Variable Speed Pool Pump vs Single Speed: Worth it for Small Pools?

Comparing Variable Speed Pool Pumps vs Single Speed

No matter what size pool you have, variable-speed pumps can help you save energy and save money over single-speed pumps. Even if you keep your single pump running for about 4 to 5 hours a day, then turn it off, the savings don’t compare.

A variable pump’s saving potential and energy conservation far outweigh the money you save by turning off your single-speed pump. The Department of Energy certainly thinks so too: Its new regulations require that new or replaced pumps in most pools be variable speed.

And perhaps more importantly, even with a small pool, you can save almost $200 dollars per year!

Follow along as we do the math and show you how a high-speed pump can better service your pool and reduce its amount of energy consumption, even when you leave it on 24 hours a day.

Small Pools, the Affinity law, and Energy Costs

Before we get into the numbers, let’s talk laws, specifically the affinity law. In a nutshell, this law consists of three formulas that allow us to predict the performance of a pump at a different speed or diameter impeller, which is exactly what we’re talking about here.

For our example, we will use a small swimming pool that is 13’ x 26’ and 4’ deep. Keep in mind that because we are talking about using the variable pump at low speeds for much of the day, these calculations are only effective for small pools. Larger pools need higher speeds, which result in more kWh and higher energy costs.

Speaking of kWh, we will use .013.31 cents per kWh for these calculations, today’s national average.^1^

The first thing we need to do is calculate the pool volume. This is the amount of water that a swimming pool holds. We used the handy calculator at SwimmingPool.com to arrive at 10,140 gallons for this size pool.

Next, we need to determine how many gallons of water your pool should filter every day. The industry standard is the total volume times three, so that means for this size pool, it should filter 30,420 gallons a day.

Single Speed Pumps and Cost

Let’s see what it costs to run a 1.5 horsepower single-speed pump for this size swimming pool. This calculation is based on running the pump five hours a day for six months out of the year.

5 hours to turn over 34,420 at 2.3 kW per hour = 11.5 kW per day 11.5 kW x .013.31 cents = $1.53 per day $1.53 per day x 30 days = $45.96 per month $45.96 x 6 months = $275.52 a year

The Low and Slow Route With a Variable Speed Pump

Now, let’s imagine that you installed a 1.5 horsepower variable speed pump in the same swimming pool. With a variable speed pump, you select the times and speeds to keep the water flowing in your pool 24 hours a day, but at different speeds. This will not only conserve energy but also lower your costs.

What? Running a variable speed pump 24 hours a day will cost less than running a single speed pump for only five hours a day? Amazingly, it’s true.

Using the same kWh cost and running the pump 24 hours a day for six months out of the year, you could set up the daily running times like this:

1 hour to turn over 5400 gallons at 3000 RPM.
3 hours to turn over 7380 gallons at 1500 RPM.
20 hours to turn over 18,900 gallons @500 RPM.
Total 24 hour turnover = 31,680

Here’s the amount of kW you would use:

1540 w/h @3000 RPM x 1 = 1540 watts.
262 w/h @1500 x 3 = 786 watts.
63 w/h @ 500 x 20 = 1260 watts.
Total watts used in 24 hours = 3,586 or 3.5 kW per day.

All of these calculations equal incredible cost savings:

3.5 kW x 0.13.31 cents = 0.47 per day.
0.47 per day x 30 days = $13.98 a month.
$14.37 per month x 6 months = $83.85 a year

Pool Pump Flow Meters: The Final Piece of the Puzzle

Now that you understand how variable pool pumps can save you money, you may be asking one question: if the pumps are variable, how will I determine how many gallons of water are running through each of the settings on the pump? In short--you can’t.

This is where pool pump meters come in. If you want to accurately gauge how many gallons of water your pool is pumping per minute, installing one of these devices on your pool equipment can make all the difference in the world. Why? Because once you know the exact amount of water your pump is pumping — at every speed - you can set the timer in a way that will save you the most money.

Is a Variable Pump Right for Your Small Pool?

As you can see with the size pool in our example, you could keep your variable speed pump running the entire day and save approximately $192 a year. What’s more, because your pool pump would be running full-time, it would help distribute your pool chemicals more evenly and contribute to the overall health of your pool.

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REFERENCES

1. Electric Rates by State (June 2021) – Electric Choice

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