Heating is one of the biggest decisions pool owners make in Ontario. Without a heater, your swimming season is roughly late June through early September. With one, you can start swimming in mid-May and keep going into October.
But heaters vary widely in upfront cost, running cost, and how well they work in our climate. This article walks through all three types so you can see the real numbers and decide what makes sense for your situation.
Why would you heat a pool in Ontario?
Ontario's swim season without a heater is roughly 10 to 12 weeks. The water in an unheated pool typically reaches a comfortable temperature (around 26 to 28 degrees Celsius) sometime in late June, and drops below that by mid-September.
A heater can stretch that to 16 to 20 weeks, depending on the type of heater and how aggressively you use it. That is close to doubling the time you actually get to use the pool.
For families who spend $75,000 to $130,000 on a pool project, getting an extra two months of use per year is a significant return. That said, heating is not free. The question is not just whether to heat, but how.
How do gas pool heaters work?
A gas pool heater burns natural gas (or propane in rural areas) to heat water as it flows through the unit. Pool water circulates from the pool through the filter, then through the heater, and back to the pool. The combustion chamber heats a series of copper tubes, and the pool water flowing through those tubes picks up the heat.
Gas heaters are the fastest way to heat a pool. They can raise the temperature of a standard pool by 10 degrees Celsius in 8 to 16 hours, regardless of the outside air temperature. That makes them useful for heating on demand, especially on weekends or before a gathering.
Gas heater costs
| Cost Category | Range (CAD) |
|---|---|
| Unit cost (installed) | $4,500 - $7,000 |
| Annual running cost | $400 - $1,200 |
| Typical lifespan | 8 - 12 years |
| Gas line installation (if needed) | $500 - $2,000 |
The wide range in running cost depends on how often you use the heater and what temperature you keep the pool at. A homeowner who heats the pool to 28 degrees Celsius every day from May through September will spend much more than someone who only turns it on for weekends.
Gas heater pros and cons
- Heats fast. You can go from cold to comfortable in less than a day. This is the biggest advantage gas heaters have over other types.
- Works in any weather. Gas heaters do not depend on outside air temperature or sunshine. They work just as well in April as they do in July.
- Lower upfront cost. Gas heaters cost less to buy and install than heat pumps.
- Higher running cost. Natural gas is not cheap, and heating a pool takes a lot of it. This is the main drawback.
- Shorter lifespan. Gas heaters typically last 8 to 12 years, compared to 15 to 20 years for heat pumps.
- Requires a gas line. If your equipment pad does not already have a gas connection, you will need a plumber to run one. In rural areas without natural gas, you would need a propane tank, which adds cost.
How do heat pumps work?
A heat pump does not burn anything. Instead, it works like an air conditioner in reverse. It pulls heat from the outside air and transfers it to the pool water. Even when the air feels cool to you, there is still heat energy in it that the heat pump can capture.
The process uses a compressor, a refrigerant, and a heat exchanger. Pool water flows through the heat exchanger and absorbs the captured heat before returning to the pool. The only energy the heat pump uses is electricity to run the compressor and fan.
Because they move heat rather than create it, heat pumps are 5 to 6 times more energy-efficient than gas heaters. For every dollar of electricity they consume, they deliver roughly $5 to $6 worth of heat.
Heat pump costs
| Cost Category | Range (CAD) |
|---|---|
| Unit cost (installed) | $5,500 - $9,000 |
| Annual running cost | $200 - $600 |
| Typical lifespan | 15 - 20 years |
| Electrical panel upgrade (if needed) | $500 - $1,500 |
Heat pump pros and cons
- Very low running cost. At $200 to $600 per year, a heat pump costs a fraction of what a gas heater costs to operate. Over 10 years, the savings can be $5,000 to $10,000.
- Long lifespan. Heat pumps typically last 15 to 20 years with proper maintenance, almost double the life of a gas heater.
- No gas line needed. Heat pumps run on electricity, which is already available at most equipment pads.
