HVAC glossary · plain English

HVAC Terms, Decoded.

Name: Air Solutions Heating & Cooling
Address: 1410 US Highway 98, Suite N, Daphne, AL, 36526, US
Telephone: +1-251-300-9817
Price range: $$

66 HVAC terms explained the way we'd explain them at your kitchen table — what the term means, why it matters in coastal Alabama, and (where helpful) the next page to read for deeper context. Reading a quote instead? Start with the cost guides.

A

AFUE: Annual Fuel Utilization Efficiency. The percentage of fuel a furnace converts into usable heat over a year. A 95% AFUE furnace turns 95% of its fuel into heat; the remaining 5% leaves through the flue. Modern condensing furnaces hit 95–98% AFUE; older atmospheric units run 70–80%.
AHRI Matched System: A specific outdoor unit + indoor coil + air handler combination certified by the Air-Conditioning, Heating, and Refrigeration Institute to deliver its rated efficiency together. Mixing unmatched components is how a 'SEER2 16 system' quietly performs like a 13. Any install quote should name the AHRI certificate number — ask for it.
Air Balancing: Adjusting dampers and registers so each room receives the airflow the duct design intended. The fix for the classic Baldwin County complaint — a bonus room over the garage that never cools while the hallway freezes. Real balancing works from measured airflow, not guesswork at the vents.
Air Filter: The disposable or washable filter protecting the blower and coil from dust — and your lungs from what the return duct picks up. Check monthly during Gulf Coast cooling season; a choked filter raises static pressure, freezes coils, and is the cheapest 'repair' in HVAC. Filtration strength is rated by MERV (see below).
Air Handler: The indoor unit that contains the blower motor and (usually) the evaporator coil. It moves conditioned air through your ductwork. In a heat pump system the air handler also houses the auxiliary heat strips for cold-snap backup.
Auxiliary Heat (Heat Strips): Electric resistance elements inside a heat pump's air handler that back up the heat pump when outdoor temperatures drop or the system is defrosting. Seeing 'aux heat' on the thermostat during a Baldwin County cold snap is normal — briefly. Aux heat running for hours costs several times what heat-pump heat costs, and usually signals a problem worth a service call.

B

Blower Motor (ECM): The motor that pushes air through your ducts. Older units use single-speed PSC motors; modern equipment uses ECMs (electronically commutated motors) that ramp smoothly, use less power, and hold airflow steady as filters load up. A failing blower shows up as weak airflow, humming, or a system that runs but barely moves air.
BTU: British Thermal Unit. The unit of heating or cooling capacity. One BTU is the energy needed to raise one pound of water by 1°F. A 36,000 BTU/hr (3-ton) AC removes that much heat from your home each hour. Sizing matters — oversized AC units short-cycle and dehumidify poorly.

C

Capacitor: An electrical component that stores and releases the surge of energy needed to start the compressor and fan motor. Capacitors are the single most common AC failure in coastal Alabama — humidity and heat both shorten their life. A weak capacitor causes hard starts, hums, or no-start conditions.
CFM: Cubic Feet per Minute — the measure of airflow. Residential cooling wants roughly 350–400 CFM per ton of capacity, and in a humid climate the low end of that band often dehumidifies better. Ducts, filter, and blower all have to support the target CFM; when they don't, efficiency and comfort both fall.
Coastal-Grade Equipment: Equipment built or treated for salt-air environments: corrosion-resistant coil coatings, marine-grade fasteners, sealed electrical compartments. Near the Gulf or Mobile Bay, standard outdoor units corrode years ahead of schedule — coastal-grade costs more up front and earns it back in service life. Air Solutions installs coastal-grade equipment within ~5 miles of the Gulf.
Compressor: The heart of the AC system — sits inside the outdoor unit. It pressurizes refrigerant to enable heat transfer. Compressor failure is the most expensive AC repair (often $1,500–$3,500); when it goes on a 10+ year-old system, replacement usually wins on the math.
Condensate Drain: The PVC line that carries water away from the AC's evaporator coil. Clogged condensate drains are the #1 cause of summer water damage from HVAC systems in Baldwin County — Gulf Coast humidity dumps gallons of water into the drain pan daily during peak season.
Condenser: The outdoor unit. Contains the compressor, condenser coil, and condenser fan. Releases the heat absorbed from inside your home into the outside air. Coastal condensers need salt-air corrosion protection — Air Solutions installs coastal-grade equipment within ~5 miles of the Gulf.
Contactor: The heavy-duty electrical switch in the outdoor unit that connects power to the compressor and fan when the thermostat calls. Contacts pit and weld over years of cycling — a stuck contactor makes the outdoor unit run non-stop even with the thermostat off, and a burned one stops it cold. One of the most common, and cheapest, Gulf Coast repairs.
Cool Club: Air Solutions' annual maintenance membership. Covers two professional tune-ups a year (spring AC + fall heat pump), priority scheduling on repairs, 15% off all repairs, and 5% off new system installs.

