HVAC, solar & EV terms, explained.
Plain-language definitions for the technical terms you'll see across our site — no jargon, no guessing.
Amperage vs. Voltage
Voltage (volts) is the electrical pressure pushing current through a circuit; amperage (amps) is the amount of current actually flowing. A home's electrical panel has a total amperage capacity (commonly 100A, 150A, or 200A) that determines how much can safely run at once — this is why adding solar, an EV charger, or a heat pump can require a panel upgrade.
BTU (British Thermal Unit)
The standard unit for measuring heating and cooling capacity — specifically, the energy needed to raise one pound of water by one degree Fahrenheit. HVAC equipment is rated in BTUs per hour; an undersized or oversized BTU rating for a home's square footage is a common cause of poor comfort and high bills.
Condenser
The outdoor unit of a split-system air conditioner or heat pump. It releases the heat collected from inside the home into the outside air, using a fan, coil, and compressor. Coastal salt air and heavy debris are common causes of condenser corrosion and reduced efficiency.
Duct Sealing
The process of sealing leaks, gaps, and disconnections in a home's air duct system. Leaky ducts routinely waste 20–30% of conditioned air before it reaches the living space, forcing the HVAC system to run longer to compensate.
Ductless Mini-Split
A heating and cooling system with no ductwork — an outdoor condenser connects to one or more indoor wall-mounted units via a small refrigerant line. Common for room additions, garage conversions, and homes where extending ductwork isn't practical.
Mini-splits vs. extending ductwork →Evaporator Coil
The indoor coil that absorbs heat from inside air as refrigerant passes through it, cooling the air before it's circulated back into the home. A clogged air filter is the most common cause of a frozen evaporator coil.
EVSE (Electric Vehicle Supply Equipment)
The formal term for what most people call an "EV charger" — the equipment (wall unit or charging station) that safely delivers power from the electrical system to the vehicle. The EVSE itself doesn't charge the battery; it manages and delivers the power the vehicle's onboard charger uses.
Heat Pump
A single system that both heats and cools a home by moving heat rather than generating it — extracting heat from outside air in winter and expelling indoor heat outside in summer. Because it moves heat instead of creating it through combustion or resistance, a heat pump is typically 3–4 times more efficient than a standard electric furnace.
Heat pump services →Level 1 vs. Level 2 EV Charging
Level 1 charging uses a standard 120V household outlet and adds roughly 3–5 miles of range per hour — slow, but requires no installation. Level 2 charging uses a 240V circuit (the same type as an electric dryer) and adds 20–30+ miles of range per hour, making it the practical choice for most daily drivers.
Level 1 vs. Level 2 EV charging →Low-GWP Refrigerant
GWP (Global Warming Potential) measures how much a refrigerant contributes to warming if released, compared to CO2. Older refrigerants like R-22 and R-410A have high GWP and are being phased out in favor of low-GWP alternatives (such as R-32 and R-454B) required in new equipment under updated EPA regulations.
NATE Certification
North American Technician Excellence — an industry-recognized, independent certification for HVAC technicians covering installation and service competency. It's not a state license; it's a voluntary credential technicians earn on top of licensing to demonstrate hands-on technical proficiency.
Net Energy Metering (NEM 3.0)
California's current framework for how solar customers are credited for excess electricity their system sends back to the grid. NEM 3.0 (in effect since 2023) credits exported solar power at a variable rate tied to wholesale electricity value rather than the retail rate used under the older NEM 2.0 program — which is a major reason battery storage has become more valuable alongside solar.
How NEM 3.0 net billing works →Panel Upgrade (Service Panel)
Replacing a home's main electrical panel with one rated for higher amperage capacity. Older homes (especially pre-1990s) are frequently underpowered for modern loads like central AC, heat pumps, solar, battery storage, and EV charging combined — a panel upgrade is often the first step before adding any of those.
Electrical services →SEER / SEER2 Rating
Seasonal Energy Efficiency Ratio — the standard measure of an air conditioner or heat pump's cooling efficiency over a typical season. Higher SEER means more cooling output per unit of electricity. SEER2 is the updated testing standard (in effect since 2023) that better reflects real-world duct static pressure; SEER2 numbers run slightly lower than old SEER ratings for the same equipment.
Short-Cycling
When an HVAC system turns on, runs briefly, shuts off, and restarts repeatedly instead of completing a normal run cycle. It's a symptom, not a cause — common triggers include an oversized system, restricted airflow, a frozen coil, or a failing safety switch — and it significantly increases wear on the compressor.
How oversized AC units cause short-cycling →Solar Inverter (String vs. Microinverter)
The device that converts the DC electricity solar panels produce into the AC electricity a home actually uses. A string inverter is one central unit serving all panels together; microinverters are installed on each individual panel. Microinverters typically perform better on roofs with partial shading, since one shaded panel won't drag down the whole array's output.
Microinverters vs. string inverters →Title 24
California's Building Energy Efficiency Standards, part of the state building code. It sets minimum efficiency requirements for HVAC systems, insulation, ductwork, and more in new construction and major renovations — relevant any time ductwork is being replaced or relocated in an older home.
Title 24 requirements for ductwork upgrades →Zoned HVAC
A system that divides a home into separate temperature zones (typically by floor or wing), each with its own thermostat and dampers, instead of conditioning the whole house to one setting. It directly addresses the common complaint of some rooms running hotter or colder than others.
Why the upstairs bedroom runs hotter →