Block off plate or pour-in insulation?

[newatthis]

We have a Jotul F500 Oslo that is plugged into an exterior brick chimney. The previous fireplace was always hard to start due to significant downdraft of cold air and the current woodstove also has a bad downdraft at cold start. It is also hard to get the stove up to proper burning temperatures, it is always a little below burn range on the magnetic Rutland thermometer. The chimney is probably not tall enough either, it is single story although the ceiling is maybe 12 feet. We have never installed a block-off plate.

Should we do the pour-in insulation to overcome the cold stack of air at the start-up, or is a block off plate sufficient? Both? How do you keep the pour-in from coming into the living room? Is the safety concern about vermiculite that there might be some asbestos contamination? What are chimney blankets? It's been over a decade and it's time to finish this project. Thanks for your expertise!

 

[begreen]

Remove the liner and wrap it with a liner insulation blanket, then reinstall. I'd add a blockoff plate to reduce cold air sinking back into the room. Also, the horizontal run from the stove to the liner should be pitched uphill toward the liner and as short as possible. That will help, but it's possible that additional height will also need to be added to the chimney top if the liner is less than 15'.

 

[bholler]

We have a Jotul F500 Oslo that is plugged into an exterior brick chimney. The previous fireplace was always hard to start due to significant downdraft of cold air and the current woodstove also has a bad downdraft at cold start. It is also hard to get the stove up to proper burning temperatures, it is always a little below burn range on the magnetic Rutland thermometer. The chimney is probably not tall enough either, it is single story although the ceiling is maybe 12 feet. We have never installed a block-off plate.

Should we do the pour-in insulation to overcome the cold stack of air at the start-up, or is a block off plate sufficient? Both? How do you keep the pour-in from coming into the living room? Is the safety concern about vermiculite that there might be some asbestos contamination? What are chimney blankets? It's been over a decade and it's time to finish this project. Thanks for your expertise!

Begreens recommendation is exactly what I would do as well

 

[stoveliker]

The block off plate won't help with downdraft (draft reversal) into the stove. So it won't help start the stove. For that you should increase the flue height as suggested above. You can also point a propane torch up the flue for a minute before lighting the kindling.

The plate will help with cold air coming into the room and help get the heat from the stove into the room rather than up the flue outside of the liner.

The insulation will help with draft (keeping the stove in better burning temps) once it's going.

 

[newatthis]

Thank you begreen, bholler, and stoveliker. Any comments regarding my question about the pour-in insulation?

 

[stoveliker]

I don't know about the asbestos thing - though I suspect that that is old news.
(It does make me worried about the vermiculite below my above ground pool liner...)

I suspect that current vermiculite sources are tested quite stringently for asbestos contamination. bholler will know better, I suspect.

That said, a blanket wrapped around the liner is much better, because the pour in insulation won't get between the liner and the clay where they touch (leading to a safety hazard - do you have 1" between the outside of the chimney (i.e. the brick or block) and any combustibles (studs, rafters, shingles)? That is code that was put in place b/c of cases where it went wrong....
A blanket (held in place with metal wiring so it doesn't bunch up while putting the liner back in the clay flue) will be much safer.

 

[stovelark]

The chimney does have a 6" liner right? If not, that and insulation would prob fix most issues. Is this an older Oslo? Not getting to burn temps? Sounds like I'd suspect the wood as well. Gelled alcohol and good dry kindling will cure most startup /reverse draft issues. I know its a pain to buy the gel, but it works well. I use it myself, smokeless startups are the norm now. I live in a raised ranch with a shorter chimney (about 14-15'), my Oslo was slower to get a head of steam going, but once it did, it was a fine heater. Good luck, insulated liner, good dry wood, almost always success.

 

[bholler]

Thank you begreen, bholler, and stoveliker. Any comments regarding my question about the pour-in insulation?

