Dampers for Wood Stove – information you need to know
Many home owners want to add a Flue Damper to their flue pipe for their wood stove.
Most modern wood stoves have their own are regulated air control on the stove. The wood stoves manual will provide instructions on usage.
EPA does not allow restricting flow. CSA B365-10 does not allow you to restrict flow unless certified product.
If your stove does not have its own regulated air control you could have a draft test performed and apply to manufacturer, providing draft test details, and request permission 
to install a key type damper. The simplest way to install a proper damper would be to purchase a length of double insulated stove pipe with damper installed. Then you are using a certified product and you have the added safety of using a properly designed product with no risk of insurance issues if you have a house fire.
Unfortunately you are not allowed to modify any product that is Certified or Engineered without an designer or engineers details specify what must be done to ensure product is still safe for its intended use.
Ultimately the fastest and cheapest method would be purchasing a section of double wall pipe with a damper already installed. Hopefully if you already have double wall flue pipe installed that particular manufacture will make the section with damper installed for it.
This a picture from WETT forum of Security pipe with Key Damper. Not sure if you could hook this up to any other manufactures single wall pipe or maybe you would have to use their pipe for entire length.
Read article on Flue Pipe Installation.
Pellet Stove Installation Guide
Wood Burning Appliance Information