Winterising a hot tub: continued use or full drainage

Short answer: you have two options in winter. Keep using it: fire regularly, cover on between sessions, and, with an electric version, leave the heating on; then nothing will freeze. Or shut it down: drain the tub fully, including the heater, pipework, filter, pump and heat pump, and cover it dry. The only dangerous state is the halfway option: a tub sitting cold for weeks with leftover water in the heater or pipework. Frozen residual water is the most common and most expensive form of winter damage, and it falls outside the warranty.

Option 1: continued use in winter

A hot tub is at its best in winter. Here's how to keep it safe:

• Wood-fired: fire it at least a few times a week, and daily during severe frost. As long as the water is warm and the cover is on, nothing freezes, not even in the heater.
• Electric or hybrid: leave the element on at bathing temperature or a parked setting of around 30 °C; see electric heating and heat pump.
• Heat pump: keeps working at low temperatures, with somewhat lower efficiency. Keep the grille free of snow and leaves.
• Filter and pump: keep the circulation running; standing water in a filter housing is the first thing to freeze.
• Cover: on between every session, brush off snow straight away; see insulated cover.
• Water: check the pH a bit more often; cold and frequent topping up shift the balance.

If you're away for a few days during light frost, a warm tub under a good cover will handle that fine. If you're away longer, or severe frost is forecast, choose option 2.

Option 2: full drainage

Do this before the first night frost or before you're away for an extended period. Work through the list completely; a skipped step is exactly where damage occurs.

1. Fire out and heater cold. Never drain a tub with a hot heater. Stop dosing a few days beforehand if you plan to discharge the water into the garden.
2. Drain the shell via the ball valve at the bottom of the tub; a hose connection lets you discharge the water in a controlled way.
3. Drain the heater. An external heater via its drain point and the bottom connection; an internal heater drains along with the shell, but check that no water remains in the firebox or under the grate. Remove the ash and let the heater dry.
4. Blow out the pipework. Remove residual water from hoses, pump and jet lines with a wet vacuum or a compressor at low pressure. Leave all valves and caps open.
5. Filter and pump. Open the drain plug on the filter housing and the pump, let everything drain out, and set the multiport valve to the winter position or between two positions so it's not under pressure. Store a filter cartridge indoors, dry and frost-free.
6. Electric element and heat pump. Disconnect power, drain according to the appliance manual; a heat pump has its own drain points. If unsure, have this done by service.
7. Clean the shell now that it's empty: waterline and walls; see cleaning a jacuzzi shell for the protocol, which also applies to a hot tub shell.
8. Cover it dry. Fit the cover securely so no rain or snow gets into the empty shell. Rain cap on the flue.

Drainage check per component

The spring check

Before refilling:

1. Check all connections, hoses and valves for cracks; recheck fixings.
2. Refit drain plugs and caps, set the multiport valve to Filter.
3. Fit a clean filter cartridge, or, with a sand filter, check the sand; see backwashing the sand filter.
4. Inspect the heater and flue; check the rain cap and heat shield are secure.
5. Clean the wooden surround and oil or stain it if needed.
6. Fill, check for leaks, and follow the start-up order in first start-up.