Will a block-off plate help poor draft due to cold air? Or make it worse? (Oslo)

Insulated liner will help with keeping a good draft (while fire is going) it will help with reducing smoke condensation thus reduce creosote build up by keeping flue temps higher. It will also help with establishing a draft on cold starts by eliminating the amount of news paper you will have to use to warm the flu up (you may still have to burn paper or maybe upgrade to a heat gun or propane torch to warm things up) A block off plate will create a more efficient stove, it will tremendously reduce the amount of heat going up the chimney, more heat going into your room. I recommend doing both, the insulated liner can be a little pricy but a block off plate is fairly cheap to do and very easy diy project, the greatest thing to know is to use the right insulation, ie fire proof, I recommend ROXUL R-15, its a great insulator, a whole bad is around $40, its rated to 2,150 deg f, if you hit that temp ever you will have bigger problems then the insulation catching fire, some members also recommend using ceramic insulation, that will def do the job but to me anyway the roxul is cheaper and easier to work with as far as mess and ich wise. You will also need the plate, you can get very creative ie dura rock, customer cut 18g sheet metal and concrete screws. Look up block off plate on this site, it will help you..good luck

What's your method for starting a fire? Are you using the top-down method?
https://www.hearth.com/talk/threads/top-down-fires.45442/#post-930002
I have a downdraft on a cold stove in my house. What I do is use the top down method and leave only about 3 inches of space from the top of the wood to the secondary tubes and then roll up newspaper, tie knots in the middle of em, and light those and immediately close the door. Sometimes they die out and I have to relight em but this will usually heat the flue enough to get the draft started without letting smoke in the home. The higher in the stove you can get the knotted up paper, the better. Once you see the flames start going up the flue open the door a little and it'll suck the air in needed to get a good fire going.

Are you using newspaper to start? I've always found it creates more smoke if the liner isn't warmed. I found a fire starter with some kindling with the door cracked seems to start the process slowly without the burst of flame and smoke that newspaper creates.

Yeah smoke will come out of all the small gaps if the draft is pushing down instead of pulling up. Use a heat gun as suggested by kennyp or blow torch aimed up at the top of the stove. Then the smoke issue will most likely go away when you light a fire.

I have the same problem. Can tell just by holding my hand by the air control if it's down drafting. Tried using a hair dryer but it ends up blowing ash all over the place. Tried top down, it worked sometimes but wasn't 100% dependable and once I managed to create a full fledged reverse draft. Total suckiness.

Now if cold air is pushing down the flue I use a piece of newspaper held up high, sometimes I have to move a baffle plate and stick the paper right in the flue opening light it and then close the door. It might burn down for a couple seconds but after a bit the cold air slug will get pushed out and can hear the rush of air up. I've gotten good at it so no more smoke outs.

Couple of other suggestions besides the ones already mentioned ...,i.e. torch, Super Cedars.

1) If you have a window nearby open it a crack and leave the side door ajar for a few minutes ... this may help establish a proper draft.

2) Besides using a torch you can also light a candle in the firebox and just let it heat things up ... it will take longer than a torch but you don't have to "babysit" it like you would a torch ... just light it a half hour or so before lighting the fire.

I would be concerned that using lots of newspaper in your scenario, would be a chimney fire risk - maybe others can chime in if I'm off base...

Just a tip that could help make it easier to warm up the chimney if you are using a torch, lay the fire newspaper and all so it's ready to go and then remove the oval plate on the top of the stove for easy and more direct access to the flue, stick the torch in there and away you go.

i used newspaper no problem sucks it up like a hoover . do preheat chimney it helps alot supercedars or fat candle will work fine running 24/7 no need already warm

To reverse the draft I use one or two sheets of newspaper, not scrunched up at all, no more than necessary to get them in the firebox, light those first, then light whatever is actually starting the fire, start with a big swoosh of flame and heat up the chimney.
I noticed no improvement in my downdraft after installing a block off plate, but I did modify my air supply to allow it to be 100% closed when the stove isn't used, this reduced air infiltration into the house, and minimizes the cooling of the liner. Closing off your air when not in use may help too, even if you can't fully stop the airflow.

TE