D

Damper: A movable plate inside ductwork that throttles airflow to a branch. Manual dampers get set once during air balancing; motorized dampers open and close automatically in zoned systems. A slipped or stuck damper is a frequent culprit behind one mysteriously hot room.
Defrost Cycle: When a heat pump runs in heating mode below ~40°F, the outdoor coil ices over. The system periodically reverses to defrost it. You'll see steam off the outdoor unit; this is normal. Faulty defrost boards are a common heating-mode complaint in Baldwin County's mild winters.
Dehumidifier (Whole-House): A ducted unit that removes moisture from the whole home's air independent of cooling, holding indoor humidity in the 45–55% comfort band even when the AC isn't running. On the Gulf Coast this is the difference-maker for shoulder seasons — mild days when the AC barely runs but the air is swampy.
Dual-Fuel System: A heat pump paired with a gas furnace: the heat pump handles most heating, and the furnace takes over below a set balance point. Common in colder climates; in Baldwin County's mild winters the furnace half rarely earns its keep, so dual-fuel makes sense here only in a narrow set of homes that already have gas.
Duct Sealing (Mastic): Closing duct leaks with mastic paste or UL-181 foil tape at joints, boots, and plenum connections. The cloth 'duct tape' at the hardware store is — famously — the one thing duct tape is bad at; it dries and peels in attic heat. In our humidity, sealing matters double: return-side leaks pull hot, moist attic air into the system.
Ductless Mini-Split: A heat pump system that uses individual indoor units mounted on the wall or ceiling instead of central ductwork. Ideal for additions, garages, sunrooms, and historic homes without ducts. Each indoor 'head' is its own zone with independent temperature + humidity control.

E

EER2: Energy Efficiency Ratio (2023 test method). Where SEER2 averages efficiency across a whole season, EER2 measures it at a steady 95°F — which is to say, an August afternoon in Baldwin County. For long, hot cooling seasons like ours, EER2 is the honest number to compare alongside SEER2.
Emergency Heat: The thermostat setting that locks out the heat pump and runs the electric heat strips alone. It exists for when the heat pump itself is broken — not for cold days. Running 'em heat' by choice multiplies your heating cost; if the heat pump can't keep up on a normal Baldwin County winter day, that's a service call, not a switch flip.
Evaporator Coil: The indoor coil where refrigerant absorbs heat from your home's air. Sits above or below the air handler. Frozen evaporator coils (low refrigerant or restricted airflow) are a common AC repair call. Coil cleaning is part of every Air Solutions tune-up.

F

Float Switch (Condensate Safety Switch): A small switch in the drain pan or drain line that shuts the system off when condensate backs up, so the overflow trips a switch instead of soaking a ceiling. If your AC dies on a humid day and the air handler pan is full, the float switch may have just saved you a drywall repair. Clear the drain — don't bypass the switch.
FORTIFIED Home: A beyond-code construction standard from the Insurance Institute for Business & Home Safety (IBHS), common in coastal Alabama for wind resistance and insurance credits. It matters to HVAC because work that penetrates the roof or attic envelope must respect the designation — tell any contractor your home is FORTIFIED before work starts.

G

Gas Furnace: A heating appliance that burns natural gas or propane and pushes the heat through your ducts. The workhorse of northern winters; in Baldwin County most homes heat with heat pumps instead, and furnaces appear mainly in older homes and dual-fuel setups. Furnace efficiency is rated by AFUE (see above).

H

Hard Start Kit: A capacitor-and-relay assist that gives an aging compressor the extra torque to start cleanly instead of slamming against high pressure. A legitimate life-extender on older units with hard-starting symptoms — and a band-aid worth understanding as such: it buys time, it doesn't rebuild the compressor.
Heat Exchanger: The metal chamber inside a gas furnace that transfers combustion heat to your air while keeping the exhaust separate. A cracked heat exchanger can leak carbon monoxide into the airstream — it's the reason furnace inspections exist and the one HVAC finding that's never optional to address.
Heat Pump: An HVAC system that both heats and cools by moving heat (rather than burning fuel). In summer it works like an AC; in winter it reverses to pull heat from outside air into your home. The most common system type in coastal Alabama because our winters rarely get cold enough to need a furnace.
HSPF / HSPF2: Heating Seasonal Performance Factor. The heating-mode efficiency rating of a heat pump. HSPF2 (post-2023) is the updated test method — the numbers are slightly lower than the old HSPF for the same equipment, not because it's worse, just because the test changed. Higher = more efficient.
HVAC: Heating, Ventilation, and Air Conditioning. The umbrella term for the equipment that controls the temperature, humidity, and air quality in your home. In residential coastal Alabama, 'HVAC' usually means a heat pump or AC + furnace combination.

