29 C.F.R. § 779.321
(d) Certain business establishments engage in the retail sale to the general public, as goods delivered to purchasers at a stipulated price, of items such as certain plumbing and heating equipment, electrical fixtures and supplies, and fencing and siding for residential installation. In addition to selling the goods they may also install, at an additional charge, the goods which are sold. Installation which is incidental to a retail sale (as distinguished from a construction or reconstruction contract to do a building alteration, or repair job at a contract price for materials and labor required, see § 779.355(a)(1) is considered an exempt activity. By way of example, if the installation for the customer of such goods sold to him at retail requires only minor carpentry, plumbing or electrical work (as may be the case where ordinary plumbing fixtures, or household items such as stoves, garbage disposals, attic fans, or window air conditioners are being installed or replaced), or where only labor of the type required for the usual installation of chain link fences around a home or small business establishment is involved, will normally be considered as incidental to the retail sale of the goods involved (unless, of course, the transaction between the parties is for a construction job at an overall price for the job, involving no retail sale of goods as such). In determining whether such an installation is incidental to a retail sale or constitutes a nonretail construction activity, it is necessary to consider the general characteristics of the entire transaction. Where one or more of the following conditions are present, the installation will normally be considered a construction activity rather than incidental to a retail sale: