Why do fireplaces work and some don't?   

1. Fireplaces work mainly because hot air rises. The air inside the chimney becomes warmer and less dense than the air outside.
   As the air rises, cooler air from the room flows into the firebox fanning the air creating more heat in an ongoing cycle.
    
2. There must be at least 101 reasons why your fireplace may not function properly. The basic obvious solutions are as followed.
   a. Is your damper fully open?
   b. Is your firewood green or wet from rain? (see FAQ # 10c)
   c. Is your chimney tall enough?
   d. Is your chimney dirty? (when was the last time it was swept? (see FAQ # 1 & FAQ #2)
   e. Is your flue large enough for the appliance opening?
   f. Is your home too air tight? (do you have a fresh air intake coming into the house?)
   g. Is your house too drafty? (do you have windows open on the upper level?)