One common place energy is being lost around the clock, is the oversized gaps around wiring and plumbing holes. You can simply use a rubber roofing boot to seal holes where air conditioning, wiring or plumbing lines penetrate the walls of your home.
Once you apply the boot you can seal around the smaller gaps by using can foam such as great stuff. Once you apply the foam it will expand and harden to leave an air tight seal. Projects like these cost pennies to complete and save so much energy that is constantly wasted. Saving energy doesn’t just save money it saves the world, so always go green and live efficient as possible.