They stopped using the mine that was heavily contaminated with asbestos in the late 70s. But there is always a risk. But pour in is not a good solution for fireplace installs

 

[begreen]

Other issues with pour-in insulation are:
• getting even distribution all the way around the liner all the way down. This probably will require pulling the liner, adding spacers to keep it centered in the chimney, then reinstalling the liner, and pour
• It's messy, especially if the liner has to be pulled due to age or failures.

 

[newatthis]

I have gotten such good advice here. I called the store that sold us the Jotul and the installation 10 years ago. The person taking my message said "I don't think we do anything like that. We can't take apart something once it's installed." Still waiting for the final word on that.

I don't know how hard it's going to be to get an individual installer to disassemble and add the insulation blanket.. We did a double wall stove pipe and a chimney liner as was customary here on hearth.com at the time, but I don't remember insulation blankets being discussed then.

 

[begreen]

The stove has a too short liner that is in a cold exterior chimney. Local topography can also cause issues in some cases.

We did a double wall stove pipe and a chimney liner as was customary here on hearth.com at the time, but I don't remember insulation blankets being discussed then.

IIRC the installation was presented as a done deal in 2015. That thread was mostly focused on mantel shielding questions. The installation was described as a "single layer, insulated flue." This is likely because at that point you were actually new at this. Clearly, you were trying to do things correctly.

If the liner isn't insulated or tall enough, it's looking like the installer didn't check code nor the stove installation manual's requirements for venting height. To resolve the poor starting, running performance and safety issues, both conditions should be remedied. In the meantime, is there a good, working CO monitor in the room?

https://www.hearth.com/talk/threads/removable-mantle-shield-project-done.141703/

 

[newatthis]

The stove has a too short liner that is in a cold exterior chimney. Local topography can also cause issues in some cases.

IIRC the installation was presented as a done deal in 2015. That thread was mostly focused on mantel shielding questions. The installation was described as a "single layer, insulated flue." This is likely because at that point you were actually new at this. Clearly, you were trying to do things correctly.

If the liner isn't insulated or tall enough, it's looking like the installer didn't check code nor the stove installation manual's requirements for venting height. To resolve the poor starting, running performance and safety issues, both conditions should be remedied. In the meantime, is there a good, working CO monitor in the room?

https://www.hearth.com/talk/threads/removable-mantle-shield-project-done.141703/

I guess my ignorance is showing. Here’s a pic behind the stove. What do I have?

The original installation company said they were going to put in quarter inch blanket, but I am aware at half inch exists. I assume that thicker is better?

 

[begreen]

Being new back then, it's understandable. The liner in this picture is uninsulated.

 

[stoveliker]

Begreen, is there a chance there is insulation around the liner when it enters the chimney?
I.e. they kept it off in the old fireplace ?

 

[begreen]

It's possible. Verification requires eyes on site.

 

[newatthis]

Being new back then, it's understandable. The liner in this picture is uninsulated.

Is the stove pipe a double wall?

 

[begreen]

Is the stove pipe a double wall?

All I see of stovepipe is a picture of the tee. It doesn't look like double-wall from 2500 miles away. Is the original invoice for this work on file? If so, what does it say was installed?

 

[newatthis]

All I see of stovepipe is a picture of the tee. It doesn't look like double-wall from 2500 miles away. Is the original invoice for this work on file? If so, what does it say was installed?

Begreen, regarding insulation, I assume 1/2" is better than quarter inch for an exterior chimney? Is there anything thicker? Although I don't quite understand how insulation will keep the pipe warmer during a cold start.

Also, do you have any comments about the discolored pipe?

 

[bholler]

Begreen, regarding insulation, I assume 1/2" is better than quarter inch for an exterior chimney? Is there anything thicker? Although I don't quite understand how insulation will keep the pipe warmer during a cold start.

Also, do you have any comments about the discolored pipe?

It will make it heat up much faster. And yes 1/2" is better than 1/4" and 1/4" doesn't give you the zero clearance code rating

 

[begreen]

Yes, proper insulation will also keep the flue gases hotter all the way up the chimney liner. This helps draft and reduces the chance of creosote buildup.