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Flow Rate Formula:
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The flow rate in a hydronic system determines how much water needs to circulate to transfer the required amount of heat. It's typically measured in gallons per minute (GPM) and is crucial for proper system design and pump selection.
The calculator uses the fundamental hydronic equation:
Where:
Explanation: The equation calculates how much water must circulate to carry away the heat load given the system's designed temperature drop.
Details: Correct flow rate ensures efficient heat transfer, prevents noise from high velocity, and maintains system efficiency. Undersized flow leads to inadequate heating, while oversized flow wastes pump energy.
Tips: Enter the total system heat load in BTU/h and your designed temperature difference (ΔT) between supply and return lines. Typical ΔT values are 10-20°F for radiant systems, 20°F for baseboard systems.
Q1: What's a typical ΔT for residential systems?
A: Most residential systems are designed for 20°F ΔT, though radiant floors often use 10-15°F.
Q2: How do I find my system's heat load?
A: Heat load should be calculated by a professional, considering building insulation, climate, and other factors. It's often in the system's manual.
Q3: Why is the constant 500?
A: It combines water's properties: 8.33 lb/gal × 60 min/h × 1 BTU/lb-°F = ~500 (actually 499.8, rounded to 500).
Q4: Can I use this for chilled water systems?
A: Yes, the same formula applies for cooling, just use the cooling load and chilled water ΔT (typically 10-12°F).
Q5: How does flow rate affect pump selection?
A: The calculated GPM, along with system pressure loss (head), determines the required pump size. Always consult pump curves.