Freeze damage is the most expensive category of pool repair. A single night below 28°F with water still in the plumbing can crack skimmer lines, split PVC fittings, and rupture heat exchanger tubes — turning a $500 annual closing into a $2,000+ spring repair bill. The physics are simple: water expands 9% when it freezes, and PVC pipe doesn't. Understanding where water sits and how to remove or protect it is the entire job.
Not all pool water freezes equally. The pool body itself — thousands of gallons of water — rarely freezes solid or causes structural damage. The danger is in small-volume spaces where water sits in exposed plumbing:
| Component | Freeze Risk | Damage Type | Repair Cost |
|---|---|---|---|
| Skimmer body | Very High | Cracked housing, separated fittings | $200–500 |
| Skimmer line (1.5" PVC) | High | Cracked pipe, separated joints | $300–800 |
| Return lines | High | Cracked fittings, wall fittings | $200–600 |
| Pump housing | High | Cracked volute | $150–400 |
| Filter tank | Medium | Hairline cracks | $300–700 |
| Heater heat exchanger | High | Cracked tubes, header manifold | $400–900 |
| Salt cell housing | Medium | Cracked cell body or flow switch | $200–500 |
| Main drain (buried) | Low | Rarely freezes — soil insulation | N/A |
For pools in climates that regularly see temperatures below 28°F, line blowout is the only reliable freeze protection method. The goal is to replace the water in each plumbing run with air, then plug the line so water from the pool can't re-enter.
Speed matters on the plug step. When blowing a return line, have the expansion plug in your hand before you start. The moment bubbles appear at the pool, the line has air in it — if you take too long to plug, water from the pool flows back in. Pre-position all plugs within arm's reach before starting the blower.
For extreme cold climates or as a backup after blowout, add propylene glycol antifreeze to the skimmer lines and return lines. This is a secondary measure — not a replacement for blowout.
Use only propylene glycol pool antifreeze (typically pink). Never use automotive antifreeze (ethylene glycol) in pool plumbing — it is highly toxic and would contaminate the pool water and be extremely difficult to remove. Propylene glycol is non-toxic, food-safe, and specifically designed for pool winterizing.
After blowing the lines and installing plugs, pour approximately 1–2 quarts of antifreeze into each skimmer. The antifreeze sits in the residual water in the skimmer body and lower skimmer pipe as backup protection for any water the blowout didn't fully clear. For lines in extremely exposed locations (above-grade plumbing in a cold climate), a higher antifreeze concentration may be appropriate.
For pools in mild climates that experience occasional brief cold snaps — not full seasonal closings — a freeze guard is the standard protection method. This is common in the US South, Southwest, and coastal regions where pools run year-round.
A freeze guard is a temperature sensor connected to the pump's automation controller. When air temperature drops below the set threshold (typically 35–38°F), the controller automatically starts the pump and circulates water through the plumbing. Moving water freezes at a significantly lower temperature than still water — circulation prevents freeze damage even during brief cold snaps.
If an unexpected early freeze hits before the pool is closed:
Log freeze events and any resulting damage in SplashLens. Accounts that suffered freeze damage in prior winters need an earlier closing date in subsequent years — this is exactly the kind of account history that prevents repeating expensive mistakes.
Document closing dates, line blowout completion, and any freeze damage history per account. Know which pools need early attention before the first freeze — not after it's already caused damage.
Open SplashLens Free →Pool plumbing typically begins to freeze when sustained air temperatures drop below 28°F for 4+ hours. The exact threshold depends on pipe diameter, depth below grade, insulation, and wind chill. Small-diameter PVC skimmer lines are most vulnerable; buried main drain lines are far more protected by soil insulation.
Never. Automotive (ethylene glycol) antifreeze is toxic and would contaminate pool water. Use only propylene glycol pool antifreeze — it is non-toxic, food-safe, and specifically designed for pool plumbing. Pool antifreeze is typically sold in pink formulations at pool supply stores.
A freeze guard temperature sensor connected to the automation controller automatically starts the pump when air temperature drops below a set threshold (typically 35–38°F). Moving water freezes at a lower temperature than still water, protecting pipes during brief cold snaps without requiring the pool to be closed.
Do not turn on the pump until temperatures rise and you've inspected all visible plumbing for damage. Running a pump against a frozen, cracked line causes flooding. Allow lines to thaw naturally, inspect for damage, then start the system at low pressure while watching for leaks.