# Chase area around wood fireplace gets too hot



## Mr_D (Dec 13, 2013)

I have an RSF Focus 320 Wood fireplace installed by the local dealer.   A carpenter and myself built the chase structure ahead of time as per the specs of the manual and talking with the dealer several times.   

The fireplace install team seemed to do a good job but when it was all done I did some checking and found the chase area gets quite hot. I asked their technicians about it but they didn't really know if that's typical because they usually close up the front wall with tile, brick, etc and head out to the next job.   In my case I don't have the tile or mantle installed yet so I still have access to the top of the fireplace and the chase area so I took some temperature readings. 

After running a few hours the chase walls get up to 188F sometimes and that worries me. I think I need to redesign the chase venting, add a fan, or adjust how it's insulated.  The RSF Focus 320 is on the main floor with cathedral ceilings.  I bought the internal blower option and the basement heat dump kit with blower. 

The chase is part of the house thermal envelope and is air sealed and insulated with 2x6 construction.  It's 2ft deep, 6ft wide and 25ft tall.  The Chase extends 7ft above the roofline and is insulated the entire way up.  The insulated SS pipe terminates 2ft above that.  It's quite tall overall.  

The stovepipe is the proper dual wall, ICC brand 7" ID 9" OD stainless steel insulated chimney.   It goes straight up with no bends of any kind.   It has the factory spec vented flashing at the top along with radiation shields and so forth where it passes next to (through) the roofline.   I also have far more than the minimum clearances of 2" to the chimney.   The chimney actually has 7" clearance to the back and front walls and 27" to the side walls.  That's far more than needed but the problem is the whole chase gradually gets really hot over the course of a few hours.   

The chase walls are 2x6 studs insulated with spray foam to R20.  It was sprayed from the outside onto the back of the drywall between the studs.  Then covered with OSB, housewrap and vinyl on the outside    The inside is fully lined with 5/8" type X drywall.   The top of the chase and the chase liner next to living rooms wall has 1/2" Durock cement board for safety rather than drywall.   Now I wish I had used Durock board on all the interior surfaces because drywall with paper facing and wood framing isn't really meant to take 180 to 190F degree's long term.

I read the temp with a fluke IR meter and also installed a J-type thermocouple up near the top of the chase and they agree on the temperature.  I also have thermocouples on the firebox, chimney flue and the outer chimney pipe.  
Firebox top = 250-330F depending on burn rate
Flue pipe 4" above firebox 400-680F
Chimney outer wall temp = 150-190F

The lower chase where it shares room air (due to no inner wall yet) stays cooler at 115F.
The upper area's of the chase run much hotter and the ceiling gets up to 188F.   I'm sure having the house walls insulated is not helping because other than the small vent at the top the heat has no where to go.  This used to be an outside wall so it's insulated.   So the upper chase area ends up being insulated on all 4 sides. 

I'm considering removing the living room drywall above the fireplace to access and remove the original insulation so the excess chase heat can flow into the house rather than being trapped in the chase.  

Or, I could add passive vents or thermostatically operated fans in the chase to send the heat back into the house, effectively cooling the chase.  It's certainly hot enough so I'm not worried about cooling the chimney itself too much.  I read 300F+ coming out the top of the chimney.

I'll try and post a picture to make things more clear.
Basically... is it ok to vent the chase heat back into the house?  especially when it's far hotter than it needs to be? 

Lastly, the fireplace installers did not install a firebreak of any kind because I have cathedral ceilings even though I think it still needs one.   The chimney didn't pass through any floors even though the house has a 2nd floor a few feet over from the fireplace.  So I installed a Durock board firebreak about 7ft above the fireplace (11ft above the floor).  I left a 1 -2" air gap around the chimney.  The durock board cuts down the  room air that was blowing out the top of the chase and also I didn't like the idea of having no firebreak at all.   RSF sells an air tight radiation shield for high efficiency houses so that implies I could seal off the firebreak completely to stop the air loss but I didn't do that till I find out more.   With the chase open to the vent at the top I was getting frost on all tiny air leaks in doors and windows since the top vent in a tall, hot chase depressurized the house a lot. 

Thanks for any insights on the best way to make this a safe install.    
Note there are 4 JPG photo's attached, but the preview only displays the first one, so far.

Regards,
Dave


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## Backwoods Savage (Dec 13, 2013)

I'm going to bump this to the top to get other opinions.

First, I think you are okay according to what I've read and when you get that finished off, then the temperatures inside the chase will go down. It might be interesting to get some better opinions though. Good luck.


