Should I blow out pool plumbing lines with compressed air during Ottawa winterization?

Yes, you should absolutely blow out pool plumbing lines with compressed air during Ottawa winterization — it is the single most critical step in protecting your pool from freeze damage, and skipping it in a climate that regularly hits minus 25 to minus 35 degrees Celsius is inviting catastrophic pipe failures. Every professional pool closing service in Ottawa includes compressed air blowing as a standard and non-negotiable part of the winterization process.

The purpose of blowing out the lines is to remove every drop of water from the underground plumbing, equipment manifold, and fittings so there's nothing left to freeze and expand. Water expands roughly 9 percent when it freezes, and PVC pipe — the material used in virtually all Ottawa pool plumbing — cannot flex to accommodate that expansion. Even a small amount of trapped water in a low point of a pipe run can generate enough force when frozen to split the pipe, crack a fitting, or blow out a glued joint. The repair costs for underground freeze damage range from $500 to $2,000 per break, and a pool with multiple breaks can easily exceed $3,000 to $5,000 in spring repair bills.

The blowing process uses a high-volume, low-pressure air compressor — typically delivering 80 to 120 cubic feet per minute (CFM) at 30 to 40 PSI. This is not a small shop compressor or a tire inflator; it's a large portable unit designed specifically for pool winterization. The high volume of air is what matters more than the pressure — you need to push a large slug of air through the lines fast enough to sweep water out ahead of it, including water trapped in low spots, elbows, T-fittings, and check valves. Professional pool service companies in Ottawa carry purpose-built pool blowers (often called "Cyclone" or "MightyVac" units) that connect directly to the equipment pad plumbing.

The technician blows each line individually and in a specific sequence to ensure complete water removal. The process typically starts with the main drain line — the deepest and longest run — because it contains the most water and takes the longest to clear. The compressor is connected at the equipment pad, and air is forced through the line until a strong, continuous stream of air bubbles is visible at the main drain in the pool bottom for at least 30 seconds with no water spray. Then the technician moves to each return line, blowing until air bubbles out of the return fitting in the pool wall, at which point an expandable rubber winterization plug is immediately inserted into the fitting to seal it. The skimmer line is blown last, and the skimmer is plugged with a Gizzmo or threaded plug.

Ottawa's extreme winter temperatures demand more thorough blowing than milder climates. In southern Ontario or British Columbia, where winter temperatures rarely drop below minus 10, a quick blow-out might be sufficient because the frost penetration is shallow and brief. In Ottawa, the frost line penetrates 120 to 150 centimetres by mid-January, and temperatures can sustain minus 20 or colder for weeks at a time. This means every centimetre of pipe — including the section running from the pool wall to the equipment pad, which is typically buried 60 to 90 centimetres deep — must be completely dry. Professional Ottawa pool technicians blow each line for 3 to 5 minutes, well beyond the point where no water is visible, because residual moisture clinging to the inside walls of the pipe can accumulate in low spots and freeze.

Can You DIY the Blowing Process?

DIY blowing is possible but requires the right equipment and carries significant risk if done incorrectly. A standard workshop air compressor delivering 5 to 10 CFM is inadequate — it doesn't move enough air volume to push water out of long or deep pipe runs, and homeowners who try it often leave water trapped in elbows, T-fittings, and low points. If you're going to do it yourself, you need a dedicated pool blower or a large compressor rated for at least 50 CFM. Pool blowers can be rented from some Ottawa equipment rental shops for $75 to $150 per day, or purchased for $250 to $500 if you plan to close the pool yourself every year.

The most common DIY mistakes in Ottawa pool blowing include not blowing long enough on each line, failing to blow the main drain line adequately because it's the deepest, not plugging return fittings immediately after blowing (allowing water to flow back in from the pool), and missing the heater bypass or auxiliary lines that branch off the main plumbing. Any of these mistakes can leave water in the system that will freeze during Ottawa's first sustained cold snap, usually in late November or early December.

Some Ottawa pool owners use pool-grade antifreeze (propylene glycol) as a backup to compressed air blowing, and this is a reasonable belt-and-suspenders approach. After blowing out the lines and plugging all fittings, pour 2 to 4 litres of non-toxic pool antifreeze into the skimmer and each return line before inserting the plug. The antifreeze settles into low spots and provides a safety margin in case a small amount of water was missed during blowing or seeps back into a line from groundwater infiltration. Pool antifreeze costs $10 to $15 per jug and provides protection down to minus 40 degrees Celsius — well beyond Ottawa's coldest recorded temperatures.

The professional advantage in Ottawa is worth the cost for most homeowners. A pool service technician has done hundreds or thousands of closings and knows exactly how long to blow each line, can feel by the back-pressure when a line is clear versus when there's still water in a low spot, and carries the right equipment calibrated for Ottawa conditions. The closing service fee of $300 to $550 that includes professional blowing is a small fraction of the potential repair cost from a single burst pipe. If you're mechanically inclined and invest in the proper equipment, DIY is viable — but understand that a mistake you won't discover until spring can cost far more than the professional fee you saved.

One final point: compressed air blowing is essential for every pool type in Ottawa — vinyl liner, fiberglass, and concrete. The pool shell material doesn't change the plumbing vulnerability. All three pool types use the same PVC plumbing that's equally susceptible to freeze damage. The difference is only in how the water level is lowered: vinyl liner pools should not be drained below 15 to 20 centimetres below the skimmer to prevent the liner from shrinking and pulling out of the track, while concrete and fiberglass pools can safely be lowered further. But the blowing protocol for the plumbing lines is identical regardless of shell type.