120V equipment
Some compact infrared saunas and many portable chillers can operate on 120V. That can reduce installation complexity, but the manufacturer may still require a dedicated circuit and specific amperage.
240V equipment
Traditional electric sauna heaters and many full-size hot tubs commonly use 240V because the equipment needs more power. That usually means a dedicated branch circuit and professional installation.
Do not plan from voltage alone
Check voltage, amperage, breaker size, conductor requirements, plug/receptacle or hardwire instructions, GFCI requirements, clearances and whether the circuit must be dedicated. The product's installation manual controls.
Why this belongs before purchase
A lower-priced unit can become the more expensive project if electrical service upgrades are required. Conversely, a compatible 120V unit can be attractive where electrical changes are difficult.