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## oconnor (Dec 13, 2013)

When I looked into ZC fireplaces, I understood that the chase was sealed above the stove as you mention. It may not be required, but makes sense, it would keep stove heat in the rooms. I don't think it would keep the chase cooler though.

Essentially, the stove would be inside the building envelope, abs the flute would be outside the envelope.

Perhaps a call to the manufacturer would be worth while.


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## Backwoods Savage (Dec 13, 2013)

I definitely would.


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## begreen (Dec 13, 2013)

Is the blower running when these temperatures were taken? It looks like the work is being done well and RSF is a quality system. Still, 190F continuous temps on a combustible make me a bit nervous. That is at the high end of the safety factor. The chase temps are already close to this and this is with it still mostly open. For sure the chase will get hotter at times once it is closed.  Have you contacted RSF for guidance? I can see why you are considering adding an upper and lower vent to the chase to reelase some of this captive heat. Keep us posted with your findings from RSF.


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## begreen (Dec 13, 2013)

One other thought would be to gravity vent the fireplace. Theoretically that should cool down the stove though there would be some heat loss in the chase from the ducts.


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## Mr_D (Dec 13, 2013)

Good point from 'begreen'.   The flue temp drops nearly 100 degree's if I turn up the internal blower to max.   The heat dump blower to the basement also pulls heat but that one pulls air from the side of the firebox and doesn't blow as much heat or affect the flue temp much.   The internal blower is optional so it should not be required for proper operation but I'm glad I have it.   I use it 24x7 to try and lower the chase temps by lowering the flue temps but it's not enough to resolve the hot chase.  With the blower off  I see 170 -188F in the upper chase ceiling and with the blower on  it drops 10-15 degrees at most.

Note that there is almost zero heat coming off the top or sides of the fireplace.  It's literally at room temp on all sides which is kind of amazing in itself. 
So all the stove output to the room comes out the front of the fireplace via the glass and the vents.  That means all the heat making the chase too hot is coming from the insulated chimney. 

*What about wrapping the insulated chimney (which is R4 at best) with ceramic blankets or 1/2" ceramic boards to hold in the heat?  *
That should reduce the heat that goes into the chase and improve the situation.  They want the chimney hot anyway right?  So this would make it even hotter due to less heat loss into the chase area.

Yes, I've talked to RSF several times. They usually respond within a day via Email and were fairly knowledgeable.   RSF Canada is International phone rates from here so I didn't call them.   Regarding high chase temps and no firestop installed by their local installer, RSF said as follows:


_In terms of the actual chase temperature, as long as the required 2” clearance to combustibles is in place, you do not have to worry about temperature.  The chimney is tested and listed to be safe at closer clearance than your chimney is installed, so you do not have to worry.  _

_I am surprised that they did not recommend installing a firestop in your chase.  There was lots of time and effort that went into making that chase as insulated as possible, but the primary place for air to enter (the top) is not being buffered.  It’s could be equated to building a home without an attic as a buffer for cold air._


I thought they would be more concerned considering how hot it gets and the chase is not even closed off yet.  
I mentioned to RSF that the gypsum board manufacturer recommends 125F max continuous heat but he didn't reply on that part.  

I would predict a fan system affecting the heat a lot.  What about the Gravity Vent mentioned by 'begreen'.  how would that be implemented?  

Keep in mind I have access to the tall living room walls and can vent into the chase from there. but actually there is still at least 12ft of chase above the living room walls up towards the roof that I can't squeeze myself into very well for servicing or adjustments.  And that is where the most heat is, at the top.   So one way to pull off the heat could be to open up an access hole high up on the living room wall and insert a 6' vent pipe up into the chase all the way to the top so it can draw hot air from the top area.  Then put a blower or fan on the lower end installed behind a normal looking HVAC grill.  The fan can draw heat from the top back into the living room through the new vent pipe.   If needed there could be 2 variable speed DC fans in push-pull mode with each one set at optimal speeds that balance out the room and chase pressure as required.  The idea is to move the heat into the living room without blowing excess conditioned air out the vent at the top of the chase or drawing in outside air.    

Has anyone tried venting a chase with fans or perhaps has a simpler solution to a hot chase?

4 JPG's attached.. 


Chase view above roofline
Chimney view before chase top added
View of top vent
Radiation shield at the top


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## oconnor (Dec 14, 2013)

Given the vent in the top of the chase, I think the chase should be considered outside the house envelope, and the air tight fire stop you mentioned installed above the fireplace. You could use spacers and durock in the chase to form a radiation shield around the flue. Unless the flue instructions specifically permit it, don't put anything around the flue for insulation. They usually require an air gap for cooling. Again, check the chimney instructions to confirm what if any air gap around it must be maintained.


