What goes in, must go out. Forced fan may be necessary if you do not have access or do not have dry wood. Your coal bed may be going down quickly, because so much heat is being used to dry the wet wood. There are boiler Officiandos, who swear by burning a mix of dry and less dry wood, extending reload times. This is probably accurate, but more wet wood = less heat in btu's for your house, because you are using the heat to dry the wood to burn. When I had a classic the first year, I DID have to add a front fan, because I did not have enough dry wood, and temps were better than - 20 f. I DID use more wood, part because of the heat being used to dry wood, part because I was moving greater volumes of air (and heat) up the chimney. You do what you have to do.
Also, if one has dry wood, recovery times will be quicker, but so what? You are still losing more up the chimney. When I learned the "better burn practices" which included having an adequate seasoned wood cut well in advance of the next winter, I did much better employing the natural draft that came with the unit.
If you are in a situation that you may need both-- add a switch (waterproof) to the fan wire on the front of the fan box, you will have the option without a lot of hassle.
Best of all, is keeping a good coal bed established, and not being too aggressive in removing your clinkers and ashes which help hold fire between cycles.