QMR: Horse Power
Horsepower ratings for pool & spa pumps are confusing & controversial. But that could soon change.

By Bob Dumas
Reprinted from Pool & Spa News September 2004

If Florida pool builder Dan Johnson could have just one wish for his industry, it would be for the development of a new system to rate the power of pumps and motors.

"It's a huge issue," says Johnson. "If this industry could change just one thing, that would be what I'd ask them to change."

Pool pump and motor manufacturers have always used horsepower as a means of rating the strength of their products.

Unfortunately, the exact definition of horsepower has become somewhat nebulous over the years. As a result, the pumps and pool circulation systems can be mismatched, resulting in turbid water and damaged equipment.

"The customers end up paying too much [for a pump] that doesn't operate properly and will have a shorter life expectancy," Johnson says. "Nothing [about having the wrong size pump] leads to any good."

Here's where the confusion starts: The pool and spa industry deals with two types of horsepower - peak horsepower and brake horsepower:

- Peak horsepower is the power available when the motor is working at maximum strength.
- Brake horsepower is the pump's shaft output in terms of torque. In other words, brake horsepower takes into consideration not just the power of the motor, but all the other factors as well - things such as the rotor and fan size, and the amount of copper that is used. These variables combine to form the service factor.

Peak horsepower is a somewhat disingenuous number because no motor can run at peak for very long. Thus, brake horsepower is the rating with which builders, service technicians and pool owners should be concerned. But finding out the brake horsepower is not as simple as just glancing at the motor plate.

Up-rated vs. full-rated
There are two numbers on the motor plate with which you need to be concerned. The first is a horsepower listing; the second is the service factor. To get the brake horsepower, you must multiply these two figures together:

Nominal horsepower x service factor = brake horsepower

But that's not the end of the story.

Suppose your motor plate listed a horsepower rating of 1 and a 1.65 service factor. Multiplying the two numbers, will give you a brake horsepower of 1.65. But what if you wanted that motor plate to list more horsepower, say 1.5? Well, if you change that number, you'd have to change the service factor as well, so that when the two figures are multiplied, the brake horsepower remains 1.65. And that's exactly what happens.

A pump with a higher horsepower listing and a lower service factor listing is called an up-rated motor. The original example is called a full-rated motor. They are essentially the same, though they have different horsepower and service factors.

However, Rob Stiles notes there are some physical differences between the two motors and offers an example. "The full-rated motor has more copper; the up-rated motor has less copper," says the pump product manager at Pentair Pool Products, based in Sanford, N.C.

But to make things even more confusing, motor manufacturers don't always use the same criteria when rating the power of their products.

"Not all ratings are the same between manufacturers. Motors have a lot of variations," Stiles says. "Some service factors [may be listed as] identical, but truth be told, they're not the same. It's a complicated issue."

The chart below reveals examples of up-rated and full-rated motors that have different horsepower ratings on their motor plates, but are the same because of their service factors.


Service Factor

Brake HP


















Approx. 2.25

It's easy to see how such a system can be not only confusing, but also provide fertile ground for deceitful selling tactics. Many consumers don't understand the difference between up-rated and full-rated motors, or even know what kind is on their pools.

Suppose a pool owner replaces an up-rated 1-horsepower motor with a full-rated 1-horsepower motor. Depending on the service factor, the full-rated motor can have significantly more power than the uprated, even though technically, they are both contain 1 horsepower. This can overburden the pool's hydraulic system.

"If you put an up-rated pump on a spa jet manifold that was designed for a full-rated pump, it just won't work," says Steve Gutai, a member of NSPI's Technical Committee and product manager for Jandy, a Petaluma, Calif.-based maker of pool accessories and products.

How this system came to be dates back to the 1960s, according to Fred Hare, a longtime industry member and territory director at Sta-Rite, a pump manufacturer based in Delavan, Wis. At the time, the industry was seeing a lot of its pumps breaking down, so a group of people approached Tipp City, Ohio-based A.O. Smith, which made most of the industry's pump motors, and asked what was going on.

