HVAC Glossary
HVAC terms, in plain English
Quotes and product pages are full of acronyms. Here’s what the important ones mean for Des Moines, IA homeowners — no sales spin.
Start here
What do HVAC terms like SEER2 and AFUE actually mean?
Three terms cover most decisions: SEER2 rates cooling efficiency (higher uses less electricity), AFUE rates how much furnace fuel becomes heat (96% means 96 cents of every dollar), and tonnage is cooling capacity, not weight (1 ton = 12,000 BTU per hour). The rest of this glossary fills in the equipment, refrigerant, and sizing terms you’ll see on a Des Moines quote.
Efficiency ratings
- SEER2
- Seasonal Energy Efficiency Ratio 2 — the cooling efficiency rating for air conditioners and heat pumps under the 2023 test method. A higher SEER2 means the system uses less electricity to deliver the same cooling.
- AFUE
- Annual Fuel Utilization Efficiency — how much of a furnace's fuel becomes usable heat. A 96% AFUE furnace turns 96 cents of every fuel dollar into heat; the rest goes up the flue.
- HSPF2 (HSPF)
- Heating Seasonal Performance Factor 2 — the heating efficiency rating for a heat pump (HSPF is the older version). A higher number means more heat per unit of electricity.
- MERV
- Minimum Efficiency Reporting Value — an air filter's rating. Higher MERV traps smaller particles, but too high a rating can restrict airflow if the system isn't designed for it.
Equipment types
- Air Conditioner
- An outdoor condenser plus an indoor coil that removes heat from your home to cool it. It cools only, so it's paired with a furnace for heat.
- Furnace
- An appliance that burns fuel (usually natural gas in Iowa) to produce heat, which a blower pushes through your ducts.
- Heat Pump
- A system that moves heat rather than burning fuel. It cools in summer and reverses to heat in winter, all from one outdoor unit.
- Ductless Mini-Split
- A heat pump with an outdoor unit and one or more wall- or ceiling-mounted indoor heads. No ductwork needed — ideal for additions, finished basements, or zoning.
- Two-Stage / Variable-Speed
- Equipment that can run at partial capacity instead of only full blast, giving steadier temperatures, better humidity control, and lower energy use.
- Dual-Fuel / Hybrid
- A heat pump paired with a gas furnace. The heat pump handles most of the season efficiently and the furnace takes over in deep, sub-zero cold — a popular Iowa setup.
Refrigerants
- R-22
- An older refrigerant that has been phased out. Recharging a leaking R-22 system is expensive and increasingly hard, which often pushes older units toward replacement.
- R-410A
- The refrigerant in most recent systems, now being phased down for its higher global-warming potential.
- R-454B
- A newer, lower global-warming-potential refrigerant replacing R-410A in much new equipment. It's a mildly flammable (A2L) refrigerant handled under updated safety standards.
Sizing & airflow
- Tonnage
- Cooling capacity, not weight. One ton equals 12,000 BTU of heat removed per hour. A typical home needs roughly 2–4 tons depending on size and construction.
- BTU
- British Thermal Unit — the basic measure of heat. HVAC capacity is rated in BTU per hour for both heating and cooling.
- Load Calculation (Manual J)
- The industry-standard method for sizing equipment to a specific home, accounting for square footage, windows, insulation, orientation, and air leakage — not just a rule of thumb.
- Static Pressure
- The resistance to airflow inside your duct system. High static pressure (from undersized ducts or a clogged filter) strains the blower and lowers performance.
- Short-Cycling
- When a system turns on and off too frequently. It's often caused by oversized equipment, a dirty filter, or a control problem, and it wears parts out faster.
Iowa local truth
“A bigger tonnage number always means better cooling.” Not in an Iowa summer. An oversized system short-cycles — it cools the air fast but shuts off before it pulls out humidity, leaving your home cold and clammy. Right-sizing with a Manual J load calculation matters far more than a big number.
How these ratings connect
Efficiency ratings (SEER2, AFUE, HSPF2) tell you how much energy a system uses. Capacity terms (tonnage, BTU) tell you how much heating or cooling it delivers. Sizing (Manual J) matches capacity to your home, and refrigerant type tells you how current the cooling technology is. A good system gets all three right: correctly sized, efficient enough for your budget, and using a current refrigerant.
Common questions
What does SEER2 mean on an air conditioner?
SEER2 is the cooling efficiency rating under the 2023 test method. A higher SEER2 means the air conditioner or heat pump uses less electricity to deliver the same amount of cooling over a season.
Is tonnage how much my AC weighs?
No. Tonnage is cooling capacity, not weight. One ton equals 12,000 BTU of heat removed per hour, and most homes need roughly 2 to 4 tons depending on size and construction.
What is replacing R-410A refrigerant?
Newer low global-warming-potential refrigerants such as R-454B are replacing R-410A in much of the new equipment sold today. They're handled under updated safety standards because they're mildly flammable (A2L).