Every house or living space is different. In order to heat a space efficiently, it is very important to the maintain room temperature using only the minimum amount of heat (wattage) necessary.
For electric heaters, the amount of heat is measured in watts.
To understand how many watts are needed, it is important to know how well your room is insulated. The more insulation, the less wattage is needed to effectively heat the space.
But with that said, you are going to need somewhere between 5-10 watts per square foot.
For homes built prior to 1980 with minimal insulation you typically need 10 watts/sqft
Home built after 1980 typically require 8 watts/sqft
And Home built within the last 10 years only require around 5 watts/sqft because of increased insulation standards in building codes.
As a good rule to follow is : For Rooms with greater than average window space or high ceilings, increase wattage by 50%
So to calculate, determine the square footage of the room. Length x Width. And multiple that by the total watts per square foot needed. It’s that simple.
So for example, if you have a 10 by 20 foot room it’s going to be 200 square feet so for a new house that means you need a 1,000W heater. It’s that simple.