Hot Deck Distribution Holes

Holes in the hot deck that distribute the flow of returning condenser water evenly across the tower fill.

Hot Gas Piping (Piping)

A means of recirculating hot discharge refrigerant back into the evaporator. The refrigerant must pass through a pressure-reducing device (hot gas bypass valve). The purpose of hot gas bypass is to maintain a minimum gas volume flow rate through the compressor to avoid surging or stalling during low load conditions. A disadvantage is that the work of compression on the recirculated refrigerant does not generate any refrigeration effect.

Hot Surface Ignition

This component replaces the traditional pilot on a gas furnace. A hot surface ignition will "turn on" when the furnace is starting and "turns off" once the burners are lit. Because this is only in use when the furnace is starting there is no wasted energy from continuous pilot operation.

Hot Water System

A heating system consisting basically of a boiler, radiators, expansion tank and interconnection piping. The system is filled with water which circulates from the boiler through the pipes and radiators where its heat is liberated, the water returning to the boiler. Such heating systems are classified as gravity or forced circulation systems, either of one or two pipes and with open or closed expansion tanks.

Hot Wire Anemometer

Measures air velocity in grilles, filters, coils and ducts.


A dwelling may be single or double e.g., duplex, townhouse, row house, split-level ranch.


Heating seasonal performance factor,  Heat Pump Heating Efficiency. It stands for Heating Seasonal Performance Factor. A higher number means the unit works more efficiently. Most new units have ratings from 7.0 to 9.4. There is no legislated minimum rating. A rating of the average efficiency of a heat pump unit when operating in the heating mode.


The process of transferring a mass of water to the atmospheric air.


A component that adds moisture to the air before it is distributed by the ductwork throughout the house.  A piece of equipment that adds water vapor to heated air as it moves out of the furnace. This adds necessary moisture to protect your furnishings and reduce static electricity.


A device used in control systems for switching plant to maintain a relative humidity at some set point. The output signal is usually sent via a relay device to the final control element.


The measure of moisture in the atmosphere. In building simulation it is often referred to as the relative humidity within a space.


An acronym for Heating, Ventilating, and Air-Conditioning.  General term and abbreviation for the industry of Heating, Ventilation, and Air Conditioning, an R may be added to represent Refrigeration.

Hydrocarbons (HC)

Chemical compounds made up entirely of carbon and hydrogen. When combusted they release carbon dioxide, nitrogen oxide, sulphur dioxide and water vapor. The carbon dioxide emissions released to the atmosphere are the primary cause of the "greenhouse effect" leading to global warming of the earth's atmosphere.


An acronym for Indoor Air Quality.


International Code Council. A national organization that publishes model codes for adoption by states and other agencies. Codes include the International Building Code (IBC) and the International Energy Conservation Code (IECC).

Ice Dam

Condition formed at the lower roof edge by the thawing and re-freezing of melted snow on the overhang. Can force water up and under shingles, causing leaks.


A pulley used on some belt drives to provide the proper belt tension and to eliminate belt vibration.


International Energy Conservation Code published by the ICC. The successor to the Model Energy Code, which is cited in the 1992 U.S. Energy Policy Act (EPAct) as the baseline for residential Energy Codes in the United States.

Ignition Transformer

A transformer designed to provide a high voltage current. Used in many heating systems to ignite fuel.


A rotating part of a centrifugal pump.

Indoor Air

The air that people breathe inside a built environment.

Indoor Air Pollution

Pollution occurring indoors from any source, indoors or outdoors

Indoor Climate

The synthesis of day-to-day values of physical variables in a building e.g. Temperature, humidity, air movement and air quality, etc which affect the health and/or comfort of the occupants.

Indoor Coil

The coil on a heat pump that is located inside. This is not to be confused with the evaporator on an air conditioning system.  The portion of a heat pump or central air conditioning system that is located in the house and functions as the heat transfer point for warming or cooling indoor air.

Indoor Vapor Barrier

Vapor barriers control the flow of exfiltration of conditioned air, which is moisture laden, into the wall sections. Vapor barriers are a polyethylene plastic that are impermeable to moisture movement. And are installed before the dry wall. The vapor barrier should be continuous with all joints taped or caulked to make the wall section as airtight as possible. Moisture in the vapor form that is allowed to enter the wall section can result in condensation, which creates a structural durability issue.

Induced Magnetism

The ability of a magnetic field to produce magnetism in metal.

Inducer Fan

The inducer fan helps send the products of combustion up the chimney or through the appropriate exhaust vent.  This component is only found on the newer generation of furnaces with efficiencies of 78% AFUE and higher.

Induction Motor

An AC motor which operates on principle of rotating magnetic field. Rotor has no electrical connection, but receives electrical energy by transformer action from field windings.

Industrial Building

A building in which the main purpose is to provide space for manufacturing and assembly processes. These are characterized by high levels of activity both mechanical and human, and often by the generation of internal pollution and heat.

Industrial Conditioning

Industrial conditioning refers to a process, which requires a controlled atmosphere. A typical specification would provide for an internal environment of 21 oc +or- 0.5 oc and 50% relative humidity +or- 2.5% at all external conditions. Industrial conditioning has clearly defined limits as opposed to comfort conditioning, which is based on statistical surveys of occupants' feelings. (see comfort conditioning).


The movement of air from the outside (ambient) to the inside through cracks in the building.


See air leakage.

Infiltration Heat Loss/Or Gains

Heat lost from a building, which is directly attributable to the effects of the cooler outside air leaking into a building and of warm indoor air leaking out.

Infiltration Rate

The rate at which outside air infiltrates a room or building. Equivalent to the fresh air change rate, usually expressed in air changes per hour (ach) or litres per second (l/s). (see air change rate, ach).

Infrared Radiation

Invisible, electromagnetic radiation beyond red light on the spectrum, with wavelengths greater than 0.7 microns.


Any person who examines any component of a building, through visual means and through normal user controls, without the use of mathematical sciences.


Attached or connected such that the installed item requires tools for removal.