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I have been asked by one of my clients to design a new fireplace for his home. There is an existing zero-clearance box with a metal-bestos type flue. The box will go but I’d like to re-use the flue. The design I have in mind uses a Rumford style fireplace. I like the height/width aspects and the relatively shallow depth of a Rumford. So far, all this sounds easy-peasy. But everything I find out about Rumford fireplaces says they are always masonry units. That’s great, but my fireplace sits on a wood framed floor in a wood structure. So the weight of masonry becomes a factor that must be considered. Here are my questions: Must a masonry unit be heavy? Can lightweight materials be substituted for concrete? (I have considerable construction experience, but I’m not a mason.) Or, perhaps there is a zero-clearance unit out there that looks like and acts like a Rumford design——if so, please tell me where. I have searched suppliers and internet and can’t locate one. Any other help or suggestions are welcome.
Thanks,
Jeff
Replies
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The lightest construction I can think of would be to form the hearth and fire opening as far as the beginning of the flue proper in refractory brick.
The flue would be a metal double-wall and the fireplace surround would be formed from sheetrock on metal studs. All voids to be packed with mineral wool insulation.
*you can't build masonry without a foundation or steel / wood posts extended to foundation..it has to be fully supported..rumford fireplaces are built to the ratios developed by count rumford in the 1700's..his book is still out there.. for pretty foolproof rumfords, try one of the superior clay units..http://www.superiorclay.com/
*A unit built of refractory bricks would be less weight than a wood-burning stove over the same floor area so it would need the same support.
*I'm in doubt that you can reuse that double wall flue. For it to clear heat properly, it is critical that the seat it rests on allow for air circulation the way it was designed. The neck of a Rumsford is tall too where your old chimney fits to a squatty unit. For something that can kill you, do it right or not at all. Don't try to compromise. Promise pleaser so I can sleep without worrying about you and yours.
*I'll ditto Mike's words and suggestion for Superior Clay products. I built a Rumford (my first)for my home using all their materials and their specs and it works perfectly. And thats not by my work but by good engineering on their part.Mike
*As I understand it, the Rumford units can use metalbestos flues. In fact, they even have an adapter available for the top of the smoke chamber to ease the transition from ceramic to metal.Check rumford.com for more info....and good luck!BestDon
*Short answer, NO! If you design a horse by committe that has all of the best things you wind up with a camel (a camel is just a horse designed by committee) I'm sorry, I wanted to use that for a while.... Masonry fireplaces like the rumford design need to be heavy, It has to have a proper foundation!
*This Old House just did a fireplace renovation using a light weight block. It was a modular unit that used a flue similar to metalbestos. Your biggest problem reusing the flue is that inserts are typically designed to run pretty air tight and the Rumford will probably require a larger flue.
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I have been asked by one of my clients to design a new fireplace for his home. There is an existing zero-clearance box with a metal-bestos type flue. The box will go but I'd like to re-use the flue. The design I have in mind uses a Rumford style fireplace. I like the height/width aspects and the relatively shallow depth of a Rumford. So far, all this sounds easy-peasy. But everything I find out about Rumford fireplaces says they are always masonry units. That's great, but my fireplace sits on a wood framed floor in a wood structure. So the weight of masonry becomes a factor that must be considered. Here are my questions: Must a masonry unit be heavy? Can lightweight materials be substituted for concrete? (I have considerable construction experience, but I'm not a mason.) Or, perhaps there is a zero-clearance unit out there that looks like and acts like a Rumford design------if so, please tell me where. I have searched suppliers and internet and can't locate one. Any other help or suggestions are welcome.
Thanks,
Jeff