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Learning Center · Glossary
HVAC & Geothermal Glossary — A to Z
48 plain-English definitions for the terms you'll see on a repair invoice, install estimate, or rebate application in Central Virginia & the Blue Ridge.
A
- AFUE
- Annual Fuel Utilization Efficiency — the percentage of a gas furnace's fuel that becomes useful heat over a heating season. A 95% AFUE furnace delivers 95¢ of heat for every $1 of gas. Most modern furnaces are 90–98%.
- Air Handler
- The indoor half of a split-system heat pump or AC. Contains the blower motor, evaporator coil, and filter housing. Sometimes called the 'fan coil.'
B
- BTU
- British Thermal Unit — the amount of heat needed to raise one pound of water by one degree Fahrenheit. HVAC capacity is expressed in BTU/hr; 12,000 BTU/hr = 1 ton.
- Blower Door Test
- A calibrated fan mounted in an exterior doorway that pressurizes or depressurizes the house to measure how leaky the building envelope is. Used to inform Manual J load calcs.
C
- Capacity
- The maximum rate at which a system can move heat, measured in BTU/hr or tons. A 3-ton heat pump has 36,000 BTU/hr of nominal capacity at rating conditions.
- Charge (Refrigerant)
- The precise weight of refrigerant sealed inside the system. Overcharged and undercharged systems both fail early; a proper charge is measured, not guessed.
- Closed-Loop System
- A geothermal ground-loop configuration where a sealed circuit of buried pipe carries a water-glycol mix between the earth and the heat pump. The Blue Ridge subsurface favors closed vertical loops.
- COP
- Coefficient of Performance — heating efficiency ratio. A COP of 4 means the system delivers 4 units of heat per 1 unit of electricity. WaterFurnace geothermal COPs sit around 4.0–5.3 depending on ground temp.
D
- Damper
- A movable plate inside a duct that opens or closes to redirect airflow. Motorized dampers are the mechanical foundation of zoning systems.
- Ductless
- A mini-split system: outdoor condenser + one or more indoor wall/ceiling heads, connected by small refrigerant lines. No ductwork; ideal for additions, sunrooms, and finished basements.
- Duct Static Pressure
- How hard the blower must push air through the ductwork. High static pressure means restricted, undersized, or leaky ducts and directly cuts efficiency + comfort.
E
- EER2
- The 2023-updated cooling efficiency rating measured at a single hot outdoor condition (95°F). EER2 tells you how the system performs at design load — the moment on the hottest afternoon when you need it most.
- Evaporator Coil
- The indoor coil that absorbs heat from your house air, letting the refrigerant boil into a gas. Sits inside the air handler or on top of the furnace.
- Expansion Valve (TXV/EEV)
- The metering device that controls how much refrigerant enters the evaporator. A thermostatic (TXV) or electronic (EEV) valve is required on modern high-SEER systems.
F
- Furnace
- A heating appliance that burns fuel (typically natural gas or propane in Virginia) or uses electric resistance to warm air, which the blower then distributes through ducts.
G
- Geothermal Heat Pump
- A heat pump that exchanges heat with the ground (via a buried ground loop) instead of the outdoor air. Because ground temperature stays far steadier than outdoor air, geothermal efficiency stays high in every season.
- Grille
- The visible cover on a return-air opening. Distinct from a 'register,' which is on a supply opening and has adjustable louvers.
- Ground Loop
- The buried pipe network that carries fluid between a geothermal heat pump and the earth. Loops can be vertical bores (300–400 ft typical here), horizontal trenches, or pond loops.
H
- Heat Pump
- A single system that both heats and cools by moving heat, not making it. Reverses refrigerant flow to run in either direction. Efficiency (HSPF2 for heating) beats resistance electric by 2–4x.
- HRV / ERV
- Heat Recovery Ventilator / Energy Recovery Ventilator — a device that swaps stale indoor air for fresh outdoor air while recovering most of the temperature (and, for ERVs, humidity) so you don't pay to condition the incoming air twice.
- HSPF2
- Heating Seasonal Performance Factor (2023 update) — the average heating efficiency of a heat pump across a heating season. Higher is better; the 2023 federal minimum is 7.5 HSPF2.
- Humidifier (Whole-Home)
- A device mounted on the furnace or air handler that adds moisture to the air during heating season, when indoor air can become uncomfortably dry.
