HVAC Glossary: A Plain-English, Fully-Vetted Guide for Homeowners & Pros
Plus: The Ideal Thermostat Temperature for Florida Summers
Comfort Control Specialists | Spring Hill, FL | 1.855.234.COOL
Use this A–Z glossary to decode heating, cooling, ventilation, and indoor-air terms you’ll see in proposals, manuals, and service reports. Section letters are grouped for quick scanning; links are vendor-neutral (government/standards/science) and italicized.
A
A-coil (evaporator coil) — A triangular indoor coil (shaped like an “A”) in the air handler or above a furnace; warm return air passes over this cold surface where heat is absorbed and moisture condenses, sending cooler, drier air to rooms. Clean fins and correct airflow are essential—dirty coils act like a blanket, cutting heat transfer and raising run time; routine service should include coil inspection/cleaning and airflow verification (DOE maintenance: https://www.energy.gov/energysaver/maintaining-your-air-conditioner).
ACCA (Air Conditioning Contractors of America) — The standards body behind residential design/quality practices: Manual J (room-by-room loads), Manual S (equipment selection), Manual D (duct design). Following these avoids the classic “oversized but uncomfortable” outcome and is referenced by codes across the U.S. (ACCA manuals: https://www.acca.org/standards/technical-manuals).
ACH (Air Changes per Hour) — How many times a space’s air volume is replaced in one hour via ventilation and leakage. In warm-humid Florida, excess ACH from infiltration brings moisture (not “freshness”), raising latent load; target controlled, balanced ventilation (ASHRAE 62.2: https://www.ashrae.org/technical-resources/standards-and-guidelines).
AFUE (Annual Fuel Utilization Efficiency) —
Seasonal furnace efficiency (% of fuel converted to usable heat). A 95% AFUE condensing furnace extracts additional heat from flue vapor and drains condensate; correct venting and condensate handling are required (ENERGY STAR basics: https://www.energystar.gov/products/heating_cooling).
Air barrier — A continuous, sealed layer (membranes, taped sheathing, caulks) that blocks uncontrolled air leakage through the building shell. Paired with insulation, it stabilizes temperature/humidity, cuts drafts, and reduces HVAC load (DOE air-sealing primer: https://www.energy.gov/energysaver/weatherize/air-sealing-your-home).
Air balance — Adjusting dampers/registers and confirming room CFM so each space receives design airflow without over-pressurizing or starving zones. Proper balancing evens out hot/cold rooms and prevents pressure imbalances that pull attic/garage air into the home (ACCA quality resources: https://www.acca.org/standards/quality).
Air handler (AHU) — The indoor unit that moves air across the coil and through ducts; includes blower (often variable-speed ECM), control board, filter rack, and sometimes electric heat strips. Correct external static pressure and clean filtration ensure the blower delivers rated CFM—a prerequisite for capacity and dehumidification (DOE airflow notes: https://www.energy.gov/energysaver/maintaining-your-air-conditioner).
B
Balancing damper — Manual or motorized valve in a duct branch that fine-tunes airflow to rooms. Proper damper settings plus sealed ductwork are essential for even temperatures and quiet operation (ACCA/QA guidance: https://www.acca.org/standards/quality).
Barometric relief — A spring-weighted damper that opens under excess building pressure to relieve air outdoors—common on commercial rooftop units to prevent door “blow-open” and keep ventilation balanced.
Blower door — A calibrated fan and gauge used to measure whole-house leakage (e.g., ACH50). Results inform targeted air-sealing that lowers HVAC load and stabilizes humidity (DOE home energy diagnostics: https://www.energy.gov/energysaver/home-energy-audits).
Blower motor (PSC vs. ECM) — PSC motors run at fixed speeds; ECM (electronically commutated) variable-speed motors modulate to maintain target airflow and reduce energy/noise, improving dehumidification by running longer at lower speed (OEM/ENERGY STAR overviews: https://www.energystar.gov/products/heating_cooling).
BTU (British Thermal Unit) — A unit of heat; roughly 12,000 BTU/h = 1 cooling “ton.” Load calculations (Manual J) determine the BTU/h capacity a home actually needs (ACCA Manual J: https://www.acca.org/standards/technical-manuals).
C
Capacitor — A start/run component that gives motors (compressor, condenser fan, blower) the phase shift/torque to start and run. Weak capacitors cause hard starts, hot motors, and nuisance trips—classic “it runs until it doesn’t” service calls.
Carbon monoxide (CO) — Colorless, odorless, deadly combustion gas. Proper appliance venting, tight flues, and CO detectors are life-safety essentials (EPA CO safety: https://www.epa.gov/indoor-air-quality-iaq/carbon-monoxide-s-impact-indoor-air-quality).
