HVAC Glossary: Terms and Definitions for Panama City Homeowners

Sizing and capacity

BTU and BTU/h

A British thermal unit is the heat needed to raise one pound of water by one degree Fahrenheit. Air conditioners are rated in BTU per hour: how much heat they can move out of the house every hour. A "36,000 BTU" unit and a "3 ton" unit are the same thing. In Bay County: the sizing calculator gives a cooling load in BTU/h and tons side by side.

Ton (of cooling)

12,000 BTU per hour, the rate at which a 2,000 lb block of ice absorbs heat as it melts over 24 hours. Residential equipment is sold in half-ton steps, and manufacturers' residential lines typically run 1.5 to 5 tons. The number on the label is a nominal rating, not the capacity the unit delivers at Panama City's design conditions (see nominal capacity).

Load calculation

The engineering estimate of how much heat enters a specific house on a design day, from walls, roof, windows, air leakage, people, appliances and ducts. It is the number a system should be sized to. In Florida the accepted method is ACCA Manual J; UF/IFAS tells homeowners the load "must be calculated, not just estimated based on square feet."

Manual J

The Air Conditioning Contractors of America's residential load calculation standard (8th edition, ANSI-recognized). It works room by room from the building's actual construction and orientation. Florida's energy code requires equipment to be sized from a Manual J (or an approved equivalent) for new systems. What a proper report contains, and how to read one, is covered in the Manual J guide.

Manual S

ACCA's equipment selection standard: the step after Manual J, where a specific unit is matched to the calculated load using the manufacturer's expanded performance data. ENERGY STAR's design supplement lists the selection windows: single-speed 90 to 115% of load, two-speed 90 to 120%, variable-speed 90 to 130%. Florida's code (8th Edition) caps total cooling capacity at 115% regardless.

Manual D

ACCA's duct design standard: sizing the supply and return ducts so the selected equipment can actually move the air it was rated for. A right-sized unit on undersized or leaky ducts underperforms, which is why ductwork deserves its own page.

Sensible load

The part of the cooling load that is pure temperature: heat coming through the roof, walls and glass, and from people and appliances, that the system must remove to hold the thermostat setting.

Latent load

The moisture part of the cooling load: water vapor that must be condensed out of the air to keep the house dry. The Florida Building Commission's energy and humidity forum put the latent share of seasonal cooling energy at about 20% for a Florida home, against roughly zero for the same house in Phoenix. It is why sizing and run time matter more here than in a dry climate; see humidity and your AC.

Sensible heat ratio (SHR)

The share of a unit's total capacity that goes to lowering temperature rather than removing moisture. A unit with an SHR of 0.75 spends a quarter of its capacity on dehumidification. UF/IFAS warns that "many high SEER units have poorer humidity removal capacity, so verify the SHR before purchasing." In Bay County, more latent capacity (a lower SHR) is generally worth having.

Design conditions

The outdoor temperature and humidity a load calculation assumes. Manual J uses the 1% condition, exceeded for roughly 88 hours a year, not the hottest day on record. NOAA's engineering data for Tyndall AFB (1988 to 2017) puts Panama City's 1% cooling design at 90°F dry bulb with a 79°F coincident wet bulb. Florida's code sets the indoor cooling design at no lower than 75°F.

Wet bulb temperature

The temperature a thermometer reads when its bulb is kept wet and air passes over it; the closer it is to the ordinary (dry bulb) reading, the more humid the air. A 79°F wet bulb against a 90°F dry bulb, Panama City's design pair, is a very humid design day and the reason latent capacity matters here.

Dew point

The temperature at which air becomes saturated and moisture condenses. The Florida State Climatologist describes typical summer dew points in the high 60s to low 70s. Building America cites a summer dew point above 55°F as the point where separate dehumidification may be needed.

Cooling degree days (CDD)

A measure of how much cooling a climate demands: for each day, the number of degrees the mean temperature sits above 65°F, summed over the year. Tyndall AFB (1988 to 2017) records about 2,745 cooling degree days a year against roughly 1,450 heating degree days, which is why heat pumps here are sized on the cooling load.

Rule of thumb (square feet per ton)

Sizing by floor area alone. A 1996 Florida Solar Energy Center survey found contractors who used it quoted anywhere from 350 to 700 sq ft per ton, with 500 the most common. The Department of Energy says rules of thumb produce "excessively oversized systems," and 40 Manual J results published by the building-science firm Energy Vanguard averaged more than 1,400 sq ft per ton. The calculator uses the convention openly and tells you which way it is biased.

