1. What is the Rheem Water Heater Size Formula?

The Rheem Water Heater Size formula calculates the required BTU/hr for a tankless water heater based on flow rate and temperature rise. This helps determine the appropriate size unit for your hot water needs.

2. How Does the Calculator Work?

The calculator uses the Rheem formula:

Where:

• \( GPM \) — Flow rate in gallons per minute
• \( \text{Temp Rise} \) — Desired temperature increase in °F
• 500 — Constant factor for water heating calculation

Explanation: The formula calculates the energy required (in BTU/hr) to heat water at a specific flow rate by a certain temperature rise.

3. Importance of BTU/hr Calculation

Details: Proper BTU/hr calculation ensures your tankless water heater can meet your hot water demands. Undersized units may not provide sufficient hot water, while oversized units waste energy.

4. Using the Calculator

Tips: Enter flow rate in GPM and desired temperature rise in °F. Both values must be positive numbers for accurate calculation.

5. Frequently Asked Questions (FAQ)

Q1: What is GPM in water heater sizing?
A: GPM (gallons per minute) measures the flow rate of water through the system. Higher GPM requires more heating capacity.

Q2: What is temperature rise?
A: Temperature rise is the difference between incoming cold water temperature and desired hot water temperature.

Q3: Why is 500 used in the formula?
A: 500 is a constant that accounts for the specific heat of water and conversion factors (8.33 lb/gallon × 60 min/hour).

Q4: How do I determine my required GPM?
A: Add up the flow rates of all fixtures that might run simultaneously. Typical shower: 2.0-2.5 GPM, kitchen faucet: 1.5-2.2 GPM.

Q5: What factors affect temperature rise requirements?
A: Incoming water temperature (varies by season and region) and your desired output temperature (typically 120°F for most applications).