Hearth build questions

[HollowHill]

Now that we have the clearances for the Progress, it's time to build the hearth, quickly. This is my first hearth build, so winging it and would appreciate the wise and experienced minds of hearth.com double checking me. With the ashlip, the r-value for the hearth is .4. The current hearth, which is flush (sort of) with the floor, is bluestone on top of concrete. But the hearth must be extended a fair bit over the wood floor (200 yr old pine). My plan is to use 1/2" Durock Next Gen and 1/4" porcelain tile laid over the existing hearth and the floor. I'm thinking this will give me .41 R-value (.39 + .02) and will be sufficient. Am I missing anything? Is anything else needed?

I'm trying to get the hearth as thin as possible because I don't think I have much room for the rear vent pipe to clear the lintel of my fireplace. The rear vent is 27.75" on center, which I think with 6" pipe would mean the top of the pipe would be at 30.75". I also need the pipe shield, which adds an inch to this, so now I'm at 31.75". I'm hoping my hearth will only raise the stove an inch, so now I'm at 32.75". Then, the pipe has to rise a 1/4" per foot and it has to go about a foot and a half or so, so I'm factoring in a 1/2" for rise. Now I'm at 33.25" and my lintel is 34". Have I got that right? Is there something I've forgotten to factor in?

Thanks.

 

[raybonz]

Now that we have the clearances for the Progress, it's time to build the hearth, quickly. This is my first hearth build, so winging it and would appreciate the wise and experienced minds of hearth.com double checking me. With the ashlip, the r-value for the hearth is .4. The current hearth, which is flush (sort of) with the floor, is bluestone on top of concrete. But the hearth must be extended a fair bit over the wood floor (200 yr old pine). My plan is to use 1/2" Durock Next Gen and 1/4" porcelain tile laid over the existing hearth and the floor. I'm thinking this will give me .41 R-value (.39 + .02) and will be sufficient. Am I missing anything? Is anything else needed?

I'm trying to get the hearth as thin as possible because I don't think I have much room for the rear vent pipe to clear the lintel of my fireplace. The rear vent is 27.75" on center, which I think with 6" pipe would mean the top of the pipe would be at 30.75". I also need the pipe shield, which adds an inch to this, so now I'm at 31.75". I'm hoping my hearth will only raise the stove an inch, so now I'm at 32.75". Then, the pipe has to rise a 1/4" per foot and it has to go about a foot and a half or so, so I'm factoring in a 1/2" for rise. Now I'm at 33.25" and my lintel is 34". Have I got that right? Is there something I've forgotten to factor in?

Thanks.

I had a bluestone hearth and removed it when I replaced my hearth. I then applied 2-1/2" layers of durock nexgen with thinset between all layers with all seams offset. Each layer was also screwed down with cement board screws spaced 8" apart. The bottom layer I used 1-1/2" screws and the top layer I used 2-1/2" (I am not 100% sure of the exact screw length I used but my posts of my install give accurate details) screws so all screws penetrated into the subfloor.. Can you post some hearth pics of your current hearth? If you search here I posted pics of the install as I went along..

Good luck!

Ray

 

[Waulie]

Ah, yes. The old hurry up and fix the hearth before the 700 lb rock arrives. I'm in the same boat.

So, you are rear venting? I don't believe the pipe shield is used for horizontal pipe runs. Why would do you need it? What are your clearnaces? I can't picture what you would need to shield the pipe from if you are rear venting straight into a flue.

Also, you forgot the thickness of the pipe itself in your measurement. Not much, but since you're close you might want to consider it. Your R-value calculation is correct. What is the concrete under the bluestone sitting on? How thick is the concrete? Also, with 200 year old pine floors I'd be tempted to extend the hearth a bit further than the minimum. A picture would be great.

 

[HollowHill]

Ah, yes. The old hurry up and fix the hearth before the 700 lb rock arrives. I'm in the same boat.

Yes, and at the last minute had to change from using bluestone (too thick) to finding a tile. It's been a scramble!

