1. What is a Tankless Gas Water Heater Calculator?

Definition: This calculator estimates the BTU (British Thermal Units) required for a tankless gas water heater based on flow rate, temperature rise, and system efficiency.

Purpose: It helps homeowners and plumbers properly size tankless water heaters for residential or commercial applications.

2. How Does the Calculator Work?

The calculator uses the formula:

Where:

• \( BTU \) — British Thermal Units per hour (BTU/h)
• \( Q \) — Flow rate in gallons per minute (gpm)
• \( \Delta T \) — Temperature difference in °F (desired - incoming)
• \( \text{efficiency\_factor} \) — System efficiency (typically 0.82 for 82% efficient units)

Explanation: The formula calculates the energy required to heat water at a specific flow rate through a given temperature rise, adjusted for system efficiency.

3. Importance of Proper Sizing

Details: Correct BTU calculation ensures adequate hot water supply, energy efficiency, and prevents overworking the unit.

4. Using the Calculator

Tips: Enter the flow rate (gpm), temperature difference (°F), and efficiency factor (default 0.82). All values must be > 0.

5. Frequently Asked Questions (FAQ)

Q1: Why is 500 used in the formula?
A: 500 is a constant that accounts for the weight of water (8.33 lbs/gal) and minutes-to-hours conversion (60 min/hr).

Q2: What's a typical efficiency factor?
A: Most tankless heaters are about 82% efficient (0.82 factor), but high-efficiency models may reach 0.95-0.98.

Q3: How do I determine flow rate?
A: Add up flow rates of all fixtures that might run simultaneously (shower: 2.5 gpm, faucet: 1.5 gpm, etc.).

Q4: What temperature difference should I use?
A: Subtract your incoming groundwater temperature (typically 50-60°F) from desired output temperature (usually 120°F).

Q5: Should I add a safety margin?
A: Yes, consider adding 10-20% to the calculated BTU for peak demand and potential future needs.