About 4 hours and the outside temp is around 43. Inside the box its about 70°. I can see some gaps the need some caulk. But im happy that I went with the 250w. It may not be good enough for brand new pups but after about 2 weeks it shouod do just fine. Hopefully it wont be so damn cold for to long and if it was regular temp for this time of the year I think it would be sufficient
