Extractor fan. I use an inline 5inch fan (that's usually for hydroponics), with some ducting to draw the hot air away and out the window.
In your case dependant on room size an open air fan behind the miners blowing the hot air towards the window might work.
On a different note. How are you finding the R4 in terms of reliability?
Thanks!
I have never had miners at home, i have them hosted up north so my experience is very low. However, I overclocked at 650 which give approx 9.2th/s, they are silent and are reliable since i have been running them.