Is the hearth from a gas fireplace enough for a stove?

[Planeweird]

Hey everyone,
I'm going to be putting a Jotul F 3 CB in the front opening of a fireplace for supplemental heating. I've got a 3000+ square foot, 3 story brick home. It's a 100 yrs old with no real insulation.
The radiant heater I use are great but the bills were HIGH this winter, so I thought I could off-set this with a stove on the first floor.
The first floor living room, dining room and kitchen equals 910 square feet and if I include the foyer(not including the double stairwell) its another 210 square feet. I can close off the foyer area with pocket doors and only heat the LR, DR, and K. And at bed time I can open a set of pocket doors and let the residual heat climb upstairs.

I thought about going with a larger stove, but want it to fit partially into the existing fireplace opening and also don't want to be run out of the living room.

Anyway, my question is this, the fireplace is currently plumbed for gas and may have always been so. However, it's shallow and it may also have been coal at one point.
I'll post photos shortly so you can get a better idea. I'll have to put some sort of hearth extension out in front of the stove to meet the 16" minimum frontal clearance. But do you think the tile underneath the existing firebox has a high enough R value for a stove? It's all flush with the surrounding hardwood floor and if possible I would love to be able to just lay a very thin extension piece under the front half of the stove. If my measurements are correct, I'll have 10" of existing tile in front of the stove, so I'm only short 6".

Thoughts?

 

[jtp10181]

Under the firebox? Or in front of? Anything inside the firebox of a masonry fireplace should be all masonry with bricks and such, not tile. If its front, my best guess would say its tile on top of wood which is not good enough for a stove.

 

[Planeweird]

Here's a picture of the fireplace as it currently is with gas logs. An F 3 CB will fit about 4 inches into the opening, and that will leave green tiles under the entire stove PLUS 10" of green tile out in front of the stove.

Sorry the picture is so small. My phone takes tiny pics.

 

[Planeweird]

Anyone? Anyone?

 

[begreen]

A wood stove can radiate a lot of heat on the floor in front of it. The stove will require 18" of hearth in front of it. The hearth needs to be insulated to R=1.1 under and in front of the stove. The mantel clearance, if wood, will need to be taken into account too. There may be enough clearance, but it's good to check in advance. You can download the F3CB manual from Jotul's website. That will have the full hearth requirements.

Also note, I suspect the stove will need a new flue system instead of the current flue if it's gas only or if there's a full existing chimney it may only need an insulated liner. This will depend on what is currently there. A certified chimneysweep or installer can determine this with an inspection.

As an alternative, perhaps there is a different location where there is more room to put a larger stove that will provide more heat with less frequent feeding. The 3CB is a great little stove, but in this case it will only be an area heater and will be challenged when the temperature drops low.

 

[Planeweird]

Begreen,

Thanks for the reply. Yes, I am about 6" shy on mantle clearance and will be fabricating a powder coated sheet metal shield with a 1" dead air space to place under the mantle lip.
The F 3 CB require 16" in front of the stove and I will have to make an extension to make up the last 6" in front. I wonder if that extra still needs that high R value or if the heat dissipates substantially out front and low like that. If not, by looking at my photo, what would you try?

Also, I was wondering about the R value of the green hearth tiles directly under the stove. Because it is gas and PERHAPS coal in the past, would you imagine that those base tiles are sufficient?

As for the liner, I will be running a rigid T with a 45% then to a short verticle rigid past the current flue opening. I'll then attach a 6" x 30' 316TI flex liner for the remaining length. It will also be rapped in an insulated blanket and I'll have a damper valve since I anticipate that draft will be strong. Does the chimney setup seem about right?

I don't really have any other options for placement, nor do I really want to. I'm hoping that since I can close off these 3 main rooms(910sq ft) it will do nicely.

I appreciate any and all input. I AM concerned about the hearth being sufficient mostly.

 

[Todd]

Can you pull up a tile and find out whats underneath? My guess would be it's not enough R value and you will have to build something else.

 

[Planeweird]

I should be able to do that. Good idea. What makes you guess it wouldn't be enough?
And actually, I had a house a block away before I bought this one that I tore the hearths out of two fireplaces and poured concrete in them, and under the tiles was a layer of brick and then many inches of dirt/sand. This current house was built the same year(1910) and in the same neighborhood. Perhaps they are the same construction type. In which case, I wonder what the R value is of the brick layer and the soil underneath.

 

[Planeweird]

BeGreen,

I forgot to mention that the existing chimney is made up of three flues. Each on is about 8x12 but I haven't seen if they are clay lined or not. It may just be brick all the way down. There is one for the living room, one for the master bedroom, and the third? I have no idea.