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## oconnor (Dec 14, 2013)

Here is a section from the Excel chimney manual that should apply to your install.

You may also completely cover the top of an FOCUS 320 as long as you maintain all fireplace standoff clearances and the 2" clearances around the chased chimney. The 2" clearance around the chimney must be open from the fireplace up to the ceiling. See Figure 13 for an example of a close clearance installation


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## Mr_D (Jan 27, 2014)

The manufacturer RSF from Canada insisted I close up the interior walls around the fireplace before reading the chase temperature. 
They said it would cool down and the open chase was the issue. 
So to evaluate the heat conditions of the chase area I closed up the wall and ran some tests to send the data back to the factory so they can help figure out what to do. 

I closed off the chase walls with Durock and monitored 3 thermocouples (chase top, middle, and flue temp) to record temperature data vs time.
As expected; with no room air to mix in the chase walls got even hotter than before.   As a result I had to stop the test early before the chase reached equilibrium temperature.  It went past 210°F near the top of the chase and was still going up when I stopped the test.  I didn't catch the max temp on the attached IR photo but it's close, and it matches the contact thermocouple readings.

RSF had a short reply last month regarding hitting > 200°F on drywall with a 125°F limit.  _"As for the heat  ...we don’t see anything wrong, we test at much higher temperatures."  _
They are either ignoring the science and related USG drywall maximum temperature ratings for drywall or not understanding the issue.
I requested what and how they tested but they didn't reply. 


*Chase temperature Test 1 setup:*

  Chimney: ICC 7" Excel dual wall stainless steel installed vertically with no interruptions or bends.
  RSF Focus 320 Fireplace installed with the factory internal blower and upper vent as per the install manual.
  All factory standoffs and clearances are installed and in effect.
  The chimney has the factory radiation shield and vent at the top of the chase.
  USG 1/2" Durock panels are in place around the fireplace front opening forming a fairly effective air barrier
  Thermocouple meters in use were calibrated using an Ektron model 1120 thermocouple calibrator.
  Optional, fireplace variable speed internal blower and air dump kit are installed and turned off for the test. 
  Fireplace air inlet is set to use outside combustion air.
  The intake air damper was set open to max for starting, then reduced to 50% position for the duration of the test.
  All temperature meter electronics are located outside of the chase area in conditions and operate at room temp.

*TEST 1 setup:  (see chart 1)*
Fireplace was filled 60% full with dry, split hardwood maple and oak.
Fire was allowed to burn without refill except for 1 small split added at time 1:10.
Test was started and allowed to heat up and cool down in 5 hours without interuption.

Test 1 recorded peaked at 201°F and would have gone higher except the fire cooled off as the wood was used up.

*TEST 2 (see Chart 2)*
Test 2 used a fuller load of wood at 75% full and saw higher temperatures. 
Chase temps near the fireplace itself in the lower area's of the chase ranged from 70-90°F and eventually maxed out at 130°F near the end of the test.  Test readings were viewed through a temporary 5x10" access hole in the Durock board for purposes of meter readings.  The meter access hole was air sealed during the test.

Chase temps further up the chase were much hotter than the lower area's and ran higher after the chase area was enclosed.
The higher up the chimney pipe I go the hotter the temps are.  Chase temps hit 150F in 1 hour, 205°F at 1.5 hours and continued up to 210°F at which point I stopped the test by closing the intake air damper and turning on the fans to try and cool it down. 

*Conclusion:*
The chase design and material selection need significant changes to provide a safe fireplace installation since it runs far hotter than the installed drywall is rated for.

Here is my list of possible fixes.   What do the pro's suggest?

Install better chase ventilation to expel more of the heat coming off the chimney.  Add an intake vent half way up the chase to assist.  
Chimney pipe temps runs 400-700°F inside anyway and > 200°F on the outside.  These temps are actually hotter as you go further up the chase due to the chase air being 120F hotter up there.  Maybe RSF  - ICC chimney makes a dual wall chimney pipe with 2 -3" of insulation instead of 1" that it has now?   that might cure it right there. 


Use high temperature thermal barrier for the chase walls instead of low temp drywall rated at only 125°F.


Vent  excess chase heat back into the house with passive vents or fan assisted air flow.


Enclose the chimney itself in 1200°F ceramic insulation (12-16" insulation pipe or use flat sheets) while respecting the 2" chimney clearance rules.  I'd give it 4-6" clearance around the pipe so it's like a high temp chase around the chimney.  The heat getting to the outer drywall would be cut by half or more and then I could vent the chase with cool outside air and the chimney would still stay hot for no creosote buildup.


