Fire Pump Sizing and Selection

A properly sized fire pump is critical to ensuring your fire sprinkler system will work appropriately and keep your building protected. Standards for sizing and selection of fire pumps are governed by NFPA 20: Standard for the Installation of Stationary Pumps for Fire Protection.

Calculating Fire Pump Pressure Requirements

Depending on the size and layout of your building, your fire pump needs to maintain a specific amount of pressure, measured in gallons per minute (GPM). Pressure requirements for your fire pump can be calculated via two different methods: the “standpipe method” or sprinkler area calculations.

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Fire Pump Calculations Using the Standpipe Method

The standpipe method for calculating fire pump pressure requirements is governed by NFPA 14, Standard for the Installation of Standpipes and Hose Systems. The standpipe method is an easy method of calculation that can be used by smaller buildings.

Under the standpipe method, calculations are based on the number of standpipes your fire sprinkler system relies on. According the protocol, the first standpipe in your building is required to maintain a pressure rating of 500 gpm. Any additional standpipes must maintain a pressure of 250 gpm, and the whole system must be pressurized to a maximum of 1000 gpm.

Because 1000 gpm is the maximum pressure allowed by the standpipe method, it is ideal for smaller buildings but becomes a problem for larger buildings that require additional standpipes.

Fire Pump Calculations Using Sprinkler Area Calculations

Sprinkler area calculations are a more complicated way to calculate fire pump size requirements, but they are extremely effective for larger buildings and buildings with a variety of fire hazards.

Before sprinkler area calculations can be made, hazard levels throughout your building must be defined. Sprinkler hazard calculations are defined as follows:

• Light Hazard – areas classified as Light Hazard contain a low quantity of combustible materials. Typically, churches, hospitals, museums, office buildings, and similar buildings are considered light hazard.
• Ordinary Hazard 1 – areas defined as Ordinary Hazard 1 contain a moderate quantity of combustible materials or have materials stored in 8-foot stockpiles. Examples of such areas may include mechanical rooms, commercial kitchens, laundry facilities, etc.
• Ordinary Hazard 2 – Ordinary Hazard 2 areas are similar to ordinary hazard 1, but may contain materials stored in 12-foot stockpiles. Examples of such areas may include stages, large library stack rooms, or repair garages.
• Extra Hazard 1 – places in your building labeled Extra Hazard 1 contain a large amount of combustible materials but no flammable liquids, such as aircraft hangars or saw mills.
• Extra Hazard 2 – Extra Hazard 2 areas also include a large amount of combustible materials, but also contain flammable liquids. These areas may be found in plastics processing plants or anywhere with flammable liquids spraying.

Most large buildings have areas in a variety of different hazard levels. In this case, the highest hazard level in the building will be used to determine the fire pump size requirements.

Selecting the Fire Pump

Once the required size for your fire pump has been determined, the next thing to do if figure out which type of fire pump is best suited. The three types of fire pumps include:

• Horizontal split case
• Inline
• Vertical turbine

Horizontal Split Case Fire Pumps

Horizontal split case fire pumps, also called double-suction fire pumps, are the most common types of fire pumps. They typically come rated for 250-5000 gpm. Interestingly, horizontal split case pumps were the first type of fire pump used in fire protection systems.

Inline Fire Pumps

Inline fire pumps usually take up less room and have lower installation costs than horizontal fire pumps, making them ideal in certain situations.

Vertical Turbine Fire Pumps

NFPA protocols dictate that positive suction pressure is required for a fire pump to work properly.  In areas where this is not possible, a vertical turbine fire pump may be required.

A properly sized fire pump is critical to ensuring your fire sprinkler system keeps safe your building and the people and property within it.