Need Advice / Help!

[JW79]

Hi - I'm new to the site. Looking for some advice...Please see the attached pics. I currently have a Lennox/Marco prefab and I want to install the Hampton H300 freestanding woodstove with the short-leg conversion kit that I have already purchased.

I have received a few estimates and the plan is to vent my woodstove through the prefab by installing a new 5 1/2 or 6" insulated liner (approx. 25ft chimney). The prefab is a zero clearance with an 8" flue. My H300 has a rear vent plate and we would use a T / 90 degree to attach. I would also install a metal surround to cover the prefab.

My problem is my current brick hearth (which is on sub-floor, not cement) is not large enough to handle my woodstove. Also, the current brick hearth sits about 3" above the hardwoods, so even if it was large enough, I do not have the clearance (even with the short-leg kit) to vent into the existing prefab if my woodstove was sitting on the bricks.

My question: What options do I have to lower and extend my hearth? The boss (my wife) loves the look of the brick and white mantel, so I'm trying to do as little demo/construction as possible. Trying to keep it simple on a budget.

My initial thought was to remove the verticle and 1st horizontal row of bricks. Install a piece of Wonderboard or Durarock that would bring me flush with my hardwood floor, then install 1" thick marble or slate. The marble/slate would sit on the wonderboard/durarock and my hardwood floor. This would give me about a 2" drop for the clearance and still keep the woodstove fairly close to the prefab. I didn't want to have my woodstove sitting in the middle of the room! That is why I would remove a few layers of the existing brick hearth, instead of simply placing the marble/slate in front of the brick that is there now.

Would this work? Any other suggestions? Any help would be greatly appreciated. Thanks in advance.

 

[begreen]

Welcome JW. Read the manual closely here. Additional heat protection is needed for the short leg kit. I think there will need to be a layer of .5" Micore under the cement board. Also, is there 57" clear between the two white mantel support legs? The stove needs 15" clearance to combustibles and is 26 7/8" wide.

A minimum of a 1/2" thick thermal floor protector with a 0.84k factor is required when installing the standard or optional short legs. This applies to
both Canada and the US. All other requirements (ie. hearth size) remain the same.

 

[Jimbob]

The EASIEST would be to look for an insert that is approved for install inside the pre-fab fireplace. It will heat well, and you wouldn't have to disturb anything else.

 

[pyper]

A K value of .84 for 1/2 inch = an R value of .6, right?
A brick, on edge has an R value of .4 I think.

This isn't stacking up too well.

What's under the existing hearth? Maybe you could tear it out, along with the correct amount of flooring, and reframe it to allow the proper non-combustible surface at an elevation that will work?

 

[JW79]

The EASIEST would be to look for an insert that is approved for install inside the pre-fab fireplace. It will heat well, and you wouldn't have to disturb anything else.

I put the cart before the horse...I love the look of the freestanding woodstoves. I was able to purchase an H300 for a great price and it is sitting in my garage now.

 

[JW79]

Welcome JW. Read the manual closely here. Additional heat protection is needed for the short leg kit. I think there will need to be a layer of .5" Micore under the cement board. Also, is there 57" clear between the two white mantel support legs? The stove needs 15" clearance to combustibles and is 26 7/8" wide.

A minimum of a 1/2" thick thermal floor protector with a 0.84k factor is required when installing the standard or optional short legs. This applies to
both Canada and the US. All other requirements (ie. hearth size) remain the same.

Could I address the required thermal floor protection with a Hearth Classics Pad from Yoders?

 

[JW79]

A K value of .84 for 1/2 inch = an R value of .6, right?
A brick, on edge has an R value of .4 I think.

This isn't stacking up too well.

What's under the existing hearth? Maybe you could tear it out, along with the correct amount of flooring, and reframe it to allow the proper non-combustible surface at an elevation that will work?

I just found the Hearth Classic Yoders website. I wonder if some existing brick removal and the installation of one of their custom pads would work?

 

[begreen]

That should work. They make a decent hearth pad.

 

[Wade A.]

JW79....I would be one to chime in with all who have noted the hearth R values, hearth dimensions, and distance to combustible requirements for your particular stove. Your options are going to have to be within those limitations if you want a safe burning stove. But you know that already, right? Right.

That said, the easiest way to get your R value of the hearth up, without excessive height build up, is to use mineral board as an underlayment. You can sandwich that between a couple layers of durarock with some thinset mortar and your deflection will be minimal. If you want to top that with stone, look up the R value for that, by thickness. A layer of aluminum roof flashing will also give you a good degree of thermal insulation/reflection. Will you be able to lower the height of the existing brick hearth and still get your R value where you need it to be? I'm doubtful of that, frankly. But, do your calculations of R value and see what thickness you wind up with. I take it that your subfloor material/thickness is already known? If not, that will be known only after you take up a course of bricks.

 

[JW79]

JW79....I would be one to chime in with all who have noted the hearth R values, hearth dimensions, and distance to combustible requirements for your particular stove. Your options are going to have to be within those limitations if you want a safe burning stove. But you know that already, right? Right.

