The Definitive Technical Guide On How To Blow Out Swimming Pool Lines For Winterization

To successfully blow out swimming pool lines, one must systematically evacuate all water from the circulation plumbing using a high-volume air inducer to prevent catastrophic freeze-expansion damage. The process requires isolating each plumbing circuit—skimmers, returns, and main drains—and maintaining a consistent low-pressure airflow until a clear air-lock is established or lines are sealed with specialized expansion plugs.

Essential Gear and Pre-Procedure Planning

Before initiating the winterization of a swimming pool’s plumbing, you must understand the hydraulic layout of your specific system. Water expands by approximately 9% when it freezes, exerting upwards of 114,000 PSI of pressure, which easily shatters standard Schedule 40 PVC pipes buried underground. Proper preparation ensures that the air volume is sufficient to displace water weight across long horizontal runs and vertical rises.

Mandatory Equipment and Tools

• High-Volume Air Blower: A specialized pool blower (like a 3HP Cyclone) is preferred over a standard air compressor. If using a compressor, you must have a regulator to keep PSI low but CFM (Cubic Feet per Minute) high.
• Winterization Plugs: Expansion plugs (rubber with wing nuts) or threaded O-ring plugs for return inlets.
• Gizzmos: Threaded plastic tubes designed to absorb ice expansion inside skimmers.
• Multi-Port Valve Adapter: A specialized fitting to connect the blower to the pump basket or the air-induction port.
• Basic Hand Tools: Large channel locks, screwdrivers for removing directional eyeballs, and a lubricant (Teflon-based) for O-rings.

Technical Benchmarks

• Target Pressure: 2 to 5 PSI (Never exceed 10 PSI to avoid pipe coupling failure).
• Estimated Duration: 1.5 to 3 hours depending on pool size and plumbing complexity.
• Ideal Temperature: Perform this task when ambient temperatures are between 45°F and 60°F, well before the first hard frost.

Systematic Execution for Plumbing Evacuation

Step 1: Water Level Management and Chemical Balancing

The blowout process begins with the physical reduction of the pool’s water level. If you are using a solid safety cover, the water level typically needs to be dropped 12 to 18 inches below the skimmer mouth. For mesh covers, 6 to 12 inches is standard. This depth ensures that once the lines are blown out and plugged, the water cannot easily re-enter the lines through the skimmer or return ports. Simultaneously, ensure the water is chemically balanced with a winterization kit to prevent scaling or staining during the stagnant months.

Step 2: Preparing the Equipment Pad

Turn off all power to the pool pump, heater, and salt cell at the breaker. Open the air relief valve on the top of the filter tank to release any residual pressure. Remove all drain plugs from the pump housing, the filter tank, the heater, and the chlorinator. Store these plugs in the pump basket so they are not lost over the winter. Set your multiport valve to the "Recirculate" position. This allows air to bypass the filter media (sand or DE), providing a direct path from the pump basket through the plumbing lines.

Step 3: Connecting the Air Source

The most effective point of air induction is through the pump’s strainer basket. Remove the pump lid and clean out any debris. Insert your air blower hose into the discharge side of the pump housing (the port leading toward the filter) or use a specialized threaded adapter.

Pro-Tip: If your plumbing has a dedicated "blowout" T-valve installed between the pump and the filter, always use that as your primary connection point to minimize stress on the pump housing.

Step 4: Clearing the Skimmer Lines

Close all valves on the suction manifold except for one skimmer line. Turn on the air blower. You will initially hear a gurgling sound as the air pushes the water column back toward the pool. Within minutes, a mist and then a steady stream of air will erupt from the skimmer.

1. Allow the air to blow for at least 30 to 60 seconds after the water has cleared to ensure the "dip" in the pipe (the P-trap or low spot) is dry.
2. Insert a Gizzmo or a rubber expansion plug into the hole at the bottom of the skimmer.
3. Tighten the plug until it is airtight.
4. Move to the next skimmer line by adjusting the valves at the manifold and repeat.

Step 5: Clearing the Return Lines

Once the suction side is sealed, redirect the air toward the return side of the system. This is done by ensuring the multiport valve is still on "Recirculate" or "Whirlpool." Air will now travel through the heater and salt cell and out to the pool returns.

1. Return lines should be blown out one by one. Use the valves at the equipment pad to close all but the furthest return line.
2. Once a steady stream of air is observed, insert a winter plug into the wall fitting.
3. Repeat this process, moving from the furthest return to the one closest to the equipment pad.
4. Warning: Ensure the plug is seated deeply and tightened firmly. If air bubbles continue to leak from the plug, the seal is insufficient and the line may refill with water.

Step 6: The Main Drain Air Lock

The main drain is the most difficult line to blow out because it is located at the deepest point of the pool. Because you cannot easily plug a main drain under ten feet of water, you must create an "Air Lock."

