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A permanent home cold plunge comes together in seven steps, in order: a level, load-rated site; a dedicated GFCI circuit; a tub sized to your body; a chiller sized to your water and your climate; a water-quality plan; freeze protection if you run outdoors; and a running-cost estimate at your own electricity rate — not someone else’s average.

Put an above-ground plunge on a level surface rated for its filled weight — often 900–1,500+ lb concentrated over a footprint of just a few square feet. Outdoors, that means a concrete pad or paver base, not a bare deck with no load check; indoors, waterproof flooring near a drain. Plan a drain-down path before you plumb anything — gravity, a submersible pump, or a hose to a floor drain — and keep the tub within reach of a dedicated GFCI outlet. A deck's code design load is 40 psf live + 10 psf dead Code — IRC R301.5; a filled plunge routinely runs several times that, concentrated in one spot. That gap is an engineer or AHJ question, not a spec-table lookup.

Cold plunge shells come in six materials: stainless steel (304/316), acrylic/fiberglass, rotomolded HDPE/LLDPE (“poly”), cedar/thermowood, galvanized stock tank, and an insulated composite shell that wraps a stainless or acrylic inner shell in a foam-injected outer cabinet. Stainless and insulated composite last longest and are easiest to sanitize; poly is the lightest and cheapest purpose-built option; stock tanks are the cheapest entry point but uninsulated and more corrosion-prone. The material that actually predicts cold performance and running cost is whether the construction has an insulation layer — not the headline wall material.

There is no honest single answer to “what does a cold plunge cost to run” — it depends on your chiller’s power draw, how hard it actually works (duty factor), your climate, and your own electricity rate. The method: take the chiller’s nameplate watts, estimate daily run-time plus standby, convert to kWh, then multiply by your rate. We refuse to hand you a national dollar figure — every incumbent in this category prints one, and none of them print your wattage, your climate, or your rate.

Winterizing means picking one of two paths: keep the system running with real freeze protection — circulation, an insulated cover, and a heater or freeze-guard mode — so moving water and heat stay above freezing, or drain and store the chiller, pump, filter, and lines. Half-measures are what crack pipes. Check your chiller’s stated minimum operating ambient before assuming it can run through winter at all.

Use all three — they do different jobs. A cartridge filter (20 microns or finer) removes particles but does not sanitize. Ozone and UV kill microbes but leave no lasting residual, so most setups add a low chlorine or bromine residual. Filtration clears the water; a sanitizer keeps it safe between plunges. Cold water slows growth but never replaces sanitation.

Size by heat load, not horsepower. Estimate first-pull BTU as gallons × 8.33 × your temperature drop (°F), then add ~20% margin and derate 15–25% for summer ambient. As a rule of thumb: 1/4–1/3 HP for 60–90 gallons, 1/2–3/4 HP for 100–150 gallons, 1 HP for large or commercial tubs. Read BTU/hr, not the HP label.