rating will add unnecessary airflow restriction and shorten the life of certain components in a furnace.

This is a method of rating the effectiveness of an air filter. The higher the number, the finer the airborne particle the filter will remove. However, higher ratings also mean higher airflow restriction. Too much restriction will cause the equipment to work harder, and one will need to replace the filter at shorter intervals. This increases operation and maintenance costs. We suggest a MERV rating of around 8 for most situations.

This term is related to “staging”—or running in different stages to operate more efficiently. A furnace, air conditioner or heat pump that has modulating output simply means it is variable in more than two or three stages. In theory, it has an infinite number of stages. Carrier’s modulating furnace operates in a range from 40 to 100 percent capacity. Carrier calls this Greenspeed Technology. Modulating equipment is matching its output to the needs of the home at all times—this is the most efficient and comfortable equipment.

This is a term relating to standard fan and pump motors. These are AC voltage motors that run at a preset speed. Some of these have a couple of speed choices to pick from but operate at that one chosen speed, which is inefficient and offers less comfort.

You will typically find this listed as ECM-PWM. This is a fan and control board that will increase the fan speed when necessary to overcome system restriction or a dirty air filter. The installer will have more preset speeds to choose from in order to better match the furnace performance to the home. Then the motor will increase fan speed when necessary to protect the equipment. Cost savings is the key benefit.

This is a Carrier marketing term used to impress upon you the tight temperature control of some equipment. The goal of this equipment is to keep your air temperature within one degree of the temperature you set on the thermostat. Modulating and variable speed equipment controlled with a communicating thermostat is required. This offers the ultimate comfort.

An important part of owning your system—regularly scheduled maintenance will help keep your system working at peak efficiency and improve longevity as well as lower the chance of a service call.

Measurement of the efficiency of an air conditioning system (condenser, furnace, and indoor coil). This method is the best air conditioner efficiency rating for our climate. It analyzes the overall efficiency throughout the summer season to calculate the rating. The condenser is the most important part of the equipment in regard to the efficiency of the system.

A Carrier feature that will turn off the furnace fan for a few minutes after the air conditioner turns off. Carrier has found that this prevents the fan from picking up some of the moisture the air conditioner just removed, for improved efficiency and comfort.

We use the terms multi-stage, two-stage, inverter-driven, modulating, or variable speed frequently when we talk about equipment. Staging refers to equipment’s ability to operate at more than one output level. Staging will increase efficiency and comfort level.

This Carrier term refers to the Infinity controller’s ability to detect a dirty filter by monitoring the air-flow resistance in the system. TrueSense helps you change filters when needed rather than on a certain time schedule.

A UV air treatment device uses ultra violet light to kill organisms as they pass through the ductwork. Some of these devices will also reduce airborne odors. Many times, these devices are used as the next step after media air cleaners in indoor air treatment. UV treatment works best with variable-speed furnaces with constant fans. This allows for the most complete health benefit of the product. Our Second Wind products meet the CLASS II Medical Rating.

An ECM controlled motor that can operate at different speeds. We often think of variable-speed fans in Infinity furnaces that will modulate up and down in speed to better match furnace operation. This allows for better humidity control, for example. Variable speed leads to cost savings and improved comfort.