The Instructions on Form 5695 state that the costs of the energy improvements are treated as paid when the installation is complete. At that point the improvement is capitalized(minus amount of credit reimbursed by IRS). So, since the heater and two doors are completed in 2010, Payment, in itself, should not be a problem.

You should keep maufacturer's certifications, and the costs of the doors must be broken down so you can exclude onsite installation and assembly.