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insulating entire fireplace/damper w/mineral wool instead of block off plate

Post in 'The Hearth Room - Wood Stoves and Fireplaces' started by _CY_, Feb 20, 2014.

  1. _CY_

    _CY_ Burning Hunk

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    was getting ready to fabricate a block off plate for my Buck 91 installation.

    here's what I did instead .. insulated entire fireplace firebox including damper with 2,000f rated mineral wool. insulation is pushed up pass damper about 2ft. entire insert is completely wrapped with insulation from all directions except bottom. zone directly above insert is about 4ft thick.

    purchased a package of 24in x 48in x 2in thick unfaced mineral wool .. 80 sq ft for $40 picked up at local building materials supplier. most building materials stores will not carry high temp insulation. but keep digging odds are someone local will have it in stock.

    home depot and lowes can order it .. it's listed on their website. but folks working there will probably never heard of it.

    holds the heat inside your insert instead of going up the chimney. substantial difference in heat output if you've got an massive outside chimney like mine.

    my fireplace makes a Buck 91 look small
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    Last edited: Feb 21, 2014

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  2. jaychino415

    jaychino415 Member

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    Thanks for sharing your pics. Have you tried it without covering the sides to compare the heat output?
  3. mellow

    mellow Resident Stove Connoisseur

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    Most people me included have done an airspace gap above the insert, this was done in fear of warping the top plate, let us know how it goes.
  4. Nick Mystic

    Nick Mystic Minister of Fire

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    I share some of mellow's concerns. Stoves are designed and built to be burned in specified ways. I'd be worried that by keeping too much heat in the stove I might damage some internal components of the stove and perhaps warp or crack some the stove pieces. Keep us posted how things work out for you.
  5. begreen

    begreen Mooderator Staff Member

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    How does one ventilate the convection jacket adequately in the event of a long term power outage? Is the intent to yank off the surround and pull insulation during an outage?
  6. _CY_

    _CY_ Burning Hunk

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    Tulsa, OK
    not concerned about overheating Buck 91 .. reason insulation was added Buck 91 simply didn't do job of heating my 2500sf single level well insulated ranch home. a major chunk of heat went up the chimney.

    fireplace room is located in middle of structure and opens up into aprox 1,500sf+ .. at 10f it just couldn't keep room warm. 1-3 year seasoned Oak 16% - 20% moisture measured with a GE protimeter.

    even changed out to new combustor with little difference in performance. 8in stainless full liner meant a roaring draft .. couldn't figure out why Buck 91 wouldn't put out enough heat for a 2500sf home ..

    after insulation .. completely different stove! after cat was burned clean .. now runs at 1500f with no problems vs before had problems with cat engaging below about 900f with new wood added .. now cat is glowing bright red/orange after new wood added at about 500f and quickly rises to 1500f.

    temps are calibrated with a digital pyrometer .. so temps given are accurate. fully setup with Honda EU2000i genset if power goes out ..

    really worked on getting Buck 91 completely airtight to too tight. from a roaring fire it was possible to snuff fire out completely by shutting off air. don't do this ... if you run it that tight .. at some point up draft will stall .. then smoke will find it's way out. on Buck 91 that would be via hole for combustor shut-off shaft. very dangerous as light smoke will slowly fill your house along with dangerous carbon monoxide levels.
  7. bholler

    bholler Minister of Fire

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    I would worry about over heating to.
  8. _CY_

    _CY_ Burning Hunk

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    yes .. little to no difference in heat output with or without side covers. firebox is really insulated .. heat output has really increased after doing this. keep in mind I've got a fireplace located on outer wall of house. so you may have same issues as me.
  9. _CY_

    _CY_ Burning Hunk

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    did this after talking to Buck technical support folks multiple times .. they had no clue on how to solve my low heat output issues with Buck 91.

    talked to an installer at local Buck Stove dealer about my low output issues with Buck 91 .. he was the one that suggested filling up entire space inside fireplace. he told me of one Buck 91 installation that he did from 20 years back. only he used standard fiberglass insulation. he said fiberglass insulation where it touched hot spots got crispy but worked just fine.

    went with mineral wool rated to 2000f for extra safety factor. not enough heat was the problem leading to insulation .. seems to have solved my output issues .. we'll see how it goes ..
    Last edited: Feb 21, 2014
  10. bholler

    bholler Minister of Fire

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    we always insulate around inserts when we install them but not tight to the stove like that I don't know if it will be a problem but it definatly could be.
  11. jaychino415

    jaychino415 Member

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    Is there a fan for the Buck 91? If yes, how do you get the air to flow from spot to another? From the front insert to the back.
    Last edited: Feb 24, 2014
  12. Bagelboy

