Should You Run Your
Pool Pump in Winter?

Start here

Closed or Open: The Only Question That Matters

Closed means no water is left anywhere it can freeze and crack something. Anything else counts as open, even a partial closure.

Which one fits where you live?

Hayward says to close unless freezes are infrequent and temperatures don't dip far below 32°F, Leslie's says to close where freezing is frequent and continuous, and Pentair says pools in states that average 60°F or more in winter don't need to close.

Sources:HaywardLeslie'sPentair

Source:NOAA's 1991-2020 normals

• Decided to close? When to Close Your Pool gives you your window.

Open pools

If Your Pool Is Open: When the Pump Has to Run

Whenever the air is at or below freezing, the pump runs nonstop until it's back above freezing. On an all-day freeze, that means through the day too.

Your state

How Often It Freezes in Every State

On any freeze night, not just the coldest, water can freeze inside equipment whose pump is off or has lost power.

Pick your state in the picker at the top for its numbers in one card, or open the full table below.

How to read the numbers

Before the first freeze

How Freeze Protection Works (and the Kind That Doesn't Protect Your Pipes)

An outdoor air sensor on automation is built to protect the whole system, and a freeze thermostat protects what its timer runs. Pentair's and Hayward's pump freeze modes aren't meant for your pipes.

• Variable-speed pump? None of the manuals we checked says what speed is enough to keep the lines from freezing. Whatever you pick, look at the pump: water should be moving through the basket and coming out of every return.

Mild days

How Long to Run It on Mild Winter Days

Start at about 4 hours a day for a single-speed pump, or 8 hours at low speed for a variable-speed pump, then adjust.

Source:Trouble Free Pool's Pool School

• Water stays clean? Try less.

• Not staying clean? Add time. The DOE suggested adding half an hour at a time.

Source:DOE, archived

No US standard sets winter run time, and the published numbers vary:

Sources:FPL, archivedSRPDOE

Light care

Light Winter Care for an Open Pool

There isn't much to do: cold water uses far less chlorine.

Pentair: "very little chlorine production is needed in cold water so long as free chlorine levels are maintained at 2.0 - 4.0 ppm" (Pentair).

• Test every two to three weeks, and skim when leaves fall. That's Pentair's routine for a partly closed pool whose equipment keeps running. Keep free chlorine in your usual range:2 to 4 ppm: Pentair1 to 3 ppm: Hayward and JandyMatched to your stabilizer: Trouble Free PoolThe dosage calculator works out how much to add.

• Keep the water at the middle of the skimmer or higher, so the pump never sucks air.

• Empty the skimmer and pump baskets before a cold night. Hayward lists a "strainer basket or skimmer basket loaded with debris" as a reason a pump won't prime, the last thing you want on the night the pump has to keep water moving.

Sources:Trouble Free PoolLeslie'sPinch A PennyHayward TriStar VS

Salt pools: the cell slows down or stops in cold water

• Some automation keeps the cell off during freeze-only runs. Hayward ProLogic: "The chlorinator will not operate if freeze protection is the only reason the pump is running." Pentair's EasyTouch does the same.

• A cell that keeps working can overshoot. Jandy says that if a freeze controller runs the pump and the cell through the winter, turn chlorine production down to 10 to 20%, or the chlorine will climb past 1 to 3 ppm (Jandy).

• Closing the pool instead? The salt water pool guide covers putting the salt system away for winter.

Cold night

Freeze Night Checklist (Power On)

Make sure water is really moving, then leave the pump running until the air is back above freezing.

Power out

If the Power Goes Out in a Freeze

No freeze protection works without power. If it's below freezing and the pump has stopped, drain the equipment.

Neither Pentair nor Hayward gives a safe number of hours, and Leslie's warns that water inside the equipment can freeze after "even a brief amount of time" without power.

Hayward's and Pentair's steps, combined.

1. 1

   Turn off every pool breaker,

   even though the power is already out, so nothing restarts on its own when it comes back.

2. 2

   Open the filter's air relief valve

   and take off the pump and filter lids.

3. 3

   Pull the drain plugs

   on the pump (often two, near the bottom), the filter, the heater and the filter's multiport (dial) valve, so freezing water has room to expand. Keep the plugs in a sealed bag (Pinch A Penny).

4. 4

   Drain the inline chlorinator, open the salt cell and take the lids off the check valves,

   and turn off the auto-fill (Hayward).

Sources:HaywardPentair storm guidePinch A PennyLeslie'sPHTA

1. 1

   Ice on the equipment? Wait.

   Hayward says "don't turn the power back on" until it melts.

2. 2

   Look for cracks first.

   Check the pump, filter, heater, valves and chlorinator. Leslie's warns that "even a small hairline crack could be a safety hazard under pressure." If anything is cracked, leave it off and call a pool pro.

3. 3

   Put it back together.

   Put the plugs, lids and salt cell back, fill the pump basket with water (Hayward: "NEVER run pump dry") and open the filter's air relief valve.

4. 4

   Stand clear and turn the power on.

   Stand clear of the pump and filter while you turn the power on (Pentair), close the air relief once a steady stream of water comes out, and watch for leaks as it comes up to pressure (Leslie's).

5. 5

   Then finish up.

   A drained heater stays off until water is circulating (Pentair). Reset any mechanical timer to the right time (Intermatic). After a long outage, Pentair says the pool may need shocking to at least 10 ppm free chlorine.

Sources:Pentair IntelliFlo3 guideIntermaticPentair, after a power lossLeslie's

After the cold

After a Hard Freeze: What to Check

Damage doesn't always show right away: Pentair notes that "cracks in frozen pipes and lines won't leak until they start to thaw."

• Once it warms up, look everything over: the pump, filter, heater, valves and any exposed pipe, for cracks or drips.

• Check waterfalls, where water may have sat (Leslie's).

• Still losing water afterward? A bucket test tells a leak from evaporation.

Source:Leslie's

What a freeze can cost, from cost sites

Questions

Frequently Asked Questions