Item 03 of 10
What holds up 20,000 pounds
A filled swim spa weighs roughly 10,000 to 33,000 pounds, and water pushes out on every wall. The frame, shell backing and base carry it.
What it is
A swim spa is a long acrylic tub set in a cabinet. The acrylic is only a skin; its strength comes from what's bonded behind it and what holds it up. Three parts share the job. The shell backing is fiberglass or plastic laid onto the acrylic. The frame, of galvanized steel, wood or molded composite, carries the walls and cabinet. The base underneath spreads the load onto the pad. Endless Pools builds its E-Series on a 14-gauge galvanized steel frame and an ABS base pan; SwimEx builds its pools from solid fiberglass composite with a balsa-wood core.
Why it matters
Length is what makes a swim spa different from a hot tub. Each long wall is 12 to 21 feet of acrylic with water leaning on it all day. Water pushes sideways as well as down, and by our arithmetic each long side of a 15-foot spa holding 46 inches of water takes more than 6,000 pounds of outward push that never lets up.
If the frame or backing lets that wall bow, the shell flexes every time the spa heats, cools and gets swum in. Over years the flexing opens hairline cracks at corners, steps and jets, and eventually one leaks.
Wood frames add a second risk: a slow leak soaks them, and wet wood rots, which is exactly why Hydropool sells its steel frames on having nothing to rot. Bare steel rusts, so makers galvanize it. If the structure has to be replaced, Master Spas' swim spa warranty leaves the cost of removing the old unit and setting the new one to the owner.
How makers do it
Galvanized steel frame on a sealed base
The good wayA zinc-coated steel frame on a molded base pan. Endless Pools uses 14-gauge galvanized steel; Jacuzzi lists galvanized steel on its J-16 PowerPro.
Thick fiberglass behind the acrylic
The good wayHand-rolled fiberglass lets the shell hold its shape on its own. PDC says its shells stand with no framed support.
Fiberglass composite vessel
The good wayThe structure itself is fiberglass, like a pool. SwimEx uses solid fiberglass composite with a balsa-wood core.
Molded composite frame
AcceptableA molded plastic frame replaces lumber. Bullfrog lists its EnduraFrame as standard on the S180XD.
Wood frame
AcceptableA lumber frame carries the cabinet and supports the shell. Endless Pools lists a wood frame on its R-Series R200.
In the showroom
Check this
- Read the spec sheet for the frame: galvanized steel, wood, composite, or not stated.
- Push hard on the top edge midway along a long side. It shouldn't move.
- Read the warranty: years on structure, and who pays to remove a failed spa.
Ask this
- What is the frame on this exact model, and is the steel galvanized?
- What's bonded behind the acrylic: hand-rolled fiberglass, or a plastic sheet?
- If the structure fails in year eight, who pays for the crane and the swap?
How each brand does it
16 of 17 brands publish enough to tell. For the rest, ask the dealer.
Every brand, A to Z (16)
- YesAmerican Whirlpool
Galvanized steel frame and ABS bottom pan on every model; the frame is warranted for life.
- PartlyArctic Spas
Self-supporting fiberglass-backed acrylic shell; four models sit on a sealed fiberglass floor, the other four on pressure-treated wood.
- PartlyArtesian Spas
Artesian says its spas use a pressure-treated lumber frame on a full ABS base; TidalFit adds full foam and a fiberglass structure behind the acrylic.
- PartlyBullfrog Spas
A molded plastic frame and base that can't rot; how it holds the long walls isn't published.
- PartlyCal Spas
A treated-wood frame and a shell Cal Spas says is reinforced with steel and wood; no laminate thickness is published.
- PartlyCoast Spas
Fiberglass-reinforced acrylic on a pressure-treated wood frame. The 2100 pages don't confirm the frame, and nothing about the base is published.
- PartlyDynasty Spas
A pressure-treated wood frame bonded to a fiberglass-backed Lucite shell, sitting on a treated-plywood bottom.
- PartlyEndless Pools
E- and X-Series sit on a 14-gauge galvanized steel frame over an ABS base pan; the cheaper R-Series is wood-framed.
- PartlyHydropool
A steel frame under a fiberglass-backed acrylic shell, warranted 10 years against cracking; Hydropool doesn't publish the steel's gauge or coating.
- YesJacuzzi
Galvanized steel frame on a moisture-proof polymer base under a three-layer acrylic shell; frame gauge and shell backing are not published.
- PartlyLPICatalina Swim Spas, Dr. Wellness
Fiberglass-backed acrylic over an ABS base on the dual-temp models; frame material isn't published except treated wood under inground models.
- PartlyMaster Spas
A coated wood frame under an acrylic shell, by Master Spas' own list; nothing published on shell backing, lumber size or frame design.
- PartlyPDC Spas
A hand-rolled fiberglass shell PDC says stands without a frame; the frame material itself is not published.
- PartlySundance Spas
Acrylic shells; Sundance's blog gives every model a SunStrong steel frame, and only the Splash 12's page says it's galvanized.
- YesSwimEx
Every SwimEx is a free-standing fiberglass shell with a balsa-wood core, built like a boat hull, with no frame or cabinet. Our checklist rates a fiberglass composite vessel best.
- PartlyWellis
Stainless steel frame and fiberglass-reinforced acrylic; gauge and frame layout aren't published, and the base is described only for the Beach Club.
Marquis doesn’t publish this.
Read nextIn-ground swim spasSwim spa sizesBest swim spasSwim spa costBest swim spas for lap swimming
Where it gets complicated
Steel isn't automatically better. In a 2013 owners' forum thread, a trade participant pointed out that a hollow steel stud resists side load worse than a solid wood one, and another said they'd never seen a wood swim spa frame fail indoors. Design and gauge matter more than the material's name, and almost no maker publishes them.