Choose a pump whose head-flow curve can deliver the chiller's required GPH at the resistance of your real loop. Then leave margin for filter fouling and uncertainty.
1. Why max GPH misleads
Maximum GPH is normally near zero head. Add hose, elbows, filter media and a chiller heat exchanger and the real flow falls. The correct pump is defined by its operating point, not by its headline number.
2. Read the pump curve
A pump curve shows available head at each flow. At shutoff head, flow approaches zero. At low head, flow approaches the advertised maximum. The operating point is where pump head equals required system head.
3. What creates system head
- Straight pipe/hose friction.
- Elbows, tees, valves and reducers.
- Filter housing and cartridge pressure drop.
- Chiller heat-exchanger pressure drop.
- Net static elevation when the geometry creates it.
4. Diameter matters a lot
The friction equation has a strong diameter exponent. That is why forcing several hundred GPH through 1/2-inch line can move a pump to a completely different operating point than 1-inch plumbing.
5. Design for a used filter, not only a new one
Filter pressure drop increases as media loads. If the clean-filter model barely clears minimum chiller flow, the installed system has little useful margin.
6. Selection workflow
- Record chiller min/max GPH.
- Choose tentative pipe size and length.
- Add the intended filter.
- Use real pump-curve points.
- Calculate the operating point.
- Reject combinations below chiller minimum.
- Check that maximum flow is not exceeded.
- Measure actual flow after installation.
7. Measure real flow
If you can safely divert the return, fill a known-volume container and time it. Repeat and average. This is one of the best commissioning measurements because it validates pump, plumbing, filter and chiller restriction together.
8. FAQ
Is a bigger pump always safer?
No. It can exceed equipment limits, add heat and use more electricity. You want enough head at the required flow, not maximum size.
Primary technical references
Run your exact setup
Use your real tub, temperature, ambient, exposure, pump, filter and plumbing. ChillSizer checks thermal capacity and real operating flow together.
Open the System Designer