Block-off and firebox Roxul n Durock install

[ADK_XJ]

Shew, it was a long time coming but finally pulled off insulating the firebox (exterior chimney) that my Regency i2400 was installed into last year. So, here's what we did with LOTS of pictures.

Here's the finished product first - per the title, I used Roxul and Durock 1/2" cement board like user @mellow and his install here: https://www.hearth.com/talk/threads/finally-got-around-to-insulating-my-fireplace.75755/page-1



back to the beginning - After finding this, I realized early last winter that the original installers had skimped on my job. I did get an M-flex liner (uninsulated from what I can tell) that was properly installed from what I could tell but opening up the stove shows a hacked up firebox and some meager fiberglass insulation:





So, I recruited my unpaid help (father in law) and this morning after a hearty breakfast we pulled the stove:





We swept the chimney (creosote was about what I expected but was not kore than

 

[ADK_XJ]

Having some trouble uploading photos via my iPad - sorry for the break:

We cleaned the chimney (couple cups of creosote collected for a whole season of burning last year - yes, I will start doing this at the end of each season from now on) - we pulled the cheesy insulation and started doing measurements. Best decision we made was to first make cardboard templates:





I thought the Durock was going to be much harder to cut but we really just had to score with a utility knife and then break off each line. Can't lie, it took us a while to get the first piece cut to fit and had to use one of those oscillating fan blade type dremel tools to do some tapering but we got together the leg and right side. I don't know if this was overkill but I knew I'd have clearance and I'd rather have it be overbuilt than underperform:

 

[ADK_XJ]

As I mentioned, this firebox is on an exterior chimney and I knew that was contributing to (in my opinion) the relatively mediocre performance of the unit over last season - again, I wasn't sure if I was overdoing it by layering the already thick metal firebox but I only wanted to do this one time:



We stuffed Roxul in the old ash trap there toward the back and cut a piece of cement board to tap over it (I'm sure that was drafting air - thanks original installers for leaving it for me to find!) - we used cobalt drill bits and sheet metal screws to put the left and right pieces flush to the metal. I'm the rear there was space to do a Roxul/Durock "sandwich" so we used 4" lag screws to set that in place:



After we did the lower rear "sandwich" I started stuffing Roxul in that hole you saw behind the liner/flue in my first picture - and stuffed some more. And some more. Ended up putting almost 3 batts of Roxul back behind that metal firebox surround - I figure that can't hurt one bit.

Then I started jamming the flue itself chock full of Roxul - this was surprisingly tough. I probably spent the most time of the entire install fighting falling crud and crap into my mouth and eyes trying to get that Roxul packed all the way up the flue.



This is when we decided to abandon doing a sheet metal block off plate and give the Durock a shot. We were feeling cocky and skipped the template but ended up doing a bunch of trimming and tapering until we finally got a piece together that we anchored to a metal lip about 2" up from the "lintel"

 

[BrotherBart]

Welcome to lungs full of short fiber insulation. I keep telling people to wear a mask with that stuff, damn it!

 

[ADK_XJ]

At this point we were really patting ourselves on the back and started cracking beers. We hefted the stove up and slid it into place - annnnd it hit the rear top Durock sheet a good 2" short of being able to attach the liner. Crap. We drank more beer and then sucked it up and pulled the stove again. Ripped out our carefully prepared Durock panel (this was not the block off piece but the one at an angle second from the bottom at the back of the firebox seen in the picture) and tried it again - success!



Lit off a small load of seasoned ash and pine splits:



Within an hour the living room was up from 55 (heat was off all day while we installed) to 70 and peaked at 73 with a really nice secondary burn going:



Did it work? Well it's only 40 out right now but I started a fire at 5pm (6 medium ash splits and some pine kindling - top down start) and after nearly 7 hours it's coaled very nicely and looks like this:



I've never had a coal bed look that good after 7 hours and the stove is cruising at around 380. Over the evening it burned really well with noticeably more intense secondary burn - talk about light show. I sort of expected the stove to get a little hotter (topped out around 500 before cruising) but I also was being real tinkery and impatient with the air control. Anyway, I'm a believer but we will really see this cold season - I'm going to reload and see how it holds up overnight.

