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HVAC, Plumbing & Electrical Glossary
Plain-English definitions of home HVAC, plumbing, and electrical terms every Mid-Missouri homeowner should know—SEER2, AFUE, GFCI, PSI, and more.
HVAC terms
- AFUE (Annual Fuel Utilization Efficiency) #afue
- A percentage measuring how efficiently a furnace turns fuel into heat over a year. A 90% AFUE furnace converts 90% of its fuel to heat. Higher AFUE means lower heating bills; modern high-efficiency furnaces run 90–98%.
- Air Handler #air-handler
- The indoor unit that circulates conditioned air through your ducts. It houses the blower and evaporator coil and pairs with an outdoor unit or heat pump.
- BTU (British Thermal Unit) #btu
- The standard unit for heating and cooling capacity. Equipment is sized in BTUs; 12,000 BTUs equals one ton of cooling.
- Compressor #compressor
- The heart of an AC or heat pump, in the outdoor unit—it pressurizes refrigerant to move heat. Compressor failure is one of the most expensive HVAC repairs.
- Condenser #condenser
- The outdoor unit that releases heat pulled from inside your home. Keeping its coil clean and clear of debris is key to efficiency.
- Ductless / Mini-Split #ductless-mini-split
- A heating and cooling system with no ductwork—an outdoor unit feeds one or more indoor units. Ideal for additions, older homes, or room-by-room comfort.
- Evaporator Coil #evaporator-coil
- The indoor coil that absorbs heat from your home's air. When airflow drops or refrigerant is low, it can freeze and stop cooling. Why is my AC running but not cooling?
- Heat Exchanger #heat-exchanger
- The furnace part that transfers combustion heat to your air while keeping exhaust gases separate. A cracked heat exchanger is a carbon-monoxide safety issue.
- Heat Pump #heat-pump
- An all-in-one system that heats and cools by moving heat rather than making it—cooling in summer, reversing to heat in winter. Very efficient in moderate climates.
- MERV (Minimum Efficiency Reporting Value) #merv
- A 1–20 rating of how well an air filter captures particles. MERV 8–11 suits most homes; MERV 13+ filters finer particles but can restrict airflow on some systems. How often should you change your HVAC air filter?
- SEER2 (Seasonal Energy Efficiency Ratio 2) #seer2
- The current efficiency rating for AC and heat-pump cooling, tested under more realistic conditions than the old SEER. Higher SEER2 means lower cooling bills.
- Short Cycling #short-cycling
- When a system turns on and off too frequently without completing a cycle—often from an oversized unit, dirty filter, or thermostat issue. It wears out equipment and raises bills.
- Ton / Tonnage #ton-tonnage
- A measure of cooling capacity, not weight. One ton equals 12,000 BTUs per hour. Correct tonnage comes from a load calculation, not a guess.
- Load Calculation (Manual J) #load-calculation
- The industry-standard method for sizing HVAC equipment using square footage, insulation, windows, and climate—far more accurate than square footage alone.
Plumbing terms
- Backflow #backflow
- The unwanted reverse flow of water that can pull contaminants into your clean supply. Backflow preventers protect drinking water and are required on certain connections.
- Dip Tube #dip-tube
- The tube that sends incoming cold water to the bottom of a water heater tank. A broken dip tube mixes cold with hot at the top, so you run out of hot water fast. Why does my water heater run out of hot water so fast?
- Hard Water #hard-water
- Water high in dissolved minerals (calcium, magnesium). It causes scale buildup in pipes and water heaters and reduces appliance life—common in much of Mid-Missouri.
- PSI (Pounds per Square Inch) #psi
- The unit for water pressure. Most homes run best at 40–60 PSI; too high stresses pipes and fixtures, too low means weak flow.
- Sediment #sediment
- Mineral and debris buildup that settles in a water heater tank, reducing capacity and efficiency. Annual flushing helps prevent it. Water heater service
- Sump Pump #sump-pump
- A pump in a basement or crawlspace pit that removes collected groundwater to prevent flooding. A battery backup keeps it running during power outages.
- Tankless Water Heater #tankless-water-heater
- A unit that heats water on demand instead of storing it, delivering continuous hot water and saving space—ideal when demand outpaces a standard tank. Tankless water heater services
- Water Hammer #water-hammer
- The banging noise in pipes when flow stops suddenly. It signals pressure shock that can damage pipes and fittings over time; arrestors fix it.
- Water Softener #water-softener
- A system that removes hardness minerals to protect pipes, water heaters, and fixtures, and improve soap performance.
Electrical terms
- Ampere (Amp) #ampere
- The unit of electrical current. Circuits and panels are rated in amps (e.g., a 20-amp kitchen circuit, 200-amp home service) to safely carry a given load.
- Circuit Breaker #circuit-breaker
- A safety switch that cuts power when a circuit draws too much current or faults—protecting wiring from overheating. It's meant to trip; frequent tripping signals a problem. Why do my circuit breakers keep tripping?
- Electrical Panel (Load Center) #electrical-panel
- The hub that distributes power to your home's circuits. An undersized or aging panel can't keep up with modern demand and may need upgrading. Does your home need an electrical panel upgrade?
- GFCI (Ground Fault Circuit Interrupter) #gfci
- An outlet or breaker that shuts off power in milliseconds if it detects a ground fault—required near water (kitchens, baths, outdoors) to prevent shock.
- Grounding #grounding
- The safety path that directs stray electrical current harmlessly into the earth, protecting people and equipment from shock and surges.
- kWh (Kilowatt-Hour) #kwh
- The unit your utility bills by—1,000 watts used for one hour. Understanding kWh helps compare the running cost of appliances and systems.
- Short Circuit #short-circuit
- When a hot wire contacts a neutral or ground, causing a sudden surge that trips the breaker instantly—often signaled by a burning smell. A wiring issue for a pro. Electrical safety inspection
- Surge Protection (Whole-Home) #surge-protection
- A device at the panel that shields all your circuits from voltage spikes (from the grid or lightning), protecting HVAC boards, appliances, and electronics.
- Service (Amperage) #service-amperage
- The total electrical capacity coming into your home—commonly 100, 200, or 400 amps. Most modern homes need 200-amp service to run today's loads safely. Electrical panel upgrades
Common questions
What's the difference between SEER2 and AFUE?
SEER2 rates cooling efficiency (AC/heat pumps); AFUE rates heating efficiency (furnaces). Higher numbers mean lower bills in each.
What does "tonnage" mean in HVAC?
Cooling capacity, not weight—one ton equals 12,000 BTUs per hour. Homes typically need 2–5 tons.
Where are GFCI outlets required?
Near water—kitchens, bathrooms, garages, and outdoors—to protect against shock.
What water pressure should my home have?
Most homes run best at 40–60 PSI; too high stresses pipes, too low weakens flow.
Want the full explanations? Browse the Learning Center for homeowner guides on HVAC, plumbing, and electrical questions.