• Measure the length of the heat zone pipe from the boiler, all the way around the loop, and back to the boiler.
• Multiply the total length of the zone by 1.5 to account for the fittings
• Multiply times .04 for pipe friction.

The formula is;

FH =( EFP x 1.5*).04

FH = Feet of head

EFP = Equivalent feet of pipe

1.5 = assumption for fittings

.04 = friction loss for 100’ of pipe

Measure 130 ft of pipe in a given zone

FH=(130 x 1.5)*.04

FH=195*.04

FH=7.8

We will use the same zone as above, 130 feet.

PSI =( EFP x 1.5*)*PL

PL = Pressure Loss

EFP = Equivalent feet of pipe

1.5 = assumption for fittings

Measure 130 ft of pipe in a given zone of type M copper

PSI=(130 x 1.5)*.015 (4 gpm flow)

PSI=195*.015

PSI=2.9 PSI

Since Chart 6 is calculated in PSI loss per lineal foot of pipe, we must convert it to Feet of Head. One pound of pressure = 2.31 ft. Yep, another calculation.

Convert PSI to Ft. Hd.

Ft. Hd. = PSI*2.31

2.9 * 2.31 = 6.7 Ft. Hd.

Now run the same formula at a 3 gpm (30,000 loop) flow rate using M tubing, and the flow is now 4 Ft. Hd. instead of 6.7 FT. Hd.
If I choose a flow rate of 2.5 gpm (25,000 loop), I would split the difference of 0.007, which is halfway between the 0.004 and 0.009 pressure drops. The Ft. Hd. now would be 3.13, which is quite different from the B&G rule of thumb of 8 Ft. Hd.
Could this slightly undersize the circulator? Yes, but since the circulator will run on the curve, it will pump more than your calculation indicates, unless it falls exactly on the line; therefore, the circulator will not be undersized.
Oversizing the circulator will not only cost more to buy and run, but also move too much water, which can affect the boiler, depending on the type of installation and boiler type. As we increase the velocity of the water, we increase the resistance to flow. Therefore, I usually use this calculation.

If you choose any of these options, including the option below, you will need to choose the proper circulator