"A.O. Smith said our industry was abusing our motors because of the water and chemicals and sunshine," Hare says. "At the time, the standard service factor for the industry was 1.4, but we needed more. So A.O. Smith put in a bigger fan, made the rotor bigger, added more copper and so forth. Now they had a service factor of 1.65."

With the nominal horsepower remaining the same, it was the service factor variables that helped make the motor strong enough to withstand the daily rigors of swimming pool work.

While the rating and labeling of the motors 40 years ago was well-intended, it has since led to some unscrupulous selling practices, as well as general confusion on the part of consumers. In fact, the marketing of up-rated and full-rated pumps has become a regional choice.

"Most of the West Coast and Southwest - Southern California, Arizona, Las Vegas - use full-rated," Gutai says. "In Florida, Texas and the Northeast, that stuff is up-rated. And the Northwest is, for the most part, up-rated, too."

As a result, experts say service techs need to carry the pump curve charts that manufacturers publish to help select the right pump, and not rely on the horsepower number on the plate. "[A pump curve is] the one thing that does not lie," says Steve Bludsworth, owner of All-Pool Service & Supply, a service company in Orlando, Fla. "It will tell you what the horsepower should be."

The fallout
The problem is even more critical now because many modern pools are more elaborately designed and include an array of waterfeatures.

"Today's consumers are demanding more of the backyard waterfeature: They want to hear it sing and see it dance," Johnson says. "It requires more hydraulic knowledge. If [the industry] doesn't address this issue now, we're not just shooting ourselves in the foot - we are cutting off our legs."

The problem is frustrating for Bludsworth, who says the horsepower rating debacle arose "purely as a sales gimmick thing." That gimmick is something that unscrupulous retailers can use against their competition.

"We have competitors who offer upgrades to 'bigger' pumps, and they're giving [the customer] the perception that they are getting a deal," says Michael Eastergard, president of Carefree Pools & Spas, a retailer and service firm in Evans, Ga. "But they're not sizing using the right hydraulic calculations. You have builders playing this game, too, switching over to up-rated pumps to give the perception that they're giving you a bigger pump."

"It should be an embarrassing thing in this industry that we don't have a uniform method," Eastergard says.

Going against the flow
The winds of change are starting to blow for the pool pump and motor industry. The National Spa & Pool Institute's Technical Committee recently turned its attention to the pump-rating issue.

Are the manufacturers and the industry at large ready and willing to embrace a change?

"It's going to take a long time, but the momentum is there to get rid of this," says Jamie Watkins, global section manager of A.O. Smith's Pump Group. "There are lawsuits in the air compressor industry [over the same issue] and some are worried that it could come into our industry."

The Technical Committee has formed a standard-writing subcommittee that it is hoped will create a new method for rating pump power. If it comes to fruition, the standard will be NSPI-10.

"NSPI-10 is trying to find a standard method of rating motors and pumps that will give builders and techs the information they need to size the pump properly," says Gutai, who will help head up the committee. "It will also give consumers the proper information they need about electrical consumption."

Current discussions include ways to have more consistent service factors, says Gutai. Another idea would be to eliminate service factors altogether and simply give every pump the proper brake horsepower rating. This would mean no up-rated or full-rated verities. That may come in the future, says Gutai, but it will take time.

"We have talked about doing it that way, but it is a bigger battle than you would think," he adds. "There are a lot of manufacturers involved."

At present, the committee is surveying the types of pumps already in the field, taking note of the product lines and service factors. "We are going to spend time doing some legwork," Gutai explains. "Then we will look at the potential for rating the pumps [based on] flow and head, and defining pumps as low, medium and high head, while identifying the electrical consumption in watts.

"But we have to have the technical rationale in place," he says. "We'll have to have plenty of representation from manufacturing [during the standard-writing process] and see how feasible it is to make this change.

"So far, I haven't heard anything negative about it."


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