1. Close all other valves so that 100% of the air pressure is directed toward the main drain.
2. Watch the surface of the pool. When large, violent bubbles begin to erupt from the floor drain, let it blow for about 30 seconds.
3. Quickly close the valve leading to the main drain while the air is still blowing.
4. This traps a column of air in the pipe. Because the air cannot escape through the closed valve and the water cannot push the air back up due to the pressure lock, the line remains dry at the "elbow" where it would be most susceptible to freezing.

Step 7: Final Equipment Protection

With all lines blown and plugged, turn off the blower. Disconnect the blower and remove any remaining water from the pump basket using a sponge or shop vac. Pour non-toxic (propylene glycol-based) pool antifreeze into the lines if you live in a region with extreme permafrost, though a proper blowout usually makes this optional. Replace the pump lid loosely to allow for atmospheric expansion.

Performance Metrics: Air Source Comparison

The choice of air induction equipment determines the velocity and volume of the blowout. High-volume air is superior to high-pressure air because it creates a "slug" of air that pushes water effectively without risking pipe bursts.

Common Winterization Failures and Field Fixes

Understanding why a blowout fails is critical to preventing thousands of dollars in repair costs. Most failures occur due to hidden water pockets or mechanical seal failures.

• Failure Scenario: Water continues to bubble out of a return after plugging.

  
  
  
  • Root Cause: A loose expansion plug or a crack in the return fitting threads allowing air to escape and water to seep back in from the pool.
  • Actionable Fix: Remove the plug and inspect the O-ring for cracks. Re-lubricate with Teflon grease. If the wall fitting is cracked, use a "high-plug" that bypasses the threads and seals deeper in the pipe.

• Failure Scenario: The air blower is running, but no air reaches the pool.

  
  
  
  • Root Cause: A closed valve at the manifold or a multiport valve set to "Filter." Air cannot pass through a sand filter efficiently and will build back-pressure.
  • Actionable Fix: Verify the Multiport Valve is on "Recirculate" or "Waste." Check that all Jandy-style valves are in the open position for the specific line being serviced.

• Failure Scenario: Main drain "Air Lock" fails, and bubbles stop after closing the valve.

  
  
  
  • Root Cause: An air leak at the valve manifold (usually the valve stem O-ring) or the pump lid seal is allowing the trapped air to bleed out.
  • Actionable Fix: Inspect the valve seats for debris. Replace the O-rings on the diverter valves if they are dry or cracked. Apply a heavy coat of pool lube to the valve covers to ensure an airtight seal.

• Failure Scenario: Skimmer Gizzmo is crushed or cracked mid-winter.

  
  
  
  • Root Cause: Water infiltrated the skimmer due to a heavy rain/snow melt and the Gizzmo was not screwed in tight enough or lacked Teflon tape on the threads.
  • Actionable Fix: Always wrap Gizzmo threads with 3-4 wraps of Teflon tape. Ensure the water level in the pool stays below the skimmer mouth throughout the winter by occasionally pumping out excess water.

Frequently Asked Questions

What is the minimum PSI required to blow out pool lines?

You should aim for high volume (CFM) rather than high pressure (PSI). Usually, 3 to 5 PSI is sufficient to move the water column in a standard residential pool. Exceeding 10 PSI puts unnecessary stress on PVC glue joints and can lead to underground leaks that are difficult to detect until the following spring.

Can I use a shop vac to blow out my pool lines?

A high-horsepower shop vac can work for shallow, above-ground pools or very short plumbing runs on small inground pools. However, most shop vacs lack the static pressure (inches of water lift) required to push water out of a deep main drain or through a long run of 2-inch PVC pipe. A dedicated pool blower is highly recommended for inground systems.

In what order should I blow out the plumbing lines?

Always start with the lines furthest from the pump and work your way closer. This ensures that the longest pipes receive the most initial air volume. Typically, the sequence is: Skimmers first, then the furthest return lines, then the closest return lines, and finally the main drain to set the air lock.

Is pool antifreeze necessary if I blow out the lines?

If the lines are blown out thoroughly and sealed with airtight plugs, antifreeze is technically redundant. However, in "heaving" soil climates where temperatures stay below zero for weeks, adding a non-toxic propylene glycol antifreeze provides an extra layer of insurance against any small amounts of water that may have condensed or seeped back into the lines.

How do I know if the main drain air lock is holding?

After closing the valve to the main drain while air was blowing, wait 10 minutes and then slowly cracked the valve open just a tiny bit. If you hear a "hiss" of escaping air, the lock was holding. If you hear nothing, the air has already escaped, and you must repeat the process and check your valves for leaks.

Professional Pool Protection Strategy

By following these technical protocols, you ensure the structural integrity of your pool's hydraulic system against the most extreme winter conditions. Precision in the blowout phase is the single most effective way to avoid costly underground plumbing repairs during the spring opening.