Learning Center · Reference
HVAC Glossary
Plain-language definitions for the heating, cooling, geothermal, and rebate terms you'll run into — written the way we'd explain them at your kitchen table. 48 terms, defined.
Category
Heating & fuel basics
- Furnace
- A heating system that warms air and pushes it through ducts. In our area furnaces usually run on propane or electricity, because there are no natural-gas mains out here. Related: Heating a rural home →
- Boiler
- A system that heats water (or steam) and circulates it through radiators or in-floor tubing for radiant heat. Common in older farmhouses and additions. Related: Heating a rural home →
- Propane (LP Gas)
- Liquefied petroleum gas stored in an on-site tank and used for heating, water heating, and cooking where there is no natural-gas line. The dominant fossil fuel for rural North Missouri / South Iowa homes. Related: Propane vs. heat pump cost →
- Heating Oil
- A fuel oil burned in an oil furnace or boiler. Still found in some older country homes; often a candidate for conversion to a heat pump or dual-fuel system. Related: Dual-fuel heat pump systems →
- AFUE
- Annual Fuel Utilization Efficiency — the percentage of a fuel's energy a furnace or boiler turns into usable heat over a year. Higher is more efficient; the rest goes up the flue.
- Heat Pump
- An electric system that moves heat instead of burning fuel — pulling heat from outside air (or the ground) in winter and reversing in summer to cool. It both heats and cools. Related: Cold-climate heat pumps in Zone 5A →
- Air-Source Heat Pump
- A heat pump that exchanges heat with the outdoor air. The most common and lowest-cost type to install. Related: Geothermal vs. air-source heat pump →
- Cold-Climate Heat Pump
- A heat pump engineered with inverter compressors and enhanced controls to keep heating efficiently into deeply sub-freezing temperatures — the type that matters for a Zone 5A winter. Related: Cold-climate heat pumps in Zone 5A →
- Dual-Fuel System
- A heat pump paired with a propane or electric backup furnace. The heat pump handles most of the season efficiently, and the furnace takes over on the coldest days. Also called hybrid heat. Related: Dual-fuel heat pump systems →
- Auxiliary / Backup Heat
- The secondary heat source (electric strips or a fuel furnace) a heat pump falls back on during the coldest weather or a defrost cycle.
- Balance Point
- The outdoor temperature at which a heat pump's output exactly meets the home's heat loss. Below it, backup heat helps out. Setting it correctly is the key to a comfortable, economical dual-fuel system. Related: Dual-fuel heat pump systems →
- Defrost Cycle
- A brief, normal mode where an air-source heat pump melts frost off its outdoor coil in cold, damp weather. You may see steam and feel backup heat kick in — it is not a malfunction.
Category
Cooling & efficiency ratings
- SEER2
- The current seasonal efficiency rating for cooling. A higher SEER2 means more cooling per unit of electricity over a season. The '2' marks the 2023 testing standard. Related: Is Daikin worth it? →
- HSPF2
- The seasonal efficiency rating for a heat pump's heating mode. Higher is better. Pair it with SEER2 to judge year-round efficiency.
- COP
- Coefficient of Performance — heat delivered per unit of energy used, at a moment in time. A COP of 3 means three units of heat for every one of electricity. Geothermal systems hold high COPs even in deep cold. Related: Geothermal on acreage →
- BTU
- British Thermal Unit — the basic measure of heating or cooling energy. Systems are sized by how many BTUs per hour they can move.
- Ton (of Cooling)
- A unit of cooling capacity equal to 12,000 BTU/hour. A typical home system is 2–5 tons; the right number comes from a load calculation, not a rule of thumb. Related: Right-sizing HVAC for Zone 5A →
- Inverter / Variable-Speed Compressor
- A compressor that ramps its speed up and down instead of only switching on and off. It holds steady temperatures, runs quietly, and is the technology behind modern cold-climate and Daikin systems. Related: What is Daikin? →
- Two-Stage / Modulating
- Equipment that runs at more than one capacity level (two-stage) or smoothly across a range (modulating), for steadier comfort and better humidity control than single-stage on/off systems.
Category
Geothermal
- Geothermal Heat Pump
- A ground-source heat pump that exchanges heat with the stable temperature of the earth instead of outdoor air. Very efficient, and a genuine fit for homes on acreage. Related: Geothermal on acreage →
- Ground Loop
- The buried piping that carries fluid between a geothermal heat pump and the earth. Its layout (horizontal, vertical, or pond) depends on your land. Related: Geothermal on acreage →
- Closed Loop
- A sealed ground loop where the same fluid circulates continuously through buried pipe. The most common residential design.
- Open Loop
- A geothermal design that draws from and returns to a well or water source rather than a sealed pipe. Requires the right water supply and discharge.
