Section 22. “Lodging house”, as used in sections twenty-two to thirty-one, inclusive, shall mean a house where lodgings are let to four or more persons not within second degree of kindred to the person conducting it, and shall include fraternity houses and dormitories of educational institutions, but shall not include dormitories of charitable or philanthropic institutions or convalescent or nursing homes licensed under section seventy-one of chapter one hundred and eleven or rest homes so licensed, or group residences licensed or regulated by agencies of the commonwealth.