Fireplace Draft

A second floor addition was constructed on my house by the previous owner. The heating system and fireplace chiminies are below the peak of the addition....about 3 ft below and about 10 feet away from the wall of the addition. When using my fireplace, the draft is not very good. What can I do, short of extending them upwards? Do you think it's also affecting my heating system draft? How would I be able to tell? Thanks....

 

Does Fireplace produce smoke back into the room? You Chimney is just right at the minimum for distance away and below the peak of a roof. The prevailing winds can have a huge impact on how well the Fireplace will draw. If it smokes back into the room the first suggestion would be look for a Fireplace flue extension. They can be as tall as 3'. Check your locally Fireplace supply stores even a Masonry supply house may have something.
Though the actually FireBox\Smoke Chamber may be built incorrectly causing the Fireplace not to draw correctly. Would be hard to say without actually seeing it.

You may just have to have a Chimney Sweep or Mason contractor look at it.

Edit: Sorry about your Heating system vents you may want to look in the Plumbing, Air and Heat forum for suggestions on that.