Clean Smokestacks Act of 2005

Clean Smokestacks Act of 2005 - Amends the Clean Air Act (CAA) to require the Administrator of the Environmental Protection Agency (EPA) to promulgate regulations to achieve specified reductions in aggregate emissions of sulfur dioxide, nitrogen oxide, carbon dioxide, and mercury from powerplants (electric generation facilities with a nameplate capacity of 15 megawatts or more that use a combustion device to generate electricity for sale) by January 1, 2010.

States that regulations promulgated under this Act may require additional emissions reductions if the Administrator determines that the specified reductions are not reasonably anticipated to protect public health or welfare.

Directs the Administrator to coordinate with other Federal and State agencies to increase energy efficiency, to increase the use of renewable energy, and to implement cost saving advanced demand and supply side policies.

Requires powerplants, on the later of the date 30 years after the powerplant commenced operation or five years after this Act's enactment, to comply with the most recent new source performance standards under CAA provisions regarding air quality and emissions limitations and with specified requirements for modified sources.