The armies of the Civil War did not normally fight during the winter months. Thousands of men whiled away their time in camps. Through these bleak months all soldiers, Union and Confederate, tried to keep warm and busy in order to survive.
Spending weeks or even months at a time in tents, shacks, or other makeshift shelters, they tried to prevent the wind from infiltrating and to buffer themselves from the cold, often wet or frozen ground. Needless to say, enlisted men had more primitive lodging than officers. It would have been an uncomfortable few months--not that the other seasons were much better. (A few battles did take place in winter months, but generally a lull occurred between Christmas and early March.)
Crimean Ovens to the Rescue
About 10 years ago, archaeological excavations in Alexandria unearthed several pieces of what was known as a Crimean Oven, a method to heat a large tent safely.
Basically, a brick-enclosed oven was built outside the tent, with a trench directing the heat inside. The advantages included the lack of smoke and fire danger inside the tent. In addition, the system warmed the ground and diminished the uneven heating from an open fire.
Still, as the illustration created by former City of Alexandria historian Wally Owen indicates, it was not exactly an easily-made contraption.
The archaeologists refer to an 1861 letter by surgeon Charles Tippler, who described the system:
A trench 1 foot wide and 20 inches deep to be dug between the center and length of each tent to be continued for 3 or 4 feet farther, terminating at one end in a covered oven fire-place and at the other end a chimney....By the contrivance a perfect draught may be obtained...."
And in that typical (now, as then) attitude of "we have found the next new best thing":
....The advantages of this mode of warming hospital tents are so obvious, that it needs only to be seen in operation to convince any observer that it fulfills everything required as regards the warming of hospital tents of the Eighth Brigade [New York}, and ascertain by observation the justness of this report.
It didn't become quite as widespread as Dr. Tippler advocated, but variations were constructed at other camps.
Talking about Weather
As obsessed as we are about the weather today (I am writing this on a day with about two inches of snow and almost nonstop TV coverage of the event), think about accommodating to the elements in the past. Without reliable heating or cooling, not to mention forecasting technology to anticipate the conditions tomorrow, soldiers and civilians had to make do with the weather that confronted them. Diary entries and letters (including those of Julia Wilbur) frequently recorded the conditions of the day--cloudy, "squally," etc., and the discomfort they created.