- Pond Loop
- A closed loop coiled and sunk in a pond or lake of adequate depth and size — often the lowest-cost loop for a property that has the water for it. Related: Pond-loop geothermal →
- Desuperheater
- An add-on that uses a geothermal system's waste heat to pre-heat household water, trimming water-heating costs.
Category
Comfort, airflow & zoning
- Ductless Mini-Split
- A heat pump with an outdoor unit and one or more wall/ceiling indoor heads, no ductwork required. Ideal for additions, bonus rooms, shops, and rooms the main system can't reach. Related: Ductless vs. whole-home zoning →
- Air Handler
- The indoor unit that moves conditioned air through the ducts. Paired with a heat pump or AC coil, it is the indoor half of a split system.
- Zoning
- Dividing a home into independently controlled areas using dampers and multiple thermostats, so upstairs and downstairs (for example) can hold different temperatures. Related: Ductless vs. whole-home zoning →
- Manual J
- The industry-standard room-by-room heating and cooling load calculation. It sizes equipment to your actual home instead of guessing — essential in a climate with −20°F to 100°F swings. Related: Right-sizing HVAC for Zone 5A →
- Load Calculation
- The math that determines how much heating and cooling a home needs, based on its size, insulation, windows, and climate. Manual J is the residential standard. Related: Right-sizing HVAC for Zone 5A →
- Static Pressure
- The resistance air meets moving through ducts and filters. Too high — from undersized or leaky ducts — strains the system and starves rooms of airflow. Related: Why some rooms are too hot or cold →
- Short Cycling
- When a system turns on and off too frequently. It wastes energy, wears parts, and leaves rooms uneven — often a sign of an oversized unit or an airflow problem. Related: Why some rooms are too hot or cold →
- Bonus Room
- A finished room over a garage or under a roofline. Because it sits outside the home's main envelope, it is notoriously hard to heat and cool from the central system. Related: Bonus room over the garage →
Category
Indoor air quality
- Indoor Air Quality (IAQ)
- The cleanliness, humidity, and freshness of the air inside your home. Farm and country homes face dust, pollen, wood smoke, and tightly sealed winters that make IAQ worth managing. Related: Indoor air quality for country homes →
- MERV Rating
- Minimum Efficiency Reporting Value — how finely an air filter captures particles. Higher MERV traps more, but must be matched to the system so it doesn't choke airflow. Related: Indoor air quality for country homes →
- HRV / ERV
- Heat- or Energy-Recovery Ventilators bring in fresh outdoor air while recovering heat (and, for an ERV, moisture) from the stale air they exhaust — fresh air without throwing away your heating.
- Humidifier / Dehumidifier
- Whole-home equipment that adds moisture in dry winters or removes it in humid summers, for comfort and to protect woodwork and finishes.
- UV Germicidal Light
- A UV-C lamp installed in the system to reduce mold and biological growth on the coil and in the airstream.
Category
Home efficiency, sizing & programs
- Climate Zone 5A
- The IECC climate zone covering our region: cold, humid winters with design temperatures well below zero and hot summers. It drives how systems should be sized and chosen. Related: Right-sizing HVAC for Zone 5A →
- R-Value
- A measure of how well insulation resists heat flow. Higher R-value means less heat lost in winter and gained in summer — a big factor in older, pre-1980 homes. Related: HVAC upgrades for aging homes →
- Right-Sizing
- Choosing equipment that matches a home's real load — not too big, not too small. Oversized systems short-cycle and feel clammy; undersized ones can't keep up in extremes. Related: Right-sizing HVAC for Zone 5A →
- Manufacturer Warranty
- The equipment maker's coverage on parts (and sometimes the compressor) for a set number of years, typically when the system is installed by an authorized dealer and registered. Related: Is Daikin worth it? →
- EPA 608 Certification
- Federal certification required to handle refrigerants. It is one of the licenses and certifications a legitimate HVAC contractor carries.
- Utility / Co-op Rebate
- A cash incentive from your electric cooperative or utility for installing qualifying high-efficiency equipment. Programs and amounts vary by provider and change often — confirm current offers with your own utility. Related: Rural HVAC rebates navigator →
- 25C / 25D Federal Tax Credit
- Federal residential energy tax credits that EXPIRED December 31, 2025. They are not available for systems installed in 2026, so we do not factor them into today's pricing. Related: Rural HVAC rebates navigator →
- USDA REAP
- The USDA Rural Energy for America Program offers grants and loans to farms and rural small businesses for energy upgrades. Intake has at times been paused — ask us whether it currently applies to your operation. Related: Rural HVAC rebates navigator →
- Rooftop Unit (RTU)
- A packaged heating-and-cooling unit mounted on a commercial roof. Common for storefronts, offices, and shops on a slab. Related: Light commercial HVAC →