I have Mt Vernon free standing pellet stove that does a good job of heating my 2200 sq ft house. How my house is laid out, the air movement does not get back to the rear hall/family rm/bathroom. In the family rm, we have a useless fireplace. From Oct -April I put 6 mil poly over the opening to stop the drafts from coming in. This spring/summer I was thinking of installing a small pellet insert in that fireplace. How do you measure the fireplace for an insert? Is this a bad idea? Will I have draft problems? What do the pro's think?