How much does extending the Ottawa swim season by one month cost in heating?

Extending the Ottawa swim season by one month — either starting in May instead of June, or swimming into October instead of closing in September — costs approximately $300 to $800 in additional heating expenses for a standard 40,000-litre residential inground pool, depending entirely on whether you use a natural gas heater or an electric heat pump and how aggressively you maintain your target water temperature during the cooler shoulder-season conditions.

The cost calculation hinges on understanding Ottawa's specific temperature profile during the shoulder months. In a typical May, Ottawa daytime highs average 16 to 20 degrees Celsius in the first half and 20 to 24 degrees in the second half, with overnight lows of 4 to 10 degrees. In a typical October, the pattern reverses — daytime highs of 12 to 18 degrees in the first half decline to 6 to 12 degrees by month's end, with overnight lows dipping to 0 to 5 degrees. Either shoulder month requires your heater to overcome a significantly larger temperature deficit compared to the core summer months of July and August, when solar gain alone keeps water temperatures above 24 degrees in most Ottawa pools.

With a natural gas heater, extending one month earlier (May) costs approximately $500 to $800 in additional gas consumption. This estimate assumes you are heating the pool from its winter-dormant temperature of approximately 10 to 14 degrees Celsius up to a comfortable 26 degrees in the first week, then maintaining that temperature against ongoing heat loss for the remainder of the month. The initial heat-up is the most expensive phase — raising 40,000 litres by 12 to 16 degrees requires approximately 670,000 to 890,000 BTU of thermal energy, which translates to 3.5 to 4.5 hours of continuous operation on a 200,000 BTU heater (consuming roughly $30 to $65 in natural gas at current Enbridge Ottawa rates of approximately $0.35 to $0.45 per cubic metre). After the initial heat-up, daily maintenance heating to replace overnight and daytime heat losses costs roughly $15 to $25 per day in May — higher than summer because the larger temperature difference between water and air accelerates heat transfer out of the pool.

With an electric heat pump, the same May extension costs approximately $150 to $350 in additional electricity. Heat pumps are three to six times more efficient than gas heaters because they move heat rather than generate it, but they work more slowly and their efficiency drops as air temperature decreases. In May, when Ottawa air temperatures frequently fall below 15 degrees Celsius, a heat pump operates at reduced efficiency — its coefficient of performance (COP) drops from the rated 5.0 to 6.0 (at 27-degree air) to approximately 2.5 to 3.5. This means the unit consumes more electricity per degree of heating compared to midsummer operation. Running a typical 80,000 to 120,000 BTU heat pump for 10 to 14 hours per day in May at reduced COP consumes roughly 20 to 35 kilowatt-hours daily, costing $3 to $6 per day at Hydro Ottawa's time-of-use rates (assuming you run it primarily during off-peak and mid-peak hours).

Extending into October rather than closing in September has similar costs but with one important difference: you are fighting a declining temperature trend rather than a rising one. In May, each successive week gets warmer, meaning your daily heating cost decreases as the month progresses. In October, each week gets colder, meaning daily heating cost increases — and the last week of October, when Ottawa overnight lows can approach freezing, may cost more to heat through than any single week in May. Total October heating cost with a gas heater runs $400 to $700, slightly less than May because you are maintaining an already-warm pool rather than heating from cold. With a heat pump, October costs $200 to $400, but heat pump performance becomes marginal in the last week of October when air temperatures at night hover near the unit's minimum operating threshold.

A solar blanket is the single most impactful cost-reduction measure for shoulder-season swimming in Ottawa. Evaporative heat loss accounts for 60 to 70 percent of total pool heat loss, and a solar blanket eliminates most of that evaporation while also trapping solar radiation during daytime hours. Using a solar blanket consistently during a shoulder month can reduce your heating cost by 40 to 50 percent — turning an $800 gas heating bill into a $400 to $480 bill, or a $350 heat pump bill into a $175 to $210 bill. The blanket also reduces chemical consumption because less evaporation means less water replacement and less chlorine loss to the atmosphere.

Pool size is the other major cost variable. The figures above assume a standard 40,000-litre pool (roughly 12 by 6 metres, 1.2 to 2.4 metre depth). A large pool of 60,000 to 80,000 litres — common in established Ottawa neighbourhoods like Rockcliffe Park, McKellar Park, and Hunt Club — costs proportionally more to heat because there is simply more water mass to warm and a larger surface area losing heat. Conversely, a smaller plunge pool or cocktail pool of 15,000 to 25,000 litres is significantly cheaper to extend into shoulder season, often costing only $150 to $400 for an extra month with gas heating.

Chemical costs for the extra month are modest but not negligible. An additional month of operation requires roughly $40 to $80 in chlorine, pH chemicals, and algaecide. In October specifically, falling leaves become a significant maintenance burden — daily skimming and increased filter cleaning are necessary to prevent organic staining, clogged skimmer baskets, and phosphate buildup that feeds algae. A leaf net cover deployed overnight during October costs $50 to $150 and saves hours of manual skimming.

Is the extra month worth the cost? For a family of four that swims three to four times per week, an extra 12 to 16 swim sessions at a cost of $300 to $800 works out to roughly $20 to $65 per swim session — comparable to a family visit to a public aquatic centre but in the comfort and privacy of your own backyard.

Want to get the most swimming time out of your Ottawa pool investment? Ottawa Pool Installation connects homeowners with local heating specialists who can calculate the precise cost of extending your season based on your specific pool size, heater type, and target temperature.