​Yes, duct work cleaning services are subject to sales tax.  These services are taxable whether performed by a general janitorial cleaning service or a business specializing in duct cleaning.

Residential or commercial cleaning services (water extraction, restoration of wall-to-wall carpet, cleaning/treatment of walls, application of protectant, application of deodorizer, cleaning of tile or grout, etc) is subject to the sales tax.  

The removal and installation/replacement of real property (for example, removal of carpet and drywall and subsequent installation of carpet and drywall) is contractor service not subject to the sales tax. 

According to the provisions of Kentucky Regulation 103 KAR 26:070, all sales to contractors, subcontractors, or builders of tangible personal property to be incorporated or fabricated into any structure or improvement to real property are subject to sales tax. This same treatment applies to sales of janitorial services to contractors.  The liability for the sales tax associated with the purchase of the property or services is on the contractor as the consumer.  

Therefore, contractors may not claim a resale exemption on the purchase of taxable janitorial services performed on their construction projects because they are not reselling the janitorial services. Furthermore, the sale of the finished construction project is realty that is not a retail sale subject to sales and use tax.