HVAC terms, translated.
The vocabulary you'll hear from technicians, spec sheets, and estimates — defined the way we'd explain them at your kitchen table.
AFUE
Annual Fuel Utilization Efficiency — the percentage of a furnace's fuel that actually becomes heat for your home over a season. A 95% AFUE furnace turns 95 cents of every fuel dollar into warmth, with the rest lost up the flue. Higher is better, and modern high-efficiency furnaces run in the 90s.
AHRI match
A certification that a specific outdoor unit, indoor coil, and air handler combination has been tested together and performs as rated. Mixing unmatched components can quietly cost efficiency and capacity, and can void warranty coverage. Quotes should reference a matched system, not just an outdoor unit.
Air handler
The indoor unit that moves air through your home — a blower fan plus a coil in a cabinet, usually in a garage, closet, attic, or crawlspace. In a heat pump system it does the job a furnace's blower does in a gas system. Your filter typically lives here or in a return grille nearby.
Balance point
The outdoor temperature at which a heat pump's output exactly matches the home's heat loss — below it, backup heat starts helping. In dual-fuel systems it's the temperature where the furnace takes over. Where this point sits depends on the equipment and how well the house holds heat.
Cold-climate heat pump ratings, explainedBTU
British Thermal Unit — the standard measure of heating and cooling energy. One BTU is roughly the heat from a single kitchen match; home equipment is rated in tens of thousands of BTUs per hour. More BTUs isn't automatically better — the right number comes from a load calculation, not square footage.
Heat pump sizing and Manual JCFM
Cubic Feet per Minute — how much air the system moves. Equipment is designed to deliver a specific CFM, and dirty filters, undersized ducts, or closed registers all steal from it. Low airflow is behind a surprising share of comfort complaints and frozen coils.
Understanding your ductworkCompressor
The heart of a heat pump or air conditioner — the pump that pressurizes refrigerant and drives heat from one place to another. It lives in the outdoor unit and is the most expensive single component in the system. Protecting it is a big part of why maintenance and correct refrigerant charge matter.
Condensate drain
The small pipe that carries away the water your system wrings out of the air during cooling and, on high-efficiency furnaces, during heating. When it clogs, water backs up — tripping a safety switch at best, dripping through a ceiling at worst. Flushing it is a standard tune-up item.
Condenser
The outdoor unit of an air conditioner or heat pump, named for the coil inside where refrigerant condenses and releases heat. It needs clear airflow on all sides to shed that heat, which is why keeping fir needles and shrubs away from it matters. In a heat pump it also absorbs heat in winter.
Defrost cycle
A heat pump's built-in routine for melting the frost that naturally forms on the outdoor coil in cold, damp weather. The unit briefly reverses, warms the coil, and often sends up a plume of steam — which looks alarming and is completely normal. Never chip ice off the coil yourself.
Cold snap heat pump playbookDual fuel
A system pairing a heat pump with a gas furnace: the heat pump handles everyday heating and all cooling, and the furnace takes over automatically in the coldest weather. It's a popular Northwest retrofit because it reuses an existing furnace while adding efficiency and air conditioning.
Heat pump vs. furnace in Western WashingtonESP (external static pressure)
The total resistance the blower must overcome to push air through your ducts, filter, and coil — like blood pressure for your HVAC system. Every blower has a rated ESP; exceed it with restrictive filters or undersized ducts and airflow, efficiency, and equipment life all suffer. Technicians measure it during a proper tune-up.
Understanding your ductworkEvaporator coil
The indoor coil where refrigerant absorbs heat from your home's air during cooling — the surface that actually makes the air cold. Because it runs wet with condensation, it's also where mold and grime like to grow, which is why coil cleanliness affects both efficiency and how the air smells.
Heat exchanger
The metal chamber inside a furnace that keeps combustion gases separate from the air you breathe while passing heat between them. A cracked heat exchanger can let carbon monoxide into the airstream, which is why inspecting it is the safety centerpiece of every furnace tune-up.
HSPF2
Heating Seasonal Performance Factor — a heat pump's heating efficiency averaged across a season, under updated test conditions that better reflect real installations. Higher is better. In the heating-heavy Northwest, HSPF2 matters more to your bills than the cooling rating on the same spec sheet.
Cold-climate heat pump ratings, explainedInverter compressor
A variable-speed compressor that can run anywhere from a whisper to full output, instead of only on or off. It matches the home's actual heating or cooling need moment to moment, which means steadier temperatures, quieter operation, and better efficiency — especially in our mild, damp climate.
Why heat pumps fit the Pacific NorthwestLine set
The pair of insulated copper pipes carrying refrigerant between the outdoor and indoor units. Its length, diameter, and insulation quality all affect performance, which is why a careful installation routes and sizes it deliberately rather than reusing whatever was there.
Load calculation (Manual J)
The industry-standard method for calculating how much heating and cooling a specific house actually needs, using its insulation, windows, orientation, and air leakage — not just square footage. It's how equipment gets sized correctly. Be wary of any quote that names a size without one.
Heat pump sizing and Manual JMERV
Minimum Efficiency Reporting Value — the 1-to-16 scale rating how well a filter captures particles. Higher numbers catch finer particles like wildfire smoke, but denser filters also resist airflow more, so the right rating depends on what your blower can handle. Most homes land between MERV 8 and 13.
MERV ratings, explainedRefrigerant
The working fluid that absorbs heat in one coil and releases it in the other — the substance that makes heat pumps and air conditioners possible. Systems are sealed and shouldn't need topping off; needing refrigerant added means there's a leak to find. Handling it legally requires EPA certification.
Reversing valve
The component that lets a heat pump switch between heating and cooling by reversing the direction refrigerant flows. It's the difference between a heat pump and a plain air conditioner. A stuck reversing valve is the classic cause of a system blowing the wrong temperature for the season.
SEER2
Seasonal Energy Efficiency Ratio — cooling efficiency averaged across a season, under updated test conditions. Higher is better, but in our short cooling season it matters less to Northwest bills than heating efficiency (HSPF2) does. Premium ductless systems post the highest SEER2 numbers on the market.
Hisense systems we installStatic pressure
The resistance to airflow inside your duct system, measured the way a doctor measures blood pressure. High static pressure — from restrictive filters, undersized ducts, or dirty coils — makes systems loud, starves rooms of air, and wears out blowers. It's a key reading in any thorough system evaluation.
Understanding your ductworkZoning
Dividing a home into independently controlled comfort areas, each with its own temperature control — either with motorized dampers in ductwork or, more simply, with ductless heads in separate rooms. Zoning stops the whole-house thermostat compromise where one room's comfort costs another's.
Best rooms for a mini-splitHeard a term we didn't cover?
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