HVAC Glossary

Alternative HVAC Solutions would like to offer the following HVAC Glossary as a helpful tool for you, our customer, to help with the various terms and technical definitions for the heating, cooling and indoor air quality industry.

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Make-Up Air -  See "Outdoor Air Supply."
Man-Made Mineral Fibers -  (MMMF) Fiber insulation products including glass wool, fiberglass, rock wool, slag wools, as well as refractory ceramic fibers, which are used for fireproofing.
Manometer -  An instrument that measures air pressure differences between locations. Tubes are usually attached to a manometer and run to the spaces where pressures are measured.
Manual D -  Manual D is the ACCA method for designing duct systems. Contractors often find it a laborious process and most duct systems are just installed, not designed. The amount of time necessary to design a duct system is certainly warranted in tract construction where the design is used repeatedly and for custom homes where the total cost of the home warrants a proper design. In short, designing a duct system is essential for proper equipment performance and customer comfort.
Manual J -  Manual J is a widely accepted method of calculating the sensible and latent cooling (and heating) loads under design conditions. It was jointly developed by the Air Conditioning Contractors of America (ACCA) and the Air-Conditioning and Refrigeration Institute (ARI).
Manual S -  Manual S is the ACCA method of selecting air conditioning equipment to meet the design loads. It ensures that both the sensible capacity and the latent capacity of the selected equipment will be adequate to meet the cooling load.
Mastic -  An adhesive paste used in the fabrication and sealing of thermal insulation on piping fittings, equipment, and duct work. It spreads easily and dries permanently. Its applications include new ducts and old, sheet metal seams, and ductboard. Not all mastics are created equal. Some are toxic, some are water-based, and some take longer to cure, making them more suitable for new construction than retrofit.
Matched System -  A heating and cooling system comprised of products that have been certified to perform at promised comfort and efficiency levels when used together, and used according to design and engineering specifications.
Material Safety Data Sheets -  (MSDS) Product safety information sheets prepared by manufacturers and marketers of products containing toxic chemicals. These sheets can be obtained by requesting them from the manufacturer or marketer. Some stores, such as hardware stores, may have material safety data sheets on hand for products they sell.
Mechanical System -  See HVAC.
Megawatt -  (MW) One thousand kilowatts (1,000 kW) or one million (1,000,000) watts. One megawatt is enough energy to power 1,000 average California homes.
Megawatt Hour -  (MWh) One thousand kilowatt-hours, or an amount of electricity that would supply the monthly power needs of a typical home having an electric hot water system.
MHPU -  (Mobile Home Package Unit) The Mobile Home Package Unit is an air conditioner with electric or gas heat or can be a Heat Pump. This unit has the condenser and air handler all-in-one package. Commonly used in mobile homes and sits outside. (Self-contained unit)
Microbiologicals -  See "Biological Contaminants."
Mildew -  A superficial covering of organic surfaces with fungi under damp conditions.
Mitigation -  A procedure or strategy aimed at reducing or eliminating an indoor air problem, either through source control, ventilation control, exposure reduction, or air cleaning.
Mixing Ratio -  (Relative Humidity) Is often used in drying applications and is the ratio of the mass of water vapor to the mass of dry air with which it is associated. Vaisala products give this output as grams of water per kilogram of dry air (g/kg).
Mold -  A fungal infestation that causes disintegration of a substance. Molds are a group of organisms that belong to the kingdom Fungi. In this document, the terms fungi and mold are used interchangeably. There are over 20,000 species of mold.
Multiple Chemical Sensitivity -  (MCS) A condition in which a person reports sensitivity or intolerance (as distinct from "allergic") to a number of chemicals and other irritants at very low concentrations.
MVOC -  Microbial volatile organic compound, a chemical made by a mold which may have a moldy or musty odor.
Mycotoxin -  A metabolic product generated by certain fungi; includes both useful substances, such as penicillin, and harmful substances, such as aflatoxin.