Too often, wood burning boilers and stoves are installed without a dedicated fresh air source. Stoves without a source of fresh air can badly pollute your home's air with dangerous flue gases--leading to asthma or other illnesses. Here are several solutions.
WHILE DOING SOME RESEARCH on fresh air intake for wood boilers, I found this fascinating illustration of a do-it-yourself fresh air return. I haven't tried building one myself, but it looks like it might just work as a low-budget way to provide the "makeup" air a wood burner needs and maintain healthy indoor air. And conveniently enough, there's a company that sells miniature heat exchanger "coils" and pipe lengths that will allow you to build this Rube Goldberg-looking contraption quite easily.
Wood Stoves: Air Needed. Some building codes do require a fresh air intake with a wood stove, so it could actually be considered a plus. Tux Turkel did a nice piece comparing wood fireplaces with other types of heat HERE.
The most low-tech solution is the Duravent wood stove thimble, which allows fresh air to come in at the point where the woodstove or pellet stove pipe exits the wall.This should preheat the air to some degree and requires no additional piping.
Another more contained way fo bring in some air to fuel the combustion in your wood stove is to install a passive vent inside a 4-inch duct. Tamarack makes a vent that's very affordable (below). A lot of wood stoves have a flange already installed, just wainting for a 4-inch air intake pipe. Put the vent inside the duct, near the outside wall where the air will be drawn from.