How many cords of wood should you burn before?

Define "it" please. Whatever "it" is may help to determine how hot the wood is burning and therefore how often "it" should be cleaned. An open fire (like a fireplace) burns with a lot of oxygen but soot and ash will still exist. When it is dampened down partially burnt products will be released. Number of cords is perhaps less important than how the chimney is built, the type of wood, how dry it is, how hot it is burned and the number of starts and stops.

A fire in a cast iron device will be limited to around 500 to 600 deg F as the device will radiate substantial amounts of heat that will cool the fire. Hotter fires will tend to warp the metal. Dampers and lower temperatures are frequently used with cast iron stoves leading to less than a complete burn. Air tight stoves attempt to give products more time to burn completely but still have a limit on temperature.

Masonry wood stoves burn with a different principal in mind. They are intended to burn very hot (around 2000 deg F) for a much shorter period of time and then hold the heat within their substantial mass to radiate at a much lower temperature over a long period of time. Due to the high burn temperature they tend to be very clean with the smallest amount of what is completely burned ash. They are fairly uncommon in the US and more common in Europe.

Cleaning of the exhaust path is an attempt to eliminate partially burnt products that have become lodged there and may ignite at some later time. This burning of the creosote buildup is also called a chimney fire and may be dangerous for a roof, the liner, or material surrounding the liner if there are cracks in the liner. It sounds like a jet engine as a large volume of air is sucked up the flue to feed the fire. As a safety measure some have flues cleaned once a year.

Every season you should clean your pipe,it doesn't matter how many cords you burn.Cleaning your wood stove pipe gives you the confident feeling that your house won't catch on fire.The pipe collects creosote from within,using a steel brush with extenders will do the job.At the end of the season,like summer do your pipe cleaning.Then you can clean the inside of the wood stove.

Good Luck

the chiminey?

once a year.