Whenever a gas corporation installs service lines, service connections or appurtenant facilities at the request of an applicant who does not immediately desire service, the applicant shall bear the entire reasonable expense of providing, placing and constructing such facilities but shall be entitled to a refund whenever gas service is begun for such part of the expense as the corporation is herein before required to assume. The refund shall be the cost of the service lines and appurtenances, less depreciation at the rate of three percent per year.