Is it okay to build the Rumford on a raised hearth and should the height of the opening be reduced if I do?
Hearths are traditionally at floor level ... but ...
Raised hearths were popular in the 1950's when modern fireplaces were low and deep and you couldn't see the fire unless your got down on your knees or built the fireplace on a raised hearth. With tall Rumford fireplaces raised hearths are still sometimes preferred in rooms with very tall ceilings or so the fireplace can be seen over a counter or footboard of a bed.
There are lots of pictures of Rumfords with raised hearths linked from our picture gallery
Whether the Rumford is on the floor or on a raised hearth 18" above the floor won't affect the draft. If you reduce the height of the fireplace opening because it's so high on a raised hearth it will draw even better but at the expense of some heating efficiency and clean burning which is related to keeping the smoke in the fire longer.
Buckley Rumford Fireplaces
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