    Bagelboy Member

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    I could be wrong, but I'll bet it will throw more heat, retain it longer, and need less reloads. I started with no insulation, did the sides and back two months after mine was installed. Worked with that a while. One month later, I then stuffed some up in the damper, and than actually place a layer on top of my insert. Nothing like what you have done here, but I'm thinking about it. When i burn, I stuff my insert with wood, get it up to about 600 degrees, and than when I shut it down, it starts to go to 500 degrees pretty quickly. By 2 hours later, it is 400 degrees, and by three hours later, it's 350 or 300 degrees. Lots of wood and coals still burning. I basically need to reload every 5 hours because my stove will be around 200 to 250 degrees. I have never seen my insert top at 650, so I'm wondering if I have similar problems you were having. Of course, because mine is an Osburn, it comes with a 1 inch gap around the stove, so the Rolex is not fully touching the stove itself.
    Last edited: Feb 22, 2014
  13. _CY_

    _CY_ Burning Hunk

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    yup there's a variable speed fan on Buck 91 .. recently upgraded to latest fan which throws out more cfm. change out was simply to have a backup fan motor on hand. installed to make sure motor was not defective before putting away. ended up leaving new fan in place and putting old blower assembly for backup.

    power failure backup is Honda EU2000i genset ...
    jaychino415 likes this.
  14. _CY_

    _CY_ Burning Hunk

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    getting lots of shoulder weather in Tulsa .. 50f w/30f nights .. will be getting a 20f night tomorrow .. winter is not over yet, not by a long shot.
    hard to tell performance with such moderate temps but Buck 91 is putting out substantially more heat .. heats up faster, hold heat longer, etc. acting like a completely different stove.

    very pleased with much improved performance of Buck 91! adding insulation by completely filling firebox and damper area may not be for everyone. but it sure seems to have cured my low heat output problems for Buck 91. which evidently was related to installing into an outside fireplace.
  15. mikey

    mikey New Member

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    By putting a block off plate with the insulation above, your stove will not only give radiant but convective heat as well.
  16. Bagelboy

    Bagelboy Member

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    I wonder if anyone else on this forum has done this!
  17. mikey

    mikey New Member

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    It's how I installed my jotul f100 in my existing fireplace, the f100 also has rear and bottom shields that help to push the heat away from the back of the stove.
  18. _CY_

    _CY_ Burning Hunk

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    cat temp still at 900f about 8 hours into burn ..
    at 10 hours cat temp down to 650f with about 2 hours of useable heat (245f blower air temp)
    most importantly room temp at 72f .. 22f outside ..

    visited Buck Stove dealer today looking at a new Buck 91 for my buddy's new house.
    noticed latest Buck 91 has firebrick on sides of firebox. my 91 only has firebrick on floor.
    this explains why insulation made such a huge improvement.

    my older Buck 91 has substantially more room inside firebox without firebrick on side walls.
    but would not hold heat near as good until insulation was added.
  19. Bagelboy

    Bagelboy Member

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    I meant did anyone install their insert and insulate like Cy.
  20. Lumber-Jack

    Lumber-Jack Minister of Fire

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    I've never heard of modern (front loading) stoves to not have fire bricks on the sides. Are you sure it's not just missing?
  21. begreen

    begreen Mooderator Staff Member

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    Several modern cast iron stoves don't have firebrick though they use interior burn plates instead often with insulation behind them.
    Lumber-Jack likes this.
  22. _CY_

    _CY_ Burning Hunk

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    pretty sure mine came without firebrick on sides. my Buck 91 is an early stove probably 20+ years old.
    construction is completely different vs newest models. for instance my combustor is 1/4in wider than current Buck 91.
    when I recently replaced combustor that I probably didn't need ..
    had to use 2x 1/8in steel plates to take up extra 1/4in gap new combustor wouldn't cover.
    Lumber-Jack likes this.
  23. _CY_

    _CY_ Burning Hunk

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    latest feedback .. outside 15f right now with 8f low tonight ... room at 69f with cat averaging 1200f .. blower always on high

    pic from earlier calibration check .. Weston off by 3f degree at room temps but was right on at 32f ice water test.
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    Last edited: Mar 2, 2014
  24. a316co2000

    a316co2000 New Member

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    how do you measure the temp of your cat?
  25. Ram 1500 with an axe...

    Ram 1500 with an axe... Minister of Fire

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    Last year when I got my stove and didn't really know how to burn real well, I called VC technical support and had a nice conversation with someone, I asked about wrapping the insert in a hi temp blanket. I was told that it was not recommend due to the fact that the insert was not designed to burn with it on.....so I decided to let it go and now passing that along to you, you might want to call buck stoves tech support and ask them.
    Now that I know how to burn correctly, I am achieving a desireable heat output in my insert room, no lower block off plate, non insulated ss liner in an outer wall masonary chimney.......I thought it was the inserts fault, it was actually mine....

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