16- to 21-foot swim spas

Less than the length suggests. The spec-sheet length is the cabinet, with the walls, seats and equipment bay inside it. 37 of the 85 makers' sheets here give an open swim length, from 7′ 11″ to 14′ 4″ (median 11′ 6″). Across every swim spa that publishes both, the open water runs a median 68 in shorter than the cabinet.

Where a sheet gives no open swim length, ask the dealer for it rather than working it out from the cabinet. Our guide to room to swim explains how much room a swimmer needs.

Of the 85 here, 67 push the water with jets, 8 with a propeller, 7 with a paddlewheel and 3 with a named system the maker doesn't explain. Jets fire water through a few nozzles, often with air mixed in. A propeller or a paddlewheel turns behind a grate and moves a wider column of water.

What you feel is the shape of the stream: how wide, how deep and how steady it is. On a running display, hold your hand across the current at full speed: it should feel wide and even. The guide to swim spa jets vs propeller compares the three, Endless Pools vs Master Spas compares two makers that sell both propeller and jet models, and the best swim spas for lap swimming are ranked by current type and open swim length.

Where there's a list price or a reported price, 16- to 21-foot swim spas run $34,999 to $74,999:

• Bullfrog Spas: $37,895 to $47,695 · Swim Series starting prices (MSRP), 1 of 1 model
• Endless Pools: $59,999 to $74,999 · Maker's list price (MSRP), 3 of 3 models
• LPI: $42,399 to $52,499 · Maker's list price (MSRP), 4 of 21 models
• Master Spas: $40,499 to $54,499 · Reported price, 6 of 7 models
• Wellis: $34,999 to $50,999 · Maker's list price (MSRP), 6 of 6 models

The other brands quote through dealers. The pad, delivery and the electrical work come on top; what a swim spa costs covers those with sources.

74 of the 79 that publish a breaker size need a 50 or 60 A circuit. Five list 30 or 40 A. 32 need two or more separate circuits (nine of them need three). 24 are dual-temperature models, where the swim side and the hot tub side each have their own controls. SwimEx puts the drive, the heater and the filter pump on separate breakers.

A licensed electrician sizes the circuit for your panel and the length of the run. The amps and circuits for every model are on swim spa electrical requirements.

About $61 a month for the typical one here, just holding temperature with the cover on, and $54 to $71 across the eight with a California listing. Swimming and colder weather add to it.

The guide to swim spa running costs explains what drives it.

27 of the 30 dual-temperature models we track are in this class. A divider splits the water so the hot side can run warmer than the swim side, each with its own heater. Every one is listed on swim spas with a hot tub side.