How to extend your swim season in Ohio

An unheated pool in Northeast Ohio is comfortable for roughly 14 weeks, Memorial Day to Labor Day. NOAA's 1991 to 2020 normals for Akron-Canton Airport show average highs of 72 degrees in May and 76 in September, but nights in the low to mid 50s in both months, and those nights pull heat out of the water. With the right setup you can add three or four weeks at each end, which turns a 14 week season into something closer to 20.

Each step below helps on its own. They work best together, and the order matters: stopping heat from leaving the pool is cheaper than adding more of it.

This is the single biggest lever, and it is the one people skip. The Department of Energy explains that evaporation is by far the largest source of energy loss from a pool. It takes only 1 Btu to raise a pound of water by one degree, but each pound of 80 degree water that evaporates takes 1,048 Btu of heat with it. Cool, dry, breezy nights, which is what May and September bring here, drive evaporation up.

A cover stops most of that. The Department of Energy calls covering a pool when it is not in use the single most effective way to cut heating costs, with savings of 50 to 70 percent possible. It also points out the catch: a cover does not save anything if you never use it. That is why ease of use matters more than the price tag.

• Solar or bubble covers are the least expensive. A transparent bubble cover reduces the sun's heating of the pool by only 5 to 15 percent while it is on, so it can stay on during sunny days. They are fiddly to handle on a large pool without a reel.
• Automatic covers run on tracks and open or close with a switch. They cost the most and get used the most. Liberty's cover page cites Coverstar's figures of up to 70 percent lower heating costs and up to 90 percent less evaporation for its automatic safety covers. Those are the maker's numbers, but the logic matches the Department of Energy's.
• Winter safety covers, mesh or solid, are for the off-season and are not practical as nightly heat covers.

A cover slows heat loss. A heater replaces what is lost and brings the water up in spring. In Ohio the choice is usually a gas heater or an electric heat pump.

A gas heater, natural gas or propane, heats quickly and, as the Department of Energy notes, can hold whatever temperature you set regardless of the weather. That makes it the tool for the cold ends of the season and for anyone who wants to heat the pool on short notice for a weekend. A heat pump moves heat from the air into the water. It costs less to run, but the Department of Energy says heat pumps work efficiently only while the outside air stays above about 45 to 50 degrees. A Brookhaven National Laboratory study also found that heat pump output drops as the air cools and that the largest units available were limited in capacity, so they heat a large pool slowly in 60 to 70 degree shoulder weather.

Size matters as much as type. The Department of Energy's sizing method starts from the pool's surface area and the difference between the temperature you want and the average air temperature, and its standard formula assumes the heater raises the water about 1 to 1.25 degrees an hour with a light breeze across the surface. Windy sites and cool nights call for a bigger heater. An undersized heater can run all day in May and still leave the pool cool.

For season extension in Northeast Ohio, that usually means gas if you want the most weeks, and a heat pump if you mainly want to keep a covered pool warm through June to mid September at lower running cost. Our heat pump vs gas guide goes through the trade-offs in detail.

Free heat is worth designing for. The Department of Energy notes that an outdoor pool absorbs 75 to 85 percent of the solar energy striking its surface. In a region with as many gray days as ours, every hour of direct sun counts, especially in May and September when the sun is lower and the days are shorter.

If you have a choice of spots, pick the one with the most afternoon sun and the fewest trees to the south and west. Check the shadow of the house in late September as well as in July, because it reaches much farther across the yard in fall. This is one of the things we look at on the site visit and show in the 3D design, since moving a pool 15 feet can gain hours of sun on the days that matter most.

Wind across the water speeds evaporation, and evaporation is heat loss. The Department of Energy suggests a windbreak of trees, shrubs or a fence in windy spots, with two conditions: it has to be high enough and close enough to the pool not to create turbulence over the water, and it should not shade the pool from the sun.

In practice, a solid privacy fence or a row of evergreens on the side facing the prevailing wind, set back far enough to leave the pool in sun, works well. Many towns already require screening around a pool, so the screening you need anyway can double as a windbreak if you place it well. Open, exposed lots and pools on a hilltop gain the most from this step.

A pool loses heat through its walls and floor as well as its surface, into ground that stays cool. Our ICF concrete pools are built with insulated concrete forms, so the walls are insulated. That helps the pool hold the heat you have paid for and is one reason ICF pools suit owners who want the longest possible season. ICF pools can also be any shape, which lets the design take advantage of the sunniest part of the yard.

Fiberglass pools, our most common build, rely on good backfill around the shell, a cover and a well-sized heater to do the same job. Both approaches work in Ohio. The right one depends on the shape you want and how much the extra weeks at each end are worth to you.

Even with a heater and a cover, there will be April and October nights when the pool is too cool to enjoy. An attached spa, whether built into the pool shell or set alongside as a spillover spa, heats in a fraction of the time because it holds a fraction of the water. It gives you somewhere warm to be outside on a 50 degree night, with the lit pool in front of you. For many families that is where the real season extension happens.

A longer season also means running the pool closer to freezing weather. NOAA's normals put the median last spring freeze at April 24 at Akron-Canton and May 5 in Chardon, and the median first fall freeze at October 26 and October 18. In about half of years the frost comes later in spring or earlier in fall than those dates.

• If you open in late April or early May, keep an eye on the forecast and keep the pump running through any hard freeze so water keeps moving in the lines.
• If you swim into October, schedule the closing before the first hard freeze rather than after it. Freeze damage to a heater or pump costs more than the extra week of swimming was worth.
• Keep the safety cover handy for cold snaps, and remember that a heated pool on a cold night steams off heat fast without a cover.

1. A cover you will actually use every night, ideally automatic.
2. A properly sized heater, sized from the pool's surface area and the temperature rise you want.
3. Good placement, planned before the dig.
4. A windbreak, often combined with required screening.
5. An attached spa, for the colder evenings.
6. Insulated ICF walls, if you are choosing a custom pool anyway.

A pool heater comes with every package; automatic covers, spas and automation are upgrades we price from the design. Our fiberglass packages start at $68,400 installed and include a Pentair variable-speed pump, which is also the most efficient way to run the circulation a heater depends on.