Just had a gas fireplace insert installed in an old masonary fireplace. It is direct vented. It's a Cosmo Heat n Glo 30k btu. It's not putting out any sort of significant heat! The flame and blower work. When they installed it - they raised it up by sitting in on two bricks so the surround could be 4 sided. Would the gap below the firebox have anything to do with the lack of efficiency of producing heat?