Heating water is one of the biggest quiet costs in a home. Showers, laundry, dishes: the tank in your basement works all day, and most of it is fed by gas or electricity. A solar water heater swaps some of that fuel for sunshine. The idea is older and simpler than most people expect, and in November 2026 it is still a sensible option for some households, though not for all. This page belongs to our hot water and heating hub, and starts with how the parts fit together.
The basic loop
Picture a garden hose lying in the sun. The water inside gets warm. A solar hot water system is that idea, tidied up and made safe for a house.
- Collectors on the roof soak up sunlight and turn it into heat.
- A fluid, usually water mixed with antifreeze, carries that heat away.
- A small pump pushes the fluid down to a heat exchanger in a storage tank.
- The tank passes warm water to your taps. When the sun has not done enough, your regular heater tops it up.
That last point matters. Nobody is asking you to live without hot water on a grey Tuesday. The solar tank simply arrives pre-warmed, so the backup heater has less work to do.
Two kinds of collector
Flat-plate collectors look like a shallow glass-topped box. Inside sits a dark metal plate with pipes attached. They are sturdy, usually cheaper, and a good match for most homes. Evacuated-tube collectors are rows of glass tubes with a vacuum around the heat-carrying part, a bit like a thermos. The vacuum cuts heat loss, so they hold up better in cold, windy conditions.
| Flat plate | Evacuated tube | |
|---|---|---|
| Typical cost | Lower | Higher |
| Cold, windy days | Fine | Better |
| Snow on the collector | Melts off sooner | Can linger, since little heat escapes |
| Repair | Replace the panel | Replace a single tube |
Neither is best everywhere. Climate, roof shape and budget decide.
Active or passive?
Most homes in cold climates use an active, closed-loop system. A pump circulates the antifreeze mix through the collectors, so nothing freezes overnight and the household water never goes up to the roof. Simpler passive systems rely on natural circulation and suit places where frost is rare. In a Canadian winter, freeze protection is the first design question to ask, because a burst pipe in January is the failure that costs the most.
The controller and the safety parts
A small controller compares temperatures at the collector and the tank. When the collector is warmer, the pump runs. When it is not, the pump rests. A sound system also has an expansion tank to absorb pressure changes, a pressure relief valve, and a mixing valve at the tank outlet so scalding water never reaches a tap. Overheating on a hot July afternoon is the other thing to design for, since a system with nobody home and no hot water use can build up a lot of heat.
What it can realistically deliver
Across a full year, a well-sized home system commonly supplies about half of the energy used to heat water, a little more in a sunny summer and a lot less in December. Here is a rough worked example. A family of four might use around 200 litres a day, and warming that water from cold mains temperature to tap temperature takes roughly 8 kWh of energy. Over a year that is close to 3,000 kWh. Half of it is about 1,500 kWh, which is the share the sun could cover. Your own figures will differ with household size, habits, shading and roof angle.
The savings come mostly from the warm months, when the backup heater may barely run. In winter the collectors still work, but short days and low sun mean the tank often needs plenty of help. Our piece on solar in Canadian winters explains why the seasonal swing is so large.
Is it the right tool for you?
Hot water collectors do one job well. If your water is already heated by electricity, they cut a large chunk of that load. If it is heated by gas, the savings in dollars are smaller. A heat pump water heater is the main rival, since it uses roughly a third to half the electricity of a resistance tank, and this heat pump comparison lays out the trade-offs. If you want to know whether collectors or electricity-producing panels would use your roof better, see panels versus solar water heating.
Questions worth asking before you buy
- How big is the tank, and does it suit our daily hot water use?
- What stops the system from freezing, and what stops it from overheating in July?
- Who services it, and how often? Antifreeze needs checking every few years, and pumps and sensors wear out.
- What does the warranty cover, and for how long?
- Does the installer hold the plumbing and any electrical licences your province requires, and who handles the permit?
Prices vary widely, so treat any figure you read, including ours, as a starting point and get written quotes. The solar hot water cost guide sets out typical ranges and what drives them. Upkeep is modest but real, and the maintenance checklist shows what a yearly look should cover.
Before you call anyone
Check the roof first. Collectors need an unshaded slope, ideally facing south or close to it, and enough room near the tank for pipework. A basement that is far from the roof means longer pipe runs and more heat lost on the way. Our roof checklist takes about ten minutes. Then look at your hot water habits for a week: how many showers, how many laundry loads, and when. Those habits size the tank far better than a rule of thumb.
Quick answers
Do solar hot water systems work in winter?
Yes, if designed for it. Closed-loop systems with antifreeze keep running in cold weather, though output is lower because of short days and low sun.
How much of my hot water can solar supply?
Over a full year a well-sized system commonly covers about half of water heating energy, with much higher shares in summer and lower shares in winter.