Rebuilding Hearth for Keystone Woodstove

[Ebeth B]

Hello all! I am readying my hearth for Woodstock's Keystone woodstove, and want to make sure I'm on the right track. Let me know if this isn't the best place to post my questions (seemed like the best fit).

First of all, the existing brick hearth (unchanged since 1929) is uneven, and the cement under the bricks is badly cracked. Additionally, there are some cracks in the bricks that surround the firebox. My plan is to remove the bricks of the hearth, patch the cement underneath with thinset (making sure it's level), put the bricks back down, and then build a hearthpad to go over the whole shebang (since the current hearth is only about 20" deep).

Is this the best way to deal with the cracked cement and uneven hearth? Any further suggestions?

I also have one question about the keystone installation. The horizontal metal bar that's in the firebox is located 27.5 inches from the current hearth. The center rear flu of the keystone is 22.75. Since it's a 6 inch flu (with converter), this will leave 1.75 inches from the top of the flu and the metal bar in my fireplace. I can build a hearthpad that's 1.25 inches, which leaves just half an inch of clearance. Is this ok?

Thanks in advance for any advice! This is my first time working on a hearth and installing a woodstove, so I need all the help I can get.

 

[Ebeth B]

Oops, meant to say 'flue', not 'flu.

 

[zzr7ky]

Hi -

I did a very similar install in 2006. I have <1' from horizontal 6" vent to my lintle. It works fine.

Mike

 

[lumbering on]

I actually emailed Woodstock when I was thinking of putting in a Keystone. They were happy to walk me through what I could do to rebuild my hearth to make it woodstock friendly. They wanted pictures and everything. Give them a try.

 

[Ebeth B]

Ok, will do. Thanks!

 

[begreen]

I think you will want to set the brick in mortar and not thinset. Note that the Keystone only needs 8" of hearth in front of the stove because it's a side loader.It looks like you may be able to recess the stove slightly and not need to extend the hearth. You will need to still be able to open the side door, so measure from the front of the stove to check. Making a cardboard mockup can help with layout. And for sure, discuss this with Woodstock.

In the chimney, plan on installing a damper sealing block-off plate. That will keep more heat in the room.Here are some instructions.
https://www.hearth.com/talk/wiki/make-a-damper-sealing-block-off-plate/

PS: Welcome to hearth.com!

 

[Woody Stover]

My hearth is 25" and the 'stone was right at the 8" clearance from the bottom front edge of the stove down to the edge of the hearth. Connection was flue collar, 7-to-6" reducer, tee with 8" snout (I think,) flex liner to the top. Will you have a full-length stainless chimney liner?
As long as you have enough clearance under the lintel to have a rise of at least 1/4" per foot of pipe, you're good.

 

[rideau]

With my Fireview, I had exactly 8 inches in front of the pad. Wish I had had more. The hardwood floor got way too hot for my liking...I believed that over time I'd have major issues with the floor becoming compromised. I always kept at least one sheepskin rug for insulation on the floor overlapping floor and hearth. So I would strongly advise building a good hearth that will give you 12 inches in front of the stove, with the stove fully in the room for better heat. It is what I would do were I doing the install today. Otherwise get yourself a nice sheepskln rug.

 

[Todd]

I'm pretty sure the Keystone requires 8" clearance in front only if you use the 7" exhaust. When you reduce that exhaust to 6" the front clearance increases to 10". I don't know if Woodstock has made that change in their manual.

 

[begreen]

Not yet, I checked right before I posted.

 

[Woody Stover]

I'm pretty sure the Keystone requires 8" clearance in front only if you use the 7" exhaust. When you reduce that exhaust to 6" the front clearance increases to 10". I don't know if Woodstock has made that change in their manual.

What's the deal on that? More heat going up the flue on the bigger pipe?

 

[Todd]

What's the deal on that? More heat going up the flue on the bigger pipe?

This came up last year, I emailed Woodstock about it and they said it just tested out that way and they were working on an update for the manual.

 

[rideau]

I would guess that with the smaller chimney you get a stronger draft at the same air setting, thus getting more oxygen in the stove and the potential for a hotter burn.

