Swimming Pool Blog
by Rob Cox, December 10, 2018
FROZEN SWIMMING POOL!
Since this post is now ten (10) years old (!), we thought it was ripe for an update, to address new concerns about frozen swimming pools and ice sheets forming during winter. Here you are then, new and improved information about freezing pools in winter!
Do swimming pools freeze solid? You betcha! Swimming pools that are not circulating can freeze solid from wall to wall within a few days below zero. The solid ice sheet can increase in thickness by up to 1/4" per day, when temperatures remain below zero for several days. In northern states of the US, pools can develop 10-12" of solid ice across the surface, during prolonged cold periods.
If your operating pool develops a thin sheet of ice across the surface, there is nothing to worry about. Even mild climate pools from LA to Phoenix, and Dallas all the way across to Jacksonville can freeze across the surface overnight. If you don't winterize your pool, be sure to keep the pump running, moving water through the pipes and equipment, so that water will not freeze within the pool plumbing.
A thin sheet of ice of 1/4" to 1/2" is not a big problem for most pools. If an ice sheet becomes much thicker than that however, as in our picture above, it puts pressure on your in ground pool tile and skimmers, or above ground pool walls, as ice expands when it freezes.
Most pool tile is frost free, built to withstand chipping from ice damage, but the best practice is to keep the winter water level under the perimeter pool tile band, if it freezes more than 1/2" thick. Ice can crack tile with hollow spots behind the tile, or it can work loose the grout and pop small pieces of tile loose. In some cases, on pools that are very full, or nearly overflowing, an expanding and lifting ice sheet can raise coping stones right off of the pool wall.
To protect a pool skimmer from Ice - you need an Ice Compensator, otherwise known as a skimmer Gizzmo. You can approximate the concept by using a 2 ltr bottle or empty algaecide bottle, filled halfway full with non-toxic Pool Antifreeze or small pebbles so that it will float semi-submerged, as the skimmer fills up with rain water or pool water. Skimmer Gizzmos, or these skimmer bottles, serve to absorb the expansion of the ice inside the skimmer, avoiding the outward pressure that can crack skimmer bodies.
Gizzmos and skimmer bottles however, cannot always protect from a complete solid ice sheet across the pool that extends into the skimmer, which has the power of a small glacier. This is why it's important to keep the winter water level below the tile (and skimmer), to prevent the solid ice sheet from forming at this level.
Vinyl liner pools can use a simple device called an Aquador or Skimmer Plug, available for above-ground skimmers and in-ground skimmers, which blocks the opening of the skimmer on the pool side, to keep all pool water (and ice sheets) out of the skimmer. These are only made for vinyl or fiberglass pool skimmers however, and do not fit concrete skimmers.
Another tip to protect pool skimmers is to place a 12"x12" square of heavy plastic between the skimmer and the skimmer lid, to keep rainwater and snow melt from dripping into the skimmer during the off-season.
Protecting vinyl liners from Ice - Ice sheets can be damaging to vinyl liners if your pool has a leak. If a liner pool loses several inches of water beneath an ice sheet, the sheet can fall, and damage the pool liner. Add water if necessary, and don't pump out pool water beneath an ice sheet. A curious thing about pool ice sheets is that as they thaw, they can develop very sharp, jagged edges which could potentially damage pool liners, but fortunately this is a rare occurrence.
Protecting pool covers from Ice - winter pool covers are built to withstand ice and snow, and there is usually nothing to worry about in that area - unless you are one of those pool owners who forgets about the pool all winter, neglecting pumping and cleaning duties. Covers that fill up with sharp sticks and heavy ice sheets 6" thick or more, could develop holes from debris or from the sharp edges of a massive shifting ice sheet during winter. Keep covers clean and keep surface water to under 1" depth to avoid these problems.
Mesh Safety Covers often appear as if they are going to break under a heavy snow or ice load, but they won't. The cover itself often freezes to the water surface, yet will spring back to a taut fit after the thaw. Do not attempt to shovel snow off of a mesh pool cover. Lower the water level before a deep freeze, never lower the water level while the pool is frozen.
This pool shown left should has a loose fitting safety cover and a water level that was quite high. Under the weight of wet snow, the cover has frozen solid into the ice sheet. Lowering the water level after the pool has frozen may cause damage to the cover, or a vinyl liner, as mentioned above.
