Anything more than 12 inches away from the tank shouldn't be a problem, Bob. If it's a concern, a person could just wrap a wet rag around the pipe between the tank and where the soldering is being done. As long as the copper pipe is wet on the outside, it can't get any hotter than 212 deg. F.

Good soldering practice involves heating the joint you want to solder QUICKLY with the torch burning like crazy. That's because the longer you're heating a joint, the warmer the surrounding joints will get, and the greater the possibility that a neighboring joint is gonna melt or even come apart on you. And, the longer you're heating a joint, the greater the liklihood that you're going to boil off all the flux inside the joint so that it doesn't take solder. In fact, some torch heads have TWO mixing tubes to heat joints twice as fast and get them twice as hot for brazing refrigeration tubing:

http://www.northwaysmachinery.com/im...I%20DS1D1W.jpg

What does happen a lot when you do anything with a water heater is sediment on the inside of the hot water supply piping loosening up and causing your hot water to turn yellow or even brown when you first turn on the water after replacing the water heater. If you have cast iron hot water supply piping, it's common to have your faucet aerators getting clogged up with sediment loosened up from the inside of the hot water supply pipes. Whenever faucets stop working properly immediately after replacing the hot water heater, check that the faucet spout aerators aren't clogged up with stuff.