Last updated: September 27, 2026
HVAC quotes, equipment labels and thermostat screens are full of terminology that assumes you already know the trade. This glossary of HVAC terms translates the heating and air conditioning vocabulary Vancouver homeowners run into most often, so you can compare quotes, read your equipment and ask better questions. This HVAC glossary covers the HVAC terms and definitions, heating and cooling terms and air conditioning terminology you're most likely to hear from a technician or see on a quote.
Terms are grouped by topic: efficiency ratings, sizing, equipment, heat pump terms, furnace terms, air quality and ductwork, refrigerants, and thermostats and controls.
Efficiency ratings
AFUE (Annual Fuel Utilization Efficiency): The share of a furnace's or boiler's fuel that becomes heat in your home over a year. An 80% AFUE furnace turns 80 cents of every gas dollar into heat, and the other 20 cents go up the flue. High-efficiency condensing furnaces reach 95% or more.
SEER2 (Seasonal Energy Efficiency Ratio 2): The cooling efficiency rating for air conditioners and heat pumps. The higher the number, the less electricity it takes to cool. SEER2 replaced the older SEER rating in 2023 with a test that better reflects real ductwork, so a SEER2 number runs lower than the old SEER figure for the same unit. Compare SEER2 with SEER2, never with the old SEER.
EER2 (Energy Efficiency Ratio 2): Cooling efficiency measured at one hot condition, not averaged across a season. It's a useful gauge of how a unit handles our hottest summer days.
HSPF2 (Heating Seasonal Performance Factor 2): The heating efficiency rating for heat pumps. The higher, the better. Like SEER2, it replaced an older version (HSPF) in 2023.
COP (Coefficient of Performance): The units of heat a heat pump delivers for each unit of electricity it uses, at a given moment. A COP of 3 means three units of heat for one unit of electricity. Electric resistance heat always has a COP of 1. See How Heat Pumps Work in Vancouver WA for why heat pumps can beat that.
ENERGY STAR: A federal label for equipment that goes beyond the minimum efficiency standards. Some utility rebates require ENERGY STAR–certified equipment.
Sizing and capacity
BTU (British Thermal Unit): The basic unit of heat energy. Furnaces are rated in BTUs per hour of output. One therm of natural gas contains 100,000 BTUs.
Ton: Cooling and heat pump capacity. One ton equals 12,000 BTUs per hour, so a 3-ton heat pump moves 36,000 BTUs per hour. The term refers to heat-moving capacity, not weight.
Load calculation (Manual J): The industry-standard method for working out how much heating and cooling a specific house needs. It accounts for square footage, insulation, windows, air leakage, orientation and local climate. Sizing by square footage alone, or replacing "same size as before," often leads to oversized equipment.
Oversizing: Equipment bigger than the house needs. It sounds safe but causes short cycling, uneven temperatures, poor humidity control and extra wear. See why sizing and installation matter.
Short cycling: A system that turns on and off too frequently in short bursts. Common causes are oversizing, a failing part or a thermostat problem. It wastes energy and shortens equipment life.
Main equipment
Air handler: The indoor cabinet containing the blower and, in a heat pump system, the indoor coil. Heat pump systems use an air handler where a gas system uses a furnace.
Blower: The fan that moves air across the heat source and through your ducts.
Compressor: The pump in the outdoor unit that pressurizes refrigerant and drives the whole cooling or heat pump cycle.
Condenser / outdoor unit: The outdoor half of an AC or heat pump system, containing the compressor, outdoor coil and fan. On a heat pump it's usually just called the outdoor unit, since its role flips between heating and cooling.
Evaporator coil (indoor coil): The coil in the air handler or on top of the furnace where refrigerant absorbs heat from your indoor air during cooling.
Split system: A system with one indoor unit and one outdoor unit connected by refrigerant lines. Most homes have one.
Package unit: All components in a single outdoor cabinet, common on commercial rooftops. See our commercial HVAC services.
