Ice Melting Equivalent -  (IME-ICE MELTING EFFECT): Amount of heat absorbed by melting ice at 32 ⁰F (0 ⁰C1 is 144 Btu per pound of Ice or 288 000 Btu per ton

Identification plate (Name Plate) – A plate mounted on the unit that Provides information such as manufacturer, part number and specifications.

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

Ignition Transformer - Transformer designed to provide a high-voltage current. Used in many heating systems to ignite fuel; provides a spark gap.

Impedance - Similar to resistance but applies to AC circuits.  The opposition a component in a circuit offers to the flow of alternating current at a given frequency. If the frequency changes,  the impendence changes too. Impendence is measured in ohms and has the symbol Z with the unit ohms

Impeller – a part of a pump that causes the fluid to move. Similar to a blade.

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

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

Inductive Reactance – The induction of Electromagnetic energy in a circuit that creates a counter or reverse voltage as the original current changes.  It may also be thought of as a resistance since it opposes the flow of alternating current. 

Inductance - A changing current in a coil produces a changing magnetic flux. The changing magnetic flux results in an induced current flowing in the coil. The unit is a Henry .

Infiltration -  The passage of outside air into building through doors, cracks around windows, etc.

Infrared Lamp -  Electrical device that emits infrared rays; invisible rays just beyond red in the visible spectrum.

Inhibitor – A chemical that prevents corro­sion or oxidation.

Instrument - Used broadly to denote a device that has measuring, recording, indicating, and/or controlling abilities.

Insulation, Electric – A substance which has almost no free electrons.

Insulation, Thermal  – A material with low heat conductivity.

Integrated Circuit (IC) - A circuit that incorporates multiple transistors and other semiconductors to a single circuit, sometimes called a "chip."

Intermittent Cycle – A cycle which repeats itself.

Interrupted Cycle – A cycle that does not repeats it self.

Interstate Commerce Commission - Government body which controls the design and construction of pressure containers.

Ion- Group of atoms or an atom electrically charged.

IR Drop – A voltage drop, IR meaning Current times resistance  and equaling voltage (Ohm’s Law).

Isobutane - A flammable hydrocarbon refrigerant.

Isothermal - Changes of volume or pressure under conditions of cons­tant temperature.

Isothermal Expansion and contraction - an action which takes place without a temperature change.