The Plain-English HVAC Glossary

AHJ (Authority Having Jurisdiction)

The authority responsible for applying and enforcing the rules for a project at a particular address. Ask the local building department which office handles your proposed HVAC work. Related: HVAC Permit Planning →

Jurisdiction

The geographic area or type of work over which an authority has responsibility. A mailing city alone may not identify the building department responsible for an HVAC project. Related: Find the Right Building Department →

Permit

An authorization from the responsible authority for a defined scope of work. Requirements and inspection steps depend on the project and location; permit approval does not replace required final inspections. Related: Replacement Permit Checklist →

AFUE (Annual Fuel Utilization Efficiency)

A seasonal rating comparing a furnace's useful heat output with its fuel energy input under the test procedure. It does not include duct losses or establish a home's actual heating bill. Related: Furnace Service →

Balance point

A temperature used in heat-pump design or controls. The capacity balance point and an economic switching point are different questions; ask which one a proposal describes and how the equipment and rates inform it. Related: Heat Pump Service →

BTU (British Thermal Unit)

The standard unit of heating and cooling capacity. Residential equipment is often sized in tons; one ton equals 12,000 BTU/h. Related: Our Services →

Cold-climate heat pump

A heat pump engineered with an inverter compressor to maintain heating capacity at low outdoor temperatures — the class of equipment that makes heat pumps viable on the Front Range. Related: Heat Pump Service →

Condenser

The outdoor unit of an AC or heat pump, where refrigerant releases the heat collected from your home. Hail-bent condenser fins are a common Colorado efficiency killer. Related: Air Conditioner Service →

Defrost cycle

A normal heat-pump operation that briefly reverses the system to melt frost off the outdoor coil. Visible steam is expected; constant heavy ice is a service call. Related: Heat Pump Service →

Dual-fuel system

A heat pump paired with a gas furnace: the heat pump handles mild weather efficiently, the furnace takes over in deep cold. Related: Heat Pump Service →

Evaporator coil

The indoor coil where refrigerant absorbs heat from your home's air. Coil failures on aging systems are a classic repair-vs-replace trigger. Related: Air Conditioner Service →

Flame sensor

A component used to confirm that a burner flame is present. A flame-sensing fault is one possible cause of a furnace shutting down after ignition; diagnosis and service belong with a qualified technician. Related: Furnace Service →

Heat exchanger

The passages that transfer combustion heat while separating combustion gases from circulating indoor air. Suspected damage needs professional safety assessment before continued use; repair and replacement options depend on the findings. Related: Furnace Service →

HRV / ERV

Heat- or energy-recovery ventilators exchange indoor and outdoor air while recovering energy. Outdoor-air intake and filtration need an equipment-specific operating plan during wildfire smoke. Related: Thermostat & Air Quality →

Hydronic heating

Heating that circulates hot water (or steam) from a boiler through radiators, baseboards, or in-floor loops instead of blowing warm air through ducts. Common in older Denver-metro homes and light commercial buildings. Related: Our Services →

Humidistat

The control that measures indoor humidity and drives a whole-home humidifier to a setpoint. Better models compensate automatically as outdoor temperature drops. Related: Humidifier Service →

Inverter compressor

A variable-speed compressor that modulates output instead of switching on and off — the technology behind mini-splits' efficiency and cold-climate heat-pump performance. Related: Mini-Split Service →

Kettling

A term used for boiling-like or rumbling boiler noises that can be associated with scale or circulation problems. The sound requires diagnosis rather than identifying a single cause on its own. Related: Our Services →

Limit switch

A furnace safety control that interrupts heating when a temperature limit is reached. Repeated trips need professional diagnosis; never bypass the control to keep the furnace running. Related: Furnace Service →

Load calculation (Manual J)

The room-by-room engineering calculation of how much heating and cooling a home actually needs. The step that prevents oversized, short-cycling equipment — insist on it before any install. Related: Our Services →

Low-water cutoff

A boiler safety control intended to stop burner operation when water falls below its safe operating level. Inspection requirements depend on the equipment and service scope. Related: Our Services →

MERV rating

A filter's particle-capture rating. Choose the highest-efficiency filter your system can accommodate. The filter size, blower capability, and pressure drop matter alongside the MERV rating. Related: Thermostat & Air Quality →

R-22 / R-410A

Refrigerants used in existing air-conditioning equipment. U.S. production and import of R-22 ended in 2020, but existing equipment can still be serviced using available supplies. Repair decisions require an assessment of cost and condition. Related: Air Conditioner Service →

SEER2

The current seasonal cooling-efficiency rating for ACs and heat pumps (higher is more efficient), measured under updated test conditions that better reflect real ductwork. Related: Air Conditioner Service →

Short cycling

Repeated brief equipment starts and stops. Airflow, controls, safety shutdowns, and sizing are possible factors; the pattern needs diagnosis and does not identify a single failed part. Related: Furnace Service →

Zoning

Controlling different areas separately through a designed duct or room-system arrangement. Suitability depends on airflow, equipment compatibility, room needs, and control design; zoning is not a universal cure for uneven temperatures. Related: Mini-Split Service →

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