Ductless mini-split: A heat pump with an outdoor unit that serves one or more wall-, ceiling- or floor-mounted indoor heads, with no ductwork. It suits older homes, additions and rooms the central system never reached.
Boiler / hydronic heating: A system that heats water rather than air and circulates it to radiators, baseboards or in-floor tubing. A combi boiler also supplies your hot water. Learn more about geothermal and hydronics.
Geothermal (ground-source) heat pump: A heat pump that exchanges heat with the ground, which stays at a steady temperature year-round, rather than with the outdoor air. It's highly efficient but costs more to install.
Gas fireplace / insert: A sealed gas appliance that heats a room or zone. Direct-vent models draw combustion air from outside and vent outside, keeping indoor air separate. Browse our fireplace catalog.
Are you in need of professional services for your home’s heating and cooling systems?
Contact Tri-Tech Heating, Inc. for expert solutions today!
Heat pump terms
Air-source heat pump: The most common type. It moves heat between the outdoor air and your home.
Cold-climate heat pump: A heat pump designed to keep producing useful heat at low outdoor temperatures, often well below freezing.
Variable-speed / inverter: A compressor that ramps its output up and down to match demand, instead of running only on or off. The result is steadier temperatures, quieter operation and better efficiency.
Reversing valve: The part that switches the refrigerant's direction so a heat pump can change between heating and cooling.
Defrost cycle: In cold, damp weather, frost builds up on the outdoor coil, so the heat pump briefly reverses to melt it. Steam rising from the outdoor unit in winter is normal defrost, not a malfunction.
Auxiliary heat (aux heat / heat strips): Backup electric resistance heat inside the air handler. It kicks in automatically when the heat pump needs help, such as during a hard freeze or defrost. It costs more to run, so it should only run occasionally.
Emergency heat: A thermostat setting that shuts off the heat pump and runs only the backup heat. It's for when the heat pump itself has failed. Leaving it on by mistake makes heating bills spike.
Balance point: The outdoor temperature below which a heat pump alone can no longer keep up with a home's heat loss, and backup heat is needed.
Dual fuel (hybrid): A heat pump paired with a gas furnace. The heat pump heats most of the season, and the furnace takes over below a set outdoor temperature, called the switchover point. See Heat Pump vs. Furnace in Vancouver WA.
Furnace terms
Heat exchanger: The sealed metal chamber that passes heat from burning gas to your air while keeping combustion gases separate. A cracked heat exchanger is a safety issue because it can let carbon monoxide into the airstream.
Condensing furnace: A high-efficiency furnace (around 90% AFUE and up) with a second heat exchanger that pulls extra heat from the exhaust, cooling it enough to form condensation. These furnaces vent through PVC pipe and need a condensate drain.
Single-stage / two-stage / modulating: How many output levels a furnace has. A single-stage furnace is either fully on or off. A two-stage furnace has a low setting for mild days and a high setting for cold ones. A modulating furnace adjusts in small steps for the steadiest comfort.
Hot surface igniter: The part that lights the gas on modern furnaces, replacing the old standing pilot light.
Flame sensor: A safety device that confirms the burners are lit. If it's dirty, the furnace lights and shuts off within seconds, one of the most common no-heat calls.
Limit switch: A safety switch that shuts the burners off if the furnace overheats, often because of a clogged filter or blocked airflow.
Flue / venting: The pipe that carries combustion gases outside. Proper venting is essential for safety.
Carbon monoxide (CO): An odorless, poisonous gas produced by incomplete combustion. Every home with gas appliances or an attached garage should have working CO alarms.
Air quality and ductwork
Indoor air quality (IAQ): The overall cleanliness, humidity and freshness of the air in your home. See our indoor air quality services.
MERV (Minimum Efficiency Reporting Value): A filter rating from 1 to 16. The higher the number, the smaller the particles it captures. Most homes do well with MERV 8–13. Very high ratings can restrict airflow in systems not designed for them, so check with your technician.
