Tankless Water Heater Calculator

Heater Size Formula:

\[ \text{Size} = \frac{Q \times \rho \times c_p \times \Delta T}{\text{efficiency}} \]

Flow Rate (Q):

L/min

Density (ρ):

kg/L

Specific Heat (c_p):

kJ/kg·°C

Temperature Rise (ΔT):

°C

Efficiency:

(0-1)

Heater Size (kW):

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1. What is a Tankless Water Heater Calculator?

Definition: This calculator determines the required size (in kW) of a tankless water heater based on water flow rate, temperature rise, and system efficiency.

Purpose: It helps homeowners and plumbers select the appropriately sized tankless water heater for their needs.

2. How Does the Calculator Work?

The calculator uses the formula:

\[ \text{Size} = \frac{Q \times \rho \times c_p \times \Delta T}{\text{efficiency}} \]

Where:

\( Q \) — Water flow rate (liters per minute)
\( \rho \) — Water density (kg per liter, typically 1.0)
\( c_p \) — Specific heat of water (4.186 kJ/kg·°C)
\( \Delta T \) — Temperature rise needed (°C)
\( \text{efficiency} \) — Heater efficiency (0-1, typically 0.98)

Explanation: The formula calculates the energy required to heat a given flow of water by a specified temperature rise, adjusted for heater efficiency.

3. Importance of Proper Sizing

Details: Correct sizing ensures adequate hot water supply while avoiding energy waste from an oversized unit or insufficient heating from an undersized one.

4. Using the Calculator

Tips: Enter your desired flow rate, temperature rise (difference between incoming water and desired output), and the heater's efficiency. Default values are provided for typical residential applications.

5. Frequently Asked Questions (FAQ)

Q1: What's a typical flow rate for residential use?
A: Standard showers use 6-9 L/min, kitchen faucets 4-6 L/min. Add up all simultaneous uses to determine total flow rate.

Q2: What temperature rise should I use?
A: Calculate as desired output temp (usually 50°C) minus incoming water temp (varies by location and season, typically 10-15°C in winter).

Q3: Why is efficiency important?
A: Higher efficiency means less energy waste. Most quality units are 95-98% efficient.

Q4: Should I round up the calculated size?
A: Yes, select the next available standard size above your calculation to ensure adequate capacity.

Q5: Can I use this for commercial applications?
A: Yes, but consider multiple units for large flow rates to improve efficiency and redundancy.