So, you are rear venting? Yes. I don't think the pipe shield is used for horizontal pipe runs. According to Lorin at Woodstock, the pipe shield can be used horizontally and has been tested that way for ceiling clearance issues.CORRECTION: Use of double wall pipe is recommended instead of using pipe shield horizontally Why would do you need it? What are your clearnaces? I can't picture what you would need to shield the pipe from if you are rear venting straight into a flue. The clearance problem I encounter that requires the use of the pipe shield is that the bottom of my wooden mantel is too close to the top of the pipe. With the pipe shield, the bottom of the mantel only needs to be 6" away from the top of the pipe shield, and it is more than that. I have moved the stove out from the opening of the fireplace by 10 inches in order to not have to worry about the top of the stove clearances to the mantel shelf. Once the mantel is not overhanging the stove, you don't have to worry about the 30" from the top of the stove to the mantel shelf (which I don't have), you only have to worry about the rear shield clearances to the mantel shelf - 7" (which I do have). This means the pipe is going under the bottom of the mantel, tho, and requiring clearance for that.

Also, you forgot the thickness of the pipe itself in your measurement. Not much, but since you're close you might want to consider it. Any idea what that might be?R-value calculation is correct. What is the concrete under the bluestone sitting on? How thick is the concrete? The concrete is on a wooden frame, but is quite thick, a foot or more. , with 200 year old pine floors I'd be tempted to extend the hearth a bit further than the minimum.Yes, planning on 10 or 11" instead of 8"A picture would be great. Will try to post that soon. Thanks for your reply.

 

[Waulie]

Sounds like your covered on the height and the clearances. 22 gauge pipe is not very thick. If you just add 1/8" to your measurement that will more than cover you.

The concrete is on a wooden frame, but is quite thick, a foot or more.

You've probably considered this, but I hope you have some beefy support holding this whole thing up. If you figure a 20 square-foot hearth with a foot of concrete, that's nearly 3,000 pounds! And another couple hundred for the tile, a 640 lb stove with a full load of wood, and you've got a lot of weight there.

 

[HollowHill]

Sounds like your covered on the height and the clearances. 22 gauge pipe is not very thick. If you just add 1/8" to your measurement that will more than cover you.

The concrete is on a wooden frame, but is quite thick, a foot or more.

You've probably considered this, but I hope you have some beefy support holding this whole thing up. If you figure a 20 square-foot hearth with a foot of concrete, that's nearly 3,000 pounds! And another couple hundred for the tile, a 640 lb stove with a full load of wood, and you've got a lot of weight there.

Good points and the vision of my new stove ending up in the basement haunts me. The original hearth is built into the chimney structure, so is already supported. I will not be adding any more concrete under the new hearth. I plan to "lay" the new hearth over the old hearth and the existing floor. So, the back of the new hearth will be on the old hearth, which has good support and the front end of the new hearth is on a big crossbeam that rests on a stone foundation wall, so that should be well supported. The span in between where the old hearth ends and the crossbeam is is about 2ish feet and I will have supporting posts into poured concrete footers to add support there. I'm hoping that will be enough.

 

[Waulie]

Good points and the vision of my new stove ending up in the basement haunts me. The original hearth is built into the chimney structure, so is already supported. I will not be adding any more concrete under the new hearth. I plan to “lay†the new hearth over the old hearth and the existing floor. So, the back of the new hearth will be on the old hearth, which has good support and the front end of the new hearth is on a big crossbeam that rests on a stone foundation wall, so that should be well supported. The span in between where the old hearth ends and the crossbeam is is about 2ish feet and I will have supporting posts into poured concrete footers to add support there. I’m hoping that will be enough.

Sounds like your probably fine. If you really wanted, you could measure that crossbeam and look up span tables online just to be sure. If the stove will actually be partially resting on the new portion of the hearth (and maybe even if not), you may want to try and not span the tiles over the transition between the old and new hearths. Adding significant new weight on the floor in the new hearth section will cause it to displace. Even though this wil be minimal, it doesn't take much at all to crack a tile. If possible, I would try to place a grout line along the transistion. If the grout line cracks, it can be pretty easily repaired.

 

[Backwoods Savage]

The Progress with the plinth should be (I was told) the same as the Fireview. I just measured and the top of the pipe is 26." If it is the same then you should have good clearance.