The ornamental design for a chimneydraftregulator, as shown and described.
FIG. 1 is a perspective view of a chimney draft regulator;
FIG. 2 is a front elevational view thereof;
FIG. 3 is a top plan view thereof; and,
FIG. 4 is a bottom plan view thereof.
The broken line showing of parts of the drawings is included for the purpose of illustrating use and environment and forms no part of the claimed design.