I

Indoor Air Quality (IAQ): The collective health of the air inside your home — humidity, particulates (dust, pollen, mold spores), VOCs, and CO. Gulf Coast homes face chronic humidity that tips into mold territory if dehumidification isn't sized right. IAQ solutions: whole-house dehumidifiers, UV coil sterilization, MERV upgrades.
Inverter Compressor: A compressor that varies its speed continuously instead of switching on and off — the technology behind 'variable-capacity' systems. Long, low, steady run times are exactly what humid climates want: better moisture removal, quieter operation, smaller power draw. The premium equipment tier for a reason.

L

Latent Load: The share of the cooling job that goes to removing moisture rather than lowering temperature. On the Gulf Coast latent load is enormous — a big part of what your AC does all summer is wring water out of the air. It's why oversized systems fail here: they cool the air fast, shut off, and never run long enough to dehumidify.
Line Set: The pair of copper refrigerant lines connecting the outdoor and indoor units — an insulated suction line and a narrower liquid line. At replacement time, existing line sets are reused only if they're the right size and clean; contaminated or undersized lines get replaced, which is one of the honest line items on an install quote.

M

Manual D: The industry standard for duct design — Manual J's sibling. Manual J calculates how much heating and cooling the house needs; Manual D designs ductwork that can actually deliver it, sizing trunks and branches for target airflow at reasonable static pressure. Full duct replacements should be designed to Manual D, not copied from whatever was there.
Manual J: The HVAC industry's standard load-calculation method for sizing equipment. Accounts for square footage, ceiling height, insulation R-values, window orientation, infiltration, and local climate data. Air Solutions runs a Manual J on every install — sized to your actual house, not a ductwork-area shortcut.
MERV Rating: Minimum Efficiency Reporting Value. The filtration rating scale (1–16). MERV 8 catches dust + pollen, MERV 11 adds pet dander + mold spores, MERV 13 adds bacteria + smoke particles. Higher MERV = better filtration but more airflow restriction — the system has to be sized for it.

P

Package Unit: An all-in-one system where the compressor, coils, and blower live in a single outdoor cabinet — no separate indoor unit. Common on slab homes, manufactured homes, and small commercial buildings. Everything being outdoors makes coastal corrosion protection matter even more.
Plenum: The sheet-metal box that connects the air handler to the duct system — a supply plenum feeding the trunks, and a return plenum collecting air coming back. Leaks at the plenum are worth finding first when sealing ducts: they're the highest-pressure joints in the whole system.

R

R-22: The refrigerant in most systems installed before 2010, phased out of US production in 2020. A leaking R-22 system can only be recharged with reclaimed refrigerant at scarcity prices, which is why a significant R-22 repair is almost always a replacement conversation instead.
R-410A: The refrigerant used in most US residential AC + heat pump systems installed 2010–2025. Being phased out in favor of R-32 and R-454B (lower global-warming-potential refrigerants). R-410A repairs are still standard but new installs in 2026+ increasingly use R-32 or R-454B.
R-32 / R-454B: The next-generation low-GWP refrigerants replacing R-410A in new installs. Both are mildly flammable (A2L classification) — modern equipment is engineered around this safely. Lower environmental impact, comparable performance.
Refrigerant: The fluid that absorbs heat at the indoor coil and releases it at the outdoor coil. AC and heat pump systems are sealed — they don't 'use up' refrigerant. If you're low, there's a leak that needs to be found and fixed before recharging. Top-offs without leak repair are bad practice.
Relative Humidity: The percentage of moisture the air holds versus what it could hold at its temperature. Baldwin County summers run 80–90% outdoors; the indoor comfort-and-mold-prevention band is roughly 45–55%. If your home reads above 60% with the AC running, something in the system — sizing, airflow, runtime — isn't doing its dehumidification job.
Return Air: The grille and duct path that pulls house air back to the air handler to be conditioned again. Undersized returns are epidemic in older homes — the system suffocates, static pressure climbs, and rooms starve for supply air. More or bigger returns are often the cheapest comfort upgrade on the menu.
Reversing Valve: The component that lets a heat pump switch between cooling mode and heating mode. When it fails, the heat pump gets stuck in one mode (usually cooling — bad in January). Reversing-valve replacement is a meaningful repair, around $700–$1,200.

