That won't be a problem at all. The miners will be outside my living enviroment but I really have a problem with ventilation in my garage. I'll have to put some fans I guess to cool the whole setup down and make some natural ventilation. I'm sure of one thing - the fire extinguisher will be there for the worst case scenario

You need to get airflow INTO / OUT OF the garage, not just around it, or overheat will happen. Fans in windows are a good place to start.
I would also control dust measures and have air ducts in more than one place to circulate cool air in and warm air out