- Slow to heat. A heat pump takes 24 to 72 hours to raise the pool temperature by 10 degrees. You cannot heat on demand the way you can with gas.
- Depends on air temperature. Heat pumps lose efficiency when the air temperature drops below about 10 degrees Celsius. In early May or late October in Ontario, they may not be able to maintain a comfortable pool temperature.
- Higher upfront cost. The unit itself costs more than a gas heater, though the lower running costs make up for it over time.
Does solar pool heating work in Ontario?
Solar pool heating uses panels (usually mounted on a roof or a ground rack) to warm pool water using sunlight. Water is pumped from the pool through the panels, where it absorbs heat from the sun, and then flows back into the pool.
Solar heating has no running cost at all. Once the panels are installed, the sun does the work. That sounds ideal, and in places like Arizona or southern California, solar heating is a very practical option.
In Ontario, it is more complicated.
Solar heating costs
| Cost Category | Range (CAD) |
|---|---|
| Panel system (installed) | $3,000 - $6,000 |
| Annual running cost | $0 |
| Typical lifespan | 15 - 25 years |
The Ontario limitation
Solar panels only work well when there is consistent sunshine and warm air temperatures. In July and August in Ontario, that is usually the case. But in May, June, September, and October, cloud cover is frequent and air temperatures are cool. Solar panels cannot reliably maintain a comfortable pool temperature during those shoulder months.
That is exactly the time when you most want a heater. The pool is already warm enough in July without one. The whole point of heating is to extend the season into the cooler months, and that is where solar falls short in our climate.
Most Ontario homeowners who install solar panels also keep a gas heater or heat pump for backup. The solar panels reduce how much the backup heater needs to run, which saves on running costs. But the upfront cost of two systems is higher than just installing one good heat pump.
Solar heating pros and cons
- No running cost. Once installed, solar heating is free to operate.
- Long lifespan. Solar panels can last 15 to 25 years with minimal maintenance.
- Unreliable in Ontario's shoulder season. When you need heating most (May, June, September, October), solar panels are least effective.
- Roof space required. You need a south-facing roof area roughly equal to 50% to 100% of the pool surface area. Not every home has that available.
- Usually needs a backup. In Ontario, solar panels alone rarely provide enough heat to make a meaningful difference in your swim season.
How do the three types compare side by side?
| Feature | Gas Heater | Heat Pump | Solar Panels |
|---|---|---|---|
| Upfront cost | $4,500 - $7,000 | $5,500 - $9,000 | $3,000 - $6,000 |
| Annual running cost | $400 - $1,200 | $200 - $600 | $0 |
| Heating speed | Fast (8-16 hrs) | Slow (24-72 hrs) | Very slow (days) |
| Works in cool weather? | Yes | Above ~10°C air | Needs sun + warmth |
| Lifespan | 8 - 12 years | 15 - 20 years | 15 - 25 years |
| 10-year total cost | $8,500 - $19,000 | $7,500 - $15,000 | $3,000 - $6,000* |
*Solar's 10-year cost looks very low, but most Ontario homeowners also need a backup heater, which adds to the real total.
What does it actually cost to run each type?
Running costs depend on your pool size, target temperature, how often you swim, and Ontario's current energy prices. Here are realistic estimates for a mid-sized pool (roughly 40,000 to 50,000 litres) heated to 27 degrees Celsius during swimming season.
| Heater Type | Monthly Cost (CAD) | Season Cost (5 months) |
|---|---|---|
| Gas heater (daily use) | $80 - $250 | $400 - $1,200 |
| Gas heater (weekends only) | $40 - $100 | $200 - $500 |
| Heat pump (continuous) | $40 - $120 | $200 - $600 |
| Solar panels | $0 | $0 |
The gas heater "weekends only" approach is worth noting. Some homeowners with gas heaters do not run them all week. They turn the heater on Friday morning and let it heat through the weekend, then shut it off Monday. This cuts gas usage significantly but means the pool is cold during the week.
