How to Blow Out Pool Lines for Winter

Why this step exists

An above ground pool's plumbing is hose. It comes off, it drains, it goes in the shed. An inground pool's plumbing is PVC buried under the deck and the yard, and it cannot be moved. Water left in it freezes, expands and splits the pipe somewhere you cannot see and cannot reach without digging. Clearing the lines is the single biggest difference between closing the two kinds of pool.

The tool, and the one warning

Use a pool line blower. Not an air compressor.

The reason is worth understanding, because it is the opposite of most people's instinct. It takes only about 3.5 psi to push water out of a pipe eight feet below the water line, and a line blower makes roughly 6, enough to clear about fifteen feet down. What the job needs is a large, continuous volume of air, held for minutes at a time. A compressor gives the opposite: high pressure in short bursts, with enough force behind it to over-pressurize a pipe or blow a fitting apart.

A big canister vac of 5 HP or more may manage skimmers and returns on a simple system. Most will not touch a main drain. A leaf blower has very little success at any of it.

Before you start

1. Lower the water below the skimmer, 4 to 12 inches.
2. Take the drain plugs out of the pump, filter and heater, and put them back loosely.
3. Scoop or pump the skimmer close to dry.
4. Pull the return eyeball fittings and the skimmer baskets.
5. Set a multiport valve to Recirculate.
6. Open the filter's air relief valve before you pressurize anything, and check the tank clamp is tight.

The skimmers

Connect the blower to the skimmer line through an adapter and blow until a mist appears at the other end, usually two to three minutes. Blow a second skimmer, a cleaner line and a spa drain each on their own; they are separate pipes and each needs its own turn.

Then protect the skimmer itself, which is the part of an inground pool that ice cracks most often. Thread in a Gizzmo, which seals the line and gives expanding ice something to crush instead of the skimmer wall, or fit an Aquador faceplate and lid, which seals the whole skimmer mouth so water never gets in.

The main drain, with trapped air

Most guides skip this one, and it is the step that works differently from everything else. The main drain is not plugged. It is held by a column of air.

1. Open the main drain valve and close the skimmer line valve, so the air can only go one way.
2. Take the pump lid off and put the blower hose into the strainer housing at the suction port.
3. Blow until bubbles break the surface of the pool over the main drain, then keep going about 30 seconds.
4. With the blower still running, close the valve.

That traps a column of air in the pipe, and the air pressure holds the water out for the rest of the winter. Because the air is doing the work, the valve has to keep sealing. If it weeps, the line refills. A rubber cork in the main intake and a plug inside the pump are the belt and braces.

This method needs a valve at the equipment that seals tightly. If yours does not, or you cannot find it, this is the step to hand to a professional. If the main drain runs through the skimmer's equalizer line rather than a pipe of its own, there is nothing to trap: the water is already below the skimmer, so thread in a Gizzmo or a plug instead.

The returns

Blow each return for two to three minutes, working from the farthest one back. Plug each one the moment its air starts bubbling, and carry on until no bubbles appear anywhere. Threaded 1.5 inch plugs with an o-ring are the standard; expandable rubber plugs with a wingnut are the other.

Keep the blower running while you plug any opening that sits under water. Openings above the water can wait until the blower is off.

In-floor cleaners and water features

An in-floor system has a head unit with its own clamp band. Take it off and blow each pop-up line separately until it bubbles in the pool, then plug it.

For a water feature, blow at its pump: lid off, air into the suction pipe toward the pool, then separately through the impeller housing.

Antifreeze, and where it must not go

After a proper blowout, antifreeze in the lines is a backup rather than a requirement. It earns its place on an inground pool more than an above ground one, because the buried lines cannot be taken off and tipped out.

Use only product labeled non-toxic pool antifreeze, which is propylene glycol. Automotive coolant is ethylene glycol and is poisonous. Roughly a gallon for every 10 to 20 feet of pipe, following what the bottle says.

Where it goes: into the lines after they are plugged, and into the skimmer on top of the plug. A jug left about a third full and dropped in the skimmer is one accepted method, giving the ice something to crush.

Where it must never go: the pump, the filter, the heater or the chlorinator. It can damage a pump seal, and in a chlorinator it can react.

Finish at the equipment pad

• Pump. Both drain plugs out, lid off, plugs in the basket so spring finds them.
• Filter. Drain open and left open. Multiport valve parked between positions. Air relief open.
• Heater. Drain plugs out. Water left in a heat exchanger is what cracks it.
• Salt cell. Cell out and indoors. Leave the control box alone.
• Vertical lines with check valves can hold water on top of the valve. A union directly under the valve lets that section drain.