I
- IAQ
- Indoor Air Quality — the overall composition of the air inside your home: humidity, VOCs, particulates, allergens, radon, CO₂. Addressed with filtration, ventilation, humidification, and dehumidification.
- Inverter Compressor
- A variable-speed compressor that ramps up or down instead of cycling on and off. Delivers dramatically better humidity control and part-load efficiency than a fixed-speed compressor.
L
- Load Calculation
- The Manual-J-driven room-by-room analysis of how much heating and cooling your home actually needs. A load calc is the difference between right-sized comfort and expensive over-sized noise.
M
- Manual J
- The ACCA-published methodology for calculating residential heating and cooling loads. A Manual J replaces rule-of-thumb square-footage guesses.
- MERV
- Minimum Efficiency Reporting Value — the filter-effectiveness scale. MERV 8 catches dust; MERV 11 catches pollen; MERV 13 catches most bacteria and fine particles. Higher MERV is not always better — restricted airflow damages equipment.
- Mini-Split
- See Ductless.
- Modulating
- A system that adjusts output continuously (0–100%) rather than being on/off. Modulating gas furnaces and inverter heat pumps deliver the steadiest indoor temperatures.
O
- Open-Loop System
- A geothermal configuration that pumps water from a well through the heat pump and discharges it (to a second well, pond, or drain). Less common than closed loops.
P
- Plenum
- The main air chamber attached to the supply or return side of the air handler. Ducts branch off the plenum.
- Programmable / Smart Thermostat
- A thermostat that follows a schedule (programmable) or learns and adapts (smart, e.g. ecobee, Nest). Communicating thermostats also relay diagnostic data back to the equipment.
R
- R-22 / R-410A / R-454B / R-32
- Refrigerant generations. R-22 (Freon) is banned. R-410A is being phased down in 2025+ under the AIM Act. R-454B and R-32 are the low-GWP replacements now shipping on new equipment.
- Rebate
- A cash-back incentive from a utility (Dominion Energy in most of our region) or manufacturer for installing qualifying high-efficiency equipment. Stackable with financing but not with the expired federal tax credits.
- Register
- The visible cover on a supply-air outlet. Has adjustable louvers to direct or throttle airflow.
- Return Air
- The air the blower pulls back from the house to be reconditioned. Undersized returns are one of the most common reasons a system 'can't keep up.'
S
- SEER2
- Seasonal Energy Efficiency Ratio (2023 update) — the seasonal cooling efficiency of an AC or heat pump. Federal minimums as of 2023 are 14.3 SEER2 in the Southeast (VA).
- Static Pressure
- See Duct Static Pressure.
- Split System
- The standard residential HVAC configuration: outdoor condenser + indoor air handler or furnace, connected by refrigerant lines. Distinct from a packaged unit.
- Supply Air
- The conditioned air the blower pushes into your rooms through ducts and registers.
T
- Ton (of Cooling)
- 12,000 BTU/hr of capacity. A 3-ton system provides 36,000 BTU/hr. The right size for a home comes from a Manual J calc, never square footage alone.
- TXV
- See Expansion Valve.
V
- Variable-Speed
- A motor that runs at multiple speeds instead of on/off. Variable-speed blowers move air more quietly, dehumidify better on low, and cut power consumption dramatically at part load.
- Ventilation
- The intentional exchange of indoor and outdoor air for IAQ. In tight new-construction homes it's mechanical (HRV/ERV); in older homes it's often incidental via infiltration.
- VOCs
- Volatile Organic Compounds — chemical vapors from paint, cleaners, cabinetry, flooring, and fuel combustion. Removed by ventilation + carbon filtration; NOT by MERV filters alone.
W
- WaterFurnace
- The Indiana-built geothermal heat pump manufacturer Airflow Systems installs as a premier WaterFurnace partner. Referenced throughout the site because it is the specific equipment on most of our geothermal installs.
- Wet-Bulb Temperature
- The temperature air would reach if cooled by evaporation to 100% humidity. A better predictor of comfort and cooling load than dry-bulb temperature — and the reason a humid day can feel worse than a hotter, drier one.
Z
- Zoning
- Splitting a single HVAC system into multiple thermostat-controlled zones via motorized dampers or dedicated mini-split heads. Helps with the common problem of an upstairs that runs hotter than the downstairs.
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