Total Horsepower and the importance of service factor

In the pool market, total horsepower (THP) is everything. It’s the max load the motor can carry without overheating or tripping the thermal overload protection. In other words, total horsepower will determine into whether or not your motor is going to operate at peak performance or max out on a hot summer day. Let’s get one thing straight though, total horsepower may be important, but calculating this number is often the most enlightening discovery for pool owners.

Let’s take you through a scenario… You’re going to start-up your pool pump for the summer only to realize the motor died somewhere since it was last run. You take a picture of the motor, visit a local pool shop, or search online and see the same motor you have outside with the same horsepower (HP). Before you buy it, however, realize that doesn’t always mean it’s going to perform as needed and could even end up dying soon after install.

What is Service Factor?

A common and many times overlooked figure on the motor nameplate is Service Factor (SF). Service Factor is the measure of overload capacity built into a motor. Basically, it is the amount of power a motor can generate above rated horsepower without serious overheating. The concept of service factor is responsible for keeping a common ground between uprate and fullrate motors in the industry as well as helping to calculate the total horsepower that will eventually power your pool pump.

What Does Service Factor Have to do with Total Horsepower?

We calculate THP in the following equation:

Total Horsepower = Horsepower x Service Factor

That means no two horsepower motors can be guaranteed the same for your applications. Only once you multiply horsepower by service factor can you determine if you have the proper equipment to run your pool.


Motors Horsepower (HP) Service Factor (SF)  Total Horsepower (THP) 
 Motor 1 - SQ1102 1HP 1.65 SF 1.65 THP 
 Motor 2 - USQ1102 1HP  1.25 SF  1.25 THP
 Motor 3 - HSQ1102 1HP  1.85 SF  1.85 THP


In the example above, three motors are rated at the same 1 HP. However, when you add service factor into the equation, they all operate at a different total horsepower.

As the industry begins to shift toward variable speed technology, issues with horsepower, service factors, and total horsepower greatly diminish. Variable speed motors are better at sensing the load of the pump and limiting themselves to work within the needed amp range, protecting themselves from failure and overload. This leads to greater pool pump efficiency and longer motor life.

By focusing solely on the horsepower of a motor pool owners can often make the mistake of installing a motor unable to keep up with the needs of their pool.

Common indicators of incorrect total horsepower can include:

  • Thermal overload trips causing the motor to cycle on and off throughout the day
  • High amperage (amp) draw
  • Unnecessary and frequent motor replacements

With the Department of Energy issuing new regulations requiring variable speed motors, pool pumps are getting more energy efficient. However, pool owners will still need to keep an eye on total horsepower and make sure they have the right motor for the job. Motors like Century’s VGreen Evo™ meet or exceed these standards and are perfect for pool owners needing a quick installation with reliable uptime. Pre-programmed operating schedules on the VGreen Evo™ help pool owners lower their overall cost of pool ownership with optimized schedules that help your summer fun last longer.

Talk to one of our expert sales professionals about how our solutions can efficiently power your business.

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