My spring broke and the opener (1/2 HP) lifted it just fine. They are not designed for this load everyday, for sure.
This was a garbage board / solid wood type door but only single size = 7 x
8'. The opener was a Genie screw mechanism type. Any 1/2 HP motor should be able to lift 400 lb. of door over a 8-10 second period and the weight is only when the door is fully closed. When it is half way up half the load is horizontal and not loading the motor.I got my car in that night and out the next day until the spring boy came to fix it again.
Best, Christopher