How many water closets require duplex pumps?

When determining the number of water closets that require duplex pumps, it is important to understand the context of when duplex pumps are necessary. Duplex pumps are typically used in plumbing systems to ensure reliability and redundancy, particularly when the number of fixtures being serviced exceeds certain thresholds.

In this scenario, the plumbing code stipulates that a duplex pumping system is generally required when there is a certain number of water closets or fixtures within a system that may lead to significant water flow demands. Having more than a specified number of water closets can create situations where a single pump may not be able to handle the load effectively, especially during peak usage times.

Based on the Massachusetts Plumbing Code, when the number of water closets reaches five, a duplex pump system is often mandated. This is due to the need for both continuous operation and the ability to handle potential failures in one of the pumps. The reasoning behind requiring a duplex system for five water closets is to enhance the reliability of the waste removal system in residential or commercial settings, ensuring that there is always a backup available in case one pump needs maintenance or fails.

Therefore, the correct response indicates that for five water closets, duplex pumps are necessary to meet the demand and ensure a properly functioning plumbing system.