Gas Tankless Water Heater Sizing Calculator

Gas Tankless Water Heater Sizing Formula:

\[ Q = \frac{BTU \times Eff}{\Delta T \times 500 \times 60} \]

BTU (British Thermal Units per hour):

BTU/hr

Efficiency (Eff):

decimal (0.00-1.00)

Temperature Rise (ΔT):

°F

Flow Rate (Q):

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1. What is Gas Tankless Water Heater Sizing?

Gas tankless water heater sizing determines the appropriate flow rate capacity based on the unit's BTU rating, efficiency, and required temperature rise. Proper sizing ensures adequate hot water supply for household needs.

2. How Does the Calculator Work?

The calculator uses the gas tankless water heater sizing formula:

\[ Q = \frac{BTU \times Eff}{\Delta T \times 500 \times 60} \]

Where:

\( Q \) — Flow rate (gallons per minute)
\( BTU \) — British thermal units per hour
\( Eff \) — Efficiency (decimal from 0 to 1)
\( \Delta T \) — Temperature rise (°F)

Explanation: The formula calculates how many gallons per minute of hot water the heater can produce based on its energy input, efficiency, and the desired temperature increase.

3. Importance of Proper Sizing

Details: Correct sizing prevents issues like insufficient hot water, energy waste, and premature equipment failure. Oversized units waste energy while undersized units cannot meet demand.

4. Using the Calculator

Tips: Enter BTU rating from manufacturer specifications, efficiency as a decimal (e.g., 0.95 for 95%), and the temperature rise needed (typically 40-70°F depending on climate and incoming water temperature).

5. Frequently Asked Questions (FAQ)

Q1: What is a typical BTU rating for residential tankless water heaters?
A: Residential units typically range from 140,000 to 199,000 BTU/hr, while commercial units can exceed 300,000 BTU/hr.

Q2: What efficiency should I expect?
A: Modern condensing tankless water heaters typically have 90-98% efficiency, while non-condensing models range from 80-85%.

Q3: How do I determine the required temperature rise?
A: Subtract your incoming groundwater temperature from your desired hot water temperature. Groundwater temperatures vary by region from 35°F to 75°F.

Q4: What flow rate do I need for my home?
A: Typical requirements: 1-2 GPM for showers, 1-2 GPM for dishwashers, 2-3 GPM for bathtubs. Add simultaneous usage for accurate sizing.

Q5: Can this calculator be used for electric tankless water heaters?
A: No, electric units use different calculations based on kW rating and voltage. This formula is specific to gas-fired units.