Yeah you won't be cooking much on most modern inserts but you can cook on many in the event of a power outage. But if that really is a big concern just get a gas range then you can cook on that. But this thread is about a freestanding stove which you can cook on any freestander
Proud Grandma bear owner!! With questions...
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Floor protection does not require an air space, but that is one way to do it. 3/8 asbestos millboard was required with a non-combustible covering such as brick or stone in your manual. Double cement board is a close equivalent today since asbestos millboard is no longer available.
Follow recommendation of cultured stone manufacturer and proper mortar.
Further reading here; https://www.hearth.com/talk/threads/3-8-in-asbestos-millboard-what-is-the-equivalent.146277/
And here;
R Value?????
R value for 3/8 inch millboard??? My manuual just calls for 3/8 inch millboard (MICORE® 300 Mineral Fiber Board,) I may want to use other material to equal this r value. Any one know the depth of cement that would be equivalent. Thanks
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My Grandma top flue is 8" too. I believe Coaly said this was to be able to run with the doos open as a "fireplace". I have an immediate 6" reducer for a 6" chimney and always run with the doors closed. Just put in the Coaly DIY no weld baffle last week and it really moved the heat to the front of stove and comparatively cleaned up the exhaust.
I might end up doing this as well with the 6" reducer. I wonder how that would be with the doors open.
I like to keep the doors open and watch the fire. Hopefully it will function just fine.
Does anybody run a 6" flue and keep the doors open? How does it work?
Open doors don't work on mine with the 6". I have to start the fire in a way that will burn for at least 15-20 minutes before opening the doors or it will pour smoke inside. Sometimes even later in the burn I can only open one door to reload. Seems that is a little worse since putting in the baffle. I'm going to try raising the front of it and inch or so before the next fire. It is a shop stove which I use maybe 20 times a year with a sub-standard chimney. YMMV
Here’s mine. As you can see I reduced it from 8 inch to 6 inch at about 12 inches above the stove mainly because of the 90 degree elbow going into the chimney. I have an unbelievable draw so the 8 inch damper is used a lot. I also open the doors to watch the fire all the time and even with the baffle installed I get no roll out smoke. Everybody’s application is different. All you can do is do it and see what the effects are. It’s not exact science
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Also the factory screen has a HUGE effect on open door smoke roll out. It has much less square inches of area ( close to 50% ) using the screen in comparison to just open doors. And thus decreases smoke into the room. I use Grandma with open doors .... sometimes with screen and sometimes no screen. But I NEVER LEAVE THE ROOM in either mode. Let the Nay Saying begin
Beautiful setup!! Looks really nice.
Do you have 6" all the way up the chimney? How high is it?
I do have the screen with this stove and I plan to use it
Maybe thats the difference. You only have a small section of 6" pipe going back into 8". I would imagine that 6" would be acting like a damper to some extent..? As opposed to going straight up all the way with 6" pipe..
I'm not really sure. I'm just learning this as I go.
Maybe I should just split the difference and go with a 7" flue all the way
Since your all new pipe and will probably be using insulated pipe, if it was me I’d use 8” all the way. Stove is 8” and just include a damper near the stove connection to control the chimney draft. I run mine hot and don’t ever have any creosote buildup. I also use a creosote log a few times a year just for kicks and peace of mind
8 inch was standard. The reasons were for open door burning with screen in place for the solid door models which the large fireplace opening becomes almost atmospheric pressure allowing smoke to move both up and in. The other reason was when these stoves were designed they were usually connected to existing chimney flues designed larger for fireplaces. A 6 inch outlet wouldn’t let enough heat out for the larger flue. A customer proving they had a chimney system that would work with a modified stove could have them special built, so you can find 8 inch outlets on the stoves normally fitted with 6 inch outlets. If you’re going straight up into an insulated chimney they work fine. They will not allow maximum BTU output due to reducing chimney capacity, explained below.
It is technically illegal to reduce exhaust all in states that have adopted the International Family of Codes. NFPA 211 allowed 1 inch reduction, but the International Mechanical Code no longer allows any reduction.
The difference venting systems create is quite complex. First, the chimney causes the low pressure area in flue, pipe and stove. Atmospheric air pressure PUSHES into this low pressure area or slight vacuum feeding oxygen to the fire. This is due to 3 factors; 1) Buoyancy of flue gases determined by chimney height, 2) Flue temperature difference between inside flue and outdoor temperature, and 3) velocity of rising gases. This is measured as draft at any given point in the system. It is normally highest ( lowest pressure) at stove outlet. NET draft is the most important. Everything else takes away from the low pressure area inside the stove. Resistance to flow is determined by elbows, pipe, outlet screen, cap, flue pipe damper, resistance through firebox, and intake air damper. Added to all these variables is atmospheric pressure at any given time, altitude, fuel moisture content, fuel species, and building depressurization.
Chimney flue diameter determines relative capacity. The larger the diameter, the more capacity, but the more heat required to cause the same draft, with slower movement, temperature drop due to expanding gases, and longer dwell time in flue.
The flue damper is a variable velocity control slowing rising gases that reduces net draft. It is used to control an over drafting chimney. It is a chimney control that affects the stove.
There are tables and charts for all the above mentioned items. Watch eBay for The Woodburners Encyclopedia by Jay Shelton. It’s the best book I’ve found explaining these things in great detail using simple terms.
You'll get a lot out of it! I thought it would be an alphabetical type encyclopedia, but it's not like an encyclopedia per se at all. There is a table of contents in the front, then a detailed index in the back. There are 97 pages of the bulk of the book, then 5 Appendix with tables, charts and graphs. So if you just want the general information how things work, the bulk of the book is ok. But you find "see Appendix I,II or III with chart #..... or table #...... throughout the book taking you deeper into the subject. I use it all the time. It was listed as further reading in all the Fisher manuals at the end of each owners manual.
I guess that's why I'm such a Fisher fan. Back in the day talking with salesmen in the showroom they were very knowledgeable about the stoves and installation, and could talk with the license holder and welders right there, unlike the sales people without a clue today. At least that's the way our local hearth shop is. I just walked into a home today to check a coal stove and they had red high temp silicone in every pipe joint as well as up the pipe seams! They said the local stove shop told them to do that and not use a barometric damper which was the reason I was there with it over drafting. A coal stoves needs a very precise draft controlled at all times to keep a constant flow through the fire bed. They sold them all the stuff to hook up their stove. What a mess pulling the pipes apart glued together! I'm supposed to be retired!
Although I dont have a grandma bear... I have a timberline petite double door model (almost the same size as grandma) with a factory 6" flue and smoke shelf.
2020 was my first full year using it 24/7.
I have noticed that it depends on outside temps and how hot the flue gets to burn with the doors open... cold days and nights there's no problem. But warmer daytime temps and slow night time temp changes it will roll a bit of smoke in the house..
Can I ask how much you paid for it? I'm trying to sell one, so wondering what I should ask for it.
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