HEPA: High-efficiency filtration that captures very fine particles. It's usually used in standalone or specially designed systems rather than a standard furnace filter slot.
HRV / ERV: Heat recovery and energy recovery ventilators bring in fresh outdoor air while transferring heat, and with an ERV some moisture, between the incoming and outgoing air. They're especially useful in tight, newer homes.
Humidifier / dehumidifier: Equipment that adds or removes moisture. Healthy indoor humidity typically sits between 30% and 50%.
Supply and return: Supply ducts deliver conditioned air to rooms. Return ducts bring air back to the system. Blocking returns with furniture starves the system of air.
Plenum: The box-shaped chamber that connects the furnace or air handler to the main ducts.
CFM (cubic feet per minute): A measure of airflow volume. Equipment needs the right CFM for its size to perform as designed.
Static pressure: The resistance to airflow in your duct system, like blood pressure for your HVAC. High static pressure from undersized ducts or clogged filters reduces efficiency and comfort.
Damper: An adjustable plate inside a duct that controls airflow. Motorized dampers make zoning possible.
Zoning: Dividing a home into areas with separate thermostats and dampers, so each area is heated or cooled only as needed.
Duct sealing: Sealing leaks in ductwork with mastic or approved tape. Leaky ducts in crawlspaces and attics can lose a significant share of the heat you pay for.
Refrigerants
Refrigerant: The fluid that absorbs and releases heat as it circulates in an AC or heat pump system. A system that's "low on refrigerant" has a leak, since refrigerant doesn't get used up.
R-22 (Freon): The old refrigerant in systems from before about 2010. Its production has ended, so repairs to R-22 systems are increasingly costly.
R-410A: The refrigerant in most systems installed from about 2010 through 2024. It's being phased down, but existing systems can still be serviced.
R-454B and R-32: Lower-global-warming-potential refrigerants used in new residential systems since 2025.
A2L: The safety class for R-454B and R-32: lower toxicity and mildly flammable. New equipment includes leak detection and other safeguards designed for these refrigerants.
Thermostats and controls
Programmable thermostat: A thermostat that follows a set schedule, lowering heat while you sleep or are away.
Smart thermostat: A Wi-Fi thermostat you can control from your phone. Many learn your patterns and report energy use. For heat pumps, choose one that handles auxiliary heat correctly. See our smart thermostat guide.
Setback: Lowering the temperature for part of the day to save energy. With heat pumps, moderate setbacks work best, since large ones can trigger costly backup heat during recovery.
Heat anticipator / cycle rate: Settings that control how often a system cycles on and off. Modern digital thermostats manage this automatically.
Questions about your system?
Tri-Tech Heating, Inc. installs and services heat pumps, ductless systems, furnaces, boilers and fireplaces across Vancouver, Camas, Salmon Creek and Clark and Cowlitz Counties. We install York, American Standard and Mitsubishi equipment, and our work is 100% guaranteed.
Learn more about HVAC installation in Vancouver WA and heat pump installation, or contact us for a free estimate on any installation.
Our office is open Monday through Friday, 8:00am to 5:00pm, and a call to (360) 891-2002 during those hours reaches a person. Outside those hours, email info@tri-techheating.com, and our on-call technician will reply with an ETA. Licensed HVAC #TRITEHI952LL, CCB #161426.
Are you in need of professional services for your home’s heating and cooling systems?
Contact Tri-Tech Heating, Inc. for expert solutions today!
Frequently Asked Questions
What's a good SEER2 rating for Vancouver WA?
Any new system must meet federal minimums. Because our summers are mild compared with much of the country, the most efficient cooling ratings often return less than a heat pump's heating efficiency (HSPF2) will. For most Vancouver homes, heating efficiency matters more.
Company Information
Tri-Tech Heating, Inc.
6406 NE 116th Ave Unit C
Vancouver, WA 98662
Phone: (360) 891-2002