 

[TheBean]

Todd is correct. 8" hearth clearance in front with 7" pipe. 10" hearth clearance in front with 6" pipe. This is based on the official testing when we certified the stove with 6" pipe. Please remember the listed clearances are MINIMUM clearances. I would always recommend trying to exceed the bare minimums if at all possible. The manual is being revised as we speak. We will happily provide the 6" certification info. to anyone who needs it for installation approval. Just give a call.

 

[Ebeth B]

Thanks for all the input! We are planning on using the 7" to 6" converter from Woodstock as well as a full-length stainless liner. I contacted a local chimney expert, and he recommended a rigid stainless steel liner. However, I've heard that the flexible liners are better for wood burning stoves because they expand and contract with the heat and collect less creosote. Thoughts?

In terms of the hearthpad, I am now planning:
1. Spray a concrete adhesive on the current, cracked and uneven cement base
2. Level the base using leveling cement
3. Apply a layer of thinset
4. Lay slate tile over that
5. Now that I have a level hearth, I can build a simple hearthpad for the keystone. I'll give the stove a good 12" of space in front just to make sure the hardwoods won't get too hot. Plus we just might invest in a sheepskin rug, just to be sure

How does this plan sound? Thanks for the great advice!

 

[Ebeth B]

Another quick update: A section of the cracked concrete came up easily with a chisel. Underneath is some rather old looking brick. Should I remove everything down to the brick level and pour a new bed of concrete on top of that?

Thanks.

 

[begreen]

Yes, if the cement comes out easily remove it. That should help get a more level bed and I think at this point you'll get a better bond against the freshly cleaned surface of the brick. I am not a mason but I think it helps to spray the cleaned brick with water first to get good adhesion. Ask around.

 

[Woody Stover]

I contacted a local chimney expert, and he recommended a rigid stainless steel liner. However, I've heard that the flexible liners are better for wood burning stoves because they expand and contract with the heat and collect less creosote.

The way I understand it, draft is slightly better with the rigid and slightly less creosote sticks to it since it is a smoother surface. It's cheaper as well (than the HomeSaver RoundFlex I used, anyway.) I would have gone with it but my chimney isn't a straight shot and it was easier to negotiate the bend with a liner. I also put insulation on the liner. You might get away without it if your chimney isn't on an outside wall but in any case it is extra insurance, so I would do it if you have the room inside your masonry chimney.

 

[elmoleaf]

I'd be wary about putting the weight of a new woodstove on that hearth extension without first understanding if it's structurally sound.
Generally, the hearth extension that supports the brick you're removing is reinforced concrete cantilevered from the chimney structure. It appears your hearth extension is undergoing structural failure (sagging) and thus the displaced brick at the fireplace front.
Go down your basement and get some pictures of this area from below.

 

[Ebeth B]

I went down to the basement and took some pics. It's hard to see what's going on down there because there is a bunch of insulation covering the bottom. Is this normal? There are two metal floor supports (to keep the floor from creaking) installed by the previous owner on either side of the hearth. Perhaps these caused the sagging? Also, I have no idea why that tube goes straight through the chimney (our house inspector had never seen it before!)

Does this look structurally sound to you all? Perhaps it's time to get a mason to come by just to make sure. Thanks!

 

[elmoleaf]

Definitely get a mason or other qualified building professional. Rigid foam should not be left exposed indoors. It is a fire hazard. It needs to be removed anyway for the mason to see what is happening with the hearth extension.
The HVAC duct running into the oversize thimble is very odd. The home inspector give you any advice about having someone review that?

 

[begreen]

First time I've see 'structural' foam. Looks pretty half-assed as does the duct heading into the thimble.

 

[Ebeth B]

Thanks for your advice, I'll call a mason today! I'm glad we didn't just build the hearth extension and put the stove on it, to be supported by nothing but foam...

A few people have looked at the duct going through the chimney, including a chimney expert (who had also never seen it before). For whatever reason someone wanted to go through the chimney instead of around it--it seems like more work to me! No one knows why they did that, but no one thought it was a problem either, so we're letting it be. Just another mystery in an old house.