Glazed absorber in an insulated enclosure. Optical efficiency ~76%, heat loss coefficient FRUL ~4.5 W/m²·K. Cost-effective for DHW and mild-climate space heating. Best where roof area is not constrained.
Vacuum-insulated tubes. Optical efficiency ~72%, heat loss coefficient FRUL ~1.5 W/m²·K. Dramatically better in cold Canadian winters. Preferred for space heating combi-systems and cold-climate DHW.
Monthly Detail
| Month | Load (kWh) | Solar Output (kWh) | Backup (kWh) | Solar Fraction |
|---|
System Summary
| Parameter | Value | Unit / Notes |
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How to Use the Solar Thermal Calculator
Select flat-plate or evacuated tube based on your budget and climate. Then choose the application: domestic hot water only, space heating only, or a combi-system for both. The calculator adjusts the monthly load profile and sizing approach for each application.
Each city loads location-specific daily peak sun hours and latitude. These drive the monthly irradiance profile and the recommended tilt angle. For space heating, cities with more winter sun (Calgary, Winnipeg) benefit more from a steeper tilt.
For DHW, enter occupant count. For space heating or combi, enter your annual heating load in kWh - available from an energy audit, utility bills, or the heat load calculator. Set the solar fraction you want to achieve.
Auto tilt sets the optimal angle for your latitude and application. Winter-biased tilt improves winter space heating output but reduces summer DHW production. Enter your backup fuel rate and installed system cost for a payback estimate.
Solar Thermal Collector Sizing for Canadian Buildings
Solar thermal systems convert sunlight directly into heat, which is far more efficient than converting it to electricity first and then using electricity for heating. A good solar thermal collector converts 55 to 75% of incident solar radiation into useful heat, compared to 18 to 22% for a typical photovoltaic panel. For thermal applications - space heating, domestic hot water, pool heating - solar thermal is often the most cost-effective solar technology per unit of heat delivered.
The collector thermal model: FR, UL, and the Hottel-Whillier equation
Collector performance is described by two parameters from the ASHRAE 93 test standard. FR(τα) is the optical efficiency - how much solar radiation the collector absorbs at zero heat loss. FRUL is the heat loss coefficient - how fast the collector loses heat to ambient air as collector temperature rises above ambient. The instantaneous useful output is Q = A × [FR(τα) × G − FRUL × (Ti − Ta)], where G is solar irradiance (W/m²), Ti is inlet fluid temperature, and Ta is ambient temperature. This calculator applies this equation month-by-month using average monthly irradiance and temperature data for each Canadian city. For a detailed hour-by-hour simulation, use Natural Resources Canada's RETScreen tool.
Flat-plate vs. evacuated tube in Canadian climates
The key difference is the heat loss coefficient FRUL. A flat-plate collector loses heat proportionally to the temperature difference between the absorber and the cold Canadian air. At -20°C ambient with a 60°C collector temperature, that's an 80°C temperature difference driving heat loss. An evacuated tube collector has a vacuum between the absorber and the glass, so convective and conductive heat loss is negligible regardless of air temperature. In Edmonton in January, a flat-plate collector may produce 30 to 50% less useful heat than an evacuated tube of the same aperture area, for the same incident radiation. The PVT collector calculator shows the trade-off when you want simultaneous electricity and heat production.
Tilt angle optimisation for heating vs. year-round DHW
A tilted collector receives different irradiance profiles depending on the angle. At latitude tilt (44° in Toronto), a south-facing collector is perpendicular to the sun at the equinoxes and intercepts reasonable radiation year-round. Steepening to latitude + 15° makes the collector more perpendicular to the low winter sun, boosting December and January output significantly - exactly the months when space heating demand peaks. This tilt also sheds snow more readily, which is a meaningful practical advantage in most Canadian cities. For summer-only loads like pool heating, a shallower tilt closer to latitude - 15° is optimal. The solar orientation calculator models tilt sensitivity in detail.
Space heating solar fraction - what's realistic in Canada
For domestic hot water, 55 to 70% annual solar fraction is achievable in most Canadian cities with a properly sized glycol system. Space heating is harder: peak demand occurs in December and January when solar radiation is at its annual minimum. The seasonal mismatch limits practical space heating solar fractions to 20 to 40% for systems sized to avoid summer overheating. Very high solar fractions for space heating - above 50% - require large seasonal thermal storage, which is expensive. Combi-systems targeting 30 to 40% space heat solar fraction plus 60% DHW solar fraction are the most cost-effective overall approach, as the DHW load provides a year-round revenue stream for the collector. Use the solar fraction calculator for detailed analysis.
Freeze protection and Canadian code requirements
CSA B214 governs solar thermal system design and installation in Canada. All outdoor collectors require freeze protection, achieved either through a closed-loop glycol circuit with a heat exchanger or through a drain-back system. Propylene glycol (food-grade) is the standard heat transfer fluid in closed-loop systems, typically mixed to protect to -35°C or lower for Edmonton and Winnipeg applications. Glycol concentration should be verified annually. The glycol loop connects to the domestic water circuit through an ASME-rated double-wall heat exchanger to prevent cross-contamination. Direct systems circulating potable water through outdoor collectors are not permitted in Canadian climates.
Frequently Asked Questions
Start with your annual thermal load in kWh, then divide by the annual specific yield of your collector type and location. A flat-plate collector in Toronto produces roughly 400 to 550 kWh per square metre per year at 45° tilt. An evacuated tube in Calgary produces 550 to 700 kWh per square metre. Divide your target annual solar energy by this yield to get the required collector area. For domestic hot water, allow 1.0 to 1.5 m² per person for flat-plate, or 0.7 to 1.1 m² per person for evacuated tube, to achieve a 60% solar fraction. Use the solar water heater calculator for a dedicated DHW sizing workflow.
For year-round domestic hot water, the optimal tilt is approximately equal to your latitude, which ranges from 44° in Toronto to 53° in Edmonton. For winter-biased space heating, add 10 to 15° to your latitude to steepen the tilt and capture more low-angle winter sun. For summer-only loads like pool heating, subtract 10 to 15° from your latitude. A steeper tilt also helps shed snow. The calculator's auto-tilt applies the correct angle for your chosen city and application. Use the solar orientation calculator to compare annual yield across tilt angles.
Residential solar thermal systems in Canada typically cost $5,000 to $12,000 installed, depending on collector type, system complexity, and region. Flat-plate systems for domestic hot water start around $5,000 to $8,000 for a 2 to 4 m² system. Evacuated tube systems for combined space heating and DHW can reach $10,000 to $15,000. Federal and provincial incentives can reduce costs by $1,000 to $5,000. Payback periods range from 8 to 18 years depending on the backup fuel displaced and local solar resource. Enter your actual quote into the calculator for a precise payback estimate.
Yes, solar thermal can contribute to space heating in Canadian buildings, but the seasonal mismatch is significant. Solar energy peaks in summer when heating demand is lowest, and drops in winter when demand is highest. Solar thermal space heating systems typically achieve 20 to 40% annual heating solar fraction in Canadian climates, supplemented by a conventional boiler or heat pump for the remaining load. Combi-systems providing both space heating and domestic hot water are the most economical approach, since DHW creates year-round load that improves payback. The solar-assisted heat pump calculator is worth comparing for cold-climate heating.
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