I recommend a freestanding wood-burning fireplace such as the Hampton H200 or equivalent. The H200 is the unit I just installed in the LEED Platinum home I built for a client of mine in Texas.
- The home was built using ICF construction and a Daikin HVAC system.
- Because of the tightness of the home and temperature retention, a wood-burning fireplace like this works great.
It is placed in the main family room and keeps the entire area warm. The fact that it will radiate heat from all sides leads to its effectiveness.
If your clients want the traditional exterior-wall fireplace, you are likely going to need to go to a Buckley Rumford fireplace. Google search the name for a local supplier.
Good luck, and congratulations on going Platinum.
For more information:
Read "We need to seal our fireplace since there is a constant cold draft coming in, and lot of heat escape. How to seal it?", a Q&A answered by Harold Remlinger.