DHW Recirculation Loop Calculator

Calculate heat loss, pump sizing, and return temperature for domestic hot water recirculation loops.

Pipe Loop Length (ft)

Pipe Diameter (in)

Allowable Temp Drop (°F)

Insulation R-Value

Tab to move between fields

Heat Loss

196 BTU/hr

Required Flow Rate

0.04 GPM

Return Temperature130 °F

Pump Size0.01 HP

How to Use This Calculator

Enter Pipe Loop Length (ft), Pipe Diameter (in), and Allowable Temp Drop (°F).
Set Insulation R-Value.
Review Heat Loss (BTU/hr) and Required Flow Rate (GPM).
Use Return Temperature (°F) and Pump Size (HP) to inform your decision.
Use the chart to visualize the results and explore different scenarios by adjusting inputs.

How the result changes with Insulation R-Value

Pipe Loop Length (ft): Total length of the recirculation loop (supply + return)
Pipe Diameter (in): Inside diameter of the recirculation piping
Allowable Temp Drop (°F): Maximum temperature drop from supply to return (typically 10-15°F)
Insulation R-Value: R-value of pipe insulation (R-4 typical for 1" fiberglass)

Identify Input Parameters
4 parameters
Pipe Loop Length (ft) = 300, Pipe Diameter (in) = 1, Allowable Temp Drop (°F) = 10, Insulation R-Value = 4 = 4 input(s) provided
Calculate Heat Loss
Heat Loss
196 = 196
Calculate Required Flow Rate
0.04 = 0.04
Calculate Return Temperature
Return Temperature
130 = 130
Calculate Pump Size
Pump Size = max(0.01
0.01 = 0.01