You will want to use a HERS rater certified through RESNET. This rater is trained to develop a Home Energy Rating on your home.
A home energy rating involves an analysis of a home's construction plans and onsite inspections. Based on the home's plans, the Home Energy Rater uses an energy efficiency software package to perform an energy analysis of the home's design. This analysis yields a projected, pre-construction HERS Index.
The rater then conducts onsite inspections, typically including a blower door test (to test the leakiness of the house) and a duct blaster test (to test the leakiness of the ducts). Results of these tests, along with inputs derived from the plan review, are used to generate the HERS Index for the home.
The HERS Index is a scoring system established by the Residential Energy Services Network (RESNET) in which a home built to the specifications of the HERS Reference Home (based on the 2006 International Energy Conservation Code) scores a HERS Index of 100, while a net-zero-energy home scores a HERS Index of 0. The lower a home's HERS Index, the more energy efficient it is in comparison to the HERS Reference Home.
Each 1-point decrease in the HERS Index corresponds to a 1% reduction in energy consumption compared to the HERS Reference Home. Thus a home with a HERS Index of 85 is 15% more energy efficient than the HERS Reference Home and a home with a HERS Index of 80 is 20% more energy efficient.
You can find a HERS rater here.
If you have your home gutted and plan on making it efficient, you should also consider getting your home certified to the Energy Star standards.
For more information:
Check Green Home Guide's nationwide directory to find an energy auditor near you.
Read Steve Saunders's Q&A "I keep hearing that I should get a home energy audit. What should I expect to pay and expect to get?" for details of audit pricing.