OH HVAC Contractor key terms

A room-by-room method of estimating heating and cooling loads from envelope areas, insulation, windows, infiltration, and design temperatures. It sizes equipment correctly instead of relying on rules of thumb.

A procedure for sizing supply and return ducts using available static pressure, equivalent length, and friction rate so the blower delivers design airflow to each room.

The outdoor winter and summer conditions a system is sized to handle, typically the 99 percent winter and 1 percent summer values for the location. Equipment capacity is matched to load at these points.

The number of degrees a refrigerant vapor is above its saturation temperature at a given pressure. Measured at the evaporator outlet, it confirms the expansion valve is feeding the coil properly.

The number of degrees a liquid refrigerant is below its saturation temperature at a given pressure. Measured at the condenser outlet, it indicates how much liquid is stacked in the condenser.

A thermostatic expansion valve that meters refrigerant into the evaporator and modulates flow to hold a set superheat. It responds to evaporator outlet temperature and pressure through a sensing bulb.

The outdoor temperature at which a heat pump's capacity exactly equals the building's heat loss. Below it, supplemental or backup heat must make up the difference.

Supplemental electric resistance or fossil-fuel heat that operates when a heat pump cannot meet the load, such as during defrost or below the balance point.

A timed or demand-initiated sequence that reverses refrigerant flow or stops the outdoor fan to melt frost from an outdoor coil, often energizing auxiliary heat to prevent cold blow.

The resistance to airflow measured across the blower assembly, expressed in inches of water column. It is used with the fan performance table to confirm the system is moving design airflow.

The volume of air moved per unit time, usually cubic feet per minute. Correct airflow is required for capacity, efficiency, and safe combustion in fuel-burning equipment.

Air supplied to a fuel-burning appliance for complete combustion and dilution of flue gases. It must be provided from outdoors or adequately sized openings per code.

The passage or vent that carries products of combustion from an appliance to the outdoors. Correct sizing, slope, and termination prevent spillage of carbon monoxide into the building.

The negative pressure that draws combustion gases up a vent or chimney. It can be natural, from buoyancy of hot gases, or mechanical, from an induced-draft fan.

Removing refrigerant from a system into a recovery cylinder or machine rather than venting it to the atmosphere. Federal law requires recovery before opening a circuit.

The working fluid in a refrigeration cycle that absorbs heat by evaporating at low pressure and rejects heat by condensing at high pressure. Handling is regulated by federal and state rules.

A DOT-approved, properly labeled vessel used to store recovered refrigerant. It must not be overfilled and must be evacuated before use.

A banging noise and pressure surge caused by a sudden stop in water flow, such as a fast-closing valve. Arrestors or properly sized piping reduce the shock.

A device that prevents contaminated water from reversing into a potable supply due to backsiphonage or backpressure. Selection depends on the degree of hazard.

The vertical separation between a potable water outlet and the flood level rim of a receiving fixture. It is the most reliable form of backflow protection.

Any actual or potential link between a potable water system and a source of contamination or pollution. It must be eliminated or protected by an approved backflow device.

A closed piping circuit that circulates heated or chilled water between a boiler or chiller and terminal units such as baseboard, radiators, or fan coils.

A pump that moves water through a hydronic loop. It must be sized for the system's head loss and flow rate, and often uses a flanged or wet-rotor design.

A vessel that absorbs the volume change of water as it heats in a closed hydronic system, limiting pressure rise and protecting components from overpressure.

The water held in a plumbing trap that blocks sewer gas from entering a building. Its depth is set by code and must be maintained by proper venting.

A vertical pipe that admits air to a drainage system and carries sewer gases to the outdoors, protecting trap seals from siphonage.

A device that trips when it detects a small current imbalance between hot and neutral, protecting people from shock. Required in many wet and outdoor locations.

The conductor that connects non-current-carrying metal parts of equipment to the grounding system, providing a low-impedance path for fault current.

Electrically connecting metal parts to ensure they remain at the same potential, preventing shock and arcing. It is distinct from grounding to earth.

A fuse or circuit breaker that opens a circuit when current exceeds its rating, protecting conductors and equipment from overheating and fire.

A switch or device that opens all ungrounded conductors to an appliance, allowing it to be safely serviced. It must be located within sight and be properly rated.

A procedure that isolates and locks an energy source in the off position and tags it so equipment cannot be re-energized while someone is working on it.

The maximum current a conductor can carry continuously under stated conditions without exceeding its temperature rating. It determines wire size and breaker selection.

The loss of voltage along a conductor due to resistance, which increases with current and length. Excessive drop reduces motor performance and wastes energy.

The state board within the Ohio Department of Commerce that licenses HVAC, refrigeration, plumbing, hydronics, and electrical contractors and enforces Chapter 4740 requirements.

The Ohio statute governing licensing of construction contractors, including HVAC, refrigeration, plumbing, hydronics, and electrical trades, and the board that administers it.

A credential issued by the board authorizing a person or business to perform or offer licensed trade work in Ohio. It is required before contracting and must be renewed.

Required hours of approved instruction a licensee must complete each renewal cycle to maintain licensure and stay current on code and trade practice.

The licensed person whose credential supports a contracting business entity's registration and who is responsible for the work performed under that license.