Install a firebreak with a radiation shield 8-10ft above the floor to address safety concerns and limit the loss of conditioned room air out the chase top vent  This should have been in the original design.  With a firestop /air block in place then the really hot section at the top could vent with cooler outside air.

I've been waiting for RSF and the local Fireplace installer to have a real reply withi a useful answer for 2 months now.  I wrote many times and called as well but I think they don't want to hear about these cases if there is a nationwide issue using low temp drywall.  The dealer said they normally just use 1/2" drywall, close 'em up and move on.  They have no idea what the interior temperatures really are.


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## oconnor (Jan 27, 2014)

Mr_D said:


> ...Maybe RSF  - ICC chimney makes a dual wall chimney pipe with 2 -3" of insulation instead of 1" that it has now?   that might cure it right there. ...



What is the model of chimney you are using? I'm surprised you mentioned a 1" insulated chimney. I thought their wood burning chimney was a 2 " unit. 1" is usually used for gas and oil venting.


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## oconnor (Jan 27, 2014)

I gave the manuals a read. I see the ICC 1" is approved for their RSF fireplaces. I did note that they require a full length radiation shield when that same chimney is used with other stoves. That may be your solution. 

Oddly, the USA instructions for excel 7" chimney show it having two inches of insulation.


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## orionrising (Jan 27, 2014)

I think your problem is the spray foam, urethane foam is hugely thermally reflective rather then absorbant and prohibits all air movement. When it first came into use they called it self extinguishing until they had some bad fires on unfinished structures, as small fires were insualted and reflected so well they flashed. It now requires a thermal barrier over installations. I believe it is 1/2 drywall minimum.


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## begreen (Jan 27, 2014)

The chase is well insulated so it doesn't surprise me that the upper chase temp is getting close to the chimney surface temp. A fireblock is required at the first story level. With one in place a screened vent at the top of the chase should alleviate concerns. If not, remove the sheetrock and replace with cement board.


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## Mr_D (Jan 27, 2014)

O'Conner, Thanks for reading all the way through this.  The chimney is the ICC 7' EXCEL, model XC-7EL48.
It's 7" ID and 9" OD, so a 7' pipe with 1" insulation on each side.    Probably R-value 3.5 or so.   I took a photo of the pipes before it was installed to see what type of insulation it had, as shown below.    It looks like rock wool to me.   

I was not aware there is a full length radiation shield available.  That's very interesting.   
They may not spec the stove to use it but I can certainly inquire about that.   That's basically what I'm trying to do, come up with a way to insulate the pipe better to keep the radiated energy away from the chase walls while not getting the interior pipe too hot either, if that is a concern.  I suspect the 2" air gap requirement supplies a bit of chimney cooling via air convection while protecting nearby combustibles at the same time.  

I measured 235°F on the outer wall of the metal chimney while it was running and the pipe was in 70°F room air at the time.  I used high temp flat black paint to make a square shape Infrared target on the pipe with an emissivity of approx *.*95.  It's painted directly on the chimney surface to get a decent IR reading.   Krylon's 1602 is supposed to provides a surface emissivity fairly close to *.*95 and that works with most IR meters.   

Each flat black IR target looks like a hot red emitter to the IR gun since that's the only place it can get a reading.  Otherwise you can't measure stainless steel due to the reflections and you end up reading the wall adjacent to it.   Other items I've painted all measure correctly compared to direct contact thermocouple temps so I think this method with prepared targets is close enough for basic calculations.  

The chimney temp appears to be cumulative as you go up.  I was able to measure chimney temps up to 8ft high so far but I wonder what it reads 27ft up near the top  where it's exposed to 200°F chase air instead of the cool 70°F air down below.


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## orionrising (Jan 27, 2014)

you could run a bit of a duct up to the top and a small ventalation fan sucking the air back in the the living space maybe?


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## oconnor (Jan 27, 2014)

The part in the image about the Canadian Install instructions is what I'm referring too. Not sure how the chimney clearances and temps would be different in the same chase with different wood burners attached - I'd seriously look into the RST and RSF insulation shield. 

I would not recommend the idea from earlier of wrapping the chimney in insulation, ceramic or otherwise. It needs the air space to cool.

I assume you have installed a block off above the fireplace, essentially making the chimney cavity a dead air space? If so, the venting it to the outside or to the room would seem easier.


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## Mr_D (Jan 27, 2014)

begreen said:


> The chase is well insulated so it doesn't surprise me that the upper chase temp is getting close to the chimney surface temp. A fireblock is required at the first story level. With one in place a screened vent at the top of the chase should alleviate concerns. If not, remove the sheetrock and replace with cement board.


