Hot Water Circulation

Based on the hot water supply system characteristics, the following methods can be used. Method A and Method B are basically for small systems. The heat loss method (Method C) is more accurate. The calculation procedure is described in detail in the book, "Engineered Plumbing Design", by Alfred Steele. It is especially useful for larger systems. However, because of its complexity for manual calculation, it is not widely used in plumbing system design. Then, Method D is introduced as an Excel template by using VBA.

A. Estimating Flowrate by Number of Risers:

Size of Riser No. of Risers Flow, gpm
1" or less 0.5
1-1/4" and 1-1/2" 1.0
2" and larger 2.0

B. Estimating Flowrate by Fixture Units (FU):

FU Flow, gpm

C. Estimation of Circulation Flowrate by Heat Loss:

Table 1. Piping Heat Loss
(Btu/hr per lineal foot for 140°F water and 70°F room temperature.)
Nominal Pipe Size Insulated Pipe (½’ Fiberglass) Bare Pipe
Sch. 40 Steel Brass, Copper, T.P. Type K Copper
½” 15352619
¾” 17433226
1” 19533832
1¼’ 21654639
1½” 25735346
2” 28916558
2½” 321087568
3” 381299081
4” 46163113103
5” 55199138127
6” 63233161149
8” 80299201188
Source: Engineered Plumbing Design, Alfred Steele, PE, CIPE

D. The Computer-Aided Hot- Water Circulation System Sizing

This VBA based template was introduced by Anjian Lu, CPD, and published on Plumbing System & Design magazine, Dec. 2004. By using this method, the required circulation flow rate and friction loss in the system are both calculated, so are the circulation pipe sizes and pump capacity.

Return to Main Menu
Product Selection