HVAC glossary for Wilmington homeowners

Equipment

Split system

The most common central system: an outdoor unit (condenser or heat pump) connected by refrigerant lines to an indoor air handler or furnace with an evaporator coil. AC Installation

Packaged unit

All heating and cooling components in one cabinet, usually on a roof or slab; common on commercial buildings. Rooftop Units

Heat pump

Equipment that moves heat into the home in winter and out in summer using refrigerant, providing both heating and cooling. Heat Pump Installation

Ductless mini-split

A heat pump with one or more wall, floor, or ceiling indoor units connected to an outdoor unit without ductwork. Mini-Split Installation

Air handler

The indoor cabinet with a blower and evaporator coil that moves air through the ducts; often paired with a heat pump. Heat Pump Repair

Furnace

A forced-air heater that burns gas, propane, or oil (or uses electric elements) and blows warm air through ducts. Furnace Repair

Boiler

Heats water to produce hot water or steam for radiators, baseboards, or radiant floors. Boiler Repair

Condensing boiler

A high-efficiency hot-water boiler that recovers heat from exhaust gases; not used with steam systems. Boiler Replacement

PTAC

Packaged terminal air conditioner: a through-wall unit common in apartments and hotels. Multifamily & Property Managers

ERV / HRV

Energy or heat recovery ventilators bring in fresh air while recovering heat (and, for ERVs, moisture) from outgoing air. Ventilation (ERV/HRV)

Components

Compressor

The pump in the outdoor unit that circulates refrigerant; usually the most expensive part to replace. AC Repair

Capacitor

An electrical part that helps motors and compressors start and run; a very common failure in summer. AC Repair

Contactor

An electrical switch in the outdoor unit that turns the compressor and fan on and off. AC Repair

Evaporator coil

The indoor coil where refrigerant absorbs heat and moisture from the air. AC Repair

Condenser coil

The outdoor coil where refrigerant releases heat. Cooling Tune-Ups

TXV (expansion valve)

Meters refrigerant into the evaporator coil; failures cause poor cooling or freezing. AC Repair

Reversing valve

Switches a heat pump between heating and cooling. Heat Pump Repair

Defrost board

Controls heat pump defrost cycles that melt ice off the outdoor coil in winter. Heat Pump Repair

Heat exchanger

The furnace part that separates combustion gases from house air; a crack is a safety issue. Furnace Repair

Flame sensor

Confirms the burner is lit; a dirty sensor makes a furnace light and then shut off. Furnace Repair

Inducer motor

Pulls combustion gases through a furnace before ignition; paired with a pressure switch. Furnace Repair

Circulator pump

Moves hot water from a boiler to radiators or zones. Boiler Repair

Low water cutoff

A steam boiler safety that shuts the burner off when water is low. Boiler Repair

Condensate drain

Carries water removed by the AC away from the unit; clogs trigger shutdowns or leaks. Cooling Tune-Ups

Ratings and sizing

SEER2

Seasonal energy efficiency ratio (2023 test method) for cooling; higher is more efficient over a season. In Delaware (DOE Southeast region), new split ACs under 45,000 BTU/h must be at least 14.3 SEER2. AC Installation

EER2

Cooling efficiency at a single hot outdoor condition; useful for peak-summer performance. AC Installation

HSPF2

Heating seasonal performance factor for heat pumps; higher means more efficient heating. Heat Pump Installation

AFUE

Annual fuel utilization efficiency for furnaces and boilers; 95% means about 95% of fuel becomes heat. Furnace Installation

Ton

A cooling capacity unit equal to 12,000 BTU per hour; most homes use 1.5 to 5 tons. AC Installation

BTU

British thermal unit, the energy to raise one pound of water by 1°F; used to rate heating and cooling capacity.

Manual J

The ACCA load calculation used to size heating and cooling equipment room by room. AC Installation

Static pressure

Resistance to airflow in the duct system; high static pressure means restrictive ducts or filters. Ductwork & Airflow

MERV

Minimum efficiency reporting value, a filter rating; higher traps smaller particles but can restrict airflow. Air Purification & UV

Refrigerants and air

R-22

An older refrigerant no longer produced in the U.S. since 2020; recharges are expensive. AC Repair

R-410A

The refrigerant in most systems installed from about 2010 to 2024; being phased down. AC Repair

R-454B / R-32

Lower-global-warming refrigerants used in new residential systems made since 2025. AC Installation

Return air

Air pulled back from rooms to the equipment; too few returns cause hot rooms and noise. Ductwork & Airflow

Auxiliary heat

Backup electric or gas heat that supplements a heat pump in cold weather or defrost. Heat Pump Repair

Zoning

Dampers and thermostats that let different areas be heated or cooled separately. Thermostats & Zoning

Indoor air quality

The cleanliness, humidity, and freshness of indoor air, shaped by filtration, ventilation, and moisture control. Indoor Air Quality