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GPM Required = Sum of Fixture Flow Rates
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Tankless water heater sizing involves calculating the required flow rate (GPM) based on the simultaneous use of water fixtures in your home. Proper sizing ensures you have adequate hot water for all your needs without overspending on an oversized unit.
The calculator uses the formula:
Where standard fixture flow rates are:
Explanation: The calculator sums the flow rates of all fixtures that might be used simultaneously to determine the total GPM requirement.
Details: Correct sizing prevents issues like insufficient hot water, temperature fluctuations, and wasted energy. An undersized unit won't meet demand, while an oversized unit costs more to purchase and operate.
Tips: Count the number of each type of fixture that could be used at the same time during peak usage. Consider your household's typical morning and evening routines when estimating simultaneous use.
Q1: What happens if I undersize my tankless water heater?
A: You may experience cold water sandwiches, inadequate hot water during peak usage, and frequent temperature fluctuations.
Q2: Can I oversize a tankless water heater?
A: While not as problematic as undersizing, oversizing increases initial cost and may lead to inefficient operation at lower flow rates.
Q3: What about temperature rise considerations?
A: This calculator focuses on flow rate. Remember that colder incoming water requires a more powerful unit to achieve desired temperature.
Q4: Should I consider future additions?
A: Yes, if you plan to add bathrooms or fixtures, factor these into your calculations for future-proofing.
Q5: What about high-efficiency fixtures?
A: If you have low-flow showerheads (1.5-2.0 GPM) or other efficient fixtures, adjust the flow rates accordingly in your calculations.