How do I know what size tankless water heater I need?
Tankless water heater sizing depends on your home's peak flow rate (GPM), which is calculated by adding up the flow rates of all appliances and showers you might use at the same time. Undersizing the unit will leave you with a shortage of hot water, while matching it correctly to your household demand ensures you do not fall short during peak usage.
What people tried
Every workaround mentioned in the threads below. We haven’t tested any of them — and nobody here is claiming they worked.
Found another way around this?
Share your steps and trade-offs so fellow engineers don't have to reinvent the wheel. No account required.
How do I know what size tankless water heater I need?
- 1Researching flow rate requirements independently and consulting plumbers for recommendations.Did this help you?
- 2Installing a traditional thermal expansion tankDid this help you?
- 3Relying on a thermal expansion control valve as an alternativeDid this help you?
In their words
Unedited, grouped by where they were said, most upvoted first within each place, each linked to the thread it came from.
“Looking at the model currently places it at a max of 6.8 gpm which by my research is way short by what is generally recommended. By what I listed above we should be around the 9 gpm closer to 10, is the recommended model by the plumber satisfactory or is he incorrect?”source ↗
Where this came up
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