A variable speed pump run at half speed for twice as long moves the same water for roughly a quarter of the electricity. The pump’s flow falls roughly in proportion to speed, but its power draw falls with roughly the cube of it, so half speed draws about an eighth of the power.
That matters because in North Texas the saving has to pay for the pump on its own, with no utility rebate to help. On a year-round pool with an old single-speed pump it usually does. The exact payback depends on your electricity rate, your pool volume, the pump you have now, and how many hours you run, so any flat number of months quoted without all four is a guess.
The physics: power falls with the cube of speed
A centrifugal pump follows three relationships known as the affinity laws: flow scales roughly with speed, head pressure with the square of speed, and power with the cube. California’s investor-owned utilities described the practical side to the Department of Energy in its 2023 pool pump motor rulemaking. Variable speed motors deliver consumer savings, they commented, by “allowing consumers to choose the lowest speed that meets their pool maintenance needs.” The saving is in finding the slowest speed that still does the job, and the cube is what makes that speed so cheap.
Drop a pump from 3,450 rpm to 1,725 rpm and you get about half the flow for about one eighth of the power. To move the same total volume of water you run twice as long, so you spend two times one eighth, which is one quarter.
| Speed | Approximate flow | Approximate power | Energy for the same total volume |
|---|---|---|---|
| Full | 100% | 100% | 100% |
| Three quarters | About 75% | About 42% | About 56% |
| Half | About 50% | About 12.5% | About 25% |
| One third | About 33% | About 4% | About 11% |
The figures are rounded and real systems deviate, particularly because plumbing losses don’t scale perfectly, but the shape is right and it’s why the industry moved.
Slower also filters better
Water moving slowly through a filter spends longer in contact with the media, which catches finer particles. A pool run long and slow is generally clearer than the same pool run short and fast, which is a second reason the schedule matters as much as the hardware.
Why the Texas math is different
North Texas pools run all year. A northern pool closed for the winter accumulates savings only in the months it runs, while a North Texas pool runs all twelve, because it isn’t winterized and the winter schedule is a freeze defense. More running hours means the savings accrue faster. Whether to run through winter covers that schedule.
Summers here also demand more turnover. August days in DFW run in the 90s, according to the National Weather Service’s climate summary, and pool water in the high 80s consumes chlorine fast and grows algae faster. The answer is more circulation. On a single-speed pump that means more expensive hours, and on a variable speed pump it means longer hours at a low speed, which is close to free.
And there is no rebate to wait for, though owners regularly defer the upgrade expecting one. Oncor, which delivers electricity to most of Collin County, publishes no residential variable-speed pool pump rebate. Entergy Texas does run a distributor program worth up to $350 per qualified pump, but Entergy serves a different part of the state. Check your own provider’s current offers once before you buy, since programs do change, but don’t build a plan around one appearing.
The regulation that has already changed the choice
Under the same September 2023 final rule, variable-speed control is required for dedicated-purpose pool pump motors from 1.15 to 5 total horsepower (THP) as of September 29, 2025. Motors from 0.5 up to 1.15 THP follow on September 28, 2027.
The rule doesn’t make anybody replace a working pump. It governs what manufacturers may produce, so when your single-speed pump fails, a like-for-like replacement may not be on the shelf. The decision is drifting from whether to upgrade toward when, and doing it on your schedule is cheaper than doing it on the pump’s. Repair or replace covers the wider decision.
How to work out your own number
Your own payback figure needs four inputs, all of which you can gather in an afternoon.
- Find your pump’s power draw. The motor label gives horsepower and often amps, and as a rule of thumb a single-speed 1.5 horsepower pump draws around 1.5 to 2 kW in service. A label bleached blank is why photographing your pad is worth doing before the sun finishes the job.
- Find your electricity rate. Take the total bill divided by kilowatt hours used rather than the headline rate, because delivery charges are real money.
- Count your real running hours. Use what the timer does, not what you intended, averaged across summer and winter.
- Multiply, then apply the cube. Current annual cost is power times hours times rate. The variable speed equivalent, delivering the same daily turnover, is roughly a quarter of that if you run at half speed for twice as long.
Set that annual saving against an installed replacement cost, which in our experience runs $1,200 to $2,500 in this area depending on the pump and the plumbing, and you have your own payback rather than somebody else’s.
The mistake that erases the entire saving
A variable speed pump installed and then left on its highest speed saves nothing, and we see it regularly. It usually happens for a reason that sounds sensible at the time: the automatic cleaner needs more flow, or the spa jets do, or somebody was told the pool wasn’t turning over. The fix is a schedule with different speeds for different jobs. An unprogrammed variable speed pump is an expensive single-speed pump.
Programming it properly
A workable variable speed pump schedule for a typical North Texas pool has four parts, adjusted to your own turnover.
- A long low-speed block covering most of the day. It does the filtration and circulation, and it is where nearly all the savings live.
- A short higher-speed block if you have a suction-side or pressure-side cleaner, a skimmer that needs real flow, or a heater with a minimum flow requirement.
- A spa or feature speed on demand rather than on the schedule.
- Freeze protection enabled and tested, which overrides everything above on the nights it matters.
A variable speed pump has a floor on how slow it can go. The component on your pad that needs the most flow sets it, usually a heater or a cleaner, along with the point at which the skimmers stop skimming. The run time guide covers finding that floor and calculating turnover.
When a variable speed pump isn’t the right purchase
A variable speed pump is the wrong purchase, or one to wait on, in three cases.
- Your current pump is already two-speed or variable and programmed badly. Fix the schedule, which costs nothing.
- The pump is new and working. Replacing functional equipment to chase a saving rarely pays back, and the savings are on running hours you haven’t yet spent.
- You’re about to move. It’s a real improvement, but it isn’t one a buyer will pay you back for on the sale price.
Now take a single-speed pump past its eighth year, running twelve months a year, on an electricity plan you haven’t looked at in three years. For that pad a variable speed pump is probably the highest-return purchase available, and our cost of ownership breakdown puts it beside the other four lines so you can see where it sits.
Before you price a new pump, find out what speed your current one is running at, because on a surprising number of pads the answer is full speed on a unit bought so it wouldn’t have to. An equipment inspection reads the pump label, the real schedule, the filter condition, and the turnover, and produces the arithmetic above for your pool. We’ll also tell you plainly when your existing pump has years left and the schedule is the only thing that needs changing, because that fix is free and it happens often.
