# How long should I run the recirculation pump on a Rinnai RE Model Series tankless water heater, like the RE199iP, to ensure hot water reaches my fixtures quickly?

Running a recirculation pump on a Rinnai RE Model Series tankless water heater, such as the RE199iP, can significantly reduce the time it takes for hot water to reach your fixtures. However, the ideal runtime for the recirculation pump can vary based on factors like the distance from the water heater to the fixtures, your specific plumbing configuration, and your preferences for hot water availability. Here's a guideline on how to determine the appropriate runtime for your recirculation pump:

1. Measure the Distance: Start by measuring the distance between your Rinnai tankless water heater and the farthest fixture that requires hot water. This distance is crucial because it determines how long it takes for hot water to travel through the pipes.
2. Calculate Flow Rate: Determine the flow rate of your recirculation pump. The flow rate is typically measured in gallons per minute (GPM) and indicates how much water the pump can move through the system in a minute.
3. Determine Desired Hot Water Availability: Consider how quickly you want hot water to reach your fixtures. Some people prefer near-instant hot water, while others are comfortable with a short delay.
4. Calculate Runtime: To calculate the runtime for the recirculation pump, use the following formula:
Runtime (minutes) = Distance (feet) / (Flow Rate (GPM) x 60)
For example, if the distance from your water heater to the farthest fixture is 50 feet, and your recirculation pump has a flow rate of 0.5 GPM, the runtime would be:
Runtime = 50 feet / (0.5 GPM x 60) = 16.67 minutes

This calculation provides an estimate of the runtime required to ensure hot water reaches your fixtures quickly. In the example above, running the recirculation pump for approximately 17 minutes should provide relatively fast hot water access to all fixtures.

1. Adjust for Preferences: The calculated runtime is a starting point, and you can adjust it based on your preferences. If you want even faster hot water access, you can increase the runtime slightly. Conversely, if you are comfortable with a slightly longer delay, you can decrease the runtime to save energy.
2. Use a Timer or Smart Control: To make it convenient, many recirculation systems come with timers or smart controls. These allow you to set specific schedules for the pump to run automatically, ensuring hot water is readily available during peak usage times. You can program the pump to run only when needed, such as in the morning and evening when you typically use hot water.
3. Monitor Performance: After setting the recirculation pump runtime, monitor its performance. If you notice that hot water is still taking too long to reach your fixtures or if you experience inconsistent results, you may need to adjust the runtime further or consider other factors, such as potential issues with your plumbing system.

It's worth noting that running the recirculation pump continuously can be energy-intensive and may not be necessary for all households. Adjusting the runtime based on your specific needs and preferences is a practical approach to balance convenience and energy efficiency. Properly setting up and fine-tuning your recirculation system can help you enjoy quick access to hot water while minimizing energy consumption.
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