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