1. What is a Tankless Hot Water Heater Calculator?

Definition: This calculator determines the required size of a tankless water heater based on flow rate, water properties, and desired temperature rise.

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

2. How Does the Calculator Work?

The calculator uses the formula:

Where:

• \( Q \) — Flow rate (gallons per minute)
• \( \rho \) — Water density (pounds per gallon)
• \( c_p \) — Specific heat of water (BTU per pound per °F)
• \( \Delta T \) — Temperature rise needed (°F)
• Efficiency — Unit efficiency (decimal, 0-1)

Explanation: The formula calculates the energy required to heat water at a given flow rate through a specified temperature increase.

3. Importance of Proper Sizing

Details: Correct sizing ensures sufficient hot water supply, energy efficiency, and prevents overloading electrical systems or gas lines.

4. Using the Calculator

Tips: Enter the flow rate (gpm), water density (default 8.33 lb/gal), specific heat (default 1.0 BTU/lb·°F), desired temperature rise, and unit efficiency (default 0.98). All values must be > 0.

5. Frequently Asked Questions (FAQ)

Q1: What's a typical flow rate for residential use?
A: Showers typically use 1.5-2.5 gpm, while whole-house systems may need 5-10 gpm depending on simultaneous fixtures.

Q2: Why is water density important?
A: The density affects how much mass needs to be heated per gallon of water.

Q3: What temperature rise should I use?
A: Typical rises are 50-70°F (from 50°F groundwater to 120-140°F hot water).

Q4: How does efficiency affect sizing?
A: Lower efficiency units require more input energy to deliver the same output.

Q5: Should I round up the calculated size?
A: Yes, always round up to the nearest available unit size for safety margin.