Learning Center

Glossary — HVAC, Insulation, Energy Efficiency

40 HVAC, insulation, and energy-efficiency terms defined in plain English — every term cross-linked to the Pure Eco Learning Center article that explains it in context.

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The trades we work in have a lot of jargon — R-value, SEER2, MERV, Manual J, HRV — and most of it is used by contractors as if every homeowner already knows it. Below are 40 of the terms you're most likely to hear from a Pure Eco technician (or from a competitor trying to sell you something), each defined plainly, each cross-linked to the article that explains it in more depth.

A

AFUE

Annual Fuel Utilization Efficiency — the percentage of fuel a gas furnace converts into usable heat over a heating season. A 90% AFUE furnace turns 90 cents of every dollar of gas into heat; the other 10 cents goes up the flue.

Air Handler

The indoor cabinet that contains the blower motor, evaporator coil, and (usually) the filter. In split systems, the air handler pushes conditioned air through the ductwork. In a heat pump, it also houses the auxiliary heat strips if any.

→ See also: HVAC services

Ambient Temperature

The surrounding air temperature — usually the temperature in the room where a thermostat is measuring, or the outdoor air temperature at the condenser. Ambient conditions affect equipment performance and capacity ratings.

→ See also: Smart thermostat savings

B

Blower Door Test

A diagnostic that measures how leaky a home is. A calibrated fan mounted in an exterior door depressurizes the house; the pressure difference tells the auditor how much air infiltrates per hour. Common part of a full energy audit.

BTU

British Thermal Unit — a measure of heat energy. One BTU is the energy needed to raise one pound of water by one degree Fahrenheit. HVAC capacity is rated in BTU/hour; residential systems typically deliver 18,000–60,000 BTU/hour.

→ See also: Annual HVAC service

C

Capacitor

An electrical component that stores and releases energy to help start and run the compressor and blower motors. Capacitors weaken with heat cycles and are the #1 failure part on SoCal condensers. Cheap and quick to replace.

Compressor

The pump that circulates refrigerant through an HVAC system. Lives in the outdoor condenser unit on a split system. The heart of the refrigeration cycle — when a compressor fails, it's often close to the whole-system-replacement decision point.

→ See also: Heat pump vs HVAC

Condenser

The outdoor half of a split-system AC or heat pump. Contains the compressor, condenser coil, and outdoor fan. Its job is to release heat collected from indoors to the outside air.

→ See also: HVAC services

Condensate Line

The drain line that carries away the water an AC pulls from indoor air. A clogged condensate line is a common cause of a shut-down system or water damage on the ceiling below an attic-mounted air handler.

→ See also: Annual HVAC service

Coolant / Refrigerant

The fluid that circulates through an AC or heat pump, absorbing heat from indoor air and releasing it outside. Modern residential systems use R-410A; newer equipment is transitioning to lower-GWP alternatives like R-32 and R-454B.

→ See also: Annual HVAC service

D

Damper

A movable plate inside ductwork that controls airflow. Used to balance air between rooms, isolate zones, or shut off supply to unused spaces. Zoning systems use motorized dampers controlled by the thermostat.

→ See also: Duct services

Ductless Mini-Split

An HVAC system with an outdoor condenser and one or more wall-mounted indoor units, connected by refrigerant lines rather than ducts. Popular for additions, room-by-room conditioning, and homes without existing ductwork.

→ See also: HVAC services

Ductwork

The system of metal or flexible tubes that carries conditioned air from the air handler to each room and returns it back. Leaky or poorly designed ductwork can waste 20–30% of a system's output before air reaches the rooms.

→ See also: Cutting your cooling bill

E

EER

Energy Efficiency Ratio — cooling output (BTU/hour) divided by electrical input (watts) at a standard outdoor test condition. EER is a point-in-time efficiency measure; SEER is the seasonal version.

→ See also: Heat pump vs HVAC

Energy Star

A joint EPA/DOE program that certifies energy-efficient equipment. Energy Star–rated HVAC systems, water heaters, appliances, and building products exceed federal minimum efficiency standards and often qualify for utility rebates.

→ See also: 2026 California rebates

Evaporator Coil

The indoor coil inside the air handler where refrigerant absorbs heat from the passing air. Dirty evaporator coils drop system efficiency dramatically; a coil clean is part of a proper HVAC tune-up.

→ See also: Annual HVAC service

F

Fan Coil Unit

An indoor cabinet with a coil and a fan — like an air handler but without the auxiliary heat strips. Common in ductless mini-splits and hydronic (water-based) systems.

→ See also: HVAC services

Filter (MERV rating)

MERV (Minimum Efficiency Reporting Value) rates a filter's ability to capture particles at various sizes. MERV 6 catches lint; MERV 13 catches PM2.5 wildfire smoke; MERV 16 is hospital-grade. Higher MERV = more static pressure on the blower.

→ See also: HVAC filter cadence

Furnace

A heating unit that burns fuel (usually natural gas in SoCal) to warm air, then blows the warmed air through the ductwork. Rated by AFUE efficiency. In heat-pump systems, there is no furnace — the heat pump handles both heating and cooling.

