HVAC, Plumbing & Electrical Glossary
Every term we get asked about, defined in plain English. SEER vs SEER2. What AFUE actually measures. Why your hard water is destroying your water heater. Updated with 2026 standards.
47 terms across HVAC, plumbing, and electrical work — all written by a licensed Utah contractor.
HVAC
Furnaces, AC, heat pumps, ductwork, efficiency ratings, sizing.
SEER
SEER is the cooling-efficiency rating of an air conditioner or heat pump — the higher the SEER number, the less electricity it uses per ton of cooling delivered over a typical Utah summer.
AFUE
AFUE is the gas-furnace efficiency rating — it tells you what percentage of the fuel you pay for actually becomes usable heat in your home versus what escapes up the flue.
HSPF2
HSPF2 is the heating-efficiency rating of a heat pump — it measures how many BTUs of heat it delivers per watt-hour of electricity over a winter heating season.
Manual J Load Calculation
Manual J is the industry-standard whole-house heat-loss and heat-gain calculation that determines exactly how big your furnace and AC need to be — too big or too small both hurt comfort and efficiency.
Heat Pump
A heat pump is an electric HVAC system that moves heat instead of generating it — it cools your home in summer like an AC and heats it in winter by running the refrigerant cycle in reverse.
Tonnage
Tonnage is the cooling-capacity measurement of an AC or heat pump — 1 ton equals 12,000 BTU/hr of heat removal, which is what one ton of melting ice would absorb in a 24-hour period.
Static Pressure
Static pressure is the resistance your blower has to push against to move air through the duct system — too high and the blower struggles, efficiency drops, and the system runs hot.
Refrigerant
Refrigerant is the working fluid inside an AC or heat pump — it absorbs heat indoors and releases it outdoors as it cycles between liquid and gas states.
Ductwork
Ductwork is the metal or flexible tubing system that carries conditioned air from your furnace or air handler to each room and returns it for re-conditioning.
Duct Sealing
Duct sealing closes the gaps, holes, and leaky joints in your duct system so the conditioned air your HVAC produces actually reaches the rooms instead of escaping into the attic or crawlspace.
MERV Rating
MERV is the air-filter rating system — higher MERV catches smaller particles (better filtration) but also restricts airflow more, which can strain your HVAC system if you go too high without sizing the filter housing properly.
Two-Stage HVAC
Two-stage equipment can run at full capacity OR a lower ~60% capacity — using low stage most of the time gives better comfort, quieter operation, and lower bills than a single-stage unit.
Modulating Furnace
A modulating furnace varies its gas input continuously from about 35% to 100% to exactly match your home's heat loss — instead of cycling on and off, it just runs longer at lower output.
AC Capacitor
An AC capacitor is a cylindrical electrical component that stores a charge to help start the compressor and fan motors of your air conditioner — when one fails the unit hums but won't start, or shuts off after a few minutes.
Contactor
An HVAC contactor is an electrically-controlled switch inside your outdoor AC unit — when the thermostat calls for cooling, low-voltage signal closes the contactor and sends 240V to the compressor and fan.
AC Compressor
The compressor is the heart of your air conditioner or heat pump — it's the pump that circulates refrigerant through the system, and replacement is by far the most expensive HVAC repair.
Blower Motor
The blower motor is the fan motor inside your furnace or air handler that moves conditioned air through the ductwork — modern systems use variable-speed ECM motors for quieter operation and better humidity control.
ECM Motor
An ECM motor is a brushless DC blower motor with electronic speed control — it uses 30–60% less electricity than older PSC motors and runs much quieter at the low speeds where most of your HVAC system actually operates.
Flame Sensor
A flame sensor is a metal rod that confirms your gas furnace's burners actually lit — if it gets dirty (very common), the furnace ignites for a few seconds then shuts off, repeating until you have no heat.
Hot Surface Ignitor
A hot surface ignitor (HSI) is a silicon-carbide or silicon-nitride heating element inside your gas furnace that glows orange-hot to light the burners — replaced the old pilot light in modern furnaces.
Furnace Control Board
The control board is the small computer inside your furnace that orchestrates the entire heating sequence — it interprets the thermostat call, runs the ignitor, opens the gas valve, monitors safety switches, and runs the blower.
Gas Valve
The gas valve is a solenoid-controlled valve that opens to deliver natural gas to your furnace's burners — the control board energizes it after the ignitor is glowing, and a flame must prove within seconds or it shuts off.
High-Limit Switch
A high-limit switch is a safety thermostat inside your furnace that shuts off the burners if the heat exchanger gets dangerously hot — usually triggered by a clogged filter or blocked ducts, not an actual furnace problem.
Heat Exchanger
The heat exchanger is the sealed metal chamber inside your gas furnace where combustion gases heat one side and house air absorbs heat from the other side — a cracked heat exchanger can leak carbon monoxide and is a furnace-replacement-level repair.
