Actually, there is a way to have multiple dampers installed.

If someone drills a hole through the side of the damper frame, out of the travel path of the damper valve plate on a masonry fireplace, you can run the cable and cable protector through that area to enable both dampers to work.

This is beneficial if someone is attempting to trap the cold air column within the chimney.

Sometimes, when using only a top mounted damper, there is still a significant cold air effect present and shutting the primary damper will stop of slow down this effect.

Sincerely,
A. Bart Ogden, President
Home Safe Hearth & Chimney, Inc.
Wichita, KS
Voice 316-265-9828
Fax 316-265-9890
www.HomeSafeKS.com