That said, the easiest way to get your R value of the hearth up, without excessive height build up, is to use mineral board as an underlayment. You can sandwich that between a couple layers of durarock with some thinset mortar and your deflection will be minimal. If you want to top that with stone, look up the R value for that, by thickness. A layer of aluminum roof flashing will also give you a good degree of thermal insulation/reflection. Will you be able to lower the height of the existing brick hearth and still get your R value where you need it to be? I'm doubtful of that, frankly. But, do your calculations of R value and see what thickness you wind up with. I take it that your subfloor material/thickness is already known? If not, that will be known only after you take up a course of bricks.

Thanks for the info.

I'll go back and measure again for my combustible material clearances. I agree, I'm afraid mineral board + 2 to 3 layers of Durarock + mortar + stone = is going to be too thick. Unsure of subfloor thickness, probaby 1/4 or 1/2 plywood. I wanted to have a code approved game plan before tearing up the bricks. I may need to though...

Any other suggestions?

 

[Wade A.]

The only other plan I might consider would be to knock a hole above the lintel of your fireplace and run your connector pipe directly to your flue. That might save you a lot of time and money in the long run. Frankly though, if I'm understanding your description, all you have currently is a double thickness of brick between your proposed stove site and the wooden sub-floor. You can look up the R value of brick, and match that against your stove requirement, but it might be that the hearth as it exists might not be suitable.

Which leads me to ask: What is beneath the sub-floor? Are you over an airspace of any depth that would permit you to build a masonry pad from below?

 

[Wade A.]

Oh, and forgot to ask: How many inches do you currently lack to get your connector pipe under the firebox lintel and up the flue? You say the short leg kit won't even give you that? I had a stove once where all I needed was 1/2" off the short legs to get to my flue. Out came the hacksaw. Of course, your hearth insulation needs to be beefed up as well in those situations.

 

[JW79]

The only other plan I might consider would be to knock a hole above the lintel of your fireplace and run your connector pipe directly to your flue. That might save you a lot of time and money in the long run. Frankly though, if I'm understanding your description, all you have currently is a double thickness of brick between your proposed stove site and the wooden sub-floor. You can look up the R value of brick, and match that against your stove requirement, but it might be that the hearth as it exists might not be suitable.

Which leads me to ask: What is beneath the sub-floor? Are you over an airspace of any depth that would permit you to build a masonry pad from below?

I haven't removed any bricks yet, but I believe it is only 1 layer of bricks then 1/2 inch of wooden plywood sub-floor?

I checked the unfinished side of my basement (the fireplace room is above the finished-side) and my floor joists are 2x10's on 16" centers running horizontal to my prefab & hardwoods (see pic in initial post).

 

[Wade A.]

The more I hear, the more I'm thinking that the suggestion to go with a hearth pad is the easiest and cheapest option. Knock back the hearth brick a course or two, come level to the finished floor with some durarock and "viola...." Not the most attractive option, I grant you.

 

[JW79]

Oh, and forgot to ask: How many inches do you currently lack to get your connector pipe under the firebox lintel and up the flue? You say the short leg kit won't even give you that? I had a stove once where all I needed was 1/2" off the short legs to get to my flue. Out came the hacksaw. Of course, your hearth insulation needs to be beefed up as well in those situations.

Only about 3/4" to clear. I would say 1" to be safe.

I'm thinking a hearth pad that meets code might be the answer? I'm doing research now online. It all depends on how thick the pads are?

 

[pyper]

I wanted to have a code approved game plan before tearing up the bricks. I may need to though...

Any other suggestions?

Your bricks are not sufficient protection on their own. You can't really devise a plan until you remove them and find out what's under them. Well, you can devise a plan, but you won't know for sure if it will work until you get the bricks out (or find some other method of determining what's under them.

Probably what you're going to need to do though is tear out the bricks and carefully cut out the flooring in an area equal to the minimum hearth size for your stove. Then trim down the tops of the studs, sister 2x2 ledgers (3/4" down from the top edge), install 3/4" ply (flush with the top of the joists), and then three layers of durock covered with tile. Or no durock covered by one of those Yoders hearth pads. The tile pads are 1 1/4 inches. Your floor is probably 3/8 with a 3/4 subfloor. So you'd need to remove 1/8" off the top of the joist, plus however much you need for clearance.

Fortunately, it's a really inexpensive job to do yourself, if you have the tools.

 

[JW79]

I wanted to have a code approved game plan before tearing up the bricks. I may need to though...

Any other suggestions?

Your bricks are not sufficient protection on their own. You can't really devise a plan until you remove them and find out what's under them. Well, you can devise a plan, but you won't know for sure if it will work until you get the bricks out (or find some other method of determining what's under them.

Probably what you're going to need to do though is tear out the bricks and carefully cut out the flooring in an area equal to the minimum hearth size for your stove. Then trim down the tops of the studs, sister 2x2 ledgers (3/4" down from the top edge), install 3/4" ply (flush with the top of the joists), and then three layers of durock covered with tile. Or no durock covered by one of those Yoders hearth pads. The tile pads are 1 1/4 inches. Your floor is probably 3/8 with a 3/4 subfloor. So you'd need to remove 1/8" off the top of the joist, plus however much you need for clearance.

Fortunately, it's a really inexpensive job to do yourself, if you have the tools.

Great info, thanks!