Which value is correct for gallons per minute per fixture unit?

Which value is correct for gallons per minute per fixture unit?

• A. 5.0
• B. 7.5
• C. 10.0
• D. 6.0

Answer: (B)

When sizing a water supply, you convert all fixtures into a common unit called fixture units and then apply a standard flow rate per fixture unit to estimate peak demand. In this context, the standard rate is 7.5 gallons per minute per fixture unit. So you multiply the total fixture units in the building by 7.5 to get the expected maximum flow the system must supply. This value reflects typical simultaneous use and keeps pipe sizing and pressure adequate without overbuilding. Using 7.5 as the per-fu rate is why this choice is correct. Values like 5.0 or 6.0 would underpredict the demand, risking undersized piping and pressure loss, while a higher value like 10.0 would overestimate and incur unnecessary cost. The 7.5 gpm per fixture unit falls in line with standard design practice for domestic water supply sizing.

When sizing a water supply, you convert all fixtures into a common unit called fixture units and then apply a standard flow rate per fixture unit to estimate peak demand. In this context, the standard rate is 7.5 gallons per minute per fixture unit. So you multiply the total fixture units in the building by 7.5 to get the expected maximum flow the system must supply. This value reflects typical simultaneous use and keeps pipe sizing and pressure adequate without overbuilding.

Using 7.5 as the per-fu rate is why this choice is correct. Values like 5.0 or 6.0 would underpredict the demand, risking undersized piping and pressure loss, while a higher value like 10.0 would overestimate and incur unnecessary cost. The 7.5 gpm per fixture unit falls in line with standard design practice for domestic water supply sizing.