1. What is a Tankless Water Heater Calculator?

Definition: This calculator determines the flow rate (GPM) and heating capacity (BTU/h) required for a tankless water heater based on fixture flow rates and desired temperature rise.

Purpose: Helps homeowners and plumbers properly size tankless water heaters to ensure adequate hot water supply.

2. How Does the Calculator Work?

The calculator uses two formulas:

Where:

• \( Q \) — Total flow rate (gallons per minute)
• \( Q_i \) — Flow rate of individual fixtures (GPM)
• \( Q_{btu} \) — Heating capacity required (BTU per hour)
• \( \Delta T \) — Temperature rise needed (°F)

Explanation: The total flow rate is the sum of all simultaneous hot water demands. The BTU requirement accounts for the energy needed to heat that flow by the desired temperature rise.

3. Importance of Proper Sizing

Details: Correct sizing ensures sufficient hot water supply while avoiding oversizing which leads to energy waste and higher costs.

4. Using the Calculator

Tips: Enter flow rates for all potential simultaneous fixtures and the temperature rise (difference between incoming water and desired output). Default values are typical averages.

5. Frequently Asked Questions (FAQ)

Q1: What is temperature rise (ΔT)?
A: The difference between your incoming water temperature and desired output temperature (typically 70°F for shower use).

Q2: Why 500.4 in the formula?
A: This constant combines water's weight (8.34 lbs/gal) and specific heat (1 BTU/lb-°F) with time conversion (60 min/hour).

Q3: Should I add all fixtures in my home?
A: Only include fixtures that might run simultaneously during peak usage.

Q4: What if my water is very cold?
A: Measure your incoming water temperature and increase ΔT accordingly (output temp - incoming temp).

Q5: How do I account for multiple shower heads?
A: Add each shower's flow rate to the calculation if they might be used simultaneously.