Yes, I agree about the fireblock.  The local installers insisted I didn't need one due to having a cathedral ceiling and the chase didn't pass through any floors.  I should have insisted but it was my first fireplace and the company that has installed hundreds of units "should" know what to do.   It's a lot harder to retrofit now but possible.

The chase goes past the living room ceiling and then about 5ft of attic space so I agree it needs a firestop.  That would also limit air loss out the top vented flashing that makes the whole house negative pressure at this time.   I'm trying to get the dealer to install the official factory radiation shield with a fire stop about 10ft up but they keep waiting for the factory to have a reply.

_> If not, remove the sheetrock and replace with cement board._
Removing 1000lbs of drywall and replacing it with something else inside a narrow, confined, 27ft tall finished chase is not very practical.  I'd rather insulate the pipe or walls with high temp insulation of some kind and figure out better venting.    Also, cement board of itself such as Durock may not be adequate.   The USG rep told me it can only be used up to 200°F because it has a low R-value of *.*39 in 1/2" panels*.  *The low R-value doesn't offer much thermal protection for materials or insulation behind the panel so it has to be installed with a thermal insulation board of some type in certain installations.


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## begreen (Jan 27, 2014)

I think a firestop and venting may be sufficient. That seems like the most practical approach.


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## Mr_D (Jan 27, 2014)

orionrising said:


> you could run a bit of a duct up to the top and a small ventalation fan sucking the air back in the the living space maybe?


Excellent idea.    I did that actually as an experiment.  I ran 24ft of 4" flex metal duct with a 4" 60cfm fan located at room level and it draws air from the top of the chase.
The air comes out of the duct into the room at 140°F.  The flex pipe isn't insulated so it cools a fair amount as it passes through the lower, cooler portions of the chase but it does help at least. 

A 60cfm fan drops the upper chase temp by 20F.  It lowers the temps from 200F down to 180F.
That's a step in the right direction but it appears I need quite a bit more air flow to make much difference using this approach.  

I'd prefer less heat getting into the chase from the chimney but 1" of rockwool in a dual wall chimney can only do so much considering there's 400-700°F flue temps on the inside of the pipe.


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## Mr_D (Jan 27, 2014)

orionrising said:


> I think your problem is the spray foam, urethane foam is hugely thermally reflective rather then absorbant and prohibits all air movement. When it first came into use they called it self extinguishing until they had some bad fires on unfinished structures, as small fires were insulated and reflected so well they flashed. It now requires a thermal barrier over installations. I believe it is 1/2 drywall minimum.



It has 5/8" USG type X drywall on the chase interior and 1/2" Durock cement board on the top and upper section where it connects with the house.  At the time I thought Durock was the best we could do for fire rating but the low R-value of cement board is a concern.


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## Mr_D (Jan 27, 2014)

oconnor said:


> I would not recommend the idea from earlier of wrapping the chimney in insulation, ceramic or otherwise. It needs the air space to cool.   I assume you have installed a block off above the fireplace, essentially making the chimney cavity a dead air space? If so, the venting it to the outside or to the room would seem easier.


Regarding wrapping the chimney... I recognize the heat buildup concern.  Since it requires a 2" clearance what if I used a 20" ID insulated pipe or just a metal heat shield?  That would give it about 5.5" of clearance on all sides like a small chase and I could vent that out the top with a larger vent or even an an air intake up high 7ft below the top if needed.

I tried blocking off the fireplace at the 10ft level with a temporary Durock firestop and left a 1" air gap around the pipe.   Without the influx of room air it ran significantly hotter so I had to remove it.  

Ultimately I think it will have a firestop that splits the chase into upper and lower cavities.  The lower level vents into the room (with accessible fans if need be) and the lower level doesn't run very hot.  The upper level then vents to the outside with as much vent as needed to cool it down.  The vented flashing at the top around the pipe may need to be changed out for something with more air flow.   The increased flow up high shouldn't affect the lower chase or living space too much due to the added fire stop.


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## oconnor (Jan 27, 2014)

I expected to see the instructions mention an airtight radiation shield where the chimney passes through the vapour barrier, like you would see in a ceiling connection box. That would be the firestop.

The heat shield is mentioned in the pic above. Excel sells one to install over the full length of the chimney when required.


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## begreen (Jan 27, 2014)

Before considering wrapping the chimney be sure the mfg agrees and provides a list of suitable insulation.


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## Mr_D (Jan 28, 2014)

begreen said:


> Before considering wrapping the chimney be sure the mfg agrees and provides a list of suitable insulation.