Open to feedback and thoughts...my biggest question will be whether I want to go back to a more airtight steel style block off plate. I can't imagine much heat is escaping past all that Roxul above the Durock...

 

[ADK_XJ]

Welcome to lungs full of short fiber insulation. I keep telling people to wear a mask with that stuff, damn it!

Ha, I actually did wear a mask for installing the Roxul - I'm remembering it was when I put the "block-off" of Durock up that I didn't mask up and got some cement chunks in the old pie hole. Let's say I've had a few more beers since the install was finished.

 

[BrotherBart]

The Durock will do it fine. Just harder to work with getting it in there but that is done.

Enjoy that heater and the after install refreshments. You earned both.

 

[kennyp2339]

Well here's my 2 cents - thanks for reminding me about measurements in the rear fireplace, I'm going to do the same exact thing at my parents, The main question is what type of beer should my dad buy for this type of project?

 

[ADK_XJ]

Well here's my 2 cents - thanks for reminding me about measurements in the rear fireplace, I'm going to do the same exact thing at my parents, The main question is what type of beer should my dad buy for this type of project?

I had a domestic light beer for the FIL and Founders All-Day IPA for myself. Good question, super important detail.

 

[quotejso]

I had a domestic light beer for the FIL and Founders All-Day IPA for myself. Good question, super important detail.

Probably light beers for the cocky stage of install then transition to something stronger for the celebratory fire. Nice job.

 

[jophysx]

I did a similar job (though not nearly as professional) improving my insert install last year, and I noticed a dramatic improvement too. For me the biggest difference was a huge reduction in ash production. I also found that the stove could cruise comfortably with great secondary burn at lower temperatures. I think insulating like this on an exterior chimney (especially the block off plate) should the standard. I wish I had known enough to insist on it when I first had the unit installed.

I'll be curious to see if you have the same experience with greatly reduced ash production. Please report back after a while.

 

[ADK_XJ]

I did a similar job (though not nearly as professional) improving my insert install last year, and I noticed a dramatic improvement too. For me the biggest difference was a huge reduction in ash production. I also found that the stove could cruise comfortably with great secondary burn at lower temperatures. I think insulating like this on an exterior chimney (especially the block off plate) should the standard. I wish I had known enough to insist on it when I first had the unit installed.

I'll be curious to see if you have the same experience with greatly reduced ash production. Please report back after a while.

I'm with you - wish I had known to insist on it but also kind of prefer now that I've done it myself and know it's "right"...I think.

I will check in mid season but this morning was the first time I woke up to the stove still producing usable heat (no blow but cruising at 160-180) and that was a solid 7 hours overnight with less than a half load.

 

[mellow]

Did you do an IR gun temp test on the outside of the chimney before and after? Curious to see what your temperature drop is.

 

[ADK_XJ]

Did you do an IR gun temp test on the outside of the chimney before and after? Curious to see what your temperature drop is.

Not concurrent with the install - I have taken thermo readings on the exterior chimney last winter and confirmed what I knew: I was heating the OUTSIDE.

As for exact temps inside and out and of the chimney at that time - I missed the boat on that.

I am, however, already observing a higher sustained temperature of the stove itself over a longer time - it takes much longer for the thermostatic blower to shut off at the end of a cycle.

 

[mellow]

it takes much longer for the thermostatic blower to shut off at the end of a cycle.

Yep, that goes to show that heat is being retained in the firebox for much longer, it will also help keep hot coals for longer making restarts easier.

 

[ADK_XJ]

Yep, that goes to show that heat is being retained in the firebox for much longer, it will also help keep hot coals for longer making restarts easier.

Here's a question: should I be getting an insulation sleeve for my liner at some point? I noticed it was just the m flex liner as bare metal that I could see going up the old flue into the chimney -'I don't have any draft issues and based on the limited amount of creosote I scrubbed out I don't think I'm getting major cool down of the smoke but could it be impacting performance from the stove itself?

 

[mellow]

If your draft is not suffering and you are sure you have the clearance to combustibles for the liner then I wouldn't bother.