Many people associate outdoor swimming with summer: barbecues, sunshine, and cooling off in the water. However, ask any Scandinavian or Canadian, and they will tell you the truth: the real season for hot tubs is winter. There is a specific kind of magic that happens when you submerge yourself in 39°C water while the air around you is freezing, frost covers the garden, and steam rises into the crisp night sky.
Yet, the idea of operating a wood-fired hot tub in sub-zero temperatures intimidates many UK homeowners. Will the water freeze? Will the stove crack? Is it too much effort to heat up when it’s 2°C outside? In this comprehensive guide, we will explore the logistics of winter bathing. We will cover freeze protection, heating strategies for cold days, and why winter might just become your favourite season to soak.
The Science of Freezing: The Enemy
The biggest risk to your hot tub in winter is ice expansion. When water freezes, it expands by about 9%. In a confined space—like the water jacket of your stove or the drain pipes—this expansion generates immense force, enough to split stainless steel or crack fiberglass.
The Golden Rule: You must never let the water freeze inside the stove or filtration system.
However, this doesn’t mean you have to drain the tub for the entire winter. A large body of water (1,500 litres) takes a long time to freeze solid. It is the small volumes in pipes and heaters that freeze first.
Strategy 1: The “Always On” Approach (For Frequent Users)
If you plan to use the tub 2-3 times a week, you can keep it filled.
1. Regular Heating: You need to fire up the stove regularly (every 1-2 days depending on the frost) to keep the core temperature above freezing.
2. Electric Frost Guard: If you have a hybrid model or electric heater, set the thermostat to 5°C. This minimal energy usage prevents freezing without costing a fortune.
3. Insulation: Your cover is vital. An insulated thermal lid traps the heat. Without it, keeping the water liquid is a losing battle against the elements. Consider adding a floating thermal blanket under the main lid for a double layer of protection.
Strategy 2: The “Drain Down” Approach (For Occasional Users)
If you only plan to bathe on special occasions (like New Year’s Eve), it is safer to drain the tub between uses.
The Critical Step: Simply opening the main drain is not enough. You must open the specific drain plug on the stove heater itself. There is often a litre of water trapped in the stove’s jacket that doesn’t drain via the main plug. If this freezes, your stove is ruined.
Blow Out Lines: If you have air jets or hydro massage, use a wet-and-dry vacuum to blow/suck residual water out of the pipes.
Tip: Even when empty, keep the lid on to prevent snow and rain accumulating and freezing in the bottom.
Heating Time in Winter
Be realistic about timing.
Summer: Tap water is 15°C, Air is 20°C. Heating time: ~2 hours.
Winter: Tap water is 4°C, Air is 0°C. Heating time: ~3.5 to 4 hours.
The stove has to work harder to overcome the cold starting temperature and the heat loss from the tub walls.
Pro Tip: Use smaller, drier logs to create a more intense fire. Keep the lid on until the very last moment. Stir the water more frequently to ensure the heat distributes evenly and doesn’t just sit at the top.
The Experience: Why It’s Worth It
Why go through the effort? Because of the contrast.
No Overheating: In summer, you often have to get out of the tub after 20 minutes because you are too hot. In winter, your head stays cool while your body stays warm. You can soak for much longer without feeling dizzy.
The Hat Trick: Wearing a woolly hat in the hot tub isn’t just a fashion statement; it’s thermoregulation. It keeps your body heat in while your face enjoys the cool breeze.
Silence: Snow dampens sound. A winter night in the garden is often quieter and more peaceful than a summer evening.
Frequently Asked Questions (FAQ)
Can I use salt to stop it freezing?
Technically yes, salt lowers the freezing point. However, to stop a hard frost, you need a very high salt concentration (like sea water), which is corrosive to standard 304 stainless steel stoves. Only use salt if you have a 316-grade stove, and don’t rely on it for deep freezes.
What if the drain valve freezes?
Do not force it! You will snap the handle. Pour warm (not boiling) water from a kettle over the external valve body. It will thaw in seconds. Insulate the valve with an old towel to prevent re-freezing.
Is it bad for the wood?
No, wood handles cold well. However, if water freezes inside a wooden tub, the expanding ice can push the staves apart. If keeping water in, float a plastic football or a piece of polystyrene on the surface. This absorbs the pressure of the expanding ice.
Conclusion
Using a wood-fired hot tub in winter requires a little more diligence, but it delivers the ultimate reward. There is no better way to beat the winter blues than by turning your cold, dark garden into a steaming, inviting sanctuary. Don’t hibernate your tub; embrace the cold.