Tankless Water HeaterBuying Guide2025-09-20
Tankless Flow Rate and Sizing
Sizing a tankless unit means matching its flow rate (GPM) to your peak simultaneous hot-water demand.
Unlike tanks, tankless units are sized by flow rate. Getting it right ensures endless hot water even during peak use.
How tankless sizing works
Add up the flow (GPM) of fixtures you might use at once — showers, taps, dishwasher — and factor the cold incoming water temperature. The unit must deliver that GPM at the needed temperature rise.
BC considerations
Colder incoming water in winter reduces a tankless unit's effective GPM, so correct sizing for our climate prevents disappointment during cold months.
Key takeaways
- Size by peak simultaneous GPM demand
- Account for cold winter inlet temperatures
- Undersizing causes lukewarm peak-time water
- Consider future demand (added bathrooms)
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Frequently asked questions
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