I'm trying to work with them and a list of suitable insulation would be great but I'm not counting on it because it's not likely they test alternate designs in detail.

They run a standard UL test for each model of stove and chimney mounted in a predefined test environment and it has to meet certain conditions. 
They probably aren't going to recommend anything other than the specific combinations and materials they tested even if the results out in the field are quite inadequate regarding safe wall temperatures.

Each mfg should specify a maximum R-value for insulated, enclosed wall assemblies around fireplaces.  
Each product has it's own output characteristics and the wall /vent system needs to dissipate the heat coming off the chimney and fireplace chassis while remaining within safe operating temperatures. 
Saying we should insulate the chase with no specs of any kind is too broad.  I'd follow a recommendation if there was one.

A high temp product of ceramic, glass or rock wool insulation panels around the chimney itself with proper spacing (or lining the chase walls) along with appropriate ventilation should be close to ideal. 
We'd have a warm chimney with reduced creosote buildup and reliable, fire rated, relatively cool chase walls.   They don't go that route due to the material expense and cheaper products such as drywall gets by in many cases.   Although they don't check temperatures after the install so how would they really know if it's adequate or not?

The rep I talked to today has been in the business for 20 years and has never actually measured how hot their products get.
Maybe exceeding US Gypsum max drywall temperature by nearly 100°F is a National sized can of worms they hope will go away.


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## NVHunter (Jan 28, 2014)

My chase is going to be ten or so feet tall with 6" duravent duratech running through it. The chase isn't going to be very big (18"x36") so I'm going to line the inside with rock wool or some other non combustible material while maintaining minimum clearances and then vent the chase at the top. Hopefully this will keep it warm enough but won't have it so hot that it's causing issues with the combustible framing and outside siding. 

Don't know what else we can do.


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## Mr_D (Jan 28, 2014)

NVHunter said:


> My chase is going to be ten or so feet tall with 6" duravent duratech running through it. The chase isn't going to be very big (18"x36") so I'm going to line the inside with rock wool or some other non combustible material while maintaining minimum clearances and then vent the chase at the top. Hopefully this will keep it warm enough but won't have it so hot that it's causing issues with the combustible framing and outside siding.
> 
> Don't know what else we can do.


That sounds pretty good and there's tons of options since it isn't built yet.  

Rock Wool passes air fairly easily so naturally it needs an outer wall that functions as an air seal of some kind to limit air intrusion and heat loss when it's not running.   I presume you're planning on drywall protected by rock wool (or other high temp insulation) as a reasonably air tight and insulated wall.  
That should be better than the average install.

Usually insulation goes between the studs of course, not on top of the drywall so that portion of it isn't traditional construction in that sense but protecting the materials has to be considered in the design.    I'm reading up on MinWool-1200 Industrial board and Thermo-12 Gold insulation to see if it's ideal for this type of application or not.  
Both are rated to 1200F and come in all shapes and sizes.  Neither is as cheap as Rock Wool though.


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## NVHunter (Feb 12, 2014)

Mr-D have you found anything new with the chase?

I was reading my Duratech chimney manual and it calls for the chase flashing to have 1/2" spacers it sits on for proper ventalation as well as 3/4" of open space all the way around the flashing and the chase structure.

Also the chimney opening on the chase flashing is 11" in diameter, leaving an inch on each side all the way around the chimney for further heat ventoff. 

Does your system have this?

I'll try and attach a photo from the manual.


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## Mr_D (Feb 15, 2014)

NVHunter said:


> Mr-D have you found anything new with the chase?
> 
> The Duratech chimney manual calls for the chase flashing to have 1/2" spacers it sits on .....and 3/4" of open space all the way around ....
> Also the chimney opening on the chase flashing is 11" in diameter, leaving an inch on each side all the way around the chimney ..
> ...



No.  This one doesn't have that much vent clearance. 

The chimney has a vent at the top but it could probably use more air flow.  You can see the clearance in my photo on page 1 of this thread called "top radiation shield.jpg"  and  "vent view.jpg".  The clearance between the chimney and the radiation shield can be seen and it's not a lot.  It also has no 1/2" spacers as NVHunter mentioned, it's tight up against the ceiling and only vents around the pipe.

The RSF Focus 320 install guide calls for 2" clearance to combustibles around the pipe which is fine but the top radiation shield looks like it has only 1/2" of clearance for air flow between the sheet metal and the stove pipe.  Also the final exit at the top is limited by a series of small, oval slots visible in the earlier photo's and that's just not much vent area which could be half the problem.