H

Heat Exchanger

The metal chamber inside a furnace where combustion heat is transferred to the air stream without mixing combustion gases into the home. A cracked heat exchanger can leak carbon monoxide and is a safety-critical inspection item.

Heat Load Calculation (Manual J)

The ACCA-standard method for sizing HVAC equipment to a specific home. Accounts for orientation, insulation, window area, occupancy, and climate. An HVAC estimate that doesn't reference Manual J is essentially a guess.

→ See also: Heat pump vs HVAC

Heat Pump

An HVAC unit that moves heat rather than creating it — cooling in summer (like an AC), heating in winter (by reversing the refrigerant cycle). Highly efficient in Southern California's mild climate.

→ See also: Heat pump vs HVAC

HERS Rating

Home Energy Rating System — a numeric score from 0 (net-zero) to 100+ (energy-inefficient) that quantifies a home's energy performance. Required on some California new construction and used by whole-home retrofit programs.

→ See also: Permits & Code

HRV / ERV

Heat Recovery Ventilator / Energy Recovery Ventilator — a device that brings in fresh outdoor air while recovering most of the heat (HRV) or heat + moisture (ERV) from the outgoing indoor air. Useful in tightly sealed homes.

→ See also: IAQ during bad-air events

HSPF

Heating Seasonal Performance Factor — the heat-pump equivalent of SEER. Measures heating output per unit of electricity over a heating season. Higher HSPF = more heat per kWh. HSPF2 is the updated federal test standard.

→ See also: Heat pump vs HVAC

Humidistat

A control that switches a humidifier or dehumidifier on and off based on a target relative humidity. Analogous to a thermostat but for moisture.

→ See also: Humidity and comfort

HVAC

Heating, Ventilation, and Air Conditioning — the umbrella term for the equipment that controls a home's indoor climate. In practice, most residential HVAC is a heating unit + cooling unit + duct distribution system.

→ See also: HVAC basics cluster

I

IAQ (Indoor Air Quality)

A composite measure of pollutants, particulates, humidity, and ventilation inside a building. Poor IAQ affects health, comfort, and cognitive performance. Filtration, ventilation, and humidity control are the three main levers.

→ See also: Indoor air quality cluster

L

Line Set

The pair of insulated copper refrigerant lines that connect the indoor and outdoor units of a split-system AC or heat pump. A damaged or improperly sized line set can hurt efficiency and cause slow refrigerant leaks.

→ See also: HVAC services

Load Calculation

The engineering process of determining how much heating and cooling capacity a home actually needs — see also Manual J. Undersized equipment can't keep up; oversized equipment cycles too fast and dehumidifies poorly.

→ See also: Heat pump vs HVAC

P

Package Unit

An HVAC system where the compressor, coils, and blower are all housed in a single outdoor cabinet — usually on a slab or the roof. Common on flat-roofed SoCal commercial buildings and some residential homes.

→ See also: HVAC services

Plenum

A sealed chamber attached to the supply or return of an air handler that distributes conditioned air into the ductwork. Supply plenum = air out to the house; return plenum = air back to the system.

→ See also: Duct services

R

R-Value

A measure of an insulation material's resistance to heat flow. Higher R-value = better insulator. Southern California attics target R-30 minimum, R-38 default, R-49 in colder inland zones.

→ See also: R-value explained

Return Air

The air pulled back into the HVAC system from the home, through return grilles, to be re-conditioned. Restricted returns (blocked grilles, undersized ducts) starve the blower and hurt overall performance.

→ See also: Duct services

S

SEER / SEER2

Seasonal Energy Efficiency Ratio — cooling output over a season divided by electrical input. Higher = more efficient. SEER2 is the updated federal test standard (2023+) that reflects real duct conditions. Modern equipment targets SEER2 15+.

→ See also: Heat pump vs HVAC

Split System

The most common residential HVAC layout: outdoor condenser (with the compressor) + indoor air handler (with the coil and blower) + ductwork. 'Split' refers to indoor + outdoor components being separate cabinets.

→ See also: HVAC services

Static Pressure

The pressure the blower has to fight to push air through the ductwork, filter, and coil. Too much static pressure (from a clogged filter, kinked ducts, or high-MERV filter without capacity) starves airflow and can freeze the coil.

→ See also: HVAC filter cadence

T

Thermostat (Programmable / Smart)

The control that senses room temperature and calls for heating or cooling. Programmable thermostats follow a set schedule; smart thermostats add app control, geofencing, learning, and remote sensors.

→ See also: Smart thermostat savings

Ton (of cooling)

A unit of HVAC capacity — 1 ton = 12,000 BTU/hour of cooling. Named after the amount of heat needed to melt one ton of ice in 24 hours. Residential systems typically range from 1.5 to 5 tons.

→ See also: HVAC services

Z

Zoning

An HVAC configuration that uses motorized dampers and multiple thermostats to control different areas of the home independently. Lets you cool the upstairs bedroom without over-cooling the downstairs living room.

→ See also: HVAC services

Need something explained in plain English?

Any Pure Eco technician can walk you through the terminology on your specific home during a free in-home consultation. Call (877) 870-7998 or reach us online.

Get a Free Consultation (877) 870-7998