How do you run an outdoor cold plunge through a Seattle or Portland winter?

Key facts

• Sea-Tac January normals: 48.0°F high, 37.7°F low, 7.0 days at or below 32°F (NOAA 1991 to 2020).
• Portland airport January normals: 47.5°F high, 36.2°F low, 8.7 days at or below 32°F.
• Penguin chillers list an operating range of 37 to 100°F with water and say to drain completely at freezing or below.
• Plunge: "All Cold Plunges Must Be Winterized in Freezing Conditions (32°F/0°C or below)."
• Renu Therapy's Cold Stoic 3.0 has a heater for freeze protection and asks owners to run it 24/7 with the lid on and set to 45°F in colder months.
• Portland requires pool and hot tub water to go to the sanitary sewer or soak in on site, not to storm drains.

What a PNW winter actually looks like

The numbers below are NOAA 1991 to 2020 monthly normals from the NCEI normals service for Seattle-Tacoma International Airport and Portland International Airport. "Freezing days" means days with a low at or below 32°F.

Two things stand out. First, the average winter low is right at the bottom of Penguin's 37°F operating floor, so on a typical December or January night a standard chiller is working at the edge of its range. Second, freezing nights are not rare. The totals are our sums of NOAA's monthly figures. Airport stations can run milder than hillside, rural or low-lying yards, and normals do not capture how cold a single arctic outbreak gets, so treat these as a floor for planning.

Freeze protection: what the makers say

The split is clear. Some systems are built to ride through a cold night with a heater and constant circulation. Others expect you to drain and bring the chiller inside whenever it freezes. In a climate with a couple dozen freezing nights spread across five months, that difference decides whether winter is easy or a chore. Ask any brand you are considering, in writing, what its chiller does at 28°F with the lid on.

Chiller or no chiller in winter

Without a chiller, an outdoor tub drifts toward the air temperature. With January highs near 48°F and lows near 37°F, our estimate is water in the 40s for much of midwinter, which many people find cold enough. That is an estimate from air normals, not a measured water temperature, and sun, wind, lid use and tub size all change it. The catch is the rest of the year. Summer highs at Sea-Tac average 77°F in July and August, so a no-chiller tub is a seasonal tool, and it still needs draining or freeze protection on hard-freeze nights.

A chiller earns its place in the PNW for three reasons: year-round temperature control, a pump and filter that keep water moving and cleaner, and, on models built for it, freeze protection. If you plan to use the tub only from November to March, a well-insulated tub with a good lid and a plan for freezing nights may be enough.

Placement, lids and rain

• Lid on whenever you are out. Renu credits its lid with "isolating the water from outdoor temperatures." In the PNW it also keeps out rain and fir needles.
• Leave room for rain. Plunge's setup guide fills outdoor tubs to 3 inches from the top, versus 4.5 inches indoors.
• Cover the chiller, but let it breathe. Penguin calls for 12 inches of open space on all sides and says not to box the chiller in. A roof over the chiller without walls is our suggestion for rain, not a maker spec.
• Check the outdoor rating. Penguin's standard chillers say "Outdoor Rated No." If yours is not outdoor rated, it belongs under cover.
• Firm, level, draining base. A full tub is heavy. Plunge asks for a flat surface that can support 1,200 lbs for its Gen 1 tubs. Gravel or pavers that shed water beat bare lawn in a wet winter.
• Keep the plug dry. Outdoor receptacles need GFCI and an in-use cover. See our cold plunge GFCI and electrical guide.

Draining and winterizing

When you drain for a freeze or a water change, where the water goes matters. Portland Environmental Services says city code prohibits discharging "heated, chlorinated, or salt-treated waters" to storm drains, and home pools may drain to the sanitary sewer without prior authorization. Bellevue Utilities lists an outdoor sewer cleanout, floor drain, shower or utility sink as sewer access, and allows dechlorinated water on your own landscaping only if it soaks in and not within 48 hours of rain. Seattle and other cities have their own stormwater codes, so check yours.

