I am installing a coal burning stove in the basement. I would like to place a cold air return input over the stove. The cold air return will need to be approximately 35 feet with two 90 degree turns to reach my oil furnace. Is the run too long? Would the addition of a duct fan or two be of benefit? Any input would be appreciated.

Thanks Tom

Is your plan to place a duct over the coal stove and then tie it in to the cold air return going into your furnace? If so, will the circulating fan be active to supply heat to the rest of the house? If you answer yes, consider that the fan will pull a draft directly over the coal stove. If the stove is not designed with a plenum for forced air heating, the fan draft could potentially pull combustion gases into the duct work and distribute them through your house. VERY unsafe. I used to have a cousin with a coal stove.................... very sad story.

Few issues come to mind
Anytime a cold air return in placed in a basement a supply air will be needed. You do not want to create a negative air pressure within a basement otherwise you will end up pulling the draft air down the chimney.
Another concern is radon. Radon typically is pulled into a basement from the stack effect of the house. With a cold air return placed within the basement and without a supply air producing the counteracting pressure the negative air pressure produced will draw in radon within the basement.
I do not suggest changing the return air that comes from the house back to the furnace. It will end up causing balance issues from within the home.
A transfer grill on the floor to allow the heat to rise to the roof above is all that I would suggest. I know many folks have installed elaborate duct systems to bring this warm air up to living levels within their homes but all have serious health drawbacks and must be carefully designed. Its much different however if the stove is on the living level of the home.
If you have not purchased the stove, and your serious about using wood as a heat source. Look into the combo oil furnace wood stove units. They are more money but offer the best of both worlds.

Thanks for your responses, but I still need info regarding my original post.

I think both answers to your original post make it clear that what you plan to do is a very bad idea. What more do you want any of us to tell you?