Tim Riegel, 59, started making fire pits out of propane gas tank ends a year ago. Now, he makes up to $16,000 per month from his side hustle.

With inflation on the rise, Tim Riegel wanted a side project for extra income — so in September 2021, he bought seven $90 propane tank ends off Facebook Marketplace. The 59-year-old intended to repurpose the tank ends as fire pits — a freestanding, open metal container for fires, typically for backyards or patios — and sell them for $400 each in his hometown of Lamar, Missouri. The fire pits proved popular: They sold out in just 10 days, and Riegel was inundated with requests for more.

Riegel started his business with seven tank ends that he bought off Facebook Marketplace for $90 each. He sold them locally in 10 days for $400 apiece. Tim Riegel

In March, he moved the side hustle online, opening an Esty store. He brought in $50,000 over the next five months, according to documents reviewed by CNBC Make It. In June, his highest-earning month to date, he made $16,000 selling fire pits, most which are priced between $600 and $1,700. "It's tough for everybody right now and I thought, 'I can make some extra income and have fun doing it,'" Riegel tells CNBC Make It. "The fun is the magic of the whole deal. September through December, I pretty much saturated my hometown with fire pits." Here's how Riegel started his unlikely business, and his plans to make it more financially sustainable:

A welder and perfectionist by training

Riegel, who oversees domestic suppliers for a furniture company during the day, says his full-time gig taught him the art of navigating e-commerce platforms. He'd previously used Etsy to source new designers and inspiration. "At first, I thought [Etsy] was just a bunch of old women sewing quilts," he says. "Then I realized I could use it to see what's out there, who's being creative. The [small] companies that are just about to break [into industries] usually start off on one of these platforms." Riegel is also a welder — he used to restore cars as a side hustle and took vocational welding classes in 2006 — and says working creatively is cathartic, even if his side hustle adds 40 extra hours of work to his schedule each week.

Riegel, a trained welder, says it can take three to eight hours to make a fire pit, depending on customizations. Tim Riegel

The idea came from a friend who made a similar fire pit from a propane tank end. It took trial and error to perfect the bronzed and customized versions Riegel now sells, he says. He wanted his fire pits to last longer than the ones sold in big retailers, which he says are "flimsy" and "meant to last maybe two years." So, he bought some scrap metal from a nearby seller and started experimenting with different legs and feet for the fire pits. "The first couple were pretty bad, but the good thing about metal is you can just cut it off and redo it," he says.

A heavy cost for heavy-weight freighting

Riegel says he spends about seven hours per month just sourcing the metal, which is becoming increasingly expensive. His profit margins are typically around 35% to 40%, but he only keeps about half of his proceeds, reinvesting the rest back into his side hustle, he says. Currently, Riegel only has one employee: He pays his 79-year-old father, Terry, $15 per hour to help recycle the tank ends and coordinate freight schedules. The 250-pound fire pits can't be easily shipped through FedEx or UPS, and Riegel's father helps maintain constant contact with the trucking companies that carry the products throughout the U.S. and Canada.

Riegel says he wants to expand the business, offering new customizations like designed lids, sizes and handles. Eventually, he also wants to make gas-running fire pits. Tim Riegel