CFM (Cubic Feet per Minute) — Airflow volume. Equipment and ducts are designed around target CFM; too little robs capacity/dehumidification, too much can cause noise and poor heat transfer.
Charge (refrigerant) — The exact mass of refrigerant in a system. Under/overcharge reduces capacity and risks compressor damage; DOE and Building America emphasize verifying correct charge and airflow in quality maintenance (DOE A/C basics: https://www.energy.gov/energysaver/central-air-conditioning).
Condensate — Water that forms when humid air hits the cold evaporator coil; drains via a pan/line. Clogged drains cause overflows and float-switch trips; clearing them is a routine maintenance item (DOE tip sheet: https://www.energy.gov/energysaver/maintaining-your-air-conditioner).
Condenser (outdoor unit) — Rejects heat outdoors; houses the compressor, outdoor fan, and coil. Maintain ~2 feet of clear space so coils can “breathe” and head pressure remains stable (DOE maintenance: https://www.energy.gov/energysaver/maintaining-your-air-conditioner).
Condensing furnace — High-efficiency furnace (≈90–98% AFUE) that cools flue gases below the dew point to capture latent heat; needs corrosion-resistant drain/vent components.
COP (Coefficient of Performance) — Heat-pump heating efficiency (output heat divided by input electrical energy). A COP of 3.0 means 3 units of heat delivered per unit of electricity used (AHRI fundamentals: https://www.ahrinet.org/resources).
D
Damper — Any device that modulates or shuts airflow within a duct (manual, motorized, zone, smoke/fire). Essential in zoning systems to send more/less air to different areas without starving the blower.
Dehumidifier (whole-home) — A dedicated appliance that removes moisture independent of cooling; valuable in warm-humid climates to keep RH in the 40–60% comfort range without over-cooling (EPA humidity & IAQ: https://www.epa.gov/mold/brief-guide-mold-moisture-and-your-home).
Duct leakage — Air escaping from supply/return ducts through seams and penetrations; wastes energy, lengthens run time, and can pull contaminants from attics/garages into the home. Research shows sealing ducts can save ~10–20% of HVAC energy, often more when ducts are in hot attics (DOE/Building America: https://www.energy.gov/eere/buildings/building-america-solution-center).
Duct liner/wrap — Insulation inside or around ducts to limit heat gain/loss and damp noise. Even insulated ducts leak if seams aren’t sealed; best practice is seal first, then insulate (Building America details: https://basc.pnnl.gov/).
Duct static pressure — The “back-pressure” the blower must push against, driven by filter resistance, coil condition, and duct design. High static = noisy grilles, weak rooms, motor stress; measuring external static is a cornerstone of professional diagnostics (DOE contractor tips: https://www.energy.gov/energysaver/maintaining-your-air-conditioner).
E
ECM (electronically commutated motor) — High-efficiency, variable-speed motor that holds target airflow across changing conditions (dirty filter, wet coil, door closed) and can run longer at lower speeds to improve dehumidification while cutting noise/energy (ENERGY STAR overview: https://www.energystar.gov/products/heating_cooling).
EER / SEER / SEER2 — Cooling efficiency metrics. EER is fixed-condition efficiency; SEER is seasonal; SEER2 (2023+) uses the M1 test with higher external static to reflect real ducts. AHRI explains the shift and new minimums (AHRI efficiency metrics: https://www.ahrinet.org/resources/technologies/air-conditioners-heat-pumps).
ERV (energy recovery ventilator) — Ventilation device that transfers heat and some moisture between incoming outdoor air and outgoing exhaust, reducing the energy penalty of fresh air while tempering humidity—useful in warm-humid regions (ASHRAE ventilation resources: https://www.ashrae.org/technical-resources).
Expansion valve (TXV/EXV) —
The metering device feeding refrigerant into the evaporator. A TXV modulates flow to maintain targeted superheat, improving coil utilization across changing loads; EXV provides finer electronic control (OEM/industry primers: https://www.ahrinet.org/resources).
Fan coil unit (FCU) — Compact air handler with coil and fan (common in multi-family/light commercial). Variable-speed FCUs reduce noise and improve humidity removal by lingering at low CFM.
Filter (MERV rating) — Media that captures airborne particles; MERV (ASHRAE method) rates efficiency for 0.3–10 μm particles. Higher MERV captures more—but raises resistance—so choose the highest MERV your blower/returns can handle without excessive static (EPA filtration basics: https://www.epa.gov/indoor-air-quality-iaq/what-merv-rating; ENERGY STAR filter cadence: https://www.energystar.gov/products/heating_cooling).
