Copyright Goodheart-Willcox Co., Inc. Chapter 12 Radiant Heating Systems 259 Fluid flow in GPM: Once the previous factors are determined, the next step is to select a circulator for the radiant flooring system. In order to meet the cal- culated heat load requirement, the proper water flow through each heating loop must be maintained. The proper flow rate per zone is based on the total heating load, the total loop length, and the supply and return temperature differential. When these parameters have been calculated, the water flow through an indi- vidual zone can be determined by referencing the chart in Figure 12-40 and by using the following information: ■ ■■ Btu per square foot of floor space ■■ On-center distance between tubing loops ■ Area in square feet being heated TIMEOUT FOR MATH Calculating Total Loop Length A room measures 12′ × 10′ with the tubing installed at 9″ on center. What is the total loop length for this zone? Answer: 12 × 10 = 120 ft2 × 1.33 = 159.6 total linear feet Note: Be sure to include any additional tubing footage measuring from the inlet of the manifold station to the zone as well as any footage from the zone back to the manifold station. 300 325 350 375 400 450 475 500 425 75 100 125 150 175 200 225 250 275 Area heated by loop (sq. ft.) 50 Total heat load (Btu/hr/sq. ft.) 45 40 35 30 25 20 15 10 5 0 12“ O.C. 9“ O.C. 6“ O.C. .10 .08 .05 .20 .15 .10 .30 .23 .15 .40 .30 .20 .50 .38 .25 .60 .45 .30 .53 .70 .35 .60 .80 .40 .68 .90 .45 .75 .83 .90 .98 1.1 1.0 1.1 1.2 1.3 1.4 .50 .55 .60 .65 .70 1.1 1.2 1.3 1.4 1.4 1.5 1.5 1.6 1.7 1.8 1.9 2.0 .75 .80 .85 .90 .95 1.0 1.6 1.6 1.7 1.8 1.9 2.0 2.1 2.2 2.3 2.4 2.5 1.1 1.1 1.2 1.2 1.3 1.3 2.6 2.0 2.1 2.2 2.3 2.7 2.8 2.9 3.0 1.4 1.4 1.5 1.5 Goodheart-Willcox Publisher Figure 12-40. Use this chart for calculating the GPM flow for circulating pump sizing.