The short version
- Moving water is your main defense. Keep the pump running through the whole freeze and make sure water flows through every line, including the spa and water features.
- Freeze protection on an automation system only works when it has power and every circuit that needs to run is assigned to it.
- If the power goes out during a long hard freeze, draining the pump, filter, and heater protects them better than waiting it out.
- Do not drain the pool itself. The big body of water holds heat; the small pockets of still water in your equipment are what crack.
- After the thaw, look for cracks and leaks before restarting, and do not fire a heater that may have frozen until it has been checked.
What February 2021 taught Houston pool owners
To protect a pool from a Houston freeze, keep water moving through the equipment for as long as temperatures stay near or below 32 degrees, and have a plan for when the power fails. The February 2021 storm showed why the second half matters.
The National Weather Service tracked that event from February 10 to 20, 2021. Bush Intercontinental fell to 12 degrees on February 16 and Hobby reached 15. Widespread power outages followed and lasted for days. Across Texas, more than 5 million people were without power at the peak, some for more than three days.
A pool pump that runs through a cold night is usually enough for a typical Houston freeze. In 2021 the pumps stopped because the power stopped, and still water sat in pipes and equipment through hours of temperatures in the teens. That is the scenario worth planning for.
Where a pool actually freezes
The pool itself is rarely the problem. Tens of thousands of gallons hold a lot of heat, and a few hours below freezing may only put a skin of ice on the surface. The damage happens where small volumes of water sit still and exposed to the wind. Water expands by about 9 percent as it freezes, and that pressure splits housings, valves, and pipe fittings.
These are the parts to worry about:
- Above-ground pipes and valves at the equipment pad, which are fully exposed to cold air
- The pump housing and strainer pot
- The filter tank and its pressure gauge
- The heater, whose heat exchanger holds water in narrow passages
- Lines to the spa, waterfalls, bubblers, and other features that may not run when the main pump does
- Any booster pump or secondary pump that sits idle
Before the freeze: a checklist
Most of this takes less than an hour, and doing it a day early beats doing it in the dark at 25 degrees.
- Empty the skimmer and pump baskets and clean the filter if its pressure is high, so flow is strong.
- Top off the water so the skimmer cannot suck air. A pump that loses prime stops moving water.
- Set valves so water flows through every body and feature: pool, spa, spillover, and water features.
- On a variable speed pump, pick a speed that actually pushes water through the farthest lines. The lowest setting may not.
- Override any mechanical timer so the pump runs continuously. A timer will shut the pump off on schedule no matter how cold it is.
- Wrap exposed pipes and valves with foam pipe insulation. Do not cover the vents of a running pump motor, which needs airflow to stay cool, and never cover or wrap a gas heater or its vents.
- Find your equipment breakers and the drain plugs on the pump, filter, and heater, so you know where they are if the power fails.
How freeze protection on automation works
Most pool automation systems include a freeze protection setting. An air temperature sensor watches for cold, and when the reading falls below a set point, usually a few degrees above 32, the controller turns on the pump and any circuits assigned to freeze protection.
It is a good safety net, but it has limits. It does nothing without power. It only runs the circuits someone assigned to it, so a spa, waterfall, or water feature left off the list can still freeze. Its pump speed may be set too low to reach every line. And an air sensor that sits in direct sun can read warmer than the air around your equipment.
Check the settings in fall, before you need them. If you are not sure what your system runs in freeze mode, or it has no freeze protection at all, pool automation can be set up or adjusted to cover every line.
Heaters need extra care
Do not count on the heater to protect your plumbing. Circulation is what protects it, and the heater is one of the parts that needs protecting. Most heaters will not fire without flow, so when the pump stops, the water inside the heat exchanger sits still in narrow passages and is exposed like any other pipe.
Heat pumps lose efficiency as the air gets colder, so a heat pump is no freeze plan either. If your automation is set to run the heater in freeze mode, that is fine, but the pump running is what matters.
If you lose power during a hard freeze, a heater is one of the first things to drain, following its manual. A cracked heat exchanger or split header is an expensive repair, and it is not always obvious until the heater leaks or will not light. That is the job for pool heater repair.
If the power goes out
A short outage with temperatures just around freezing is usually survivable, because moving water stays warmer than the air for a while. A long outage with temperatures well below freezing, like 2021, is different. If the power is out and the forecast says it will stay below freezing for many hours, drain the equipment:
- Turn off the breakers for the pool equipment first, so nothing restarts while it is open.
- Open the air relief valve on top of the filter.
- Remove the drain plugs from the pump and the filter, and drain the heater the way its manual describes. Let everything empty.
- Put the plugs in the pump basket or a labeled bag so they are easy to find later.
- Leave the pool full and the pool water alone. Do not try to break surface ice.
Generators and backup power
Some owners keep the pump running with a generator. Pool pumps are usually wired directly to a breaker rather than plugged in, so connecting a generator safely takes a transfer switch or generator inlet installed by an electrician. Never backfeed a panel through an outlet with a homemade cord: it can electrocute you or a utility worker on the line. The CDC says to run generators outdoors more than 20 feet from windows, doors, and vents, and never inside a home or garage, even with the doors and windows open.
After the thaw: what to check
Once temperatures are back above freezing, do a slow, careful restart rather than flipping everything on at once.
- Walk the equipment pad and look for cracked housings, split pipes, loose unions, and water pooling where it should not be.
- Put every drain plug back and fill the pump strainer pot with water so the pump can prime.
- Open the air relief valve on the filter, restore power, and start the pump. Close the valve once a steady stream of water comes out.
- Watch the pump run for a few minutes and check for drips at every fitting while the system is under pressure.
- Compare the filter pressure with your normal reading. A big change can mean a blockage or a broken part inside.
- Do not fire a heater that sat full of still water during a hard freeze until it has been inspected.
- Test chlorine and pH. Salt systems stop making chlorine in cold water, so levels may have dropped.
- Skim out leaves and branches the storm dropped, so they do not stain the plaster or feed algae.
