Temperature wise, you have to judge how your Boxer acts..I know mine love to go out and play in the cold, but they only stay out for maybe a couple hours and then back inside...Heat & humidity, which we deal with in the south really seems to get to them more...Samson, my 11 yr old, has a lot of difficulty with it, so play is monitored in the summer, exercise and walks are done early as well...I don't use extra clothing for mine in the winter, it really isn't necessary, but I know some people do.. Summer time, I keep lots of cool water handy, also I am thinking of getting a couple cooling mats, especially for Samson....Watch your Boxer, if he is panting an awful lot, that can be a sign of distress, I have used a towel dipped in cool water and drape it around the chest, or stick the paws in water to help cool...Basically, if you find the weather a bit tough, your Boxer will as well....Hope this is some help
Well, living in Hawaii I'm afraid I can't give you a great winter temp range. However, even with the temp here being so moderate, Eddie has a hard time in the mid-day sun which reaches about 85. He is good for about 10 minutes in the backyard before scratching at the door wanting more water. We HAVE to do our walk very first thing in the morning and then again after the sun goes down. He has also gotten a little pink from the sun on the white portion of his chest. I'm not sure what Eddie is gonna think when we move back to the Mainland in a few years. I guess we will have to get him a sweater. Hope that helps.
Duke does NOT like cold weather. I saw an above post saying that their dogs are ok in cold weather for a couple of hours at a time. Duke lasts about 5 minutes outside in the cold, then scratches at the door to get in-LOL! Maybe it's because he's on the small side and doesn't have much body fat. He does better in the heat, but we're careful not to exert him too much when it's in the 90's.
Living in thailand I can only talk about the heat..... However, I agree with samsonsmom you need to take them out early. I notice if the pavement is warm britney gets warm fast...since they sweat out their paws.
I don't take her out when the sunlight is too hot either.