It is a common practice to boil down maple sap into syrup in a predominantly outdoor facility, much like the one Lynn Chadwick uses. The basic reasons for this has to do with the shear amount of everything. Like we've said in previous posts, it takes 40 gallons of sap to make just 1 gallon of syrup, so that alone takes up a large area. But perhaps one of the biggest benefits of being outside (or in a highly-ventilated area) is being able to deal with the huge amount of steam that is let off. 30 gallons of it for just one batch.
As you can see, the process of boiling down the sap isn't rocket science, but it does require attention. The heat has to be constant, and you need to be wary of any charred pieces from the sides of the pan. These won't ruin the batch, but it could give the syrup an off flavoring if you aren't careful. Sometimes additional filtering is done to help ensure quality.