A (23) B (23) C (41) D (27) E (28) F (15) G (12) H (21) I (20) K (5) L (11) M (16) N (15) O (11) P (21) R (22) S (37) T (14) U (12) V (11) W (10)
Manual (nonautomatic)

Requiring personal intervention for control. Nonautomatic does not necessarily imply a manual controller, only that personal intervention is necessary.

Marked (nameplate) Rating

The design load operating conditions of a device as shown by the manufacturer on the nameplate or otherwise marked on the device.

Mass Wall

A wall with a heat capacity exceeding (1) 7Btu/ft2 or (2) 5 Btu/ft2 x F provided that the wall has a material unit weight not greater than 120 lb/ft3.

Mean Temperature

One-half the sum of the minimum daily temperature and maximum daily temperature.

Mechanical Cooling

Reducing the temperature of a gas or liquid by using vapor compression, absorption, desiccant dehumidification combined with evaporative cooling, or another energy-driven thermodynamic cycle. Indirect or direct evaporative cooling alone is not considered mechanical cooling.

Mechanical System

The system and equipment used to provide heating, ventilating, and air conditioning functions as well as additional functions not related to space conditioning, such as, but not limited to, freeze protection in fire protection systems and water heating.


Midwest Energy Efficiency Alliance

Metal Building

A complete, integrated set of mutually-dependent components and assemblies that form a building consisting of a steel-framed superstructure and metal skin.

Metal Building Roof

A roof that (a) is constructed with a metal, structural, and weathering surface; (b) has no ventilated cavity; and (c) has the insulation entirely below deck (i.e., includes neither a composite concrete and metal deck construction nor a roof framing system that is separated from the superstructure by a wood substrate), and whose structure consists of one or more of the following configurations: (1) metal roofing in direct contact with the steel framing members, (2) insulation between the metal roofing and the steel framing members, or (3) insulated metal roofing panels installed as described in 1 or 2.

Metal Building Wall

A wall whose structure consists of metal spanning members supported by steel structural members (i.e., does not include spandrel glass or metal panels in curtain wall systems).

Metal Halide Lamps

A type of high intensity discharge (HID) lamp in which most of the light is produced by radiation of metal halide and mercury vapors in the arc tube. Available in clear and phosphor-coated lamps.


Instruments that measure electric voltage, current, power, etc.


Midwest Insulation Contractors Association.

Model Energy Code (MEC)

The Model Energy Code. The MEC was first published in 1983, with subsequent full editions published in 1986, 1989, 1992, 1993, and 1995. The MEC became the IECC, first published in 1998.

Motor Power Rated

The rated output power from the motor.


A multi-family building is a residential building three stories or fewer in height that contains three or more attached dwelling units. Multi-family buildings include apartments, condominiums, townhouses, and rowhouses. Hotels and motels are considered commercial rather than residential buildings.