Flue — Vent path for combustion byproducts from furnaces/water heaters. High-efficiency (condensing) equipment uses corrosion-resistant venting and drains condensate; improper venting risks CO hazards (EPA CO guidance: https://www.epa.gov/indoor-air-quality-iaq).
Fresh-air intake — Duct that intentionally brings in outdoor air to dilute pollutants/manage pressure; pairing with ERVs or smart controls improves IAQ with less energy penalty (ASHRAE 62.2: https://www.ashrae.org/technical-resources/standards-and-guidelines).
G
Geothermal (ground-source) heat pump — A heat pump exchanging heat with the ground via buried loops/wells, which stay relatively stable year-round. Higher COPs yield low operating costs, though install cost is higher (DOE geothermal basics: https://www.energy.gov/eere/geothermal/geothermal-heat-pumps).
Glycol — Antifreeze (often propylene glycol) in hydronic or ground loops to prevent freezing. Proper concentration protects coils/loops without overly penalizing pump power or heat transfer.
Grille / register — Room outlets: grilles (fixed) and registers (with adjustable dampers). Correct sizing/placement minimizes noise and drafts while delivering design CFM.
I
IAQ (Indoor Air Quality) —
How clean/healthy indoor air is, influenced by particles (dust/pollen/smoke), gases (CO₂/VOCs), and microbes. Improve IAQ via source control, balanced ventilation, right-sized filtration, and moisture management (EPA IAQ overview: https://www.epa.gov/indoor-air-quality-iaq).
Infiltration —
Uncontrolled outdoor air leaking through cracks, recessed lights, gaps. In Florida, infiltration brings moisture more than “freshness,” raising AC load and musty odors; air-seal and ventilate on purpose.
Insulation (R-value) —
Resistance to heat flow; higher R slows attic/wall heat gain so your AC isn’t playing catch-up at 4–7 p.m. Installation quality (no gaps/voids) matters as much as the number (DOE insulation types: https://www.energy.gov/energysaver/types-insulation).
Inverter (variable-speed) compressor —
Modulates capacity instead of only ON/OFF, matching output to load to smooth temperature/humidity and cut energy/noise (AHRI fundamentals: https://www.ahrinet.org/resources).
ISO 16890 / MERV (filter ratings) —
Standards describing particle capture. Homes generally see MERV labels; choose the highest MERV your system can handle without excessive static (EPA filtration: https://www.epa.gov/indoor-air-quality-iaq/what-merv-rating).
J
Joule (J) —
Unit of energy. HVAC proposals typically quote kWh (1 kWh = 3.6 million joules) for electricity and BTU for capacity.
K
kW vs. kWh — kW = power (rate); kWh = energy over time (what you pay for). A 3.5-ton heat pump may draw ~2–4 kW while running; hours of runtime determine the kWh on your bill (ENERGY STAR HVAC overview: https://www.energystar.gov/products/heating_cooling).
Kickspace (toe-kick) heater — Small fan-assisted heater tucked in a cabinet toe-kick. Common in colder climates; in Florida, used for spot heating in additions.
L
Latent heat (moisture load) — The “hidden” energy tied to water vapor. Your AC must remove sensible heat (temperature) and latent heat (humidity); a house can read 74°F yet feel sticky if latent loads are high. Slower blower speeds and clean coils help wring moisture (psychrometrics intro: https://www.ashrae.org/technical-resources).
Load calculation (Manual J) — Room-by-room sizing math that matches equipment to real heat gains/losses, preventing “too big, too clammy.” (ACCA Manual J: https://www.acca.org/standards/technical-manuals).
LRA (Locked-Rotor Amps) — The very high current a motor pulls at startup. Weak capacitors/tight compressors spike LRA and trip breakers; soft-start/ECM strategies can mitigate where appropriate.
Low-ambient kit — Controls that keep a condenser operating reliably in cool outdoor temps (mostly commercial/process cooling).
M
Makeup air — Intentional outdoor air brought in to replace exhausted air (range hoods, dryers). Without it, homes can go negative pressure and pull humid/garage/attic air in through leaks.
Manual D (duct design) — Calculates duct sizes, friction rates, and returns so each room gets design CFM without high static; paired with Manual J (loads) and Manual S (equipment) (ACCA: https://www.acca.org/standards/technical-manuals).
Manual S (equipment selection) —
Translates Manual J loads into properly matched equipment (capacity at design temp, coil match, dehumidification).
MERV (filter efficiency) —
Numeric scale (1–16) for particle capture. Higher isn’t always better—match to blower/return capacity to avoid starving airflow (EPA primer: https://www.epa.gov/indoor-air-quality-iaq/what-merv-rating).
