RAISING HEARTH UNDER ZERO-CLEARANCE FIREPLACE - INSTALL IS TOMORROW!!! PLEASE READ MY UPDATE POST A

[njkev]

Hi group,
My new EPA Phase II High Efficiency Heatilator Constitution "Zero Clearance" wood burning fireplace will be installed in a couple of days. I want to raise the hearth under the fireplace by about 8" before the installer arrives. (The extended hearth will be raised by the same sometime later of course.) What is the BEST way to raise the hearth under the fireplace? I was considering either 2x8 lumber or four 16x8x8 cement blocks (one on each corner), and then either 3/4 Plywood or 1/2 cement board on top of that. The 2x8 lumber method is obviously required more work but would be a sound structure since it will be nailed or screwed into the existing framing and allows an extended hearth to be easily mounted too. Which method is preferred, or is there another one I am over-looking?
Thanks,
Kevin

 

[RocketMan]

Hey Kevin,

Don't know how much help I can be, but I'll tell you what I'm doing...

I'm anxiously awaiting the arrival of my Northstar fireplace and have started the demolition of my gas fireplace, and rough framing for the new one. I'm using 2x8's (4 of them) under the fireplace, and extending out to the hearth (north-south) 16 inches. An additional 2x8 will then be attached to the extensions (east-west), forming the front of the hearth extension, and another 2x8 nailed to the wall forming the back hearth extension. On top of all of this, and the hearth end caps, will be covered with 3/4" plywood. My plan is to raise the hearth to just under the face plate (5 3/4 inches). I haven't figured out how I'm going to do this yet, as only non-combustibles are allowed in this area.

I hope this helps. Don't forget to take some photos!

Kirk

 

[njkev]

Hi Kirk,
Thanks for your response. Congrats on your "Northstar", my "Constitution" is the sister model! I just did my demolition of my Superior wood fireplace and chimney pipe yesterday during Tropical Storm Hannah!

I think we have a similar look in mind except that I want to either tile or stone the entire 5 3/4" area under the fascia (face plate), while you intend to raise your hearth extension to just under the bottom of the Fascia (for a ~14" extension height?). Please correct me if I misunderstand though, you are extending the 2x8's from the back of the chase through the opening by 16" (for a total of 40", or 43" if adding in the end cap depths) as to create the raised hearth & hearth extension as a single platform. Don't you need a total of 44" to cover the 24" depth of your hearth and the 20" for the hearth extension? I would seem you are short by 1". (BTW...actual 2"x8" lumber dimensions are 1 1/2" x 7 1/2").

I was considering to do the single platform too...until I realized that I have to add at least 1" to 2" of cement board and Micore, and then another 1 1/2 inches if I opt for a stone hearth extension instead of tile. It would only leave ~2" remaining area under the fascia for which to stone. Therefore, I am holding off on the hearth extension until I know for sure what the Boss (my wife!) wants.

Kevin

 

[RocketMan]

Hey Kevin,

My hearth math is: 16" extension + 1.5" 2x8 + 1/4" scratch coat + 1.5" stone = 19.25" with a 3/4" overhang of the 20" hearthstone. You're right in I'll have to build up the entire hearth to match the non-combustible portion of the hearth. Perhaps it would be smarter to build the left and right wings separately to match the built-up center section. This could be easily done with 2x4 "stub walls". You've got me thinking...

Kirk

 

[njkev]

Hi Kirk,
Are you doing a stone, tile, or marble surround? Did you notice the 60" mantel height requirement?? I have been talking with another guy in this forum with an installed "Northstar", and he told me he originally had his mantel up at 60" but it looked like sh*t! He since lowered it down to 4" above the highest point of the arch. He has monitored the temp over the past 2 years, and has NEVER seen it any higher than room temperature with a ROARING fire! I will likely put it 6" above the arch for additional peace-of-mind though. In fact MOST manufacturers seem to allow the mantel at 6" from metal as long as the depth of the wood of the mantel does not exceed 1 1/2".

BTW...how much are the "Northstar" units up in Minnesota? The shops here in NJ are asking manufacturer's suggested FULL retail. I priced my "Constitution" at four local shops.....all wanted $4613! Interestingly...I priced the unit at $3800 including delivery (within Montana) at $3800! Seems as though they are gouging here in NJ!
Kev

 

[RocketMan]

I'm am going with the Owens Corning Dressed Fieldstone in the Bucks County color, and using their hearthstones. Yeah, I noticed the mantel height requirement. It does seem kind of high. In fact, I'm searching for some kind of cultured stone that could be used as the mantel shelf/cap. I have 18 foot ceilings and do not want to run the stone up that high (cost/weight/perhaps overbearing). So my plan is to run the shelf/cap the entire width of the stone with a small overhang on each side.