A heat pump works differently. Because it heats slowly, most heat pump owners leave it running continuously during swimming season. It maintains the temperature rather than trying to recover it quickly. Despite running more hours, the electricity cost stays low because of the efficiency.
Which heater is best for Ontario's climate?
For most homeowners in London and Southwestern Ontario, a heat pump is the best overall choice. Here is why.
Ontario's swimming season with a heat pump runs roughly from mid-May through mid-October. During most of that period, daytime air temperatures are above 15 degrees Celsius, which is well within a heat pump's efficient operating range. The only weeks where a heat pump struggles are the very beginning and very end of the season, when overnight lows drop below 5 to 8 degrees Celsius.
The running cost difference is substantial. Over 10 years, a heat pump owner typically spends $2,000 to $6,000 on heating. A gas heater owner spends $4,000 to $12,000 over the same period. That is $2,000 to $6,000 in savings, which more than covers the higher upfront cost of the heat pump.
The heat pump also lasts longer. At 15 to 20 years, you may never need to replace it during the typical ownership period of a home.
When a gas heater makes more sense
A gas heater is the better choice in a few specific situations:
- You only swim occasionally. If you use the pool mainly for weekend gatherings or a few weeks in the summer, a gas heater's ability to heat on demand is more practical than a heat pump running continuously.
- You want to swim in very cool weather. In late October or early April, when air temperatures are regularly below 10 degrees Celsius, a gas heater can still heat the pool. A heat pump cannot.
- You have a hot tub or spa attached to the pool. Keeping a spa at 38 to 40 degrees Celsius requires a lot of heat. Gas heaters handle this more effectively than heat pumps.
What about solar blankets?
A solar blanket (also called a solar cover or bubble cover) is a large sheet of plastic with air bubbles that floats on the pool surface. It is not the same as solar panel heating. It is much simpler and much cheaper.
A solar blanket does two things:
- Traps solar heat. The bubbles focus sunlight into the water, raising the temperature by 4 to 8 degrees Celsius over several sunny days.
- Prevents heat loss. Most heat escapes from a pool through evaporation off the surface. A solar blanket blocks that evaporation, keeping the heat in the water overnight.
A solar blanket costs $100 to $300 for a standard pool size. A roller system to make it easier to put on and take off costs another $200 to $500. For a total of $300 to $800, it is by far the cheapest way to keep your pool warmer.
If you have a heater, a solar blanket can cut your heating costs by 50% or more because the heater does not have to work as hard to maintain the temperature. If you do not have a heater, a solar blanket on its own can add a couple of weeks to each end of your swim season.
Every pool owner in Ontario should have a solar blanket, regardless of what other heating system they use. It is the single best return on a small amount of money.
How much can heating extend your swim season?
Here is a realistic look at when you can expect to swim in the London, Ontario area, depending on your heating setup:
| Heating Setup | Typical Swim Season | Approximate Weeks |
|---|---|---|
| No heater, no blanket | Late June - early Sept | 10 - 12 weeks |
| Solar blanket only | Mid-June - mid-Sept | 12 - 14 weeks |
| Heat pump + blanket | Mid-May - mid-Oct | 18 - 22 weeks |
| Gas heater + blanket | Early May - late Oct | 20 - 24 weeks |
| Gas heater (weekends only) | Late May - early Oct | 14 - 18 weeks |
The difference between no heater (10 weeks) and a heat pump with a blanket (20 weeks) is roughly double the swim season. For a family that uses their pool regularly, that extra time matters.
How do you size a pool heater?
Pool heaters are measured in BTUs (British Thermal Units) for gas heaters and kilowatts for heat pumps. The size you need depends on your pool volume, the temperature rise you want, and how quickly you want to reach that temperature.
