Best swim spas for lap swimming

Of the 73 swim spas whose makers publish an open swim length (the water between the current and whatever sits behind you), we started with the 57 built for swimming: no pool systems, hot tub hybrids or swim spas with a single fitness jet pump.

We grouped them by current: propeller or paddlewheel, then airless jets, then other jets. That order follows our swim current guide: a propeller or paddlewheel pushes a wide column of water, airless jets push narrower streams, and other jets often mix in air, which gives you less to pull against. Within each group the longest open swim area wins; ties go to deeper water, then more swim pumps. We show the top swim spa in each group and the top one from a second brand. Nothing else feeds the ranking.

A current wide enough for your shoulders and smooth enough to pull against. Endless Pools describes standard jets as narrow, turbulent and full of air, against the broader, smoother stream of its propeller current. PDC makes the same comparison for its propeller models. Both are makers describing their own design, so hold your hand across the current on a running display before you take either at its word.

Speed control decides whether two swimmers can share it. Endless Pools gives its E500 31 pace settings.

More than your height. With arms overhead, standing reach averages about 1.2 times height in the US Army's 1988 body survey, so a six-foot swimmer is over seven feet long before a kick. In a short lane your hands reach toward the outlet, your feet touch the seats and you shorten your stroke to fit.

The longest open swim areas are in the longest tubs: see 16- to 21-foot swim spas and the full range in swim spa sizes. For picks on warranty as well as room, see the best swim spas; for two of the most-compared training brands, see Endless Pools vs Master Spas.