AK HVAC key terms

A room-by-room method of estimating how much heat a building loses in winter and gains in summer, used to size heating and cooling equipment correctly instead of guessing from square footage.

The outdoor winter and summer temperatures a system is sized to handle, chosen so equipment meets demand on all but the most extreme days. Alaska sizing uses very low winter values.

A measure of how cold a climate is over a season, calculated from the difference between a 65 degrees F reference and the average daily outdoor temperature. Higher values mean more heating energy needed.

A unit expressing the gap between a base temperature and the average outdoor temperature for one day, used to estimate seasonal energy use for heating or cooling.

The portion of total cooling load that changes air temperature, as opposed to moisture removal. A low ratio means much of the load is latent, which matters in humid or tightly built spaces.

Heat energy absorbed or released when moisture changes state, such as water evaporating or vapor condensing, without changing temperature. It drives dehumidification and humidification loads.

The total heat content of air, combining its sensible temperature and the latent energy of the moisture it carries. Technicians compare indoor and outdoor enthalpy to judge ventilation and economizer decisions.

A graph showing relationships among air temperature, humidity, moisture content, and heat content. It is used to plot air conditions and analyze heating, cooling, and humidification processes.

The percentage of moisture air holds compared with the maximum it could hold at that temperature. Warmer air can hold more, so relative humidity changes when air is heated without adding moisture.

The temperature at which air becomes saturated and moisture begins condensing on surfaces. Air cooled below its dew point forms condensate, which is why evaporator coils and cold pipes drip.

Annual fuel utilization efficiency, a rating of how much fuel energy a furnace or boiler converts to useful heat over a heating season. Higher percentages mean less fuel wasted up the flue.

A high-efficiency gas or oil furnace that cools flue gases enough to condense water vapor and recover latent heat, reaching efficiency above roughly 90 percent. It requires a drain for condensate.

The metal component that separates hot combustion gases from the air being delivered to the building, transferring heat without mixing the two streams. Cracks can leak carbon monoxide into supply air.

A failure in the metal separating flue gases from supply air, allowing carbon monoxide and other combustion products into the occupied space. It is a serious safety hazard requiring shutdown and replacement.

The air supplied to a burner to support burning of fuel. In tight Alaska homes it must be piped or ducted from outdoors so appliances burn cleanly and do not backdraft.

Reversal of normal vent flow that pulls combustion products into the building instead of up the chimney, often caused by depressurization, exhaust fans, or blocked flues. It creates carbon monoxide risk.

A colorless, odorless gas produced by incomplete combustion that binds to blood and can be fatal. Testing and proper venting, combustion air, and CO alarms are required safeguards.

A heating system that moves heat with water or a water-glycol mixture through pipes to terminal units such as radiators, baseboard, or radiant floors, rather than with forced air.

A pump that moves heated water through a hydronic loop, overcoming pipe and fitting friction. Correct sizing and balance prevent noisy flow, cold zones, and short cycling.

A tank that absorbs the increased volume of water as it heats in a closed hydronic system, limiting pressure rise. It contains a diaphragm or air charge that maintains system pressure.

An antifreeze additive mixed with water in hydronic or solar loops to prevent freezing in cold spaces or during outages. Concentration affects heat transfer and pump sizing.

Equipment that moves heat from one place to another using a refrigeration cycle, providing heating by extracting outdoor heat and cooling by reversing the flow. Cold-climate models operate at very low outdoor temperatures.

The ratio of heat delivered by a heat pump to the energy it consumes, expressed as a number such as 3.0. Higher values mean more heat per unit of electricity and vary with outdoor temperature.

A timed or demand-initiated mode in which a heat pump temporarily reverses or stops heating to melt frost from the outdoor coil. It prevents capacity loss and ice buildup in cold weather.

A four-way valve in a heat pump that changes refrigerant flow direction so the indoor coil becomes the evaporator in cooling or the condenser in heating.

The coil where refrigerant absorbs heat and boils, cooling the air or water passing over it. It operates at low pressure and below the dew point, so it also collects condensate.

The coil where refrigerant releases heat and condenses from vapor to liquid, rejecting heat outdoors in cooling or indoors in heating. It operates at higher pressure and temperature.

