Pool Pump Motor HP vs THP: What's the Real Rating?

Two power figures on one listing

Pool pump listings often show two different horsepower figures for the same motor. One is the plain horsepower number, usually written as HP. The other is the total horsepower figure, written as THP. Both describe the same motor, but they measure different parts of its rating.

THP stands for total horsepower. In pool pump listings, THP expresses the motor's maximum continuous output when its service factor is applied. The service factor is a standard motor rating that indicates how much overload the motor can handle on a continuous basis. A pump that lists both figures gives you a fuller picture of the motor than one that lists only the HP.

• HP in the model name and title
• THP in the specification line or feature bullets
• Service factor in the detailed specs or manual
• Both figures on the motor data plate

What motor horsepower means

Motor HP is the nominal horsepower rating of the pump motor. On a pool pump listing, this is the figure that usually appears in the product title or model name. When a listing says "1 HP pump", the HP is the motor's base rating.

HP describes the motor's output at its designed operating point. The number is a measure of power, the rate at which the motor can do work. Pool pump listings use HP as a quick label for the pump's size, which is why two pumps with the same HP figure can still have different hydraulic characteristics.

For a closer look at how horsepower figures are used across pool pump listings, see the article on pump horsepower explained. It covers the common ways HP appears in titles and what the terms mean in plain language.

What total horsepower adds

THP, or total horsepower, is the motor's HP multiplied by its service factor. The service factor is a number that describes how much above its base rating the motor can run continuously without damage. A motor with a base rating of 1 HP and a service factor of 1.65 has a THP of 1.65.

The THP figure matters because it states the motor's full continuous capacity in one number. When a listing shows both figures, the THP is the higher one. That is why the same motor can appear as "1 HP" in one part of a listing and "1.65 THP" in another.

For the direct relationship between service factor and total horsepower on pool pumps, the article on SF and THP walks through the calculation and how it shows up in listings.

How the service factor connects the two

The service factor is a motor rating standard, not something unique to pool pumps. It appears on motor data plates and describes continuous overload capacity. A service factor of 1.0 means the motor is rated to run at its base HP continuously. A service factor above 1.0 means it can run at a higher output continuously.

On pool pump listings, the service factor is sometimes implied rather than stated. If a listing says "1 HP, 1.65 THP", the service factor is 1.65. If a listing shows only "1.65 HP", the seller may be using the THP figure as the headline.

A motor with a higher service factor has more continuous capacity than the base HP suggests. When two pumps have the same base HP, the one with the higher THP is built to deliver more continuous work. That is one of the reasons a THP figure can clarify a comparison.

Why listings use both numbers

Sellers use THP because it describes the motor's actual continuous capacity, and because the number is larger than the base HP. The same motor can be listed as "1 HP" in the model name and "1.65 THP" in the description. Neither figure is wrong; they describe the motor at different points in its rating.

Some listings show only HP, particularly for above ground pool pumps. Others show both HP and THP, often for inground pumps. When a listing shows both, the THP is the figure to read for the motor's full continuous rating.

ENERGY STAR's pool pump certification criteria classify pumps by hydraulic horsepower, or hhp, which measures the pump's water-moving output rather than the motor's input rating. The certification program's key product criteria list hhp thresholds for pump size classes. That page does not describe a motor's HP or THP; it groups pumps by size for the certification program.

Comparing pumps by HP and THP

When you compare two pumps, the HP figure gives you a quick size label, but the THP figure tells you more about the motor's continuous capacity. If one listing shows "1 HP" and another shows "1.25 HP", the difference may be small. But if their THP figures differ more, the motors are not equivalent.

For a direct comparison of the two figures across pump types, see the article on horsepower versus THP. It covers how the two numbers relate and when one matters more than the other.

For above ground pool pumps, HP is typically the only power figure in the listing. For inground pumps, THP often appears alongside HP. The guide to inground pool pumps and the guide to above ground pool pumps sort pumps by the power figures stated in their listings.

When you replace an existing pump, the safest approach is to match the power figure on the old pump's data plate. If the old pump shows both HP and THP, match both. If you have questions about which figure to match, ask the maker and an installer.

This site does not match pump power to pool size or calculate which HP you need. That work belongs to the maker's sizing page and a licensed installer. The article on oversizing explains why buying a pump with more power than the pool needs is not a simple upgrade.

Questions for the maker and installer

Before you buy, ask the maker for the motor's full rating details. The data plate on the motor lists the base HP, the service factor, and the THP. A maker's manual or specification sheet should state all three.

Ask an installer to confirm that the replacement pump's power figures match the old pump. The installer can also confirm that the pump suits the pool's plumbing. This article cannot advise on wiring, bonding, or electrical connections; a licensed electrician, the maker's manual, and the local building office decide those.

The guides on this site compare pool pumps by the figures stated in their listings, including HP and THP. For specific recommendations, see the best 2 HP and up pool pumps, the best variable speed pool pumps, and the best dual speed pool pumps.

What to pick for your situation

Questions

Is THP the same as horsepower?

No. THP is the motor's total horsepower, which is its base HP multiplied by its service factor. A 1 HP motor with a 1.65 service factor has a 1.65 THP rating.

Do all pool pumps list THP?

No. Above ground pool pumps often list only HP. Inground pumps may list both HP and THP, depending on the listing. If THP is missing, look for the service factor in the detailed specs.

What does the service factor mean on a pool pump?

The service factor is a motor rating that shows how much continuous overload the motor can handle above its base HP. A service factor of 1.65 means the motor can run at 1.65 times its base HP continuously.

Should you match HP or THP when replacing a pump?

Match the figures on the old pump's data plate. If the old pump shows both HP and THP, match both. If you are unsure, ask the maker and an installer.

Why does one pump appear with two horsepower numbers?

The lower number is the motor's base HP. The higher number is the THP, which includes the service factor. Both describe the same motor, and the THP is the motor's maximum continuous rating.