I do 10 miles each way.

That's a comfortable distance.

12 miles would be better. 15 I could do, but more than that I'd be facing burnout.

It helps that our winters are mild. 10 miles in the snow would be a test.

We do have killer heat and humidity in the summer (and summer here begins in May and runs into October).

It helps that I have a locker and a shower at work. I don't think I could do it without the shower.