88–90°F is the sweet spot for a swim spa in cooler weather.

Yes, keep it between 88 and 90. That’s warm enough so you don’t tense up when you first get in, but cool enough that you won’t overheat during a swim. If you’re doing actual laps or high-intensity resistance swimming, you might even drop it to 85–87 to keep your core from cooking. But for floating, light paddling, or just lounging in cold air? 88–90 is ideal.

Most swim spas default to around 85, which feels great in summer but will have you shivering the second you step out on a 50°F day. Bump it up a few degrees. Your muscles will thank you.