Mini-split (ductless or ducted) —
Heat pump with an outdoor unit and compact indoor air handlers (wall/ceiling/ducted). Great for additions/bonus rooms or duct limitations; inverter-driven for quiet, efficient, targeted comfort (AHRI directory: https://www.ahridirectory.org).
N
NATE (North American Technician Excellence) —
Independent certification for HVAC techs; indicates training/testing beyond minimum licensing (NATE: https://www.natex.org).
Nitrogen pressure test —
Dry nitrogen pressurizes refrigerant lines after repair/installation to confirm leaks are gone before charging.
NFPA 90A/90B —
Standards covering air-conditioning/ventilating system safety (fire/smoke in ducts/plenums); contractors follow them for code compliance (NFPA: https://www.nfpa.org/).
O
OEM (Original Equipment Manufacturer) — The brand that built your unit; OEM specs dictate design airflow, charge, and controls. Following OEM procedures protects efficiency and warranty.
Orifice/piston (fixed metering) — Simple metering device that feeds refrigerant at a fixed rate; cheaper than TXV but less adaptable to changing loads.
Outdoor reset (hydronics) — Boiler control that lowers water temperature when it’s milder outside—saves energy and stabilizes comfort (DOE hydronics intro: https://www.energy.gov/energysaver).
Occupant-centric controls — Systems that sense presence, CO₂, or humidity to adjust ventilation and setpoints; paired with ERVs and variable equipment for comfort/efficiency.
P
Packaged unit —All-in-one outdoor cabinet housing compressor, coil(s), and blower; connects to supply/return ducts. Useful when indoor space is limited.
Plenum —Large supply/return air box attached to the air handler/furnace where ducts connect. Leaky plenums = lost capacity and dusty returns; sealing is low-hanging fruit (Building America: https://basc.pnnl.gov/).
Psychrometrics —
The science of moist air—how temperature, humidity, and enthalpy interact. Explains why dry 76°F feels better than clammy 74°F, and why “Fan ON” can re-evaporate coil moisture (ASHRAE resources: https://www.ashrae.org/technical-resources).
PTAC — Packaged Terminal Air Conditioner—self-contained wall unit (hotels/senior living). Efficient models may use heat pumps and occupancy sensors.
Pressure mapping (static pressure) — Measuring supply/return static to diagnose airflow bottlenecks. High static = loud registers, weak rooms, higher bills (DOE airflow tips: https://www.energy.gov/energysaver/maintaining-your-air-conditioner).
Q
Q = 1.08 × CFM × ΔT — Rule-of-thumb formula for sensible cooling/heating capacity (BTU/h), where ΔT is the temperature change across the coil. Latent capacity uses moisture (grains) relationships (ASHRAE fundamentals: https://www.ashrae.org/technical-resources).
QI / QA (Quality Installation/Assurance) — ACCA/ANSI standards ensure equipment is sized/charged/air-balanced correctly so label efficiency shows up in real homes (ACCA QI/QA: https://www.acca.org/standards/quality).
R
R-410A / R-454B / R-32 (refrigerants) — Modern systems are transitioning away from R-410A to lower-GWP refrigerants such as R-454B and R-32 (EPA SNAP: https://www.epa.gov/snap).
Recovery unit (refrigerant) — Machine that safely pulls refrigerant from a system for recycling/disposal—recovery is required by federal law (EPA Section 608: https://www.epa.gov/section608).
Return path (returns/undercuts/jump ducts) — How air gets back to the air handler. Poor return paths cause pressure imbalances and starve rooms; good returns are as vital as supplies (Building America: https://basc.pnnl.gov/).
Refrigerant glide (blends) — Some blends boil/condense across a temperature range (“glide”). Techs must charge/interpret subcool/superheat correctly for accurate diagnostics (AHRI fundamentals: https://www.ahrinet.org/resources).
S
Sensible vs. latent — Sensible changes what the thermometer reads; latent changes moisture content. Great Florida comfort = handling both well (psychrometrics: https://www.ashrae.org/technical-resources).
Static pressure (external static) —Total resistance the blower sees. High static from restrictive filters, tight coils, or undersized ducts reduces airflow/comfort and stresses motors; measuring static is core to pro maintenance (DOE tips: https://www.energy.gov/energysaver/maintaining-your-air-conditioner).
SEER2 (cooling efficiency) — 2023+ seasonal efficiency rating using updated test conditions (higher external static to reflect real ducts) (AHRI explainer: https://www.ahrinet.org/resources/technologies/air-conditioners-heat-pumps).
