1. What is a Tankless Water Heater Size Calculator?

Definition: This calculator determines the required size (in BTU/h) for a tankless water heater based on peak flow rate 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:

• Size — Required heater capacity (BTU/hour)
• Peak GPM — Maximum flow rate needed (gallons per minute)
• ΔT — Temperature rise required (°F difference between incoming and desired water temperature)

Explanation: The formula calculates the energy needed to heat water at your maximum flow rate by your desired temperature increase.

3. Importance of Proper Sizing

Details: Correct sizing ensures:

• Adequate hot water during peak demand
• Energy efficiency
• Longer equipment lifespan
• Prevention of cold water "sandwich" effect

4. Using the Calculator

Tips:

• Determine your peak GPM by adding flow rates of all fixtures that might run simultaneously
• Calculate ΔT by subtracting your incoming water temperature from desired output temperature
• For electric units, divide BTU result by 3,412 to get kW requirement

5. Frequently Asked Questions (FAQ)

Q1: What's a typical ΔT for showering?
A: For 105°F shower water with 50°F incoming water, ΔT would be 55°F.

Q2: How do I find my peak GPM?
A: Add flow rates (typically 1.5-2.5 GPM for showers, 0.5-1.5 GPM for faucets) of all fixtures that might run together.

Q3: What if my calculated size is between standard unit sizes?
A: Always round up to the next available size to ensure adequate capacity.

Q4: Does altitude affect sizing?
A: Yes, at higher altitudes you may need to increase size by 4% per 1,000 ft above sea level.

Q5: Should I add a safety factor?
A: Many professionals add 10-20% to the calculated size to account for variations in incoming water temperature.