This Revivalty Engineering knows MEP/FP building terms can sometimes be confusing. This is why we've created the definitive MEP/FP Terms and Definitions Glossary below. Still have questions? Reach out to us...

 3-Way Switch

A type of electrical switch that allows you to control a light or fixture from two different locations. It’s commonly used in hallways or staircases where you need to turn a light on or off from either end. The switch works in pairs and is wired to control the same fixture from two separate points. A 4-way switch allows you to perform the above from 3 locations.

 Air Handling Unit (AHU)

Mechanical equipment that controls and circulates air as part of an HVAC system. It helps to filter, cool, heat, and distribute air throughout a building.

Automatic Transfer Switch (ATS)

A device that automatically switches the power supply from the primary electrical source (typically the utility grid) to a backup power source (such as a gas or diesel generator) in the event of a power failure. The ATS ensures that electrical power remains uninterrupted, providing a seamless transition during outages.

Authority Having Jurisdiction (AHJ)

The AHJ refers to the official or agency that has the legal authority to enforce building codes, standards, and regulations. This entity is typically responsible for approving designs, inspecting work, and ensuring that construction projects comply with safety and code requirements.
In practical terms, the AHJ could be:
• Local building departments (city or county inspectors)
• Fire marshals
• Health departments (for plumbing or water systems)
• Electrical inspectors
• Etc.

Backflow Preventer

A device used to prevent the reverse flow of water, ensuring that contaminated water doesn't flow back into the clean water supply. AHJ’s will often require a backflow preventer form to be filled out by an engineer or contractor.

Cassettes

A type of ceiling-mounted HVAC unit that provides both heating and cooling, typically used in spaces where a ducted system isn't ideal. Cassettes distribute air in multiple directions and are often used in commercial or residential spaces with limited ceiling height and duct space. These typically work with ductless split systems.

Clash Coordination

The more specific process of MEP coordination which involves identifying and resolving conflicts or "clashes" between different building systems (like mechanical, electrical, plumbing, or fire protection) during the design and construction phases. It ensures that systems don't interfere with each other, helping to avoid costly rework and delays. Clash coordination is typically done using 3D modeling software (BIM - Building Information Modeling) to visualize and adjust designs before construction begins.

Condenser

A piece of equipment that cools down refrigerant gas from an air conditioner or refrigerator, turning it back into a liquid form so it can cycle again.

Dampers

Valves or movable plates in air ducts that control airflow. They are used to regulate ventilation, temperature, and air pressure in HVAC systems. Dampers can be electronic or mechanical.

Dehumidifier

A device used to remove excess moisture (humidity) from the air in a building or space. It helps to maintain comfortable indoor air quality, prevent mold growth, and protect sensitive equipment or materials from moisture damage.

Design-Build

By definition, a design-build entails a single party being in charge of both the design and delivery of the project. In practice, it typically implies an owner or general contractor building the project without a set of formal blueprints, typically by relying on rough sketches, calculations, and experience from similar past installations.

Domestic Water

Water that is used for general consumption in a building, including drinking, cooking, bathing, etc. It’s distinct from fire protection or irrigation water. When a contractor, civil engineer, AHJ, etc., requests a domestic water main size or domestic water calculations, they will typically want to know the size of the main water pipe serving the space (1/2", 1", 2", etc.).

Ductless Mini-Split

Also known as a ductless system, this entails a heating and cooling system that doesn't require ducts. It uses small air handlers inside each room connected to an outdoor compressor unit, offering flexibility and energy efficiency. These units typically pair with ERVs to ensure fresh air is still circulated within the space.

Electrical Switchgear

A collection of electrical devices used to protect, control, and isolate electrical equipment in a building or industrial setting. Switchgear includes circuit breakers, fuses, switches, and other devices designed to interrupt the flow of electricity in case of an issue like an overload or short circuit. Switchgear can entail something as simple as a 100 Amp Disconnect or a custom-ordered 4000A Electrical Switchboard.

Exhaust Fan (EF)

A fan used to expel hot, moist, or stale air from a building, often found in kitchens, bathrooms, or industrial spaces. Unlike ERVs, exhaust fans do not provide return air.

Fault Current Calculations

A critical calculation used to determine the maximum electrical fault current (short-circuit current) that could flow in a system during a fault condition. These calculations are essential for selecting protective devices (like circuit breakers and fuses) that will safely interrupt the flow of current and prevent equipment damage or fire hazards.

Fire Pump

A specialized pump designed to provide a reliable and high-pressure water supply for fire protection systems, like sprinklers or standpipes. Fire pumps are typically used when the standard water pressure is insufficient to meet the needs of a fire protection system.
Example: In a tall building, a fire pump might be needed to ensure that water reaches the top floors in case of a fire emergency.

Firestop

Materials or devices used to seal gaps and openings around fire-rated walls, ceilings, or floors to prevent the spread of fire and smoke.

Flow Switch

A device in piping systems that detects the flow of water or other liquids. It is used to ensure proper operation of systems like sprinklers or pumps.

GFCI (Ground Fault Circuit Interrupter)

A safety device in electrical systems that shuts off power if it detects a difference between the hot and neutral wires, preventing electrical shocks. Codes require GFCI protection for receptacles in kitchens, outdoors, near water sources, and other places.