Oversizing

Installing more cooling capacity than the load calls for. In a humid climate the unit satisfies the thermostat before it has run long enough to dry the air. An FSEC study of 368 new Florida homes found more than half had capacity above 120% of their Manual J load, and 38.5% of surveyed Florida contractors admitted oversizing on purpose, most often at the customer's request.

Short cycling

A system starting and stopping in brief bursts instead of running long, steady cycles. The usual cause is oversizing; the results are poor humidity control, more wear from repeated starts, and, in Florida field data, 9% more cooling energy for units oversized by 20 to 50%.

Nominal capacity vs. AHRI rating

The "3 ton" on a label is a nominal figure from a standard rating test (95°F outdoors, 80°F indoors, 67°F wet bulb). Real capacity at Panama City's design conditions, split into sensible and latent, comes from the manufacturer's expanded performance tables. Florida's code states the AHRI nominal value "shall not be used for equipment sizing."

Occupant load

The heat people add. Manual J counts occupants as the number of bedrooms plus one, at 230 BTU/h sensible and 200 BTU/h latent each, so a four-bedroom home adds about 2,150 BTU/h. That is small next to the roof, windows and ducts, which is why head count rarely changes the answer.

Efficiency and ratings

SEER2

Seasonal Energy Efficiency Ratio, version 2: cooling delivered per unit of electricity over a simulated season, measured under the test procedure that replaced SEER in 2023. It describes efficiency, not size. Since January 1, 2023, split-system air conditioners installed in Florida (Southeast region) must be at least 14.3 SEER2 below 45,000 BTU/h and 13.8 SEER2 at or above; ENERGY STAR starts at 15.3. DOE notes SEER and SEER2 "are not directly comparable."

EER2

Energy Efficiency Ratio, version 2: efficiency at a single hot test condition rather than across a season. It is the better indicator of how a unit performs on a 90°F Bay County afternoon, and it appears on the same AHRI certificate as SEER2.

HSPF2

Heating Seasonal Performance Factor, version 2: the heating-side efficiency of a heat pump. The federal minimum for split heat pumps is 7.5 HSPF2 (6.7 for packaged units). With fewer than 1,500 heating degree days a year, it matters less in Panama City than SEER2 and SHR do.

ENERGY STAR

The EPA and DOE certification for equipment that beats the federal minimum by a set margin; for split air conditioners the current threshold is 15.3 SEER2. ENERGY STAR also publishes sizing guidance, including quantified shade and sun adjustments, though written for room units only.

AHRI certificate

The document from the Air-Conditioning, Heating and Refrigeration Institute that confirms a specific outdoor unit, indoor coil and air handler combination and its rated SEER2, EER2 and capacity. Ask for it on any quote: the rating belongs to the matched combination, not to the outdoor unit alone.

Single-stage, two-stage and variable-speed

How many output levels a compressor has. Single-stage is on or off. Two-stage has a low and a high. Variable-speed (inverter) equipment modulates across a wide range and can run at low capacity for hours, which is the behavior humidity control in Bay County rewards; it is why Manual S allows a wider selection window for it.

Equipment and parts

Split system

The usual residential layout: an outdoor unit (condenser or heat pump) connected by refrigerant lines to an indoor air handler or furnace with an evaporator coil. It is the most common layout in single-family homes.

Packaged unit

All the components in one cabinet, usually on a slab or roof, with ducts running straight into the house. Common on manufactured homes and small commercial buildings. Federal minimums are lower (13.4 SEER2) and are enforced by manufacture date rather than installation date.

Heat pump

An air conditioner with a reversing valve, so it can move heat into the house in winter as well as out of it in summer. Florida's code sizes heat pumps on the cooling load with the same 115% ceiling. See heating and heat pumps.

Condenser (outdoor unit)

The cabinet outside holding the compressor, the condenser coil and a fan. It rejects the heat collected indoors. It is also the component that lives in the salt air, which is why coastal specification starts here; see salt air and your AC.

Compressor

The pump at the heart of the system, which pressurizes refrigerant so it can carry heat outdoors. It is usually the most expensive single part, and the one most exposed to the wear of repeated starts from short cycling.

Evaporator coil

The indoor coil, where refrigerant absorbs heat and moisture condenses out of the passing air. UF/IFAS identifies dirt on this coil as the single most common cause of poor efficiency. It is also where formicary corrosion occurs.

Condenser coil

The outdoor coil: thin aluminum fins on copper tubing, or all-aluminum on newer designs, that shed the house's heat to the outside air. Near the Gulf it is the part most exposed to salt.

