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Hearth clearances on Majestic prefabs


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You're suppose to to have 18" of non combustable material on all sides of the opening. If that's a 12" tile, the diagonal is close to 17".

On the other hand, if you ever tried to intentionally burn a piece of scrap laminate flooring, you might just walk away from that.[;)]

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You're suppose to to have 18" of non combustable material on all sides of the opening. If that's a 12" tile, the diagonal is close to 17".

On the other hand, if you ever tried to intentionally burn a piece of scrap laminate flooring, you might just walk away from that.[;)]

Thanks Gary. It measures about 4 1/2 - 5 inches on three sides. What's your source?

Marc

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I believe that opening is just over 6 square feet. Measure it.

If that opening is less than 6sf, the material at the sides and top ofthe opening has to be a 8 inches wide; if it is larger than 6sf it needs to be 12 inches wide.

If that opening is less than 6sf, the hearth extension in front only needs to be 16-inches or more. If it is greater than 6sf, the hearth extension needs to be not less than 20inches deep. (09IRC 1001.10 per CodeCheck)

ONE TEAM - ONE FIGHT!!!

Mike

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Which edition of Code Check?

The IRC has two sets of requirements for masonry units, depending on how large the fireplace opening is.

If the opening is less than 6 square feet, the hearth extension need only extend 16" in front of the opening and 8" to either side.

If the opening is 6 square feet or more, the hearth extension is supposed to extend 20" in front of the opening and 12" to either side.

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Mine is from 2007 and is per NFPA 211 (12.5.1.2). No mention of the size of the opening.

Does that apply specifically to manufactured fireplaces?

No, this is under Fireplace stoves (solid fuel). I see nothing specific to manufactured or masonry site built units, at all.

I found it in the building section. I had been in the HVAC section.

Sorry, Marc. I think I need a newer edition to learn to look in the right place.

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The numbers that Mike & I cited refer only to masonry fireplaces. If that's a factory-built fireplace, then there are no IRC perscriptive sizes for the hearth extension and we're back to the need for the installation instructions as Marc mentioned at the get-go.

Couldn't you send an email to Majestic?

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The numbers that Mike & I cited refer only to masonry fireplaces. If that's a factory-built fireplace, then there are no IRC perscriptive sizes for the hearth extension and we're back to the need for the installation instructions as Marc mentioned at the get-go.

Couldn't you send an email to Majestic?

I could but probably wouldn't get a response before this report is sent out.

Should of done that last night. It's manufactured. The brick is an adhered thin veneer.

Marc

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Marc, the newer 36" models call for a 16" hearth in front. You might want to take a look thru a couple of those newer manuals yourself. A mantel shelf needs to have a foot of clearance but I don't know about the brick veneer without a mantel. Even so, the newer models won't be this model, so best to have it confirmed by an expert.

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Marc,

Manufacturer specs for hearth extension bases generally reference required R values for the material used. According to the CSIA if the extension is flush with the floor and if the subfloor underneath is not dropped down as viewed from the basement of crawl space then it's most likely going to be wrong. I have asked about this 2-3 times of the CSIA or their members and the answer is always the same as above.

This is one of those conditions where they get BillieBob out to evaluate and he'll usually say it's ok. Sorry to say that there have been times that I have not reported on it simply because I didn't want to get into some p---ing match over it.

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This house is built on a slab, flat with a brick shelf along portions of the perimeter.

While I'm here, the label had clearances for the bottom, sides and top of the appliance but no information on clearance to combustibles around the opening. Seems odd that they didn't specify that too.

Marc

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  • 3 weeks later...

As with all factory built fireplaces, the requirements are found in the listed instructions and not the code, which refers to masonry fireplaces. Often, 36" fireplaces only require 16" hearth extensions out from the Fp with as little as 8" to each side of the opening, whereas most other sizes require at least 20" out and 12" to sides. All factory built fireplaces require some form of insulative protection to combustible floors as stated in the manual. This used to be expressed in terms of k factor but recently the industry moved to R valves. Note that some large and very hot fireplaces may require even larger hearth extensions with even more insulative protection. Marc, there is only so much room on a rating plate and that plate is not a substitute for the full instructions.

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