1. What is an Instant Hot Water Heater Size Calculator?

Definition: This calculator determines the required size (in kW) of an instant/tankless water heater based on desired flow rate and temperature rise.

Purpose: Helps homeowners and plumbers properly size tankless water heaters for efficient and adequate hot water supply.

2. How Does the Calculator Work?

The calculator uses the formula:

Where:

• \( \text{Size} \) — Required heater power in kilowatts (kW)
• \( \text{Flow Rate} \) — Desired water flow in gallons per minute
• \( \Delta T \) — Temperature rise needed (°F)
• \( 0.044 \) — Conversion factor (accounts for water's specific heat)

Explanation: The formula calculates the energy needed to heat a specific water flow by a certain temperature rise.

3. Importance of Proper Sizing

Details: Correct sizing ensures adequate hot water supply while avoiding oversized, inefficient units. Undersized heaters can't meet demand.

4. Using the Calculator

Tips:

• Determine your peak flow rate (sum of all fixtures that might run simultaneously)
• Calculate ΔT as desired output temp minus incoming water temp (typically 40-70°F rise)

5. Frequently Asked Questions (FAQ)

Q1: What's a typical flow rate for a shower?
A: Standard showerheads use 1.5-2.5 gal/min, while low-flow models use 1.0-1.5 gal/min.

Q2: How do I find my incoming water temperature?
A: Measure with a thermometer or use local averages (50°F in northern climates, 60°F in southern).

Q3: What if I need the size in BTUs?
A: Multiply kW result by 3412 to convert to BTU/hr.

Q4: Does this account for efficiency losses?
A: No, consider adding 10-20% for high-efficiency units or hard water areas.

Q5: What's the maximum temperature rise possible?
A: Most residential units can achieve 60-70°F rise at moderate flow rates.