The old 6000 gas fireplace has found a new home at my mother-in-law's lake cabin. I plan on practicing my stone laying skills on her fireplace.

The fireplace prices varied greatly from dealer to dealer. One dealer was over retail, another would go 10% off, and the guy I went with matched Obadiah's price (with shipping), and beat them on the pipe!

Kirk

 

[njkev]

Hi Kirk,
Thanks for the info. I am not committed to tile or stone at this point. I'll let the wife decide on it. So your hearth extension is going to be about 14" high then?

 

[njkev]

All,
I have decided to use four (or so) 8x12x16 cement block to raise the hearth 8" under the fireplace. I am still not sure whether to use 1/2" Durok or 3/4" plywood on top of the cement block. I prefer to use the Durok because it extends the non-combustible properties of my hearth, while the plywood sort of defeats the purpose! However, I am concerned that the Durok will stress and "crack" when the installers place the full weight (600 lbs or so) on it. The unit is a ZC, but I will have peace of mind with the added isolation from the wood framing. Anyone have any thoughts?

 

[njkev]

Hmmm.....alot a reads on my post but not getting a whole lot of advice.

 

[M1sterM]

All,
I have decided to use four (or so) 8x12x16 cement block to raise the hearth 8" under the fireplace. I am still not sure whether to use 1/2" Durok or 3/4" plywood on top of the cement block. I prefer to use the Durok because it extends the non-combustible properties of my hearth, while the plywood sort of defeats the purpose! However, I am concerned that the Durok will stress and "crack" when the installers place the full weight (600 lbs or so) on it. The unit is a ZC, but I will have peace of mind with the added isolation from the wood framing. Anyone have any thoughts?

Durock has just about no structural strength, so I'd be pretty worried about relying just on that. How much space will be between each brick? Can you build a solid base of blocks, with no gape between, and then lay the sheet of Durock over it?

 

[njkev]

Each pair of block covers the 24" of the chase depth to the front edge of the fireplace opening perfectly. The fireplace opening is 46" wide, so there will be roughly 14" between each pair of block. I might put one more centered between the four block for added stability.

The required width is 41" wide, so I could add a 2 x4 to the left and right side of the opening to reduce the width to 43"; thereby reducing the gap to 11". I could then add two additional block, a 8x8x16 and 8x8x8, thus further reducing the single 11" gap to two 1 1/2" gaps.

BTW, my chase is external and does not go to the ground level; it is supported by the house framing only. The fireplace is roughly 600lbs by itself, and I am reluctant to add more block than necessary.

 

[gpcollen1]

If you really need to raise it, why not just mix and pour a few bags of concrete??

 

[njkev]

Mixing concrete is a lot of work. Besides....(as I've stated)....The unit is to be installed tomorrow, and much time for concrete to cure.

 

[wellbuilt home]

You could either use the 8 x8 x16 blocks or 2x8 with ply wood and nail the hearth on the front later, make your hearth the same size as the shelf on the mantle . You could use a stone shelf set in the CS stone with stone corbels to hold it up We use real stone that matches the cultured stone to make a arch over the fire box opening. You could end the stone work with the same arch with a key stone in the center .

 

[njkev]

Thanks for the advise "WELLBUILT HOME".

I set up the hearth under the fireplace with four 8x12x16 cement blocks, one centered 8x8x16 cement blocks, and 3/4" plywood on top. I never realized that the length (16") and width (12") of a cement block are actually 1/2" reduced same as lumber! The height dimension however is a true 8". One the unit is installed I intend to surround the fireplace with 1/2" Durok cement board. Roughly what distance to the left, right, and above the arch of the "Constitution" fireplace do you recommend I use the cement board assuming I want to add either a marble or stone surround?

I noticed that people that did not have a raised extended hearth put stone work or tile on the 6" below the fascia. But people that do raise the hearth generally do not put stone work or tile below the fascia, and simply raise the extended hearth just under the fan outlet. My wife insists that she wants BOTH the raised extended hearth and either stone work or tile on the 6" area below the fascia? Is that sound reasonable? Are there any reasons NOT to do it that way? I calculate that the extended hearth height will be roughly 9 1/2" with tile, and about 11" if she decides on 1 1/2" stone slab instead. If she decides in the end that she does NOT want the stone under the fascia, then the height of the extended hearth could be as high as 16" assuming 1 1/2" stone slab! That would be one hell of a high hearth

BTW....Do you happen to have any photos of the stonework you had described in your previous post?
Thanks,
Kevin