Correct. The hearth needs to extend at least 16" in front of the stove door, but there is no harm and some benefit to extending if further.
Drolet 1800i dimension issues
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The difference being that the Jotul and BK stoves were/are freestanding and this is an insert with no legs. I'm not sure there is an insert with a low R value hearth requirement for a flush hearth installation. The Sirocco 25 for example needs R=1.06 for a flush hearth install.
Easy Livin’ 3000
Minister of Fire
You are spot on, ash. I was pretty frustrated by the SBI requirements compared to others that I looked at. They must have a bigger team of lawyers. Can't fight it though. Just gotta follow the manual requirements.
Comparing freestanding to insert requirements is comparing apples to oranges. One has legs, the other doesn't. Likewise, a cast iron jacketed stove is going to have closer clearance requirements than some inserts. Not all inserts are designed the same; some have convective jackets on the sides and some have the bare steel of the firebox extending into the room. Likewise some inserts have convective tops and some have the stove top exposed. There are advantages both ways. Testing results have more to do with clearances than lawyers do.
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Easy Livin’ 3000
Minister of Fire
Right you are, begreen. If my memory serves me, I compared similar stoves when I was researching (fully jacketed steel inserts) when comparing. SBI seemed to have the "safest" level of clearances of most that I looked at. Not a complaint, just makes things more complicated to get to code.
The advantage is that the SBI inserts are a bit more radiant and one can cook on the top. I haven't run one, but would suspect that the SBI inserts are better than some for heating in a power outage with no fan running. The compromise is larger clearances.
Easy Livin’ 3000
Minister of Fire
Hadn't thought of that, a real positive. We do put a humidifier on ours, and plan to cook beans, soup, and chili in the future.
So there's multiple dimensions in the diagram. A is the dimension for the existing hearth extension measured from the fireplace opening. C is how far from the fireplace opening the insert's face is. B is the dimension that is constant depending on the hearth (raised within spec or not). D is the additional extension needed as necessary. The formula given is D=B-(A-C) and if it's 0 or negative, no additional extension is needed. Based on your photo, the distance of A-C is 10". B is 29". So D is 19". If you're going to use the Micore and have it start at the insert or even in the fireplace, it just needs to measure out 29" in front of the insert measured from the face.
When you look at page 35, notice is says Note 1 for dimension B in the table. Also note that the examples in the table are for a raised hearth. Here's the text for Note 1, found on page 37:
From door opening. The depth of the hearth extension in front of the insert is included in the calculation of the floor protector’s dimensions. The masonry hearth should be at least 4" (102 mm) higher than the combustible floor in front of it and a floor protection must extend at least 16" (406 mm USA) and at least 18" (457 mm Canada) with an R value of 1.24 or more. If the hearth elevation is lower than 4", the non-combustible (B) floor protector in front of the insert should have an R value equal or greater than 2.00 and shall extend 29" (737 mm) in front of the unit.
So let's break that down. The first two sentences in your case is the 10". The next sentence, since your hearth is not higher than 4", your extension cannot be 16". The next sentence applies to you, since the hearth is lower than 4", and it defines B as 29" with R value of 2.00 in front of the unit aka from the face of the insert.
Hope that helps.
Easy Livin’ 3000
Minister of Fire
A level installation requires 16" of 5" deep hearth slab in front of the stove, from the face. Plus, 13" (or) more of hearth extension, with a minimum of R=2. That's what the picture describes with zero ambiguity.
If the hearth slab is out more than 16", than less than 13" of R=2 extension is needed.
What is not described, is less than 16" of hearth slab at least 5" deep, in front.
1" of micore works, as long as it starts at least 16" from the face of the stove.
No matter how much you want to interpret the words to contradict the picture, the picture is perfectly clear.
Would you argue that 1" of micore on top of a wood floor could be the entire hearth slab?
If not, how much less than 16" would be ok?
Why even specify 16", if all 29" could be "extension"?
For the existing hearth, the only thing defined is the slab needs to be 5” thick. No particular depth is given.
The only defined depth is B, which is either 16” or 29” at the appropriate R value, which includes the existing extension.
I’ve asked this before, but what text in the manual says A has to be 16” deep and 5” thick? Not trying to argue, just wondering where this is coming from...what am I missing?
The only defined depth is B, which is either 16” or 29” at the appropriate R value, which includes the existing extension.
I’ve asked this before, but what text in the manual says A has to be 16” deep and 5” thick? Not trying to argue, just wondering where this is coming from...what am I missing?
It certainly remains clear as mud to me....
Whats the bottom line? 29" in front of the insert is clear, but how thick for how long?
