Does having gable end vents work against soffit vents and a ridge vent?
The Short Answer is “it could”. It’s all in the details; How many Square inches of soffit ventilation do you have? How many square inches of Ridge Vents do you have? How many square inches Gable Vents do you have and how far are the Gable Vents from the ridge?
If the Gable Vents are very close to the top of the Gable and you have close to 50% if your total ventilation in your soffits and you turn off your fan, your system will work just fine.If the Gable Vents are down from the top of the Gable a bit (3 feet or more) then blocking them is a good idea.Air flows just like water, to the line of least resistance. If hot air is exhausting out the Ridge Vent and air can be drawn from the Gable Vents, then the air below the Gable Vents will not move as you would like for it to.Your goal should be to get as close to 50/50 high low ventilation as you can. For Sure, turn off the fan.
I hope this information helps.