How do I measure the amount of energy consumed by a device?
For most loads, you can look at the ratings that are marked on them and estimate how many hours per day you will use them. The heater will be more difficult. You need to calculate how much heat is lost given the area of the walls roof and floor. You use the difference in temperature between the outside and the air around the walls ground and roof. You must find the thermal resistance or insulation value for the type of construction, windows etc. You must also calculate the heat gain through areas exposed to the sun. You need climate data for the average outside temperature. You can calculate everything using a spreadsheet or use a program that has a lot of the necessary information pre-loaded. In some countries, such programs are available from the government.