Glossary
Home-Comfort Glossary
The HVAC, plumbing, electrical, and smart-home terms you'll run into on a quote — defined in plain English, with links to the guides that go deeper.
20 terms, in alphabetical order. Looking for something specific? Use your browser's find (Ctrl/Cmd + F). Still unclear on a term in your quote? Ask us for a free 2nd opinion.
- AFUE (Annual Fuel Utilization Efficiency)
- The percentage of fuel a furnace converts into usable heat over a year. An 80% AFUE furnace turns 80% of its gas into heat; high-efficiency condensing furnaces reach 95%+. Heat pump vs. furnace →
- A2L Refrigerant
- A class of mildly flammable, low global-warming-potential refrigerants (such as R-454B and R-32) now replacing R-410A in new air conditioners and heat pumps under federal rules. The refrigerant change →
- BTU (British Thermal Unit)
- A unit of heat energy. Heating and cooling capacity is measured in BTUs per hour — the more BTU/h, the more a system can heat or cool.
- COP (Coefficient of Performance)
- A heat pump's efficiency ratio — how much heat it moves per unit of electricity used. A COP of 3 means three units of heat delivered for every one unit of energy consumed.
- Ductless Mini-Split
- A heat pump system with an outdoor unit connected to one or more wall- or ceiling-mounted indoor heads. It heats and cools specific zones without ductwork.
- Heat Pump
- An electric system that moves heat rather than burning fuel, providing both heating and cooling from one unit. A strong fit for the Central Coast's mild climate. Heat pump vs. furnace →
- HSPF2 (Heating Seasonal Performance Factor 2)
- The seasonal heating-efficiency rating for heat pumps under the current test standard. Higher HSPF2 means lower heating costs.
- Indoor Air Quality (IAQ)
- How clean and healthy the air in your home is — affected by filtration, ventilation, and humidity. IAQ equipment includes better filters, air purifiers, and fresh-air ventilation.
- Inverter / Variable-Speed
- Compressors and motors that modulate their output up and down instead of simply switching on and off. They run quieter, hold steadier temperatures, and use less energy.
- Load Calculation (Manual J)
- The industry-standard method (ACCA Manual J) for sizing HVAC equipment to a home's actual heating and cooling needs — based on square footage, insulation, windows, and orientation rather than a rule of thumb. What size AC do I need? →
- MERV (Minimum Efficiency Reporting Value)
- A 1–16 scale rating how well an air filter captures particles. Higher MERV traps smaller particles, but very high ratings can restrict airflow if the system isn't designed for them.
- R-410A
- The HFC refrigerant used in most air conditioners and heat pumps for the past decade. It has a high global-warming potential and is being phased down, so new systems now use A2L refrigerants. Do I have to replace my R-410A AC? →
- R-454B / R-32
- Two A2L refrigerants with much lower global-warming potential than R-410A, now standard in new equipment. R-454B is common in residential systems built for the 2025 transition. The refrigerant change →
- Refrigerant
- The working fluid inside an AC or heat pump that absorbs heat in one place and releases it in another as it cycles between liquid and gas.
- SEER2 (Seasonal Energy Efficiency Ratio 2)
- The updated cooling-efficiency rating for central AC and heat pumps. Higher SEER2 means lower cooling bills; most new central systems sold today must meet a SEER2 minimum that varies by system type and region. AC installation cost →
- Smart Thermostat
- A connected thermostat (such as Google Nest) that learns your schedule, can be controlled from your phone, and helps reduce energy use. Homepatible is a Google Nest Pro Elite installer.
- Tankless Water Heater
- A water heater that heats water on demand as it flows through, instead of keeping a tank hot around the clock — saving space and standby energy.
- Title 24
- California's Building Energy Efficiency Standards, part of the state building code. It sets energy requirements for new construction and many alterations, including HVAC changeouts. Title 24 & A2L explained →
- Tonnage
- A measure of an AC or heat pump's cooling capacity. One ton equals 12,000 BTU/h. Correct tonnage comes from a load calculation — bigger is not better. What size AC do I need? →
- 25C Tax Credit
- The federal Energy Efficient Home Improvement Credit — up to 30% of project cost with annual caps (for example, up to $2,000 for qualifying heat pumps). Always confirm eligibility with a tax professional. Rebates & incentives →
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