Whats the bottom line? 29" in front of the insert is clear, but how thick for how long?
Unless someone can point out what I’m missing, thickness will be dependent on the materials used to get to an R value of 2.
Ashful
Minister of Fire
That is correct. The 5" number is an "if" statement, not a design specification. They say:
1. IF the hearth is raised 5" or more, then you need R 1.24.
2. IF the hearth is NOT raised 5" or more, then you need R 2.00.
Since your install is flush with floor, final material thickness will be whatever you need to get to R 2.00.
1. IF the hearth is raised 5" or more, then you need R 1.24.
2. IF the hearth is NOT raised 5" or more, then you need R 2.00.
Since your install is flush with floor, final material thickness will be whatever you need to get to R 2.00.
Easy Livin’ 3000
Minister of Fire
Here's the picture. For a level install hearth must be 5" thick and extend at least 16" in front of stove face. This is designated by the continuous slab in the picture and measurement "A".
What makes this confusing is the depth of the install is a variable (C). If it's a flush install, "C"=0, and A + D = B = 29.
So, a flush install requires at least 13" of R=2 protection beyond hearth slab.
An install that sticks out 2" needs at least 15" of the R=2 protection beyond the hearth slab.
This makes intuitive sense, as I believe they are trying to get 29" total of ember protection from the opening of the stove when loading, etc.
29" would be serious overkill. The math is wrong. In the US the hearth protection needs to extend at least 16" in front of the stove face. In Canada it's 18". Here is the table and formula for the calculation.
Note that there is no harm in extending the hearth protection further if more protection is desired or if it saves cutting a tile.
This isn't that confusing. Again, where does it say that A has to be 16"? Please point that text out. As I've stated, the only requirement for dimension A is that it's 5" thick.
C isn't confusing either, it's just the difference of where the insert's face is vs the fireplace opening. You're correct that A+D=B=29" ONLY IF the insert's face is flush with the fireplace opening. Once C is something different, the formula becomes D=B-(A-C) to account for the face not being flush.
If they performed the tests according to the UL standard, it is what it is, is it not? The table is for a raised hearth, hence Note 1 for dimension B.
Seems like the whole equation is void in this case. Its void because of note 1 on page 37. "From the door opening. The depth of the hearth extension in front of the insert is included in the calculation of the floor protector's dimensions(depth as in height above the floor, not thickness). The masonry hearth should be at least 4" higher than the combustible floor in front of it and a floor protection must extend at least 16" with an R value of 1.24 or more. If the hearth elevation is lower than 4", the non-combustible (B) floor protector in front of the insert should have an R value equal or greater than 2.00 and shall extend 29" in front of the unit.
That seems to void out everything else to me, that no matter what the equation produces I need 29" in front of the stove with an R value of 2.0.
To me, the best most logical permanent solution is to extend the hearth out that far. Given that I have about 10" or 11" already, I only need to extend the hearth 18" or 19".
For now I am just going to run a hearth pad. I got one from tractor supply. Its only got a R value of 1.5 but it will work for now as a temp solution.
That seems to void out everything else to me, that no matter what the equation produces I need 29" in front of the stove with an R value of 2.0.
To me, the best most logical permanent solution is to extend the hearth out that far. Given that I have about 10" or 11" already, I only need to extend the hearth 18" or 19".
For now I am just going to run a hearth pad. I got one from tractor supply. Its only got a R value of 1.5 but it will work for now as a temp solution.
Easy Livin’ 3000
Minister of Fire
I'm with you. I thought I had it figured out, but now I'm just not sure. I also have 10" of original hearth slab. I think I'll stick to my long-term plan of extending my slab to get to 16", and then for the final 13", cut down into floor joists just enough to add the cement board (for structure), micore (for R=2 protection) and nice faux wood ceramic tile on top (for aesthetics). Hopefully it'll all be pretty level when done.
You're right that Note 1 does require 29" at R 2.0 in your case, but it doesn't void the equation. All Note 1 does is define the makeup of dimension B, which includes the part of A in front of the insert and D. Plug it all into the equation and that's how we get to 19" of additional extension needed at R 2.0.
Sounds like a game plan.
I'd just double check with SBI on the side clearances to your wood surround. There isn't anything in the manual stating a minimum dimension for how far it can protrude from the brick to not have to meet the clearance. Since you really want to keep that, I'd hate to hear down the road that you're noticing heat damage to it (just read the very beginning of Section 8). They may say it's fine as is.
blacktail
Minister of Fire
Easy Livin’ 3000
Minister of Fire
Dro lay in French Canada (SBI headquarters) and Dro let in red States.
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