Calculate TDH for your pool plumbing. Essential for selecting the correctly sized pump and ensuring efficient water filtration and turnover. Understanding the friction loss in your pipes and fittings is key to maximizing your pump's performance and longevity.
TDH is measured in feet of head (or meters), and you build it from four inputs. First, static head: the vertical rise water must climb, typically just a few feet for an in-ground pool whose pump sits near water level, but larger for above-ground or elevated equipment pads. Second, pipe friction: enter the total developed length of your suction and return plumbing (add roughly 1 foot per actual foot, since long horizontal runs still cause loss) and the pipe diameter, usually 1.5 in (38 mm) or 2 in (50 mm) PVC. Third, fitting losses: count 90-degree elbows, tees, and valves, each adding an 'equivalent length' of pipe. Fourth, equipment loss: the clean-filter, heater, and salt-cell pressure drops, usually given as a feet-of-head figure. Gather your design flow rate in GPM (or LPM) too, because friction loss scales with flow. Measure pipe size at the pump, not the skimmer, since plumbing often steps up.
Method: TDH = static head + friction loss (pipes) + fitting losses + equipment losses, all in feet. Friction loss is read from a chart for your pipe size at your flow rate. Worked example: a pool needs 60 GPM (227 LPM). Static lift is 5 ft. The return run is 50 ft of 2 in PVC; at 60 GPM, 2 in pipe loses about 3.5 ft of head per 100 ft, so 50 ft = 1.75 ft. Suction side is 40 ft of 2 in = 1.4 ft. Four 90-degree elbows at ~5 ft equivalent length each = 20 ft of pipe = 0.7 ft. A clean cartridge filter adds 4 ft, and a heater adds 3 ft. Total TDH = 5 + 1.75 + 1.4 + 0.7 + 4 + 3 = 15.85 ft (about 4.8 m). You then read the pump's performance curve at ~16 ft of head to confirm it delivers your 60 GPM.
Accuracy matters because pump curves are steep: undersizing TDH makes you buy a pump that chokes below the flow your heater or salt cell needs, while oversizing wastes electricity and can exceed the filter's max design flow, blowing media or shortening cartridge life. The most common mistakes are using a pipe's nominal length instead of developed length (ignoring elbows), forgetting that a dirty filter can add 10-15 ft of head over a clean one, and reading friction loss at the wrong flow rate. Always size around a clean-filter TDH for flow targets, but verify your pump won't stall once the filter loads up. Re-estimate TDH whenever you re-plumb, add a heater or chlorinator, or upsize pipe. If a salt cell or heater flow switch won't trip, your real TDH is higher than calculated, recheck for partially closed valves or a clogged skimmer basket before assuming the pump is undersized.
TDH is the total resistance your pump must overcome to move water through the system, including the vertical height (static head) and friction loss in pipes and filters.
You need TDH to read a pump's 'performance curve.' If you buy a pump that is too small for your TDH, you won't get enough flow for your heater or salt cell to work.
You can lower TDH by using larger diameter pipes, high-flow valves, and keeping your filters clean. Lower TDH allows the pump to move more water using less electricity.