How are Ottawa pool lines blown out?

Blowing out pool lines is one of the most critical winterization steps for Ottawa pools, and doing it thoroughly is the difference between a smooth spring opening and a $2,000 to $10,000 plumbing repair bill. The process uses a wet/dry shop vac or a dedicated air compressor to force all standing water out of every underground plumbing line before Ottawa's hard freezes arrive — typically by mid-October at the latest.

The process works line by line. You start by dropping the water level in the pool to about 30 centimetres below the skimmer mouth (for vinyl liner pools) or below the return fittings, depending on your pool type. The pump is then used to circulate water out of the lines as much as possible before switching to compressed air. An air compressor — ideally one capable of delivering at least 20 to 30 CFM at low pressure — is connected to the equipment pad, typically at the pump or filter inlet, and air is forced through each line in sequence: skimmer lines first, then main drain, then return lines.

Each line is blown until you see bubbles aggressively churning at the pool end, which confirms the line is clear of water. The moment bubbling stops or slows, you plug that fitting immediately — a winter plug or expansion plug is inserted into the return fitting or skimmer throat while air is still flowing, so no water can be sucked back in. This is the step most DIYers get wrong. If you remove the air source before plugging, water wicks back into the line and you are right back where you started.

The main drain line deserves special attention. Most Ottawa pool builders install a main drain with a freeze plug or a Gizzmo-style device, and the line is blown from the equipment pad until bubbles appear at the drain cover. Some contractors prefer to leave a small amount of antifreeze (pool-safe propylene glycol, never automotive antifreeze) in the skimmer throat as added insurance against any residual moisture.

A few critical warnings: Never blow lines with a standard household air compressor running at high pressure — you risk damaging fittings and liner. Low volume, sustained airflow is what clears lines, not a burst of high pressure. Also, never assume a line is clear just because you blew it once — if the pool water level is still above the return fitting when you blow it, water will flow back in the moment you stop.

This is genuinely one of those tasks where the margin for error is very low and the consequences of getting it wrong are severe in Ottawa's climate. A single freeze-thaw cycle through a water-filled underground line can crack PVC fittings, split the pipe, or damage the equipment pad manifold. If you have any doubt about whether your lines are fully cleared, having a professional pool closer do it once while you watch is worthwhile — you will learn the process and have peace of mind. You can find experienced pool service professionals through the Ottawa Construction Network directory at justynrookcontracting.com/directory.