Invest in a Good Cover. Make sure your hot tub cover is well-insulated and has a tight-fitting seal. A high-quality cover in good condition will help your hot tub maintain a constant high temperature, even when the weather is frigid.
Monitor the Water Level. Check your water level frequently and add more as necessary. If the water level falls too low in cold weather, things may freeze and damage your hot tub.
Keep the Water Clean. Make sure you clean and maintain your water and filters as usual. Simple problems can become harder to fix in below zero weather.
Change Your Water Early. If your tub will be due for a scheduled water change during winter, it is best to take care of it earlier in the year. Changing water while the outside temperatures are low presents a risk of water freezing and damaging your spa.
Turn Down the Jets. Use the jets less than you would in other seasons, and turn them off when not in use. The jets work by blowing air into the water, which can lower the temperature.
Be Smart About Soak Times. The longer you stay in your spa, the higher your body temperature climbs. While it may be tempting to linger in the warmth of your hot tub when the outside air is cold, try to limit your soak time to about twenty minutes.
Stay Hydrated. It’s always important to stay hydrated when you’re using your hot tub. During the winter, you may want to drink warm or room-temperature beverages while soaking to keep yourself hydrated. Alcohol can increase the effects of dehydration, it’s best to abstain from drinking alcoholic beverages in your spa.
Have a Plan for when you're done. Cold weather can be dangerous, especially when you’re wet. At the end of your soak, when you leave the warmth of your hot tub and face the cold winter air, make sure you keep a bathrobe and shoes or slippers nearby, and get indoors as quickly as possible after leaving your hot tub.
Use accessories to add warmth and comfort. Add heating lamps, or a towel warmer, or maybe a weatherproof rug to protect feet from the frozen ground.