 

[begreen]

Sounds like you have been thinking the installation through correctly. The hearth concerns are valid. Check with the Jotul dealer and your inspector re: hearth requirements in front of the stove. The laws changed and now require 18" in front of the stove door. I can't recommend taking a chance on the hearth in front of the stove. Often that is hotter than under the stove (where there is an ashpan and heat shield). The stove will radiate a lot of heat in front of it. We have 18" of hearth in front of the stove and the floor 24" in front of the stove still gets quite hot. Also, sparks pop out when adding a new log, etc.

When the fire has been raging hot and the stove has been at 650 for several hours, you will be thinking about those few inches of protection. Best to get it right from the start or pick a stove with lower hearth requirements. For example, the F400 only requires a non-combustible hearth if there is a bottom heat shield installed under the ashpan. That would still require extending the hearth, but it could be done so that it looks like an intentional border to the existing hearth.

Start with careful investigation. Is there a crawlspace or basement under the fireplace and hearth so that you can see how it was built and supported? Some houses have the fireplace base extended under the hearth. If so, that may be a good sign. However, if it might just be supported by the flooring underlayment and a backer board. That would not be good.

 

[jtp10181]

Its not technically a "gas" fireplace right now, its seemingly a wood fireplace with a gas log installed. Technically the hearth should be fairly robust to meet code for the wood fireplace, but often times it is just tile on top of wood sub-floor.

The R vale of just the ceramic tile is next to nothing, nothing worth considering anyway. If there is brick underneath and then sand, that would be worth figuring out the numbers on to see if its good enough.

The entire hearth needs to be built to the mfg specs for the unit. I have never seen one where different sections of it require different levels of protection. They usually take the max protection needed in any given spot and use that for the entire hearth in the specs.

 

[Planeweird]

Well I went in the basement and checked the support structure for the hearth. It seems as though its basically a "boxed" area cut into the floor joists that is filled with between 6-8" of brick, stone,sand/soil, or a combination of all of these. There are decking boards encasing the "box" of material and small arched joists supporting the whole thing. It seems well designed to carry the weight of the brick/sand/stone. With 6-8" of thickness, I'm pretty comfortable with the R value of the existing hearth. Now I just have to figure out what to do about the 8" of hardwood that will be unprotected in fron of the stove. It sucks that the stove calls for an R1.1. If I want a nice clean look, I guess I don't any choice but to build on top of the existing hearth so that I get that extra 8".

 

[edthedawg]

Sounds like you either get into a really complex and risky piece of surgery to extend the deep protection, or you build a hearth over the existing tile work. You COULD go to the trouble of matching the tile, cutting out the hardwood, piecing in a sheet of micore and a sheet of Durock, and then the new tile, but you'd have to go very deep into the floor (over an inch) to make that work. if you DO go that route, take it from me - go a LOT larger than you think you need to. You'll be happy you did.

I extended my tile inlay work and THEN realized (too late) that I hadn't gone nearly big enough, and wound up burying all my hard work under a raised hearth... *sigh*.

 

[Planeweird]

Ed,

I agree completely. Cutting into the floor and matching the tiles is my preference, but inspecting closer, I realize that the green hearth "tiles" are in fact large bricks with a fire glazed green topping on them. SOOOOo.....that would require my pulling them up and replacing ALL of the hearth to get a level and color matched appearance. I think I will just micore/durock/tile right on top of the existing hearth from the back of the firebox out onto the wood to get what I need. I found some nice saddle brown quarry tiles that will blend in nicely and then I'll trim it out to match the herringbone patterned oak floors.

By the way, yours looks great even if it did take more work than you wanted. Who are you an engineer for? I went to Embry Riddle and am a pilot.

BeGreen,
Since you have an F 3 CB, do you think that it will be sufficient to "space heat" my three rooms downstairs(910sq ft)?

 

[Todd]

Just thought I'd throw this out there. A Woodstock Keystone or Palladian stove only requires an 8" front heart clearance since it's a side loader, but requires a 16" side clearance. Maybe it would fit without having to extend hearth?

 

[Planeweird]

Unfortunately, no those wont fit in the opening and if they sit out front, they are too deep for the available hearth. Thanks for the suggestion though. But they sure are pretty aren't they. Man!

 

[edthedawg]

Thx for the compliments. I had to bury the nice one w/ the raised one both fast and cheap. Here's before, nice, and as it sits now... (see attached - unfortunately out of order...)

The inset tile work cost us hundreds and took a few weeks to cut the floor properly, then cut, arrange, set, and grout the tile. The raised hearth, in all, cost under $200 and was done in a weekend.

I'm an engineer for P&W;. Turbine airfoil repair. What do you fly?

 

[Planeweird]

Well I'm definitely a P&W;fan but I fly a turbo commander with Garrett engines. Noisy buggers.