Grease Interceptor

A plumbing device used to capture and remove grease, oils, and other solids from wastewater before it enters the main sewer system. Grease interceptors are typically installed in kitchens, restaurants, and food processing facilities to prevent grease buildup in the plumbing system, which can cause clogs and blockages. These devices help maintain proper wastewater flow and prevent environmental contamination. Sizing usually requires coordination with the Authority Having Jurisdiction (AHJ). The cost of an underground grease interceptor, which can range from $50,000 to $100,000, often surprises new restaurant owners.

Heat Pump

In simple terms, heat pump technology works by transferring heat rather than creating it. It is a piece of mechanical equipment that can both heat and cool a building by transferring heat between the indoors and outdoors. During winter, it extracts heat from the outside air and moves it indoors; in the summer, it works in reverse to cool the space by removing heat from inside and releasing it outside.

Heat Pump Water Heater

Just like a heat pump, a heat pump water heater is a type of water heater that uses a heat pump to transfer heat from the air or ground to heat water. They are much more energy-efficient than traditional water heaters in warmer weather and warmer climates by acting as a small air conditioner, pulling heat from the environment to warm water.

HVAC (Heating, Ventilation, and Air Conditioning)

The system used in buildings to control the indoor climate, including heating and cooling, air quality, and humidity.

Hydronic System

A heating or cooling system that uses water to transport heat through pipes, typically to radiators or fan coil units, to regulate temperature. Such systems are typically controlled from a boiler but can also be connected to a water heater and take care of both space and water heat.

Isolated Ground

A specialized electrical grounding system that prevents noise or interference from affecting sensitive equipment like computers or medical devices.

J-Box (Junction Box)

An electrical box used to protect electrical connections, providing a safe place to join wires together and prevent short circuits or fires.

Knuckle Joint

A mechanical connection used in fire protection systems, typically in sprinkler systems, that allows for flexible movement or adjustment while maintaining a secure connection.

Louver

A ventilation opening or cover with slanted blades, usually on windows, ducts, or walls, designed to allow air to flow while blocking rain, dust, or direct sunlight.

Make-Up Air Unit

A system used to introduce fresh, outside air into a building to replace air that has been exhausted by ventilation systems, such as exhaust fans or kitchen hoods. The make-up air unit ensures that the indoor air pressure remains balanced and that there is enough ventilation to maintain air quality and comfort. These units often include filters, heating or cooling elements, and sometimes humidity control to treat the incoming air before it enters the building. These are most commonly found in commercial kitchens.

MEP Coordination

The process of ensuring the mechanical, electrical, and plumbing systems are designed and installed without interfering with each other, making the entire system work efficiently.

MEP/FP

Acronym for Mechanical, Electrical, Plumbing and Fire Protection Engineering: Services will typically also include Fire Alarm.

NEC (National Electrical Code)

A set of safety standards and regulations published by the National Fire Protection Association (NFPA) to ensure safe electrical installations in buildings. The NEC covers everything from wiring methods to electrical panel requirements and is updated every three years to reflect new technologies and safety practices. It's important to check with your state and the Authority Having Jurisdiction (AHJ) to determine which year of the NEC to follow, as many states may have amendments that add additional regulations beyond the national code.

NFPA 241 Report

A report that outlines the fire protection measures in place during construction or renovation of a building. It is a requirement under NFPA 241 (Standard for Safeguarding Construction, Alteration, and Demolition Operations) to ensure safety from fire hazards during the building process.

Pressure Reducing Valve (PRV)

A valve used to reduce the incoming water pressure to a safer, more manageable level for plumbing systems or equipment.

Redundant Ground

Not to be confused with Isolated Ground, a redundant grounding system is a grounding system used to ensure electrical safety in case the primary grounding system fails. It typically involves multiple ground connections to different points, ensuring that electricity has a safe path to flow in the event of a fault, preventing electrical shock or fire hazards.
This is typically code-required in critical facilities like hospitals but is also used in data centers. Redundant grounding ensures that even if one grounding system fails, the electrical system remains safe and functional.

Riser Diagram

A diagram that demonstrates how power, water, HVAC, etc., gets distributed throughout a building and/or a space within it. Electrically, these are often called One-Line Diagrams or Single-Line Diagrams.

Standpipe System

A vertical pipe system in buildings used by firefighters to provide a reliable source of water flow for firefighting on each floor. These typically run within stairways.

Tankless Water Heater

A water heater that heats water on demand, rather than storing hot water in a tank. When you turn on the hot water tap, the unit heats the water as it passes through, providing an endless supply of hot water without the storage space and standby energy needed for a storage tank. These typically must be gas, as tankless electric water heaters can be overly taxing on the electrical system.

Hydrant Flow Test

A test performed to measure the water flow and pressure available from a fire hydrant. This test is critical for determining whether the water supply in an area is sufficient to fight a potential fire within a building. It is often required by fire marshals or AHJs (Authorities Having Jurisdiction) when designing new fire protection systems. Typically, civil engineers, general contractors, or project owners will order this test to ensure that the available water pressure is adequate for systems like sprinklers or standpipes in a new building. Hydrant flow tests are generally conducted during warmer weather, usually when the temperature is at least 50°F for three consecutive days.

VAV Unit (Variable Air Volume Unit)

An HVAC system component that adjusts the amount of air supplied to a room or zone based on the temperature or load requirements. VAV units are used in buildings with multiple zones that have varying heating or cooling needs. Most commonly, these are found in office and medical spaces within large buildings. They allow for more efficient energy use by delivering just the right amount of air at just the right temperature to each space.

Zoning

In HVAC, zoning refers to dividing a building into separate areas that can be individually controlled for temperature, airflow, and humidity.