*New Chimney Sleeve: *  (same one oconner mentioned actually)
RSF finally came up with 1 suggestion after 2 months of waiting. 
They suggested the local dealer install an ICC brand 11" metal liner around the original 9" (7" ID) stove pipe to lower chase temperatures.  Apparently they use a liner around the chimney for installs in Canada but the US doesn't have the same requirement.  The additional metal sleeve will vent out the top and I'd expect it to reduce the heat in the chase somewhat.  The chimney assembly will then be like a triple wall but the outer section of air goes out the top. 
RSF didn't provide any specs on how much the temperature should drop. 

It's not clear how the new liner will be vented because if it vents back into the chase at the top all the heat captured by the liner would dump back into the chase. Meanwhile if it only vents the liner portion then the chase doesn't have a vent anymore.   The chase probably needs to vent not only for chimney heat but also for summer heat if it's closed in with no ventilation.  Any thoughts?

*New firestop to be installed:*
At my suggestion the local dealer agreed to work with me to install a firestop half way up the chase since it has no firestop in their original recommended design. 
With the chase open from the fireplace all the way up to the chase top 27 feet above we lose a lot of conditioned air out of the vent at the top. 
That's why I pursued having a firestop installed, not only for safety but also to buffer the conditioned air blowing out through the chase top.

The tall chimney with no bends and a tall chase with no firestop causes a continuous draw on the house making the whole structure negative pressure.  This makes portions of the house colder (like an open fireplace) as outside air has to replace all the air that goes out the top.   The house is fairly well sealed (maybe too much) but with that much negative pressure the house now cools off a lot faster than it used to with the influx of outside air getting pulled in.  The indoor humidity also dropped from 60% last year to 30% this year due to the high air exchange rates.  I'm hoping a midpoint firestop that buffers the air will fix the heat loss

*Sealed radiation shield ?*
The dealer plans to install a vented  firestop with a 2" air gap around the chimney.  The firestop gets installed about 10ft above the fireplace and the new 11" metal liner would extend from the firestop up to the chase top.   I proposed they install a sealed radiation barrier at the firestop instead to limit the house air going out the chase top.  RSF makes one just for that purpose for efficient houses where it maintains the vapor barrier integrity.   Then if necessary we add a small intake air vent just above the firestop to supply outside air for the new 11" liner to vent with. 

The dealer plans on using a vented firestop which can only vent  by consuming conditioned house air  unless I somehow convince them to use the sealed version instead.  Their plan would waste house air 24x7 forever whether the fireplace is on or not.

*Chase wall protection*
It looks like they'll have to remove the chimney and top radiation shield to get the new 11" liner installed,  When the chimney is out there would be room to install wall protection in the event that the new liner/vent doesn't lower the wall temps enough.   I'm considering installing 2" mineral wool board such as IIG  "Minwool 1200" or Roxul RHT-80 board to line the chase walls.  2" rock wool board at R-4 per inch would lower temps enough to protect the drywall by dropping it about 50°F which would bring the drywall temps back into the safe range below 125°F.   Rock Wool board is rated for 1200F operation and doesn't melt till 2000°F.  The Roxul version costs only $.40 cents/ board foot at 1" thick or 80 cents for the 2" version so this is cheap insurance.  I can do the whole chase for $100 + shipping,  

The rockwool board would add a significant safety factor for the chimney and also protect the drywall from long term heating so it's fire rating remains intact.

If the dealer agree's and my logic is on track the chase redesign accomplishes 5 things:

Sealed Firestop - adds better protection for the house and keeps conditioned air in the house rather than venting it out the chase top.
Metal chimney liner lowers chase temps to manageable levels.  (might require dedicated intake air vent).
1200°F Rockwool boards for chase wall adds protection for fire events and lowers drywall temps to safe levels below 125°F.
Upper chase area can be cooled with outside air without affecting the house or conditioned air.
Lower chase heat can be redirected back into the living space via passive vents for more efficient heating.

I know this level of planning, safety, and thermal efficiency is past what the dealer will care about but it should be a good overall design. 
We'll see.  Right now we're waiting for the proposed 11" liner to arrive.


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## E Laszlo (May 22, 2014)

Wow, the suspense is killing me! Any updates? I'm building an interior chase in a new construction house right now. After reading this, I'd like to incorporate some of your proposed designs... if they work.  Keep us posted!


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## Mr_D (May 23, 2014)

It worked!

The high temperature's inside the upper chase area are resolved.
This is perhaps one of the few installs that always has a warm chimney but it never gets too hot either.

