This is a fantastic idea! The positive pressure from the fans of the miner plus the stack effect of the heat should creat a lot more draft than just the fans by themselves. Depending on the price of power, if it's close to break even if might be worth it. Hard to say if the added effect of the heat would be better than more powerful fans instead to create the airflow. However, if you put something like a food dehydrator between the miner and the exhaust chimney then it would definitely be worth it. Plus, if there is ever any coolness in the house the miner is probably all you would need to keep things comfortable. 

Makes me think I should try using the miners as hot air exhaust fans in my yurt, they run on solar power anyway and it would save the power from running the existing exhaust fan. Been wanting to add cooling tubes that would draw air in from the ground below the platform as well. Thanks for the ideas!!