1. What is the Flow Rate Formula?

The flow rate formula calculates the required pump capacity in gallons per minute (GPM) based on the system's heat load and temperature difference. This is essential for proper circulator pump sizing in hydronic heating systems.

2. How Does the Calculator Work?

The calculator uses the flow rate formula:

Where:

• 500 — Constant that accounts for the weight of water (8.33 lbs/gal) × 60 (minutes/hour) × specific heat (1 BTU/lb-°F)
• Heat Load — Total heat output required by the system in BTU/hour
• ΔT — Temperature difference between supply and return lines in °F

Explanation: The formula determines how much water needs to circulate to transfer the required heat energy at the specified temperature difference.

3. Importance of Proper Pump Sizing

Details: Correct pump sizing ensures efficient system operation, prevents energy waste, reduces noise, and extends equipment life. Oversized pumps waste energy while undersized pumps can't deliver sufficient heat.

4. Using the Calculator

Tips: Enter heat load in BTU/hour and temperature difference in °F. Typical ΔT values are 10-20°F for radiant floor systems and 20-30°F for baseboard systems.

5. Frequently Asked Questions (FAQ)

Q1: What is a typical heat load for residential systems?
A: Residential systems typically range from 20,000-100,000 BTU/h depending on home size and climate.

Q2: How do I determine my system's ΔT?
A: Measure supply and return water temperatures during operation, or consult system design specifications.

Q3: What's the 500 constant in the formula?
A: It combines the weight of water (8.33 lbs/gal), minutes per hour (60), and water's specific heat (1 BTU/lb-°F).

Q4: Should I add safety factor to the calculated flow rate?
A: Most modern circulators can handle slight variations, but adding 10-15% safety factor is common practice.

Q5: Does this work for chilled water systems?
A: Yes, the same formula applies for cooling systems, just with different typical ΔT values (usually 10-12°F).