For most residential pools in Ontario (30,000 to 60,000 litres), here are the typical sizing ranges:
| Heater Type | Small Pool (30,000L) | Medium Pool (45,000L) | Large Pool (60,000L) |
|---|---|---|---|
| Gas heater | 200,000 BTU | 300,000 BTU | 400,000 BTU |
| Heat pump | 80,000 BTU (24 kW) | 110,000 BTU (32 kW) | 140,000 BTU (41 kW) |
Undersizing a heater is one of the most common mistakes. A heater that is too small for your pool will run constantly, never quite reach the target temperature, and wear out faster. It is better to go one size up than one size down.
Your pool installer should calculate the correct size based on your specific pool model and your heating goals. If they are not asking about your temperature preferences and intended swim season, that is a concern.
What are the most common heating mistakes?
After installing hundreds of pools, here are the heating mistakes we see most often:
- Buying a gas heater and then being surprised by the gas bill. Gas heaters are cheaper to buy, but the running cost adds up. Make sure you understand the monthly cost before choosing gas.
- Not using a solar blanket. This is the easiest win. A blanket costs $100 to $300 and can cut heating costs in half. There is no reason not to use one.
- Undersizing the heater. A heater that is too small for your pool will run all day and still not reach your target temperature. It costs more to operate and wears out faster.
- Expecting solar panels to carry the full load. In Ontario, solar panels alone are not enough to meaningfully extend your season. They work as a supplement, not a primary heat source.
- Heating without insulation. If your pool shell is not properly insulated during installation, heat escapes through the ground. Spray foam insulation around the shell during installation makes the heater more effective and reduces running costs.
- Running the heater with no cover. Heating a pool without a cover is like heating your house with the windows open. Most heat loss happens through evaporation at the surface. A cover prevents that.
What we typically recommend
For most of our clients in London and Southwestern Ontario, we recommend a heat pump paired with a solar blanket. This combination gives you a long swim season (mid-May to mid-October) at the lowest running cost.
The heat pump handles the heavy lifting. The solar blanket reduces how hard the heat pump needs to work. Together, they typically cost $200 to $600 per year to run, and the heat pump lasts 15 to 20 years.
For homeowners who want the absolute longest season possible, or who have an attached spa, we recommend a gas heater as a primary or backup. Some homeowners install both a heat pump and a small gas heater, using the heat pump for daily maintenance and the gas heater for quick recovery on cold weekends.
Whatever you choose, the heater should be planned during the pool design phase, not added as an afterthought. The gas line, electrical capacity, and equipment pad layout all need to account for the heater from the beginning.
Frequently Asked Questions
What is the best pool heater for Ontario?
For most Ontario homeowners, a heat pump is the best overall choice. It costs $200 to $600 per year to run compared to $400 to $1,200 for a gas heater. The main downside is that heat pumps work slowly and lose efficiency when air temperatures drop below about 10 degrees Celsius, which matters in early spring and late fall.
How much does it cost to heat a pool per month in Ontario?
With a gas heater, expect to spend $80 to $250 per month during swimming season, depending on your target temperature and how often you run it. A heat pump typically costs $40 to $120 per month. A solar blanket used on its own adds no monthly cost but only raises water temperature by a few degrees.
Can solar panels heat a pool in Ontario?
Solar panels can warm pool water in Ontario during July and August when there is plenty of sunshine and warm air temperatures. However, they are not reliable enough on their own in May, June, September, or October. Most Ontario homeowners who install solar panels also keep a gas heater or heat pump as a backup.
Does a solar blanket actually work?
Yes. A solar blanket can raise water temperature by 4 to 8 degrees Celsius over several sunny days and dramatically reduces heat loss overnight. It costs $100 to $300 and is the single cheapest way to keep your pool warmer. Used alongside a heater, it can cut heating costs by 50% or more.
How long does it take a heat pump to warm a pool?
A heat pump typically takes 24 to 72 hours to raise the temperature of a standard-sized pool by 10 degrees Celsius, depending on the pool volume, air temperature, and the size of the heat pump. A gas heater can do the same job in 8 to 16 hours. This is why many homeowners leave the heat pump running continuously during swimming season.
