Screening in porches make them feel very small all of a sudden.
If you have a roof on it, just get a good space heater. Either that, or build a fireplace on one side and get some awesome partitions that GTFO of the way fully when it is nice out.
Otherwise, I agree with the ppl saying you won't use it again. I mean, you have plenty of rooms in your house you can open all the windows in, right?