The short answer is closed.
And in most stoves it’s better to close the door as soon as possible. The reason is quite simple. With the door closed, your stove is up to 60% more efficient than if you have the door open. That means more heat in the room and less expense for you.
The confusion probably stems from people who are used to that instant blast of heat that comes from lighting an open fire. With a wood burner, you’re not supposed to feel the heat from the flames. Not directly, at least.
The flames in the firebox heats the metal panels that make up your stove. They, in turn, heat the rest of the room. It’s a more efficient way of heating your home than an open fire because less heat escapes.
If you think about it, closed is the obvious answer. Otherwise some enterprising company would have stopped putting the doors on and sold them at a cheaper price!
When to close the doorAssuming you’ve set your stove with newspaper and kindling, as soon as you’ve lit the newspaper is usually the best time to close the door. You should already have the air vents open while lighting the stove, so there is still a good air supply.
Some stove manufacturers prefer you to keep the door slightly open during these initial stages of the lighting process. Check your manufacturer’s manual to see if this is recommended for your stove.
You’ll soon learn what works best for your stove from experimenting. Even if you are leaving the door ajar, as soon as the stove is properly lit you should close the door.