The number of degrees refrigerant vapor is above its saturation temperature at a given pressure. Measuring it at the evaporator outlet verifies proper charge and expansion valve operation.

The number of degrees liquid refrigerant is below its saturation temperature at a given pressure. Measuring it at the condenser outlet helps confirm charge and metering device performance.

A metering device that regulates refrigerant flow into the evaporator by responding to superheat at the coil outlet, keeping the coil properly fed across changing loads.

The piping that carries water removed from air by a cooling coil to a safe disposal point. It needs proper slope, trapping, and freeze protection so it does not overflow or back up.

The pressure exerted by the air stream against duct walls, measured to evaluate fan performance and airflow. High static pressure signals restriction and reduced delivered airflow.

The resistance the duct system and components impose on the blower, measured at the equipment outlet and inlet. It is compared with the fan rating to confirm adequate airflow.

Air escaping from joints, seams, and penetrations in ductwork, wasting energy and reducing delivered airflow. Sealing and testing are especially important when ducts run through cold spaces.

Material wrapped around or lining ducts to limit heat loss or gain and control surface condensation. In cold climates, placement of the vapor barrier matters to prevent trapped moisture.

A low-permeability material that limits moisture movement through building assemblies. Correct placement keeps warm moist air from reaching cold surfaces where it condenses and causes damage.

Unintentional air entering a building through cracks, gaps, and penetrations. It adds heating load and can cause drafts and moisture problems in cold climates.

A condition in which indoor pressure falls below outdoor pressure, often from exhaust fans or duct leakage, drawing outdoor air in and potentially causing appliance backdrafting.

Outdoor air supplied to replace air exhausted by fans, hoods, or other exhaust devices, keeping building pressure balanced and supporting combustion and ventilation needs.

An adjustable plate inside ductwork used to regulate airflow to individual branches so each space receives its design share of air during commissioning.

Determining the volume of air moving through a duct or terminal, commonly with a manometer, flow hood, or anemometer, to verify the system delivers design airflow.

A temperature-sensing safety control that stops a fan or burner and often closes a damper when air or water temperatures drop near freezing, protecting coils and piping from frost damage.

A control device operating typically at 24 volts that switches heating and cooling equipment based on space temperature, often with fan, staging, and setback functions.

A safety device on boilers, tanks, or piping that opens at a set pressure to release excess pressure and prevent rupture or explosion. It must be sized and piped to a safe discharge.

A safety procedure that isolates energy sources and applies locks and tags so equipment cannot be re-energized while a technician services it. It prevents shock, burns, and unexpected startup.

Gear such as gloves, eye protection, respirators, and insulated footwear worn to reduce injury risk from chemicals, sharp edges, electricity, and cold. Selection follows the task hazard.

The process of removing refrigerant from a system into a recovery cylinder rather than venting it to the atmosphere, as required by environmental regulations. Recovery equipment and cylinders must be rated for the refrigerant.

A DOT-approved, color-coded pressure vessel used to store recovered refrigerant. It must not be overfilled and should be labeled with the refrigerant type and quantity.

A required EPA credential for technicians who service or dispose of equipment containing regulated refrigerants, demonstrating knowledge of safe handling, recovery, and environmental rules.

A test instrument that measures voltage, current, and resistance to troubleshoot electrical circuits and controls. Safe use requires correct range selection and category-rated probes.

An official authorization from a local building authority required before installing or altering heating, ventilation, or refrigeration systems, allowing inspection of the work for code compliance.

The adopted regulations governing installation, alteration, and inspection of heating, ventilating, and refrigeration systems, including clearances, venting, combustion air, and safety controls.

A credential issued by the state that authorizes a business to offer and perform contracting work for compensation. Operating without one can bring fines and contract problems.

Required coursework that license holders complete during each renewal period to keep their credentials current and stay informed about code and safety changes.

A legal claim against property for unpaid work or materials. Filing deadlines and notice requirements are strict, so contractors must document and follow statutory procedures carefully.

A written modification to the scope, price, or schedule of a contract signed by both parties. It protects the contractor from doing extra work without documented compensation.

A device that adds moisture to indoor air, often needed in cold climates where heating dries the space. Proper control prevents condensation and mold on cold surfaces.