FMI fireplace chimney problem

Hi everyone.
Recently, I installed FMI Bungallow wood burning fireplace including 8" chimney pipe. I followed all of instructions.
Problem: 10 min after I start the fire, water is dripping from last elbow return. Dripping usually last for 10 minutes. Then it will stop, and as long as fire is on, there no more water dripping. Next day, same story.
I suspect, there is condensation between inner and outer pipe, until inner pipe is hot enough, to evaporate that condensation. Please, need any advice, before I'll cover everything with sheetrock.

has it been raining outside?
or are you burning super wet wood?

Water is dripping while bright sunshine. If I use very wet wood, there would be condensation inside the inner pipe. This is coming from outer pipe. It's about 4-5 oz. of water. After 10 min of burning dropping stops.

sorry, never had that issue...