Air handler

The indoor cabinet containing the blower and the evaporator coil (and electric heat strips, if fitted). It is usually in a closet, the garage or the attic; in the attic, any condensate problem becomes a ceiling problem.

Blower and fan speed

The indoor fan that moves air across the coil and through the ducts. Its speed setting affects both capacity and dehumidification: too much airflow across the coil removes less moisture. Building America advises considering fan speed before upsizing equipment.

Capacitor

A cylindrical electrical component that gives the compressor and fan motors their starting and running boost. A common failure point and an inexpensive repair. Electrical components in the outdoor cabinet share the salt exposure of everything else out there, though field data on their life near the coast is thin.

Contactor

The electrical switch that connects power to the compressor and outdoor fan each time the thermostat calls for cooling. A contactor whose contacts have pitted or welded can leave the outdoor unit running when the thermostat is satisfied, or not starting at all. Like the capacitor, a routine repair item rather than a reason to replace a system.

Refrigerant line set

The two copper lines running between the outdoor and indoor units; the larger suction line is insulated. Where copper tubing meets an aluminum coil, the brazed joint is a dissimilar-metal point, which Carrier's coastal units sleeve in heat-shrink.

Condensate drain and drain pan

The moisture the evaporator coil pulls from the air collects in a pan and leaves through a drain line. Heavy dehumidification means heavy condensate; DOE advises passing a stiff wire through the drain channels occasionally. Algae in the warm line is a common blockage.

Float switch

A safety device in the drain pan or line that shuts the system down when condensate backs up, before it overflows. A system that stops on a hot day with water in the pan has usually been saved by this switch, not broken by it.

Air filter and MERV

The filter protects the coil and blower. MERV is its efficiency rating (higher catches smaller particles, but restricts airflow more). DOE recommends checking every month or two in the cooling season, more often in constant use, and notes a clean filter can lower consumption by 5 to 15%.

Thermostat and setpoint

The control, and the temperature it is asked to hold. Lowering the setpoint does not make a system cool faster; it makes it run longer, which in a humid climate is often what you want. A home that reads 74°F and feels sticky has a humidity problem (sizing, airflow, duct leakage or the need for a dehumidifier), not a thermostat problem.

Coastal and humidity

Coastal-rated equipment

A manufacturer's designation for units built for salt air: coated or all-aluminum coils, a protected cabinet, sealed brazed joints. Carrier's coastal line carries a five-year parts warranty where the failure mechanism is seacoast corrosion; Trane offers epoxy-coated models for sites within one mile of salt water. Standard warranties generally exclude corrosive atmospheres. Full detail in salt air and your AC.

Galvanic corrosion

Corrosion that occurs where two different metals touch in the presence of an electrolyte: the less noble metal (aluminum, against copper) becomes the anode and wastes away. Humid salt air dissolving onto a copper-aluminum coil supplies the electrolyte.

Chloride (pitting) corrosion

Localized attack on aluminum where chloride ions disrupt the protective oxide film. Published work in the ASHRAE Journal notes that aluminum alloys are susceptible to it, and peer-reviewed exposure studies show the rate falling sharply with distance from the shoreline while remaining measurable miles inland.

Formicary (ant-nest) corrosion

A different problem, often confused with salt damage: pinhole leaks in indoor copper coils caused by organic acids from household chemicals and building materials. It occurs indoors, not in the salt air, and ASHRAE notes it is rarely found in marine systems.

E-coat, epoxy and factory coil coatings

Protective layers applied to coils to slow salt attack. Daikin's Blue Fin coating is rated for 1,000-plus hours of salt spray; Trane offers epoxy-coated models; Carrier uses zinc-clad all-aluminum coils in its coastal line. A coating is a delay, not a cure: rinsing still matters.

Relative humidity (RH)

How much moisture the air holds as a share of what it could hold at that temperature. The EPA recommends keeping indoor RH below 60%, ideally 30 to 50%, to limit mold; FSEC treats a sustained 70% as the level where mold growth becomes likely. Panama City has no official outdoor RH normal; the nearest station, Apalachicola, averages 86 to 88% on July and August mornings.

Whole-house dehumidifier

A ducted unit that removes moisture independently of cooling. NREL found that in humid climates the air conditioner alone meets only 50 to 65% of the moisture load at part-load conditions, so a right-sized system that still cannot hold 60% RH in a shoulder month is a dehumidifier problem, not a reason for a bigger unit. See humidity and your AC.