Subcooling / Superheat — Tech measurements showing liquid-line temperature below saturation (subcool) and suction-line temperature above saturation (superheat). They prove charge and metering health (DOE A/C basics: https://www.energy.gov/energysaver/central-air-conditioning).
Smoke detectors in returns — Commercial/large systems often require duct smoke detection to shut fans on smoke; life-safety integrations follow code and NFPA standards (NFPA: https://www.nfpa.org/).
T
Thermostat (smart) — Learns schedules, staggers starts, and (with compatible systems) manages blower speeds/dehumidification. Works best when the house envelope is tight and airflow is on-spec (ENERGY STAR smart thermostats: https://www.energystar.gov/products/smart_thermostats).
Tonnage (cooling tons) — 1 ton = 12,000 BTU/h. Correct tonnage comes from Manual J—not house size or rules of thumb (ACCA Manual J: https://www.acca.org/standards/technical-manuals).
TXV / EXV (expansion valves) — Meter refrigerant into the evaporator; TXV targets stable superheat across changing loads; EXV offers finer electronic control (AHRI resources: https://www.ahrinet.org/resources).
Thermal bridging — Heat bypassing insulation through framing/steel. Continuous exterior insulation and careful detailing reduce bridging and peak loads (DOE envelope basics: https://www.energy.gov/energysaver).
U
U-factor — Inverse of R-value (overall heat transfer). Windows/doors list U-factor; lower is better for reducing heat gain (ENERGY STAR window primer: https://www.energystar.gov/products/residential_windows_doors_and_skylights).
UV-C lights (coil irradiation) — Ultraviolet lamps that irradiate the coil/drain-pan area to limit biological growth and maintain heat-transfer surfaces. They’re not whole-home disinfectants but help keep coils cleaner (ASHRAE IAQ resources: https://www.ashrae.org/technical-resources).
V
VAV (Variable Air Volume) — Common in commercial buildings: supply-air temperature held roughly constant while airflow varies to meet zone loads.
Ventilation rate (ASHRAE 62.2) — Residential standard for minimum mechanical ventilation to manage IAQ; in warm-humid climates, pair ventilation with dehumidification/ERV strategies (ASHRAE 62.2: https://www.ashrae.org/technical-resources/standards-and-guidelines).
VRF / VRV (Variable Refrigerant Flow/Volume) — Multi-zone inverter systems that modulate refrigerant flow to many indoor units. Excellent part-load efficiency and zoning flexibility; requires precise design/commissioning (AHRI on VRF: https://www.ahrinet.org).
W
Wet-bulb temperature — A measure combining heat and humidity—key to how “hot” air feels and to AC capacity calculations. Techs use wet-bulb to calculate target superheat on fixed-metering systems (ASHRAE fundamentals: https://www.ashrae.org/technical-resources).
Wind washing — Air movement through/around attic insulation that reduces its effective R-value (e.g., wind at soffits). Baffles and air-sealing preserve insulation performance (DOE attic details: https://www.energy.gov/energysaver).
WSHP (Water-Source Heat Pump) — Heat pumps that exchange heat with a building water loop or tower; common in multi-unit/commercial buildings for modular efficiency (DOE technology overview: https://www.energy.gov/eere/buildings/).
X
X13 (constant-torque) motor — Efficient electronically controlled motor that maintains torque across static changes better than PSC but with simpler control than full ECM variable-speed—helps airflow stability as filters load.
Y
Y-wire (thermostat) — Compressor control terminal. Multi-stage/inverter systems may use Y1/Y2 or communicating protocols for finer capacity control.
Yard clearance (condenser) — Keep ~2 feet clear around outdoor units so coils can breathe; trim shrubs/debris for stable head pressure and efficiency (DOE maintenance: https://www.energy.gov/energysaver/maintaining-your-air-conditioner).
Z
Zoning (residential) — Motorized dampers and dedicated thermostats/sensors that send more/less air to different areas. Works best with ducts designed for zoning and equipment staged/variable to avoid high static (ACCA zoning/QA resources: https://www.acca.org/standards/quality).
Zonal imbalance — Rooms that run hot/cold due to duct design, leakage, solar gain, or poor returns. Solutions typically involve air sealing, duct resizing/sealing/balancing, and load-aware controls—not just a bigger unit (Building America: https://basc.pnnl.go
If your AC is running nonstop this summer, it’s more than an inconvenience—it’s a red flag. Whether it’s caused by poor insulation, low refrigerant, or simply the thermostat being set too low, there are real solutions that save energy, increase comfort, and extend your system’s life.
Trust the experts at Comfort Control Specialists to help you stay cool and confident—no matter how brutal the Florida heat gets.