TXV
A TXV is the metering device that controls refrigerant flow into your AC's indoor evaporator coil — it adjusts continuously based on cooling load, making the system more efficient than older fixed-orifice systems.
Plumbing
Water heaters, softeners, filtration, pressure, fittings, repairs.
Water Hardness
Water hardness is the amount of dissolved calcium and magnesium in your water, measured in grains per gallon (gpg) — most Utah cities deliver 12–28 gpg, well into the 'very hard' range.
Water Softener
A water softener is a tank-based ion-exchange system that swaps calcium and magnesium in hard water for sodium, eliminating scale buildup throughout the plumbing.
Reverse Osmosis
Reverse osmosis is a multi-stage water filtration system that forces water through a semi-permeable membrane to remove dissolved minerals, chemicals, and contaminants — typically installed under the kitchen sink for drinking water.
Tankless Water Heater
A tankless water heater heats water on demand as you turn on a hot-water tap, instead of constantly keeping 40–80 gallons hot in a storage tank.
Pressure Regulator
A pressure-reducing valve is a small device on the main water line that drops incoming city-water pressure (often 90–150 psi in Utah) down to a safe 55–75 psi for household plumbing.
Thermal Expansion Tank
A thermal expansion tank is a small bladder tank installed near the water heater that absorbs the water expansion when your heater heats cold water — preventing dangerous pressure buildup in closed plumbing systems.
PEX Tubing
PEX is a cross-linked polyethylene plastic pipe used for residential water supply lines — it's flexible, freeze-resistant, easier to install than copper, and has been the dominant Utah residential plumbing material since around 2005.
ABS Pipe
ABS is black plastic drain-waste-vent pipe used for residential plumbing — it's solvent-welded with one-step cement, performs well for sewer and vent piping, and is the standard Utah residential DWV material under code.
Plumbing Vent Stack
A vent stack is the vertical pipe extending from your home's drain system through the roof — it equalizes pressure so drains can flow freely and keeps sewer gases out of the living space.
P-Trap
A P-trap is the curved section of pipe under your sink or shower that holds a small water seal — that water plug stops sewer gases from coming back up through the drain into your living space.
Electrical
Panels, breakers, GFCI/AFCI, EV chargers, wiring, safety.
Main Electrical Panel
The main panel (or 'service panel,' 'load center,' 'breaker box') is the central electrical distribution point in your home — where utility power comes in, is metered, and is divided into the individual circuit breakers that protect each room and appliance.
AFCI and GFCI Protection
AFCI and GFCI are two types of advanced circuit breakers that protect against different electrical hazards — AFCI prevents fires from arcing wires, GFCI prevents shocks from ground faults.
EV Charger
A Level 2 EV charger is a 240-volt circuit and wall-mounted unit that adds 20–40 miles of range per hour of charging — about 5x faster than the 120V Level 1 cord that ships with most EVs.
Subpanel
A subpanel is a smaller electrical distribution panel fed from your main panel — used to extend service to a garage, basement, addition, or detached shop without rerouting every circuit back to the main.
Neutral Bar
The neutral bar is the metal bus inside your electrical panel where all the white (neutral) wires terminate — it must be bonded to ground only at the main service panel, never at a subpanel.
Electrical Grounding
Grounding is the safety system that connects your electrical panel to the earth via ground rods, water pipe, or building steel — it provides a low-impedance path for fault current to trip a breaker fast during a short circuit.
Service Disconnect
The service disconnect is the main breaker (or fused switch) that disconnects all power coming into your home — it's typically a 100A, 150A, or 200A breaker at the top of your electrical panel.
kW vs kWh
kW (kilowatt) is a rate of power — how fast you're using electricity right now. kWh (kilowatt-hour) is a quantity of energy — what you actually get billed for, based on how long that power flowed.
Amperage
Amperage is the rate of electrical current flow, measured in amperes (amps) — it's the volume of electricity moving through a wire, and every circuit is sized by its amperage capacity.
General
Industry units, ratings, and shared concepts.
BTU
A BTU is the standard unit of heat in U.S. HVAC — one BTU is the energy needed to raise one pound of water by one degree Fahrenheit. Furnaces and ACs are rated in BTU per hour.
Load Calculation
A load calculation is the engineering analysis we do to size HVAC equipment (Manual J), ductwork (Manual D), or electrical service correctly — too small and the system can't keep up, too big and it short-cycles and wears out fast.
Building Permit
A building permit is the formal authorization from your Utah city or county to do major HVAC, plumbing, or electrical work — required for safety, code compliance, and to protect your home's resale value.
Have a term we should add?
We update the glossary regularly. If we missed something you're trying to understand, just call and ask — we'll explain it and add it to the list.
(801) 407-9320