Based on the quantity and type of windows you select, you need to know that this addition will disrupt your spring system which acts as a counterweight. We calibrate all spring systems with a maximum variation of +/- 5% of the total weight of the door, meaning you should plan for the additional cost of readjusting your spring system. If your door weighs around 125 lb. (57 kg) and you add a row of windows to the top section, say four 21″ x 13″ (53 x 33 cm) windows, the door will become unbalanced and the spring system must be readjusted. Don’t tell yourself this isn’t important, and it’s the opener that opens and closes the door.A door opener only replaces human strength. A well-balanced door weighs only about 8 to 10 lb. (approx. 4 kg), easy enough to be lifted with one hand. In addition, in order to not weaken the structure of the door sections, there are some limitations regarding window size. Last, when a complete row of windows is installed in the top section, this section must be reinforced when an electric door opener is connected there. We add a reinforcement bar along the entire width of the door.