The minimum flow rate is a key specification for tankless water heaters, indicating the least amount of water (measured in gallons per minute, GPM) that must flow through the unit to activate heating. If flow drops below this threshold, the heater may not turn on, resulting in no hot water. Understanding the minimum flow rate helps match household water usage to the heater’s capabilities for consistent performance and efficient operation.
/ˈmɪnɪməm floʊ reɪt/
The minimum flow rate is a key specification for tankless water heaters, indicating the least amount of water (measured in gallons per minute, GPM) that must flow through the unit to activate heating. If flow drops below this threshold, the heater may not turn on, resulting in no hot water. Understanding the minimum flow rate helps match household water usage to the heater’s capabilities for consistent performance and efficient operation.
Why does minimum flow rate matter?
It determines whether a tankless heater turns on. If flow is too low, the unit won’t activate.
Source: The Cooling Company
Flow rate thresholds determine when tankless heaters activate.
A homeowner ensures bathroom fixtures deliver enough flow to meet a tankless heater’s minimum requirement, preventing cold-water interruptions during showers.
When choosing a tankless water heater, review both minimum and maximum flow rates so the unit activates reliably and meets peak demand.
“When choosing a tankless water heater, review both minimum and maximum flow rates so the unit activates reliably and meets peak demand.”
Minimum flow rate is unique to tankless water heaters and is not required for traditional tank systems.
What is a typical minimum flow rate?
It varies by model, but many tankless heaters activate around 0.4–0.6 GPM.
Can low-flow fixtures prevent activation?
Yes. If total flow is below the unit’s minimum threshold, it may not turn on.
Does maintenance affect minimum flow?
Yes. Scale buildup or clogged filters can reduce flow and prevent activation.
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