Pool Pump Hydraulic Horsepower vs Total Horsepower

Pool pump hydraulic horsepower vs total horsepower comes down to this: hydraulic horsepower (hhp) is the water power the pump actually delivers on a standard test, and total horsepower (THP) is a rating of the motor. Hydraulic horsepower is the one that tells you what the pump can do, and since 2021 it is the one federal efficiency rules are written around.

The gap between the two is not a fixed conversion. Among certified pumps rated 1.5 to 1.65 motor horsepower, hydraulic horsepower runs from 0.341 to 1.242, a 3.6-fold spread. Two pumps with the same horsepower on the box can move very different amounts of water, and replacing a pump "like for like" by horsepower can leave you with one far too big or too small.

The three horsepower numbers on a pool pump

Hydraulic horsepower (hhp). The power delivered to the water on the federal test procedure. It reflects flow and pressure together, so it is a direct measure of the pump's capacity. ENERGY STAR publishes it on every certified record as "rated hydraulic horsepower."

Total horsepower (THP). A motor rating. Pentair's white paper on the 2021 federal rule pairs it with service factor horsepower: the motor's rated horsepower multiplied by its service factor, the extra load the motor is rated to carry. Since 2021, manufacturers must print THP and WEF on the pump's rating label.

Nameplate, "up-rated" or "full-rated" horsepower. Older industry terms for motor size. The 2021 rule replaced them with THP labeling, so you will still meet them on older pumps and in older parts listings.

Jandy's guide to the rule puts hhp at roughly half of THP as a rule of thumb. The certified data shows how loose that rule is.

Hydraulic horsepower vs total horsepower in the certified data

ENERGY STAR's records publish hydraulic horsepower alongside a rated motor horsepower for each pump. Across the 108 distinct in-ground designs on the list retrieved 17 October 2026, after grouping records that share identical measurements:

Measure	Value
Median ratio, hhp ÷ rated hp	0.572
Lowest ratio	0.227
Highest ratio	0.753
Designs rated 1.5 to 1.65 hp	35 designs, hhp 0.341 to 1.242
Designs rated 2.7 hp	15 designs, hhp 1.341 to 1.860

The median is close to Jandy's rule of thumb, but individual pumps sit far from it. At 1.5 to 1.65 rated hp, the smallest is the Blue Torrent BT TBVXL150S at 0.341 hhp and the largest is a Hayward TriStar XE record at 1.242 hhp. One is more than three and a half times the other.

The figure at the top of this page shows every design. The dashed line is "hhp equals half the rated horsepower"; the shaded strip is 1.5 to 1.65 rated hp. If the rule of thumb held, every mark would sit on the line. They scatter widely above and below it.

Every rated horsepower on the list

Here is the full spread, by the rated motor horsepower each record publishes.

Rated hp on the record	Designs	hhp range
0.85	6	0.409 to 0.490
0.9	2	0.587 to 0.670
1	5	0.434 to 0.650
1.2	1	0.771
1.25	6	0.680 to 0.890
1.3	5	0.580 to 0.703
1.5	9	0.341 to 1.019
1.65	26	0.559 to 1.242
1.67	1	0.718
1.7	2	1.050
1.75	1	1.005
1.85	5	1.150 to 1.248
2	3	1.180 to 1.270
2.2	6	0.629 to 1.246
2.21	1	1.546
2.25	4	0.969 to 1.643
2.6	1	1.640
2.7	15	1.341 to 1.860
3	6	0.685 to 1.735
3.65	1	1.563
3.9	1	1.808
3.95	1	1.883

Look at the 3 hp row: the smallest design rated 3 hp delivers 0.685 hhp, less than several pumps rated 1.25 hp. The 2.2 hp row runs from 0.629 to 1.246. A motor rating sets an upper bound on what the motor can deliver, not what the pump's hydraulics actually turn into water flow.

Why hhp decides the efficiency rules

The federal standard for dedicated-purpose pool pumps, 10 CFR 431.465, covers self-priming and non-self-priming pool filter pumps below 2.5 hhp, and its minimum efficiency equations are written in hhp. For self-priming pumps the rule splits at 0.711 hhp:

• 0.711 hhp and up: minimum WEF = −2.30 × ln(hhp) + 6.59
• below 0.711 hhp: a separate, lower line

ENERGY STAR uses the same 0.711 hhp boundary for its own minimum. Because the minimum falls as hhp rises, the same WEF can be excellent for a large pump and poor for a small one.

The boundary also creates a step. Under ENERGY STAR's Version 2.0 lines, a self-priming pump at 0.70 hhp needs a WEF of 5.41, while one at 0.711 hhp needs 7.37. A pump that creeps over the boundary faces a much higher bar. That is one more reason to compare a pump's WEF against the minimum printed on its own record, as the weighted energy factor guide recommends, and the DOE pool pump rule explained covers what the federal rule requires.

Hydraulic horsepower and flow

Hydraulic horsepower combines two things a pump does: how much water it moves, and how hard it pushes against the resistance of the plumbing. A pump that moves a lot of water against little resistance and one that moves less water against more resistance can have similar hydraulic horsepower.

For choosing a pool pump, the more useful companion number is the flow at each certified test point, which every record publishes. Across the certified designs, the median flow at the high-speed test point rises with size: about 52.3 gpm for pumps under 0.711 hhp, 61.1 gpm for 0.711 to under 1.2 hhp, and 74.0 gpm for 1.2 hhp and up. At the low-speed point the medians are about 25.0, 31.3 and 31.3 gpm.

