Tankless Water Heater GPM Calculator

Tankless Water Heater GPM 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):

Unit Converter ▲

Unit Converter ▼

From:	To:

1. What is the Tankless Water Heater GPM Formula?

The tankless water heater GPM formula calculates the flow rate (gallons per minute) that a tankless water heater can produce based on its BTU rating, efficiency, and desired temperature rise. This helps determine if a unit can meet your hot water demands.

2. How Does the Calculator Work?

The calculator uses the tankless water heater GPM formula:

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

Where:

\( Q \) — Flow rate in gallons per minute (GPM)
\( BTU \) — British thermal units per hour
\( Eff \) — Efficiency factor (0.00 to 1.00)
\( \Delta T \) — Temperature rise in degrees Fahrenheit (°F)
500 — BTU required to heat 1 gallon of water by 1°F
60 — Minutes per hour conversion factor

Explanation: The formula calculates how many gallons of water can be heated per minute based on the heater's energy output and the desired temperature increase.

3. Importance of GPM Calculation

Details: Proper GPM calculation ensures your tankless water heater can supply enough hot water for simultaneous uses (showers, faucets, appliances) without temperature fluctuations.

4. Using the Calculator

Tips: Enter BTU rating from your heater's specifications, efficiency as a decimal (e.g., 0.95 for 95% efficiency), and the temperature rise needed (desired output temperature minus incoming water temperature).

5. Frequently Asked Questions (FAQ)

Q1: What is a typical GPM for tankless water heaters?
A: Residential units typically provide 2-10 GPM depending on BTU rating and temperature rise requirements.

Q2: How do I determine the temperature rise needed?
A: Subtract your incoming groundwater temperature from your desired hot water temperature. Typical groundwater is 50-60°F, desired shower temperature is 105-110°F.

Q3: What efficiency should I use?
A: Modern tankless heaters are 90-98% efficient. Check your unit's specifications for exact efficiency rating.

Q4: Can I run multiple fixtures simultaneously?
A: Add the GPM requirements of all fixtures you plan to use simultaneously and ensure your heater's calculated GPM meets or exceeds this total.

Q5: What if my calculated GPM is too low?
A: Consider a higher BTU unit, reduce simultaneous hot water usage, or install multiple units for different zones.