The best cold plunge chiller for a bathtub

Yes, but a bathtub is close to the worst-case job you can give one, and it is honest to say so up front. A standard bathtub holds roughly 40-60 gallons and has essentially no insulation - a single skin of acrylic or porcelain against room air - so it gains heat continuously and a chiller has to keep working the whole time you are in it. Worse, you drain a bathtub after each use, so the chiller starts from room-temperature water every session rather than topping up an already-cold tub. It works; it is just slow and less efficient than the same chiller on a small insulated tub. Set your expectations accordingly, and start it well before you plan to get in.

More than you would guess, because the bathtub's lack of insulation works against you. A 1/3 HP unit will get there eventually but can take hours from a fresh fill, and may struggle to hold a low temperature against a warm bathroom. A 1/2 HP unit is the sensible floor for bathtub duty, and a 1 HP unit with a published cooling capacity - like the TURBRO's 9,300 BTU - is what you want if you care about being cold on demand rather than on a schedule. None of these publishes a bathtub-specific rating, because none is designed as a bathtub product; we are matching general chillers to the job.

This is the caveat the listings skip, and it matters more here than anywhere else on the site because a bathroom combines mains electricity, water and a wet floor. Treat it seriously: plug the chiller into a GFCI-protected outlet, keep the unit itself out of any splash zone and off a wet floor, never run the cord across standing water, and follow the manufacturer's manual over anything written here. If you are adding an outlet or are unsure your bathroom circuit has the headroom and protection, have a licensed electrician confirm it before you buy. When in doubt, site the chiller in a garage or utility room and run the hoses to the tub.

None of these five publishes an amperage figure, which is itself the finding - you cannot confirm the draw from the listing. The EONIX is explicitly 110V and designed to plug into a standard outlet, which is why it leads for bathroom use, but a bathroom's outlets are shared 15-20A GFCI circuits that may also feed a hair dryer or heater, so headroom is not guaranteed. Ask the manufacturer for the nameplate draw before you buy, and if you are running a larger unit, treat a dedicated circuit as the safe default. Our electrical section covers how to reason about the load.

For most people, yes - and it is the honest recommendation even on a page about bathtub chillers. A purpose-built insulated tub holds temperature with far less chiller effort, keeps its water between sessions so you are not chilling from scratch every time, and keeps the electricity out of your bathroom. Chilling a bathtub makes sense when you cannot site a tub anywhere else, or you want to try cold plunging with equipment you already own. If you find you use it, an insulated tub is the upgrade that lowers both your running cost and your risk.

Less per hour than people expect, because a chiller cycles rather than running flat out - but a bathtub pushes that number up, because the poor insulation means more cycling to hold temperature, and the daily drain-and-refill means a full pulldown every session. None of these five publishes a rated wattage, so we will not invent one. We work the running-cost method through in full on the cost-to-run page using the EIA national average of 18.83 cents/kWh, and let you substitute your own utility rate.