Fireplace blower manifold

[ddstrain]

We have a fire place that looks surprisingly like the fireplaces you see in Cracker Barrel restaurants. I love burning wood for heat and would like to make the fireplace more efficient. Most of manifolds I can find online are for "standard" size fireplaces, not large fireplaces (my 7 year old can walk into the fireplace without stooping). In the blizzards we had in the mid-Atlantic last winter we kept most of the house quite toasty with the fireplace despite the power being out all night. I just want to try to keep more of the heat from going up the flues. Does anyone out the have a design idea for a blower/manifold for a really large fireplace?