There is no energy auditor certification program in New Hampshire. Energy auditors may have a nationally recognized BPI certification, issued by the Building Performance Institute. As is the case with any services you buy, you should get itemized quotations from several energy auditors, and check their references. The New Hampshire Residential Energy Performance Association, a trade group whose members are residential energy auditors and weatherization professionals, publishes a consumer guide listing contractors by region and area of specialization.
Eversource (PSNH) offers free energy audits to its residential customers. PSNH will underwrite an energy audit of your home and pay up to $4000 for efficiency improvements that will reduce electric usage. (You will pay for any improvements that reduce fossil fuel usage.)
Unitil and other New Hampshire electric utilities have teamed up with Manchester and Laconia Community Colleges to offer an 8-week BPI training course preparing students for BPI certification, an essential accreditation for energy auditors and other home contractors. Contact the colleges directly for more information.