Activation Flow Rate is the minimum amount of water flow needed to activate a tankless water heater. Measured in gallons per minute (GPM), this rate varies by model and determines whether the heater turns on at low-demand fixtures.
/ˌæktɪˈveɪʃən floʊ reɪt/
Activation Flow Rate is the minimum amount of water flow needed to activate a tankless water heater. Measured in gallons per minute (GPM), this rate varies by model and determines whether the heater turns on at low-demand fixtures.
What is activation flow rate in a tankless water heater?
It is the minimum water flow, measured in GPM, that must pass through a tankless heater to turn it on. If flow falls below that threshold, the unit will not activate.
Source: The Cooling Company
Water heaters activate only when flow meets the minimum GPM.
Understanding activation flow rate helps homeowners choose a tankless unit that matches daily water usage so hot water turns on reliably at sinks and showers.
Always check the manufacturer's activation flow rate before selecting a tankless water heater and compare it to your typical low-flow usage.
“Always check the manufacturer's activation flow rate before selecting a tankless water heater and compare it to your typical low-flow usage.”
Traditional tank water heaters do not use activation flow rates because they store and continuously heat water.
Why won't my tankless water heater turn on?
If the flow rate is below the unit's activation threshold, it will not fire. Low-flow fixtures, clogged filters, or low pressure are common causes.
Can activation flow rate change over time?
Yes. Scale buildup, clogged inlet screens, or reduced water pressure can effectively raise the activation threshold.
How do I choose the right activation flow rate?
Compare the model's minimum GPM to your lowest-flow fixtures and expected usage. A professional can measure flow rates to confirm fit.
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