If you only need a 3' air duct and don't want to buy the parts separately, this kit from Amazon would work. https://amzn.to/3uNHgIZ

I was so focused on trying to explain why the vent is important and how I built mine that I completely forgot to tell you that I have noticed a difference since installing this vent.

My house is plagued with air gaps so this was really important. Before the air vent, I was unable to keep my main living area comfortable using only the wood stove IF the temperature outside dropped below 25F. Now, the temps can drop to single digits and it stays nice inside. I should also mention that I resealed my basement door which was the largest gap bringing in the cold air.

I used the 4" hole saw from Harbor Freight because its the cheapest but I DO NOT recommend this. The center drill bit doesn't extend beyond the hole cutter far enough to start a precise hole.