Can I do the install myself (for example, windows, insulation, or HVAC) and still get the tax credit?
Yes, you can install the eligible product yourself, you are not required to have a particular contractor do the install.
Many of the energy efficient tax credits allow the cost of installation/labor to be included in the eligible amount (view installation cost details). However, if you install the product on your own, you can not claim a labor charge for the installation. There is no basis for which to charge the government for your time.