1. Watch the forecast. A predicted low at or below 32°F is the trigger most makers use.
2. If your system has freeze protection, keep it powered, circulating and lidded as the maker directs.
3. If not, unplug the chiller, drain the tub, chiller and hoses, and remove the filter.
4. Store the chiller somewhere above freezing, such as a garage.
5. Refill and restart once nights are reliably above freezing.

What it costs to run in winter

A chiller's draw is set by its compressor, for example 450 watts for a Penguin 1/2 HP and 830 watts for a 1 HP. What changes in winter is how many hours it runs. With air in the 40s, the chiller has less heat to pull out of the water, so run time should drop. That is our reasoning, not a published figure. Freeze protection pulls the other way, because a heater element or an all-night pump uses power. To estimate your bill, log run hours and use the formula and Washington and Oregon rates in our chiller cost guide.

Related guides

• Do you need a permit for a cold plunge in Seattle or Portland?
• Can you put a cold plunge on a deck?
• Cold plunge chiller power use and cost to run
• Cold plunge GFCI and electrical requirements
• Outdoor saunas in rainy climates
• Cold plunge collection
• Best cold plunges of 2026, ranked by use case
• Renu Cold Stoic 3.0 vs BlueCube C1 for outdoor winters
• Cold plunge water care with soft Seattle and Portland water

Frequently asked questions

Can I keep an outdoor cold plunge running through a Seattle or Portland winter?

Usually, with planning. Average winter lows at Sea-Tac and Portland airport sit in the mid to upper 30s °F, and freezing nights are occasional rather than constant. Most chillers we checked must be drained or protected once air or water reaches freezing, so the real job is handling the 25 to 31 freezing nights a typical winter brings, not the average day.

How many nights does it freeze in Seattle and Portland?

NOAA's 1991 to 2020 normals list about 7.0 January days with a low at or below 32°F at Sea-Tac and 8.7 at Portland airport. Adding November through March gives about 25 days at Sea-Tac and 31 at Portland. Normals are averages for airport stations, so colder or higher yards can see more, and a single cold snap can bring several in a row.

Do I need a chiller for a cold plunge in the Pacific Northwest winter?

Not for cold water in midwinter, but most people want one year round. With January highs near 48°F, an uncovered tub without a chiller will likely sit in the 40s, which is our estimate from NOAA air normals, not a measurement. From spring to fall the water warms well past that, and a chiller also runs the pump and filter that keep water clean.

What happens if my cold plunge chiller freezes?

Freezing water expands and can crack chiller coils, pumps, fittings and filter housings. Renu Therapy states that cracked components from freezing are not covered by its warranty, and Plunge says winterizing is required to maintain its warranty. Penguin says to disconnect and drain its chiller completely if ambient temperatures drop to freezing or below.

Should I leave my cold plunge running in freezing weather?

It depends on the brand. Renu Therapy tells Cold Stoic 3.0 owners to keep the unit running 24/7, keep the lid on and set 45°F in colder months, and its heater provides freeze protection. Plunge and Penguin instead say to drain and winterize once it freezes. Ice Barrel's chiller alerts below 33°F water and tells owners to winterize the chiller.

Does rain hurt an outdoor cold plunge?

Rain adds water to an open tub, and Plunge sets its outdoor fill line at 3 inches from the top versus 4.5 inches indoors to leave room. Penguin's standard chillers are not outdoor rated, and only its outdoor 1/2 HP HE model is designed for all weather except freezing. Keep the lid on, keep the electrical connection dry and covered, and check the chiller's outdoor rating.

Where can I drain a cold plunge in Portland or the Seattle area?

Into the sanitary sewer, such as an outdoor sewer cleanout, a floor drain or a utility sink, according to Portland Environmental Services and Bellevue Utilities. Treated water should not go to a storm drain or the street. Dechlorinated water can soak into your own yard where it will not run off, and Bellevue says not within 48 hours of rain.

Does a cold plunge cost more to run in winter?

The chiller itself should run less, since cooler air means less heat to remove. That is our reasoning, not a maker figure. Freeze protection can add cost: a heater element or a pump running all night uses power. For watts and a cost formula using EIA July 2026 rates for Washington and Oregon, see our chiller cost guide.

Keep reading

Browse our cold plunges collection, see all guides, or ask us a question about your project.