Minimum Ventilation Requirement

The minimum quantity of outdoor or conditioned air entering a building, which is needed to maintain acceptable indoor air quality. (see acceptable air quality).

Miter

To cut ends of two pieces of wood at an angle so they can be joined to form a corner.

Mixing Fan

Small fan used to aid the mixing of room air and tracer gas before and/or during ventilation rate measurements.

Mixing Flow Ventilation

Mixing flow describes a method of air distribution from an air conditioning or ventilation system. It is the most widely used method of supplying air into an atmosphere being air-conditioned. This form of air distribution commonly uses ceiling diffusers or wall grilles at high level. Most air conditioning and air-handling units are manufactured for the mixed flow air distribution market.

Mobile Home/Trailer

A house trailer a complete livable dwelling equipped with wheels so that it may be towed from place to place by a truck or automobile, depending upon its size and the highway regulations of the states through which it will travel.

Model Energy Code (Mec)

The Model Energy Code is cited in the 1992 U.S. Energy Policy Act (EPAct) as the baseline for residential Energy Codes in the United States. It has been succeeded by the International Energy Conservation Code (IECC) published by the International Code Council (ICC).

Modular Construction

Prefabrication in three dimension. Entire rooms are built in a factory and shipped to their eventual location, where very little ansate labor is required.

Modulating

A control action that adjusts by minute increments and decrements.

Moisture Barrier

The insulation material placed in a wall, floor or other parts of a structure to form a barrier against the passage of vapor or moisture in order to prevent condensation within such walls or floor.

Moisture Content

The weight of the water in wood expressed as a percentage of the weight of oven dry wood.

Molding

Milled piece of lumber used to hide a joint or add a finished look.

Monitor Roof

A type of framing which includes an elevated central section. It is generally encountered in industrial buildings and provides better lighting and ventilation.

Monitoring

The process of collecting, analyzing, and reporting data.

Mortar

Mixture of cement , sand, water and sometimes lime used as an adhesive for laying brick, stone, ceramic tile and concrete block.

Mortise

Recess made in a piece of wood to receive a lockset, hinge or other piece of hardware.

Mosaic

A decoration made of small pieces of glass, stone, ceramic or other material laid in mortar or mastic to form a design.

Mullion

A thin, vertical bar of wood, lead or stone that divides multiple windows, panes of glass, wall panels, screens, etc. A major structural vertical or horizontal member between window units or sliding glass doors.

Multizone

A building or part of a building that comprises a number of zones or cells.

Muntin

A slender horizontal bar of wood or metal that divides panes in a window or panels in a door.  A secondary framing member (horizontal, vertical, or diagonal) to hold the window panes in the sash. This term is often confused with mullion.

Muntin Grilles

Wood, plastic, or metal grids designed for a single-light sash to give the appearance of muntins in a multilight sash, but removable for ease in cleaning the window.

Nailing Fin

An integral extension of a window or patio door frame which generally laps over the conventional stud construction and through which nails are driven to secure the frame in place.

Natural Convection

The movement of a fluid caused by temperature differences (density changes).

Natural Ventilation

The movement of outdoor air into a space through intentionally provided openings, such as windows and doors, or through non powered ventilators or by infiltration.

Negative Pressure

A condition that exists when less air is supplied to a space than is exhausted from the space, so the air pressure within that space is less than that in surrounding areas.

Neoprene

A synthetic rubber which is resistant to hydrocarbon oil and gas.

Neutral Pressure Level

The level at which the air pressure difference, derived from the stack effect between inside and outside a building is zero.

Neutralizer

The substance used to counteract acids, in refrigeration system.

NFRC

National Fenestration Rating Council.

Night Setback Control

An energy management function which acts to reduce the occupancy temperature by a few degrees, with the heating ticking over to maintain it. It is not usually as effective compared to the modern practice of intermittent heating, where the system is switched off overnight.

No-Cutout Shingles

Shingles consisting of a single, solid tab with no cutouts.

Nominal Size Tubing

A tubing measurement which has an inside diameter the same as iron pipe of the same stated size.

Non-Condensable  Gasses (Air)

Air that enters the evaporator through a vacuum leak and migrates to the condenser (in low-pressure chillers only). This affects the condenser head pressure, condenser refrigerator approach temperature and condenser heat transfer efficiency.

Non-Expansive Soil

A soil which does not contain a significant amount of clay minerals which experience considerable volume changes in response to changes in the moisture content.

Non-Loading Bearing Wall

A wall which supports no load other than its own weight.

Normal

Conforming with an accepted standard or model, corresponding to the median or average for type, appearance or function, i.e., natural standard or regular.  As in "operating within normal parameters" or "operating according to specs".

Normal Operating Controls

Homeowner operated devices such as a thermostat, wall switch or safety switch.

Normal Slope Application

Method of installing asphalt shingles on roof slopes between 4 inches and 21 inches per foot.

Not Inspected

Not applicable or not inspected due to conditions or circumstances existing at the time of the inspection.

NPLV - Non-Standard Part Load Value

A single number, part-load efficiency indicator calculated using the ARI method referenced to rating conditions other than ARI standard. The 1998 standard adopted NPLV for situations when a single chiller is not intended to operate at standard ARI rating conditions.

Obscure Glass

Any textured glass (frosted, etched, fluted, ground, etc.) used for privacy, light diffusion, or decorative effects.

Occupancy Rate

The number of people expected to occupy a given space.