The certificates are seen as a way to encourage NI home owners to make their houses more energy efficient and to provide some guidance to prospective buyers on how much it will cost to heat a home.
Jason Walsh is Ireland correspondent of the Boston-based Christian Science Monitor newspaper and has contributed to other publications including the Irish Examiner, the Irish Times, the Guardian, the Independent, the Sunday Times, the Washington Times, El Mundo, PressEurop and USA Today.