So the larger pumps are not mainly faster at low speed; they have more headroom at high speed. If your pool only ever needs filtration flow, a smaller pump can do it, and the larger pump's extra capacity is only worth paying for if something in your system needs high flow.

The 0.711 hhp boundary in the data

The certified list shows the boundary at work. Designs just below 0.711 hhp are measured against the small-pump line, designs just above it against the standard line, and the difference in their ratios is stark:

Pump	hhp	WEF	Class minimum	WEF ÷ minimum
Jandy VS FloPro (WEF 11.0 record)	0.703	11.0	5.41	2.033
SPLASH; CIPU 72554S / NORTHFLO PMP-72554001	0.697	9.4	5.42	1.734
XtremepowerUS 75016	0.715	10.2	7.36	1.386
SPLASH; CIPU 72554	0.717	9.4	7.36	1.277
DAB E.SWIM 150	0.718	9.527	7.35	1.296

Two pumps with the same WEF of 9.4, at 0.697 and 0.717 hhp, sit 1.734 and 1.277 times above their minimums. A difference of 0.02 hhp moved them into different classes. When you compare pumps near this size, check which side of the line each sits on.

Why the motor rating runs high

A motor horsepower figure describes what the motor can deliver at its shaft, and a total or service factor horsepower adds the extra load the motor is rated to carry beyond that. The pump's hydraulics then turn shaft power into water flow and pressure, with their own losses. So hydraulic horsepower is always smaller than the motor rating, and by how much depends on how well the wet end, the impeller and volute, is matched to the motor.

That is why two pumps can share a motor rating and differ so much in hhp. A manufacturer may fit the same motor to a smaller and a larger wet end, or rate a motor generously to leave headroom. Neither is wrong, but neither tells you how much water reaches the pool.

Common sizing mistakes

• Replacing by horsepower. An old pump's motor horsepower says little about its flow. Matching it with a new pump of the same rating can land anywhere in the wide ranges in the table above.
• Assuming bigger is safer. A larger pump costs more at its high speed, and older pools often had more pump than they needed. A variable speed pump can be turned down, but its high-speed hours still cost more on a bigger pump.
• Ignoring the plumbing. Hydraulic horsepower is measured on a standard test resistance. A pool with small pipes or a long run to the pump will get less flow from the same pump than the test shows.
• Comparing WEF across sizes. A higher WEF on a smaller pump does not make it the better buy if it cannot move the flow you need.

How to use hhp when choosing a pump

1. Work out the flow you need. Pool volume divided by turnover time gives gallons per minute. The turnover calculator does it.
2. Shortlist by hhp and measured flow, not motor horsepower. Every certified record shows the flow at its test points. A pump whose high-speed test flow comfortably exceeds your need is big enough.
3. Do not oversize. A bigger pump costs more to run fast. In the certified data, the median high-speed draw rises from about 513 W for pumps under 0.711 hhp to about 1,082 W for pumps of 1.2 hhp and up, while low-speed draw barely changes. See how many watts a variable speed pool pump uses.
4. Then compare efficiency against the class minimum. The most efficient pumps by size are ranked that way.

A worked example

Four certified pumps, smallest to largest:

Pump	Rated hp	hhp	High-speed test flow	High-speed W
Hayward TriStar VS (0.448 hhp record)	0.85	0.448	48.44 gpm	369.09
Jandy VS FloPro (0.703 hhp record)	1.3	0.703	55.90 gpm	553.85
Pentair INTELLIFLO 1.5 VSF	1.5	0.896	60.46 gpm	659.47
Hayward TirStar VS (1.240 hhp record, also sold as TriStar VS 900)	1.85	1.240	67.69 gpm	891.57

Each step up in hhp brings more flow at the high test point and more watts to get it. The motor rating moves too, but not in step: 0.85 to 1.85 rated hp is a little more than double, while hhp goes up nearly three times.

Note also that the Hayward model name "TriStar VS 900" appears on certified records at both 0.448 hhp and 1.240 hhp. A model name alone does not tell you the size; the hhp on the record does.

Reading the label on your own pump

A pump made since July 2021 should carry THP and WEF on its rating label. It may not show hhp; Pentair's white paper notes that hhp labeling is voluntary, and that Pentair adds it to its own labels. If the label lacks it, look the model up on the certified pump list, where every record shows its rated hydraulic horsepower.

An older pump will usually show only a motor horsepower and perhaps a service factor. To estimate what a replacement should deliver, the more reliable route is the flow your pool needs, worked out from its volume, rather than the old motor's horsepower.

The short version

Hydraulic horsepower is what the pump does to the water; total horsepower is what the motor is rated for. The certified data shows the two are only loosely related, so when you compare or replace a pump, use the hydraulic horsepower and test flows on its certified record, and size from the flow your pool needs rather than from the old motor's rating.

Sources

• ENERGY STAR Certified Pool Pumps dataset, retrieved 17 October 2026: all hhp, rated hp, flow and wattage figures.
• 10 CFR 431.465: coverage below 2.5 hhp, the 0.711 hhp split and the minimum WEF equations.
• ENERGY STAR Pool Pumps Key Product Criteria: the Version 2.0 minimum WEF lines either side of 0.711 hhp.
• Jandy, guide to the DOE pool pump regulations: the hhp-to-THP rule of thumb and the THP and WEF labeling requirement.
• Pentair, "Why Hydraulic Horsepower Matters" white paper: definitions of hhp, THP and service factor horsepower, and voluntary hhp labeling.
• Pinch A Penny, 2021 pool pump regulations: the move from special-, max- and full-rate terms to THP.

Compare pumps on measured water power and flow, not the motor rating, and hydraulic horsepower vs total horsepower stops being confusing.