A certified energy auditor uses the latest in diagnostic technology to test your home for air leakage, duct leakage, air quality, insufficient or oversized HVAC equipment (usually oversized), proper insulation quality and quantity, lighting, the quality and fit of doors and windows, and anything else related to the building envelope (the conditioned living space). Once the results from the audit are compiled, recommendations that are specific to your home can be made. This allows you to invest in the repairs or upgrades that will give you the most improvement for your money. What we often find is that replacing windows / doors and HVAC systems are lower down the list. Often a little air sealing, duct sealing, and insulation improvements are all that is needed and compared to the other option, a lot cheaper too.
As a good friend of mine once said, “Don’t throw money at the problem, throw knowledge; it’s a lot cheaper”.