After the ice and snow melts, a good method to lower water level in a winter pool is to place an Automatic Cover Pump into the pool skimmer. This will pump down to the bottom of the tile band, and maintain the water level. Another option is to place the pump on the first step of the pool entry stairs. If the pool is already frozen more than 1/2" thick, wait for a bit of a thaw before lowering, or break up the ice first before and while lowering the water level.
For safety pool covers, be careful not to lower the pool more than 12" below the tile line. This could damage a safety pool cover which needs the water level to help support the snow load. The best place for the water level in a safety cover on an in ground pool is 1-10" below the tile. Depending on how wet the winter is ~ you may need to lower the water level several times.
Protecting pool pipes from freezing. Pool pipes located above the ground can crack if they pump is not running when temperatures dip below 32° for several hours. PVC pipes and valves are very rigid. Water inside of PVC pipes turning to ice will first expand to fill every available air space inside the pipe and equipment, and if expansion continues it will crack pipes, valves, pumps, filters and/or heaters.
If you can't run the equipment due to power failure or mechanical failure, remove the drain plugs on the pool equipment, to quickly drain down the plumbing, then cover the equipment with heavy blankets. You can also wrap the above ground PVC plumbing with a heating cable for pipes, which can prevent freezing pipes to well below freezing.
Do Above Ground pools freeze? You bet they do, even faster than inground pools, and it's even more important to keep the water level out of the skimmer when it freezes, or face damage as shown in the picture here. Above ground pools in freezing climates (more than 3 days in a row of below 32° temps), need to use an Ice Compensator to absorb the outward ice sheet expansion, which puts lots of pressure on pool walls and uprights.
Above ground pools use Air Pillows to keep the ice sheet from freezing completely solid across the pool. Above Ground pool walls can only take so much ice expansion, and if ice sheets grow into the skimmer, and the water level is pumped out accidentally or the pool water leaks out thru the liner, it can cause real damage to pool walls or the liner.
Air Pillows act as 'ice equalizers', to prevent a continuous ice sheet from forming. Use enough air pillows to cover approximately 10% of the water surface, to compensate for the 9% expansion of ice as it expands. and use Skimmer Plugs to keep pool water out of the skimmer.
Do Saltwater pools freeze solid? Yes, saltwater pools will also freeze solid during winter. The added salt however will allow the pool to remain liquid a few degrees below 32°, but it will freeze solid too, just like a non saltwater pool.
Can my pool handle the weight of the ice? Actually ice weighs less than an equal volume of water, since it contains more air than water. When the pool surface freezes solid, it won't weigh any more than the water that it is displacing. But if your pool cover is not pumped off, and the ice starts spilling over the top rail of your aboveground pool, that could cause some problems! Be sure to keep your pool cover clean and mostly pumped off during winter.
Can you prevent a pool from freezing? Well no, not if you experience below freezing outdoor temperatures for several days in a row without daytime warming, and the pool filter pump is not running to create circulation. Some folks ask about using pond heaters, but these only heat a small area around the floating disk, to allow for some venting and oxygenation of winter fish ponds. Some folks ask about adding Pool Antifreeze to the water, and no that is not a feasible idea. And neither is covering the pool and putting a space heater underneath. Running the filter pump non-stop during freezing temps, being sure all valves and pipes have water moving through them, is the best way to keep the ice sheet from forming very thick, besides heating the pool with a gas heater!
It's 30° outside, why is my pool not frozen? Water holds heat at lower depths, and this heat keeps the upper layers warm. Inground pools also have a good insulator in the surrounding soil. It can take a few days of below freezing temperatures to cool the entire body of water enough, so that surface layers will stay below freezing temperatures. Daytime warming and bright sunlight can also hinder the process, while windy conditions can accelerate a pool's heat loss.
Should I drain the pool then? No! All pool types (in-ground, above ground, on-ground) need to keep water in the pool during winter, do not drain your pool to avoid the ice! In ground pools can pop out of the ground, and above ground pools can collapse inward, and the liner will shrink and discolor. Pool plaster finishes also needs water to maintain a certain moisture content, or it can discolor, erode and delaminate more easily.