S

Salt-Air Corrosion: The slow chemical attack of airborne salt on coil fins, cabinets, fasteners, and electrical contacts — the tax every outdoor unit near the Gulf or Mobile Bay pays. It's why equipment near the water fails years earlier than the same model inland, and why coastal-grade coatings and an occasional fresh-water coil rinse are worth it.
SEER / SEER2: Seasonal Energy Efficiency Ratio. The cooling-mode efficiency rating of an AC or heat pump. As of 2023, SEER2 replaced SEER (updated test method, slightly lower numbers for the same equipment). New residential systems run SEER2 14–22; higher = more efficient + lower utility bills.
Short Cycling: When an AC turns on and off rapidly without completing a full cooling cycle. Common causes: oversized equipment, low refrigerant, dirty coil, faulty thermostat. Short cycling shortens equipment life and prevents proper dehumidification — a real problem in humid Baldwin County.
Smart Thermostat: A connected thermostat with scheduling, remote control, and usually a humidity readout — genuinely useful on the Gulf Coast for watching indoor humidity, not just temperature. One caution: heat pumps with auxiliary heat need the right thermostat configuration, or a 'smart' schedule can quietly run the expensive heat strips.
Split System: The standard residential arrangement: an outdoor unit (condenser) and an indoor unit (air handler, or furnace + coil) connected by a line set. 'Split' just distinguishes it from a package unit, where everything lives outside in one cabinet.
Static Pressure: The pressure pushing against the blower motor as it forces air through your ductwork + filter. High static pressure (undersized ducts, dirty filter, kinked flex) makes the system work harder, raises bills, and shortens motor life. Air Solutions checks static pressure on every install + tune-up.
Subcooling: A diagnostic measurement (in °F) that tells a tech how much refrigerant is in the system. Combined with superheat, it's how a competent HVAC tech actually verifies a system is properly charged — not just by guessing or topping off.
Superheat: The other diagnostic measurement (in °F) used alongside subcooling to verify refrigerant charge. Wrong superheat = compressor damage over time. Any tech recharging a system without measuring both is guessing.
Surge Protector (HVAC): A hard-wired protector at the outdoor disconnect or panel that absorbs voltage spikes before they reach the system's control board and compressor. On the Gulf Coast — thunderstorm country, plus hurricane-season grid restarts — it's cheap insurance for some of the most expensive electronics in the house.

T

Thermostatic Expansion Valve (TXV): The valve that meters refrigerant flow into the evaporator coil based on cooling demand. Modern systems use TXVs for efficiency. Failed TXVs cause poor cooling, frozen coils, or short cycling. Repair is moderate cost (~$400–$700).
Ton (HVAC): The traditional unit of HVAC capacity. 1 ton = 12,000 BTU/hr. Most Baldwin County homes need 2–5 tons depending on size and insulation. 'Ton' has nothing to do with weight — it dates from when AC capacity was compared to the cooling effect of a ton of melting ice.
Two-Stage System: Equipment with a high and a low output stage instead of just on/off. It spends most of its life on low — longer, gentler cycles that dehumidify better and hold temperature steadier. The sensible middle tier between single-stage and fully variable-speed equipment in a humid climate.

U

UV Coil Light: A germicidal UV-C lamp mounted at the evaporator coil to keep biological growth from colonizing the one spot in your house that's cool, wet, and dark all summer. In Gulf Coast humidity, coils grow things — the lamp keeps the coil clean, the airflow open, and the musty 'dirty sock' smell away.

V

Variable Speed: Equipment (compressor or blower) that runs at multiple speeds instead of just on/off. Variable-speed systems run quieter, dehumidify better, and use less power. The premium tier in residential equipment — strongly worth it in humid Gulf Coast climates.
Ventilation: The V in HVAC — the controlled introduction of outdoor air. In dry climates, more is better; on the Gulf Coast every cubic foot of outdoor air arrives carrying moisture your system must remove, so ventilation here should be deliberate (right-sized, sometimes with dedicated dehumidification), not accidental through leaky ducts and gaps.

W

Warranty (Parts vs. Labor): Two different promises. The manufacturer's parts warranty (commonly 10 years when the equipment is registered) covers the component; the contractor's labor warranty covers the work of replacing it. Fine print that bites: most manufacturer warranties require licensed installation and can be voided by an unlicensed one — one more reason the license number belongs on the quote.

Z

Zoning: An HVAC setup with multiple thermostats controlling separate areas of the home via dampers in the ductwork. Lets you cool the bedrooms at night without freezing the unused first floor. Mini-splits have native zoning; central systems can be zoned with retrofit dampers.