HVAC Glossary

AFUE measures how efficiently a furnace converts fuel (gas or oil) into heat. It's expressed as a percentage — a 95% AFUE furnace converts 95% of fuel into heat, with only 5% lost.

The indoor unit of your HVAC system that circulates air throughout your home. It contains the blower fan, evaporator coil, and air filter. In Florida, air handlers are often installed in garages, attics, or closets.

A replaceable filter in your HVAC system that removes dust, pollen, pet dander, and other particles from the air. Filters are rated by MERV (Minimum Efficiency Reporting Value) — higher numbers catch smaller particles.

AHRI (Air Conditioning, Heating, and Refrigeration Institute) is an industry organization that certifies HVAC equipment performance. When equipment is AHRI-certified, its efficiency ratings have been independently verified.

The motor inside your air handler that powers the fan to push air through your ductwork. Modern systems often use variable-speed blower motors for better efficiency and comfort.

A unit of measurement for heat energy. One BTU is the amount of heat needed to raise one pound of water by one degree Fahrenheit. AC systems are rated in BTUs per hour — a 3-ton system produces 36,000 BTU/hr.

An electrical component that stores energy and helps start the compressor and fan motors. Capacitors are one of the most common parts to fail in Florida's heat, often causing the AC to stop cooling.

The "heart" of your AC system, located in the outdoor unit. The compressor pumps refrigerant through the system, compressing it from a gas to a liquid to enable the cooling cycle.

The outdoor unit of your AC system that releases heat from your home to the outside air. It contains the compressor, condenser coil, and a fan. The condenser works with the indoor air handler to complete the cooling cycle.

The drain line that removes moisture collected by your AC. As warm humid air passes over the cold evaporator coil, water condenses and drips into a pan, then flows through the drain line outside.

The network of tubes (usually metal or flexible material) that distributes conditioned air throughout your home and returns air back to the system. Properly sized and sealed ductwork is critical for efficiency.

A device that removes excess moisture from indoor air. Whole-home dehumidifiers integrate with your HVAC system to maintain comfortable humidity levels (ideally 45-55%).

A hybrid heating system that pairs an electric heat pump with a gas furnace. It automatically switches to whichever fuel source is most efficient based on outdoor temperature.

A measure of cooling efficiency at a specific outdoor temperature (95°F). Unlike SEER which averages over a season, EER shows performance during peak heat. Higher EER = better performance on the hottest days.

The cold coil inside your air handler where refrigerant absorbs heat from your home's air. As warm air blows across the cold coil, it's cooled and dehumidified before returning to your rooms.

A government-backed certification for energy-efficient products. ENERGY STAR certified HVAC equipment exceeds minimum federal efficiency standards, helping you save on utility bills.

A heating unit that burns fuel (usually natural gas) to warm air, which is then distributed through ductwork. In a split system, the furnace often contains the blower that circulates air year-round.

A safety device in your condensate drain pan that shuts off the AC if water backs up due to a clogged drain. This prevents water damage to your home.

An HVAC system that can both cool and heat by reversing the refrigeration cycle. In cooling mode it works like an AC; in heating mode it extracts heat from outdoor air and moves it inside.

Heating Seasonal Performance Factor — measures heat pump heating efficiency over a season. HSPF2 uses updated testing (2023+). Higher numbers mean better efficiency when heating your home.

Heating, Ventilation, and Air Conditioning — the industry term covering all systems that heat, cool, and ventilate buildings. Your home's HVAC system maintains comfort year-round.

The cleanliness and healthiness of air inside your home. IAQ is affected by pollutants, allergens, humidity, and ventilation. Good IAQ reduces allergies, illness, and respiratory issues.

Advanced compressor technology that allows the system to vary its speed rather than cycling on/off. Inverter systems run more continuously at lower capacity, providing better comfort and efficiency.

A detailed analysis (often called Manual J) that determines the exact heating and cooling capacity your home needs. It considers square footage, insulation, windows, orientation, and local climate.

The pair of copper tubes that connect your outdoor condenser to your indoor air handler. Refrigerant flows through these insulated lines to transfer heat between indoor and outdoor units.

Minimum Efficiency Reporting Value — a scale (1-20) rating air filter effectiveness. Higher MERV catches smaller particles. MERV 8-11 is ideal for most homes; MERV 13+ approaches hospital-grade filtration.

A ductless HVAC system with an outdoor unit connected to one or more indoor wall-mounted units. Each indoor unit cools/heats its zone independently. Great for additions, garages, or homes without ductwork.

An all-in-one HVAC system where heating and cooling components are housed in a single outdoor cabinet. Common on commercial buildings and some homes without space for indoor equipment.

The main ductwork box attached directly to your air handler where conditioned air enters (supply plenum) or returns (return plenum). Plenums distribute air to the branch ducts running throughout your home.

The chemical compound that absorbs and releases heat as it circulates through your AC system. Common types include R-410A (Puron) and the phased-out R-22 (Freon). Refrigerant doesn't get "used up" — if you're low, there's a leak.

Air drawn from your living spaces back to the HVAC system to be filtered, conditioned, and recirculated. Return vents are typically larger than supply vents and should never be blocked.

Seasonal Energy Efficiency Ratio — measures cooling efficiency over a typical season. SEER2 uses updated testing standards (2023+). Higher numbers = more efficient. Florida's minimum is 15 SEER2 for new installations.

The most common AC setup: an outdoor unit (condenser) and an indoor unit (air handler or furnace) connected by refrigerant lines. "Split" refers to having components in two locations.

The resistance to airflow in your duct system, measured in inches of water column. High static pressure means your system is working harder to push air, often indicating duct problems or dirty filters.

The control device that senses temperature and tells your HVAC system when to turn on/off. Modern smart thermostats add WiFi control, learning features, and energy usage tracking.

A measure of cooling capacity. One ton equals 12,000 BTU/hour of cooling — historically, the heat needed to melt one ton of ice in 24 hours. Most Jacksonville homes need 2.5-5 ton systems.

Uses ultraviolet light to kill mold, bacteria, and viruses. Often installed at the evaporator coil to prevent biological growth and improve indoor air quality.

Motors or compressors that adjust their speed based on demand rather than just cycling on/off. Variable speed provides better comfort, efficiency, humidity control, and quieter operation.

Manufacturer coverage for parts (and sometimes labor). Most HVAC equipment has 5-10 year parts warranties when properly registered. Extended warranties and labor coverage are often available.

Dividing your home into separate areas with independent temperature control using dampers and multiple thermostats. Each zone can be set to different temperatures based on use and preference.