Part load

Any hour when the house needs less than the system's full capacity, which in Panama City is most of the summer: NREL modeling found a code-built home in Houston needs its AC to run only about 35% of the time at the 1% dew-point condition. Humidity problems live at part load, not on the hottest day.

Hurricane Michael (2018) and equipment age

The Category 5 storm that made landfall near Mexico Beach and Tyndall AFB on October 10, 2018, damaging more than 45,000 structures in Bay County according to the National Hurricane Center. Much of the county's housing was repaired or rebuilt afterwards, so a large share of its HVAC equipment is likely to date from 2019 or later, and homes rebuilt to the current energy code often need less cooling than the house they replaced.

Ducts and airflow

Duct leakage

Conditioned air escaping from supply ducts, or attic air being drawn into return ducts, through joints and holes. In a Florida Solar Energy Center field study of 24 homes, duct repair alone cut air-conditioning energy use by 18%. Covered in attic ductwork in Florida homes.

Return leak

The worse kind of duct leak: a return duct in a 120°F attic pulling in hot, humid attic air and feeding it to the coil. FSEC modeling found a 15% return leak from the attic can cut a system's effective capacity and efficiency by half.

R-8 duct insulation

The insulation level Florida's energy code requires on ducts in an attic. The number is thermal resistance; older homes may have thinner duct insulation, or insulation that has slumped off entirely.

Duct leakage test

Pressurizing the duct system with a calibrated fan to measure how much air escapes. It is the only way to know whether a comfort problem is a sizing problem or a duct problem, and it belongs in any replacement quote.

Conditioned space

The part of the house the system heats and cools: the figure to use for any square-footage estimate. Leave out the garage, unconditioned porches and attic. Ducts inside the conditioned space lose far less than ducts in the attic.

Static pressure

The resistance the blower works against to push air through filters, coil and ducts. High static pressure (from a restrictive filter, undersized returns or flex duct crushed in an attic) cuts airflow and capacity. A technician measures it in inches of water column. See attic ductwork.

Refrigerants, codes and permits

R-22

The refrigerant common in systems installed before 2010. The EPA banned new R-22 equipment in 2010 and ended production and import in 2020; servicing relies on recovered or stockpiled supply. Owners are not required to replace R-22 systems, but a major R-22 repair is usually poor value.

R-410A

The refrigerant that replaced R-22, with a global warming potential of 2,088. Under the EPA's Technology Transitions rule, new systems using refrigerants above 700 GWP were restricted from January 1, 2025. A May 2026 EPA rule removed the installation deadline for R-410A systems whose components were made or imported before 2025, so remaining stock can still be installed. Existing R-410A systems can still be serviced, though AHRI warns refrigerant prices are likely to rise. See the refrigerant change explained.

R-454B and R-32

The lower-GWP refrigerants in new equipment: R-454B (GWP 466) in Carrier, Bryant, Lennox ducted, Rheem, York and Trane; R-32 (GWP 675) in Daikin, Goodman and Amana. Both are A2L class.

A2L

The safety classification for the new refrigerants: low toxicity, mildly flammable. It is why R-454B cannot simply be put into an existing R-410A system, and why new equipment is designed and installed to different rules.

GWP (global warming potential)

How much heat a gas traps over 100 years compared with carbon dioxide. R-410A is 2,088; R-454B is 466; R-32 is 675. The EPA threshold that triggered the current transition is 700.

Florida Building Code, Energy Conservation (FBC-EC)

The state energy code, 8th Edition (2023), in force since December 31, 2023. Section R403.7.1 requires Manual S sizing from a Manual J load, prohibits safety factors, bars the AHRI nominal rating from sizing and caps cooling capacity at 115% of the calculated load. The 9th Edition (2026) restructures that limit into Manual S-style maxima by equipment type, adds a 1.20 times cap on sensible capacity and requires latent capacity to meet the latent load.

Florida Statute 553.912

The statute on air conditioners. It states the Legislature's intent that replacement systems be installed with "equipment sizing analysis and duct inspection," but exempts existing equipment from sizing requirements, which is why change-out enforcement varies by building department.

Change-out and permit

Trade shorthand for replacing a system in an existing home. A mechanical permit is normally required for a change-out in Florida; whether the building department also demands a load calculation varies by jurisdiction. Bay County Builders Services and the City of Panama City Building Department are the offices to ask.

DBPR license (CAC / CMC)

Florida's Department of Business and Professional Regulation licenses HVAC contractors as Class A or Class B air conditioning contractors (Class B limited by system size) or as mechanical contractors. Certified licenses carry a CAC or CMC prefix. Check the number on the DBPR website before any work is agreed.