What Size Tankless Water Heater Do You Need for a Family of 5?

To determine the appropriate size of a tankless water heater for a family of five, you need to consider both the peak hot water demand and the temperature rise required. Here’s a detailed guide to help you make an informed decision.

1. Calculate Peak Hot Water Demand

To calculate the peak hot water demand, estimate the maximum flow rate needed when multiple fixtures are used simultaneously. Common flow rates for fixtures are as follows:

Shower:2.5 gallons per minute (GPM) Kitchen faucet:2 GPM Bathroom faucet:1.5 GPM Dishwasher:1.5 GPM Washing machine:2 GPM

For a family of five, the following usage can be estimated:

2 showers: 5 GPM 1 kitchen faucet: 2 GPM 1 washing machine: 2 GPM

This adds up to approximately 9 GPM during peak usage.

2. Determine Temperature Rise

The temperature rise is the difference between the incoming water temperature and the desired output temperature. For example, if your incoming water is 50°F and you want it heated to 120°F, the temperature rise would be 70°F.

3. Choose the Right Heater

Tankless water heaters are rated by their flow rate at a specific temperature rise. Carefully check the specifications of the heaters you’re considering to ensure they can provide the required flow rate at your desired temperature rise.

4. Recommended Size

For a family of five, you generally want a unit that can provide at least 8-10 GPM at your desired temperature rise. Some models may be capable of higher flow rates if needed.

5. Consider Installing Multiple Units

In some cases, especially if your peak demand is very high (like multiple showers and appliances running simultaneously), you might consider installing multiple units to meet your needs.

Conclusion

When selecting a tankless water heater for a family of five, aim for a unit that can deliver 8-10 GPM at your desired temperature rise. It's also a good idea to consult with a professional plumber to assess your specific needs and ensure proper installation.

Additional tips and considerations for tankless water heaters include:

Ensure you install a perfectly positioned expansion tank to handle the system’s pressure changes. Regular maintenance can extend the life of your tankless water heater and improve performance. Consider the lifespan of the heater units, as some manufacturers offer warranties and long-term performance guarantees.

Remember, when calculating your water heater's size, accuracy and careful planning are crucial to avoid short-term and long-term issues that can arise from choosing the wrong size.