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Solar Attic Fan Calculator

Size a solar attic fan from your attic floor area and target air changes. Canadian calculator with NBC vent area, fan power, and CRA payback math.

Solar Attic Fan Calculator

Required ventilation
1,521 m³/h
Recommended fan power
21 W
Solar panel size
25 Wp
Net free vent area (intake)
0.43 m²
Annual kWh displaced
154 kWh
Annual savings
$22
Payback period
37.1 years

How to use this calculator

Enter seven values and the calculator returns the airflow your attic needs (m³/h), the matching fan motor power, the solar panel size that drives it, the intake vent area required by NBC 9.19, and the annual electricity savings versus a comparable grid-powered attic fan.

  1. Attic floor area (m²) — measure the heated footprint of your home directly under the attic. A typical 2,000 sq ft Ontario or BC home has about 90 m² of single-storey attic; a two-storey home 50 to 60 m².
  2. Average attic height (m) — for a typical 5:12 pitch hip or gable roof the average internal height is 1.3 m. Higher-pitch Victorian or Maritime homes run 1.6 to 1.8 m.
  3. Target air changes per hour — 8 ACH for most of Canada, 10 for southern BC and southern Ontario, 6 for the territories.
  4. Cooling-season run hours — annual hours the attic exceeds 27 C thermostat trigger. Toronto and Montreal average 700; Vancouver 350; Calgary 500; Halifax 400; Whitehorse 100.
  5. Grid attic fan power (W) — the AC-powered alternative. A typical 1,400 m³/h mains attic fan (NuTone NF1500, Air King) draws 220 to 280 W.
  6. Electricity rate (C$/kWh) — your delivered rate. Statistics Canada 2026 averages: Quebec C$0.078, Manitoba C$0.103, BC C$0.124, Ontario C$0.140, Alberta C$0.165, Maritimes C$0.180.
  7. Solar attic fan installed cost (C$) — fully installed including unit, soffit vents if needed, and licensed-roofer labour.

Why solar attic fans matter less in Canada — but still have a role

Canadian summers are short compared to the US Sun Belt or Mediterranean Europe. NRCan CanmetENERGY’s residential energy use survey shows that for the median Canadian home, space cooling accounts for only 1.5 percent of annual energy use, compared to 15 to 25 percent for Florida or Texas homes. That structurally caps the energy-savings case for active attic ventilation.

The argument for solar attic fans in Canada is moisture management more than heat extraction. NRCan’s Air Sealing the Attic guide notes that the leading cause of attic mould in Atlantic Canada and Quebec is humid summer air that condenses on cold sheathing when night temperatures drop. A solar attic fan with a humidistat clears that air before condensation forms. The energy savings versus passive ventilation are negligible — but avoided mould remediation runs C$3,000 to C$8,000 over 20 years for a typical attic, which is a serious economic lever.

How the calculator derives the answers

Required volumetric airflow follows from your attic volume and target ACH:

V_attic = floor_area_m² × average_height_m
Q (m³/h) = V_attic × ACH

A 90 m² Ontario home with 1.3 m average attic height at 8 ACH needs 936 m³/h.

Fan motor power follows brushless DC datasheets. Solatube Solar Star and Attic Breeze data sheets cluster at 14 W per 1,000 m³/h. So that 936 m³/h fan draws about 13 W during peak operation.

The PV panel sized to drive the fan at solar noon under STC with a 0.85 system derate is roughly 16 Wp — well below the 100 W threshold that would trigger CSA C22.2 No. 107.1 grid-connect requirements. The unit is treated as low-voltage equipment by CEC 64-216.

Net Free Vent Area at the intake follows NBC 9.19.1.2:

NFVA = floor_area_m² / 300  m² minimum (or /150 for low-slope)

For 90 m² that is 0.30 m² total NFVA — typically delivered by replacing 6 m of continuous soffit panels with vented type, or fitting 8 circular soffit vents at 600 mm centres.

Payback economics in Canada

Annual energy displaced is the grid attic fan’s wattage times its annual run hours. For a 240 W mains fan running 700 hours per year, that is 168 kWh annually. At Ontario’s 2026 average C$0.14/kWh that is about C$24 in direct electricity savings. Payback on a typical C$900 installation against energy savings alone is 35+ years — longer than the warranty.