The modifications I mentioned before have been completed and the chase walls now runs about 100°F cooler than before.
Original chase wall temps were hitting 210°F with the firebox loaded at 60% full and the air damper set at medium.
Running the air damper fully open or burning a larger load of wood such as is shown in their product brochure would have easily hit 230F or more inside the house walls.
Now it runs 90-110°F inside the chase enclosure and the heat loss of conditioned air exiting out the top is also resolved.

After waiting 4 months for RSF fireplaces and the local dealer to come up with a solution they implemented a combination of solutions.
Then the local dealer tried to charge me an additional $1800 in labor and parts on their 2nd service call to fix the issues that have been there since it was installed last October.  Fortunately I was able get the labor portion of the 2nd bill removed since they can't really charge 26 hours labor to come back and fix it since it was not installed in a safe and code complient manner in the first place.  They were trying to charge for installing inadequate venting and removing it as well as the time to install the right one plus all the original and adjusted components as well.  They wouldn't have had to come back at all if they knew more about the heat generated by these systems and gave adequate install guidelines but they had never really tested and evaluted an installed wood burning fireplace before.

This install took a lot of research and calculations regarding convection and conductive heat transfer and high temp material choices.  The local dealers install crew also learned a lot and while they may not routinely use all of what was implemented I'm sure that future installs in this area will be safer due to what we learned on this one.

Here is how we fixed it.

*New Chase top with better ventilated flashing*
The original top vent had rows of small holes with minimal surface area.  The new ventilated flashing at the top of the chase has at least 5x the surface area.  This should have been used from the beginning.

*Chase wall protection*
I lined the chase walls with 2" of Rock Wool 2000°F rated Insulation.  The R-8.5 insulation value (at 2") protects the drywall from chimney radiation and dropped the surface temperature of the drywall 50°F by itself, almost down to safe levels. 210°F readings are now down to 160°F after this modification. The rock wool was cut for a snug fit and held in place with long decks screws capped with 1.5" washers.

*11" ICC brand metal liner*
We installed an 11" metal liner pipe around the original 9" (7" ID) dual wall stove pipe.  This is an original, optional factory part that they routinely install in Canada but not in the US due to less stringent requirements here.  The metal shields the walls from the chimney heat radiation and provides a 1" air buffer around the chimney that allows the heat to go out the top through the new ventilated flashing.
This retrofit lowered the walls temps another 40F down to around 125F now.
We added seven 1" air intake holes around the bottom perimeter of the new 11" liner just above the firestop.  This allows it to pull air from the chase area into the liner and exit out the top as it's heated.  Upper chase makeup air comes in through a new 4" outside air vent located half way up the chase exterior wall just above the firestop and that air gets pulled into the bottom of the new liner via convection through the 1" air holes we added.  In actual use the 4" side air vent was larger than needed and it chilled the chase area considerably.  I reduced the upper chase air intake vent down to a 2x3" size and that's working good.

*New top air vent for the chase area*
The new upper chase air intake needs somewhere to vent the heated chase air into so we also added a 5" round, screened air vent that goes out the chase top.  It exits through the ventilated flashing.  This allows any heated air to exit out the top using convection only and it works fine.  There's no humidity issues inside the chase anymore because conditioned room air is no longer being dumped into the chase as cooling for around the chimney system as was required in the original,inefficient, inadequate design.  The new design with a dedicated chase air intake just above the sealed firestop resolved the problem of major conditioned air loss out the chase.
Now it now uses outside air just like the stove combustion itself.
The new air vent design and other adjustments maintains a chase temperatures around 90- 115°F with no fans or automatic electronics needed.  The chimney pipe itself is still nice and warm too due to the new liner keeping a 1' warm air buffer around the chimney.  I measured 515°F coming out the top of the chimney pipe above the roof while the flue temp at 1ft above the fireplace was at 600°F during a typical size fire.  515°F coming out the top should maintain a nice clean chimney.

*New Firestop*
A Firestop was installed half way up the chase. It's constructed of 2x4 framing with a floor of Durock board backed with 4" of industrial rock wool.  This component was missing in the original design and now it serves 2 purposes, it blocks conditioned air from exiting the chase and of course it serves as a fire stop as well.
It's a 2000°F rated firestop to go along with the fireproof walls.

*Air vents*...  Lastly I need to install some passive air vents that allow the chase area in the living room to dump it's extra heat back into the room.  I see temps at the top of this section around 110-120F and that warm air may as well contribute to heating the room rather than staying in the chase.  The air vents will be just below the cathedral ceiling with another vent near floor level.


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## E Laszlo (May 23, 2014)

Well done... and thanks for the update!!


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