Multi-level heat-loss calculator (Québec)

Independent site: no ads, no cookies, no affiliate links. Nothing you enter is sent anywhere: the calculation runs in your browser.

Your home

Area and length units m² and m sq ft and ft

Location (design temperature)Your town isn’t listed? Pick the nearest one with a similar climate; the NBC notes that interpolation may not be valid.

Indoor temperature (°C)22 °C: the heating value used in the NRCan guide.

Levels

From lowest to highest. The attic ceiling applies to the last level in the list. Exposed perimeter: do not count shared (party) walls.

Whole house

Attic ceiling insulation

Airtightness (year built)ACH50: air changes per hour at 50 Pa (blower-door test).

Continuous mechanical ventilation (L/s), optional0 if no fan runs continuously.

HRV sensible recovery efficiency (%), optionalValue from your HRV’s spec sheet; 0 for a plain exhaust fan.

Important: simplified estimate, not compliant with CSA F280 or Manual J. Heat pump capacity must be confirmed by a load calculation done by a professional, ideally with an EnerGuide evaluation (blower-door test included), and the installation entrusted to a contractor licensed by the RBQ.

Calculation method

Temperature difference: indoor temperature (22 °C by default, as in the NRCan guide) minus the location’s January 2.5% design temperature (NBC 2020, Table C-2).
Walls, ceiling, windows: loss = area × difference ÷ RSI (or area × U-factor × difference for windows). Wall area = exposed perimeter × ceiling height, minus windows. Rim joists and floors over a garage are not counted separately.
Basement (approximation): the above-grade part is treated like an ordinary wall. For the below-grade part and the slab, we follow the principle published by the NRC (Latta and Boileau, 1969): heat crosses the soil along circular arcs to the surface, so soil resistance increases with depth. Soil conductivity: 0.8 BTU/(h·ft·°F), about 1.38 W/(m·K), the average value in that document. High bound: difference between indoors and the outdoor design air, as in that document (conservative). Low bound: difference with the mean annual air temperature, which deep soil stays close to, estimated as 18 − degree-days ÷ 365 (site estimate). Soil type, snow and the water table can change the result a lot. Slab: base resistance RSI 0.2 (site estimate), plus the insulation entered.
Air leakage: natural air changes ≈ ACH50 ÷ 20. This divisor is a heuristic in wide use (attributed to Lawrence Berkeley National Laboratory), not a measurement; in high wind or extreme cold, leakage can be higher. Loss = 0.33 × air changes per hour × volume (m³) × difference.
Ventilation: loss = 1.2 × airflow (L/s) × difference × (1 − sensible recovery efficiency). 0.33 and 1.2 are the heat capacity of air (about 1.2 kJ/m³·K), expressed per hour or per second.
Conservatism: no solar or internal gains (people, appliances) are subtracted, as is usual for peak heating.
Range: the low bound takes the best value of each preset (highest RSI, lowest U-factor and leakage), the high bound the worst. A value you enter yourself adds no range; the below-grade part of the basement always keeps one.
Load at −8.3 °C: design load × (15.6 + 8.3) ÷ (15.6 − design temperature), per Equation 4 of the NRCan guide; in Montréal (−23 °C), about 62%.

Presets and sources

Values offered in the lists; “site estimate” = no public source found for this exact value
Preset	Value	Source
Walls: before 1950, 1950 to 1979, 1980 to 2011	RSI 0.7–1.4 · 1.4–2.4 · 2.8–3.6	Site estimate : assumed typical thicknesses (none, 50 to 89 mm, 140 mm of batts) × RSI of glass fibre batts, 0.55 to 0.76 per 25.4 mm (NRCan, Keeping the Heat In, 2012, Table 3-1), plus the other layers. No public by-era series for Québec was found.
Walls: current requirement	RSI 4.31 (under 6,000 DD) · 5.11	Québec Construction Code, Section 9.36, Table 9.36.2.6.-A, total thermal resistance of the insulated portion (GCR technical sheet 9.36, French). Zoning uses the Table C-2 degree-days.
Ceiling: before 1950, 1950 to 1979, 1980 to 2011	RSI 1.0–2.5 · 2.1–3.5 · 3.5–5.3	Site estimate, same method (NRCan, Table 3-1).
Ceiling: current requirement	RSI 7.22 · 9.00	Same Code table (GCR sheet).
Foundation walls	RSI 0.2–0.3 · 2.1 · 2.99	Uninsulated and “about R-12”: site estimate. 2.99: Code requirement for foundation walls (GCR sheet).
Soil around the basement (low bound)	18 − DD ÷ 365	Site estimate of the mean annual air temperature from the Table C-2 degree-days (Montréal: 6.5 °C; Saguenay: 2.4 °C).
Windows: single, clear double, low-E double	U 5,91 · 2,73 · 1,53–1,82	Typical centre-of-glass values (Kesik and Papp, Ryerson University, Table 1); a complete window often loses a little more. Storm window: NRCan says it cuts the loss of single glazing by almost half (Keeping the Heat In, Section 8), hence U 2.96.
Windows: ENERGY STAR or triple	U 0,80–1,22	ENERGY STAR Canada maximum 1.22 W/(m²·K) (Version 5.0 specification); triple glazing as low as 0.8 (NRCan, Section 8).
Airtightness: before 1950 to 2019	ACH50 9.0–13.7 · 5.3–7.7 · 3.1–4.4 · 2.2–3.1	Measured averages by decade (EnerGuide tests, Alberta, British Columbia, Saskatchewan: Ismaiel and Chen, 2019, Table 1) and 1997 NRCan/CMHC Canadian averages (13.7 before 1921; 3.1 for 1991–1997) reported by Ismaiel et al., 2022. No public Québec series was found.
Airtightness: new, R-2000	ACH50 2.5–3.2 · 1.2–1.5	Modelling assumptions of the NBC 2020 (9.36.5.10.(9)); NRCan’s R-2000 Standard (1.5 at most) and a measured average of 1.23 (Ismaiel et al., 2022).

Frequently asked questions

How is this different from the quick BTU-per-square-foot estimator?

The quick estimator applies Hydro-Québec’s per-square-foot benchmarks. This calculator instead adds up the losses through each wall, window, ceiling and basement, plus air leakage and ventilation, at your location’s design temperature. It therefore accounts for your home’s insulation, windows and airtightness.

Why a range rather than one number?

Without measurements, the thermal resistance of the walls and the airtightness of the house are not known exactly. The presets therefore give a low bound and a high bound. A blower-door test and the real values of your walls, attic and windows narrow the range.

Does this replace a CSA F280 calculation?

No. It is a simplified method based on load-calculation principles (area × temperature difference ÷ resistance). It does not comply with CSA F280 or Manual J. To choose and install a heat pump, have a load calculation done by a professional; an EnerGuide evaluation also measures the home’s airtightness.

Should I size the heat pump on the top of the range?

Not necessarily. The NRCan guide offers two approaches: capacity at −8.3 °C close to the load at that temperature, with backup heat in extreme cold (option 4C), or capacity at the design temperature close to the design load (option 4D), often with a cold-climate model. Always compare with the model’s actual capacity at those temperatures.