Dumb question about stove pipe to furnace connection

[Badfish740]

So I got my double wall stove pipe from Lowes the other day and I think I'm missing someone. I have a 45 degree elbow which will come off of the outlet (top) of the furnace. I thought it would fit over the outlet, but they seem to be about the same diameter. Is there some sort of adapter that goes between the outlet and the stove pipe?

 

[DAKSY]

If you are attempting to install the D/W connector pipe in the correct position
- not upside down - & it doesn't fit, you probably need a stove adapter.
I don't know if Lowe's carries them or not, but you should be able to
contact the pipe mfr to get one...

 

[freeburn]

Try flipping it over. With single wall, the crimped end will go into the collar on top so that the creosote drips backward into the stove instead of coming out of the pipe. Not sure about double wall. Echo DAksy there, stove adapter.