How to Winterize a Hot Tub, and When to Keep It Running

To winterize a hot tub, drain it on a day above freezing, before the first 32°F night, then remove the water left in the pumps, heater and plumbing the way your owner’s manual describes. Many owners don’t need to: a tub kept filled, heated and covered protects itself. Drain-and-winterize is for a tub nobody will use or check, or one facing a long power outage in freezing weather.

Below, four current owner’s manuals are set against NOAA climate normals for 21 US cities.

Keep it running or winterize: what the manuals say

No manual says to winterize just because winter is coming. Jacuzzi and Sundance say the spa protects itself against freezing when operating properly, and Jacuzzi’s and Bullfrog’s freeze modes run the pump, and the heater if needed, when a freeze is detected.^2,4,3

The Hot Spring manual recommends draining or winterizing a tub left unused over 14 days with nobody to maintain the water, or unused in severe cold.¹ Bullfrog’s manual wants a weekly check; for two to six weeks of no use it drops to 80°F, and beyond six weeks it offers vacation mode or winterizing.³ Jacuzzi suggests winter operation for owners who soak twice a week or more, in F3 “Standard” mode where it is very cold.^5,6

What keeping it running costs this winter

By our running-cost estimates, the median certified tub kept at 102°F with its cover on uses $56 of standby electricity from December through February in Miami, $149 in Minneapolis and $230 in Boston, before soaking time.^11,12 Electricity prices matter as much as cold: Boston costs more than Fargo, which gets ten times as many 10°F nights.

Freeze risk where you live

NOAA’s 1991–2020 normals show how often US ZIP codes reach the manuals’ temperatures.¹⁰ Hot Spring warns that below 10°F with strong wind the jet pump can partly freeze even while the water stays hot.¹ Seventy percent of ZIP codes average at least one night a year at or below 10°F. Sundance runs filtration 24 hours a day below 32°F; 74% of ZIP codes have a January average low at or below freezing.⁴

Only 7% of ZIP codes get a 28°F hard freeze in fewer than half of winters, so simply draining and walking away is rarely safe. Even where January lows average above freezing, 71% of ZIP codes see a hard freeze in most years, the same pattern behind the temperatures that freeze pipes.

Dates are medians, so half of years come earlier. Look up yours with the frost date tool and your zone with the zone lookup.¹³

When to winterize a hot tub

Jacuzzi’s timing guide: start when daytime highs stay below 60°F, finish before nights drop below 32°F for consecutive nights, work on a day above 40°F, and never drain below freezing, because water in the lines can freeze before you finish.⁵ Hot Spring’s winter advice is stricter: finish any drain and refill before temperatures fall below freezing, so our tables date the first 32°F night.⁸

The chart at the top shows all three dates for 18 cities. In 9 of the 18, including Fargo, Denver, Nashville and Atlanta, the median first frost comes before highs drop below 60°F, so the frost date is the one to plan by. The same deadline applies when you close a pool.

How to drain and winterize, as the manuals describe it

Hot Spring warns that mistakes can mean freeze damage not covered by warranty; it, Jacuzzi and Sundance recommend the dealer.^1,2,4 Otherwise, follow your own manual; these are the shared steps.

1. 1

   Sanitize, then shut down

   Bullfrog has you super-sanitize first, so water left in the plumbing doesn’t grow bacteria.³ Caldera’s guide does the reverse: it lets the chlorine fall to 0 on a test strip, typically 3–4 days.¹⁶ Then turn the power off as your manual directs.

2. 2

   Drain the shell

   Open the drain valve with a garden hose routed away from the foundation; sanitized water can harm plants.¹ Move water from the seats into the footwell and vacuum out the rest.^2,4

3. 3

   Empty the pumps and heater

   Jacuzzi and Sundance remove the pump drain plugs, releasing one to two gallons.^2,4 Bullfrog also loosens the pipe unions and leaves them open until spring.³

4. 4

   Clear the jets and lines

   Where it falls below 32°F, Hot Spring requires a 5-gallon vacuum/blower shop vac on every jet, top down, then the filter fittings and floor drain.¹ Sundance leaves the air controls open.⁴

   

5. 5

   Filters out, cover down

   Hot Spring stores the filter dry; Bullfrog puts it back clean.^1,3 Fasten the cover tie-downs and lay plywood on top to carry snow.^1,3

Hot tub antifreeze: only some manuals use it

Use only Propylene Glycol as your anti-freeze

Hot Spring pours it into every standpipe, fitting and jet after vacuuming. Bullfrog offers ½ to 1 gallon in the filter hole instead of vacuuming that pipe.^1,3 The Jacuzzi J-200 and Sundance 780 manuals use none.^2,4 Google’s AI answer cited 1 to 3 gallons from a YouTube video; no manual we read gives that. Hot Spring’s spring opening uses three teaspoons of dichlor per 250 gallons, twice its normal superchlorination dose, to destroy the antifreeze, then a second drain.¹ Our pool volume calculator estimates a built-in spa’s gallons.

When the power goes out in freezing weather

Jacuzzi and Sundance say to check the power during severe cold and remove all water if an outage is prolonged.^2,4 Jacuzzi’s guide treats more than 24 hours in freezing weather as the signal.⁵ Until then, its outage page says to keep the cover on, add blankets, top up with hot water from an indoor faucet in extreme cold, and treat a full drain as a last resort; afterward, test and shock the water.⁷

Search answers quote 48 to 72 hours and suggest a heater in the equipment bay; both trace to forums and dealers, not a manual, so we leave them out. Powering a tub from a generator is electrician’s work; see our portable generator safety guide.

Keep the cover locked, full or empty

Always use a locked safety cover when the spa is not in use

CPSC’s safety alert counts more than 700 deaths in spas and hot tubs since 1980, about a third of them drownings of children under five.⁹ Hot Spring says to keep the spa covered empty or full.¹

Restarting in spring

the water remaining in certain sections of the piping may still be frozen.

Jacuzzi and Sundance advise asking the dealer before restarting a tub that sat empty in freezing weather.^2,4 Hot Spring doesn’t recommend refilling below 50°F air.¹ Typical highs pass 50°F around February 19 in Denver, March 22 in Chicago and April 5 in Minneapolis. Then rebalance with our hot tub chemical levels guide.