Insulating the old fireplace for an insert

[burnafterreading]

A couple of questions/confirmation for insulating the fireplace for the insert. PE Neo1.6le insert, into the old exterior brick fire place and chimney. Its an old 1918 economy craftsman, in North Puget Sound. Heating mainly the living, dining, kitchen and a bedroom...about 700sq ft with 9' ceilings. The house has alot of windows, poorly insulated and not well sealed...but the climate is relatively mild rarely gets in to the teens but most of the winter is between 35-45 degrees F.

Prepping for the install, I demo'd the backwall and the smoke shelf of the fireplace to make enough space for the insert. Ended up with quite abit more space than anticipated...could have fit in a Neo 2.5. Anyway the Neo 1.6 is going in mainly because I think it will be enough considering the small area and mild climate. It will have an insulated block off plate, pre-insulated liner and outside air intake.

I'm in the process of making something very similar to below:

Kaowool behind the insert

Good idea or bad idea? I figured that it would keep the heat from being absorbed by the back of the hearth and transfered right outside. Will this help any?

www.hearth.com

In order to take up some space, have a nice clean finish appearence (though not visiable behind the surround) but more importantly to insulate and get better convection heat and avoid the exterior FP heatsink. The back wall will have about a 5" space behind the corrugated sheet metal. There will also be a 2-3" gap/space between the insert and the corrugated sheet metal. The plan is to ceramic batt 1" insulation between the sheet metal and the insert...is this the correct thing to do? And where do I specifically attach the ceramic wool...on the insert or on the sheet metal? Another question, do I need to also put insulation in the 5" space at the back...behind the sheet metal between the exterior bricks?

Thank you all, I have learned alot and will continue to do so. May you, your family and friends be well and find peace in these times.
Tim

 

[begreen]

The insulation gets attached to the brick. I would skip the metal, but if anything is used, I would use flat sheet metal or cement board and probably double up on the kaowool to 2", or use Roxul 3.5" unfaced batt material.

 

[burnafterreading]

Thank you @begreen

 

[Geoff C]

I cut roxul batts to fill in the empty space then covered it with cement board to keep the dust down. I think there is about a 5” gap between the stove and the cement board. Before it was over 12”

 

[unimog1300]

 

[begreen]

unimog, what is that material?

 

[unimog1300]

unimog, what is that material?

Roxul foil faced 2". Got it at Grainger.

 

[Ctwoodtick]

unimog, what is that material?

Roxul foil faced 2". Got it at Grainger.

How do you like it?

 

[begreen]

unimog, what is that material?

Roxul foil faced 2". Got it at Grainger.

Looks great and offers a dust barrier. I wonder about the adhesive used to bond the foil to the Roxul. What is the product temp rating?

What's holding the pieces in place?

 

[webby3650]

Most inserts that I’ve ever dealt with have a sealed convection shell, dust from the roxul becoming airborne isn’t an issue.

 

[begreen]

Most inserts that I’ve ever dealt with have a sealed convection shell, dust from the roxul becoming airborne isn’t an issue.

True it shouldn't be, but there are people that have concerns about this due to asthma, etc.

 

[webby3650]

True it shouldn't be, but there are people that have concerns about this due to asthma, etc.

Soft woodburners?

 

[Ctwoodtick]

Most inserts that I’ve ever dealt with have a sealed convection shell, dust from the roxul becoming airborne isn’t an issue.

I know that my Jotul insert has a small gap around where the stove collar is that could let bits fall through.

 

[webby3650]

I know that my Jotul insert has a small gap around where the stove collar is that could let bits fall through.

I know that a few inserts don't have a well sealed jacket around them and this is a possibility.

 

[unimog1300]

The Roxul seems to work well. It's easy to work with. It's fairly ridgid and cuts nice. Each one is held in place by friction fit. B Hollar says I need to tape each seam. I'll do that after I'm done burning for the year. I might add a sheet metal piece below the Roxul that's on the top. I also added two thermocouples at the same time. One is 18" up the insulated liner above the connection to the insert, the other is for the cat. I close the bypass at a way lower temp than I used to with the original cat probe. Have a temp alarm set for 1590* and it's only gone off one time. Opened the bypass and dumped the heat for about 10 seconds and it was over. 1550* has been the next highest, started burning 10/5/19 and 24/7.

 

[begreen]

Nice. If you get a chance can you add your stove to your signature line?

 

[Nick Mystic]

I'm surprised no one commented on the section of your initial post where you say, "Prepping for the install, I demo'd the backwall and the smoke shelf of the fireplace to make enough space for the insert." It sounds like you partially destroyed part of the original fireplace. I'm trying to picture what this might have done to the integrity of the remaining fireplace and chimney? Inserts are meant to be installed inside working masonry fireplaces as I understand it. Am I missing something?

 

[begreen]

It bears clarification. Removing a few smokeshelf bricks and grinding out the upper back slope of the fireplace is not uncommon in order to fit an insert, but within limits.

 

[burnafterreading]

Ahhh a terrifying thought. Consulted with the installers before going at it...besides the install is on hold until ? because of the covid thing . And yes, this was part on the installation, but I got to have something to do besides walk the dog and watch Netflix with the Mrs. The exterior chimney and exterior FP are in good condition and structurally sound. That side of the house is well protected from sun and weather. The exterior had been pointed and inspected and the concrete foundation/huge ash pit of the FP is not cracked nor sinking and goes all the way to the basement floor about 8 feet down. The interior FP firebrick back was fairly shallow and angled and there is 10" of brick on each side of the fire place opening. So took out the back firebrick wall. There are/were three layers of bricks...interior back wall fire bricks, a layer of poorly laid rubble bricks and then the solid layer of exterior brick. Once I took out the slanted forward fire bricks to get clearance, the rubble layer was basically crumbling down along with the part of the smoke shelf but only as wide as the interior width of the chimney walls...chimney is still well supported. The exterior FP bricks and chimney are in good shape and seemly well supported. I was surprised how much I took out...but did not see why the rubble layer would do anything but eventually...actually quite readily crumble in on the installed insert. What was left is a gap of about 5" between the back wall/exterior bricks of the FP and the insert and there is plenty of room for the liner to drop down to the insert. Thus why I want to do a block off plate and some sheet metal enclosure; in part because of the amount of space, but also to seal off that space due to potential dust and to seal off the insulation. Also to prevent exterior bricks acting as a heat sink.