HVAC & electrification, in plain English.

Heat pump

An electric system that both heats and cools by moving heat instead of burning fuel — essentially an air conditioner that can run in reverse. Far more efficient than combustion heating. See heat pump service.

Electrification

Replacing gas-burning appliances (furnaces, water heaters) with efficient electric equipment like heat pumps. The core of California's clean-energy building direction.

Ductless / Mini split

A heat pump with an outdoor unit connected to slim indoor "heads" by a thin refrigerant line set — no ductwork required. Ideal for older homes, ADUs, and additions. See ductless explained.

HPWH (Heat Pump Water Heater)

A water heater that uses a heat pump to warm water from surrounding air — several times more efficient than a gas tank. Plum installs heat pump water heaters only. See HPWH vs. gas tank.

SEER2

Seasonal Energy Efficiency Ratio 2 — the current standardized measure of cooling efficiency. Higher SEER2 means more cooling per unit of electricity.

HSPF2

Heating Seasonal Performance Factor 2 — the standardized measure of a heat pump's heating efficiency over a season. Higher HSPF2 means more heat per unit of electricity.

COP (Coefficient of Performance)

The ratio of heat delivered to energy consumed at a given moment. A COP of 3 means three units of heat for every one unit of electricity — why heat pumps beat combustion.

AFUE

Annual Fuel Utilization Efficiency — the efficiency rating for combustion furnaces. A 95% AFUE furnace turns 95% of its fuel into usable heat; the rest is lost.

Ton

A unit of HVAC capacity (12,000 BTU/hour). Residential systems are commonly 1.5–5 tons. The correct tonnage comes from a load calculation, not square footage alone.

BTU

British Thermal Unit — a measure of heat energy. HVAC capacity is often expressed in BTU/hour; 12,000 BTU/hour equals one ton.

Manual J / Load calculation

The industry-standard method for sizing heating and cooling to a home's actual heat gain and loss. A real Manual J — not a rule-of-thumb guess — is the foundation of a comfortable, efficient system. See how to compare quotes.

Inverter

Technology that lets a heat pump or AC vary its output instead of running only full-on or off. Inverter-driven systems are quieter, more efficient, and more comfortable.

Line set

The insulated refrigerant tubing (about three inches) connecting a mini split's outdoor unit to its indoor heads. Clean line-set routing is a hallmark of a quality install.

kWh (kilowatt-hour)

The unit your electric bill is measured in — one kilowatt of power used for one hour. Heat pump operating cost is estimated from kWh used times your electricity rate.

Title 24

California's building energy code, which sets efficiency standards and makes heat pumps the prescriptive default for new construction and major remodels. See California 2026 rules.

Reach code

A local building code that "reaches" beyond the state minimum — many Peninsula cities adopt reach codes that favor or require electric heat pumps in new construction. See permits & reach codes.

AHJ (Authority Having Jurisdiction)

The local government body — usually a city or county building department — that issues permits and enforces code for your project. Requirements vary by AHJ.

Permit

Official approval from your AHJ to perform work, followed by inspection. Plum pulls and manages permits for your installation so the work is code-compliant and documented.

SGIP

Self-Generation Incentive Program — a California incentive that can apply to qualifying battery storage and, in some cases, heat pump water heaters. Eligibility and funding change over time. See the Rebate Hub.

CCA (Community Choice Aggregator)

A local agency that buys power on behalf of a community — like Silicon Valley Clean Energy or Westlight Energy — and often offers electrification rebates Plum is approved for. See the Rebate Hub.

Mitsubishi Diamond Contractor

A contractor trained and certified by Mitsubishi Electric to install its systems. The Elite (Diamond) tier is the top level; Plum HVAC holds it. See what is a Diamond Contractor.

Last updated June 25, 2026 · Reviewed by Sam Moosavi, Owner, Plum HVAC. Educational reference only — confirm specifics for your project during an in-home visit.