Calculating your needs

  Ecotherm advisers will gladly calculate your needs for free.

Power calculation is a very important step; it has to be precise so you purchase what suits your needs. A vague calculation could lead to an oversized radiator purchase where you would overpay unnecessarily or worse, you would have an insufficient radiator that would not provide the expected comfort.

Ecotherm’s calculation method is very precise. Our advisers use all the following criteria:

• General insulation level of the house,  Exterior temperature,  Interior temperature desired by the customer,  Floor level (for example, basement or 1st floor),  The volume needed to heat, not only the surface,  • The window surface.

Our advisers will be pleased to assist you in calculating your needs (even on blueprints) and to give you an estimate. This service is free with no obligation and professional work is guaranteed.

Here is the formula to calculate the power needed:

Watts required = L x W x H x G x DT


L = length, W = width, H = height, all in feet. G = insulation coefficient in watts / cubic feet. DT = Temperature difference between the one required in a room (example: +19°C) and the average outdoor temperature on cold days (example: -20°C). In this example the temperature difference is 39°C. 

Example : A house built in the 80′s in Montreal with original insulation and regular window surface. The room to heat is on the 1st floor, its size is 15 feet long by 11 feet wide by 8 feet high. The temperature desired is 20°C.

Chart 1 indicates an outdoor temperature of -20.1°C. The temperature difference is 20 – (-20) = 40.1°C. Chart 2 indicates a coefficient G of 0.027 for ground level. If it were in the basement, coefficient G would have been 0.018.

Calculation is: 15′ x 11′ x 8′ x 0.027 x 40.1°C = 1429 WattsA 1500 Watts radiator would be the right choice to heat this room.

Chart 1 – Average temperatures on cold days 
Montreal’s surrounding areas Temperature Regions Temperature Regions Temperature
Brossard -20.4  Chicoutimi -25.0   Rivière-du-loup  -21.9
Joliette -20.5 Drummondville  -22.9  Sherbrooke  -22.8 
Laval -19.6  Gaspé  -23.3 Sorel  -22.9 
Mont-Tremblant -24.0 Granby  -18.2  St-Georges  -21.4 
Valleyfield -19.6  Mont-Laurier  -25.1  Thetford-Mines  -21.4 
St-Hyacinthe -18.2  Montréal  -20.1  Val-D’Or  -28.6 
St-Jean-Richelieu -21.3  Ottawa  -20.0  Victoriaville  -21.4 
St-Jérôme -21.5  Québec  -22.4     
St-Sauveur -24.0  Rimouski  -21.1     

 Chart 2 : G coefficients

Very good insulation Good insulation Correct insulation Bad insulation
Main floor and up 0.023 0.027 0.032 0.060
Basement 0.015 0.018 0.021  

Very good insulation corresponds to, for example, a construction built after the late 90′s. Good insulation corresponds to, for example, a construction built between the 70′s and 90′s, or a construction built before the 70′s which had its insulation well renovated. Correct insulation corresponds to, for example, a construction built before the 70′s which never had its insulation renovated. Low insulation corresponds to, for example, a garage.

Notes: These calculations are provided as an indication only and do not bind Ecotherm in any way in case of misapplication. Ecotherm recommends you choose a heater with a power above the result of your calculations. If you have above average window surface area in your home, you must add more power proportionally to this additional surface area.