A Raleigh-based company that ships air filters on a regular basis to homeowners has raised $6.9 million in a private equity offering, according to a filing Thursday with the Securities and Exchange Commission.

FilterEasy Inc. raised the money from 35 investors, according to the filing. It has now raised a total of $11.4 million, having raised $4.2 million in July 2016.

Investors include Arsenal Venture Partners with participation from NC State Endowment Fund, Bonaventure Capital, Cofounders Capital, IDEA Fund Partners, John Replogle, and Triangle Angel Partners, according to the company.

The company was founded in 2014 and delivers air filters to homes on a schedule determined by the purchaser.

Its website offers air filters in over 40 different sizes and three quality levels, which covers most residential needs. Homeowners sign up for the service, select a filter size and tell FilterEasy their delivery schedule, such as every three months.

CEO Thad Tarkington and COO Kevin Barry founded the company while attending North Carolina State University. As the business model proved successful and the business grew rapidly, Tarkington and Barry shifted their focus from school to business.

Private companies similar to FilterEasy, which rely on a Reg D exemption, aren’t required to register securities offerings with the SEC, but instead they must file a Form D electronically with the SEC after they sell the securities.