The economics improve significantly when you include cooling-load reduction (NRCan estimates 5 to 12 percent AC savings on homes with ductwork in the attic — unusual in Canada, but found in some BC and Alberta builds) and avoided moisture remediation. Stacked together, payback drops to 5 to 8 years for high-humidity coastal markets.

There is no specific federal grant for solar attic fans, but the Canada Greener Homes Initiative (relaunched under the 2025 budget) provides up to C$5,000 in rebates for energy retrofits if you bundle attic ventilation with R-60 insulation upgrades. BC’s CleanBC Better Homes program offers up to C$1,200 in stacked rebates for whole-home retrofits that include ventilation upgrades.

Sizing rules of thumb

  • One 1,000 to 1,400 m³/h solar attic fan per 90 to 130 m² of attic floor area.
  • Mount on the south-facing slope for best PV performance, regardless of which slope you would otherwise prefer for exhaust geometry.
  • Always pair with new continuous-soffit vents — most pre-2000 Canadian homes have plenum soffits with limited intake.
  • Include the humidistat option (most premium units bundle it for under C$50 extra) — it matters more than the thermostat in this climate.

Sources

NBC 2020 Division B Section 9.19 (Roof Spaces); NRCan CanmetENERGY Residential Energy Use Survey 2024; NRCan Air Sealing the Attic technical brief; CSA C22.2 No. 107.1 General use power supplies; CEC C22.1 Section 64 PV systems; NuTone NF1500 mains attic fan datasheet; Solatube Canada Solar Star RM-1200 specifications; Attic Breeze AB-3024 distributor specs; Statistics Canada Table 25-10-0021-01 electricity prices; Canada Greener Homes Initiative program guidelines.

Frequently asked questions

How many CFM does my Canadian attic need?
Energy Star Canada and NRCan target 8 to 10 air changes per hour for residential attics. Use 8 ACH for Atlantic Canada, Quebec, Ontario, and the Prairies; 10 ACH for southern BC and the Okanagan; 12 only for southern Vancouver Island and unusually hot inland sites. Multiply attic floor area in m² by average attic height to get m³, then by ACH to get m³/h.
Does a solar attic fan make sense in a Canadian climate?
Marginally — and only in three cases. First, in southern BC or southern Ontario where cooling-season hours exceed 600 per year. Second, for moisture management in shoulder seasons (spring melt humidity, fall condensation) when the humidistat function matters more than the thermostat. Third, on homes with cathedral ceilings or low-slope roofs where passive NBC 9.19 ventilation is structurally limited. For most Prairie or Atlantic homes, attic insulation upgrades to R-60 deliver more energy savings per dollar.
What does NBC 9.19 require for attic ventilation?
National Building Code section 9.19.1.2 requires unobstructed roof-space ventilation with a minimum of 1 m² of net free vent area for every 300 m² of insulated ceiling area, distributed so that at least 25 percent is at the top of the space and 25 percent at the bottom. For low-slope roofs under 1:6 pitch this rises to 1:150. Solar attic fans count as high-level exhaust but do not replace the low-level (soffit) intake requirement.
How do Canadian winters affect a solar attic fan?
Modern brushless DC units (Solatube Solar Star, Attic Breeze Canada) handle Canadian winters fine — they simply do not run when the thermostat snap-disc reads below 20 C. The humidistat function is more relevant: switching the fan on at 70 percent attic RH helps clear moisture-laden air before it condenses on cold sheathing, which is one of the leading causes of attic mould in Atlantic Canada.
What does a solar attic fan installation cost in Canada?
Expect C$750 to C$1,100 fully installed. The unit itself is C$450 to C$650 (Solatube Canada, Attic Breeze AB-3024 imported via Canadian distributors). Labour by a roofer with PV experience adds C$200 to C$400. Some provinces — notably BC under the CleanBC Better Homes program and Quebec under Rénoclimat — include attic ventilation upgrades in retrofit grants if bundled with insulation work.

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