Variable speed pumps, and the honest answer for an above-ground pool

What a variable speed pump actually does

A conventional pool pump has one speed: on. A variable speed pump uses a motor that can be run at a range of speeds, so instead of moving your water fast for a few hours it can move it slowly for many.

The reason that saves energy rather than just spreading it out is that the power a pump draws rises much faster than the flow it produces. Halving the speed does not halve the consumption — it cuts it far more than that — so the same daily turnover achieved slowly costs substantially less than the same turnover achieved quickly. On a large inground pool with a big pump running most of the year, that difference is the single biggest energy saving available in pool ownership, which is why the category exists and why it is now the default at that end of the market.

Why the sums change on an above-ground pool

Three things, and they compound.

The pump is small. A saving expressed as a percentage of consumption is worth what the consumption is. At the EIA US residential average of 18.34 cents per kWh, every 100 W of pump run 8 hours a day for a 120-day season costs about $17.61 — so the whole seasonal electricity bill of a 300 W pump is roughly $53. A large fraction of a small number is a small number. Our pump electricity guide has the full table.

The season is short. An inground pump running most of the year has three times the hours to accumulate a saving over. A seasonal pool has 120 days.

The equipment does not match. Variable speed pumps are built for rigid plumbing, hard-wired supply and inground filtration. Above-ground pools use flexible hose with brand-specific fittings and plug-in pumps — the mismatch our fittings guide describes — and hard-wiring anything is an electrician’s job rather than a purchase, as our electrical safety guide sets out.

What ENERGY STAR’s own numbers imply here

There is a useful published data point. ENERGY STAR states that a certified above-ground pool pump saves about $20 a year and is about 11 percent more efficient than a standard one. That is the efficiency upgrade available in this class, and it is a $20-a-year figure rather than a transformative one.

Set against the price of a new pump, that is a long payback. And the same $20 is available for nothing by cutting three hours a day off the run time, which brings us to the actual recommendation.

What to do instead

Work out your real turnover requirement. Gallons divided by the pump’s published system flow rate gives one complete turnover — about 3.6 hours on a 1,718-gallon pool with a 475 GPH system, about 5.3 hours on 3,955 gallons with a 750 GPH system. One to two turnovers a day is the target, and most above-ground pools are run for considerably longer than that out of habit. Our run-time guide derives it properly.

Fit a timer. This is the variable-speed equivalent available to this class: it converts the run-time decision from something you have to remember into something that happens. At the national average rate, every hour a day removed from a 300 W pump is about $6.60 across a season, and roughly double that on a large sand filter pump. Our timer roundup covers what to buy, and the timer must be outdoor-rated, matched to the pump’s amperage and fitted downstream of the GFCI.

Keep the filter media fresh. A loaded cartridge raises the resistance the pump works against, so it draws similar power and delivers less — and you compensate by running it longer. Our cartridge roundup covers the interval.

Size correctly when you do replace. An oversized pump costs about $17.61 a season for every extra 100 W it draws. That is the real efficiency decision in this class, and it only comes up when you are buying anyway — our pump sizing guide has the method.

The one case where it is worth a look

A large above-ground pool at the 18-foot, 7,000-gallon end, left up year-round in a mild climate, running a sand filter pump for long hours. There the pump is bigger, the hours are longer and the plumbing is closer to inground practice. Our large pool equipment guide covers that end of the category, and it is the only place on this site where the question is genuinely open.

Everywhere else, the honest answer is that the technology is excellent and it is solving a problem your pool does not have.