Help With BTU Calc For Gas Fireplace

mgmmike

Here's the deal, I have approx. 1,075 sq ft of reletively open space in my single story house. The builder installed a fireplace rated at 11,000 - 17,000 BTU to serve as a secondary heat source in the event my main unit malfunctions. This has proven to be extremely inefficient.
The unit is installed in a unobstructed hollow chase that leads directly to the attic area. It is a direct vent through this chase staraight up through the roof. The unit has no restricter plate at the flue opening. It has a fan that needs much to be desired(almost no airflow). He has agreed to replace the fireplace with one that is rated at 17,000 to 25,000 BTU's. I am concerned that this will not provide enough heat to keep the area warm enough until the main heater becomes available. I didn't mention that this is a propane unit. Are my concerns valid or am I worrying too much. I'd welcome any input.