Waste-Oil Heater Keeps Greenhouse Heating Costs Low

Glenn Brendle uses a waste-oil heater to grow fresh produce all year for minimal costs.

Tilling

Brendle heats three greenhouses with used vegetable oil from the restaurants to which he supplies produce.

Photo by Malcolm McRay

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Glenn Brendle, owner of Green Meadow Farm in Gap, Pennsylvania, makes his living by growing organic herbs, fruits and vegetables. He works with a network of 15 to 20 local farmers offering a wide array of fresh food – fresh as in harvested the previous day – to chefs across Pennsylvania. For decades, this co-op has provided a year-round banquet of delights: blueberries, honey, asparagus, eggs, cream, prime rib, sweet corn, microgreens and ham, to name just a few.

What is the key to Brendle’s success? “We owe most of it to the greenhouse vegetable-oil heating plan,” he says.

Anyone who owns a greenhouse and heats it throughout winter knows that fuel prices are a significant detriment to their bottom line during the cold months. Many a greenhouse owner, hearing the blower constantly kick on during a sub-zero winter’s day, might feel like they’re feeding the furnace with $100 bills instead of natural gas. But Brendle is able to heat 4,200 square feet of greenhouse space all year long for free. His fuel? Used vegetable oil from restaurants.

With free fuel, Brendle is able to grow not only tomatoes, but tender mixed greens, flavorful herbs, baby beets of colorful hues, and refreshing citrus and cardamom all through winter. “This makes a huge difference in my customer base,” he says.

What’s more, he gets enough vegetable oil to heat three greenhouses, the house, the shop, and his hot water. He also powers two trucks, a tractor and a skid loader on waste vegetable oil. “We’re not 100 percent off the grid,” he says, “but we’ve been running off the grid several days a week now.” Not bad!

This whole endeavor began on a winter day in 2001 when Brendle was delivering farm-grown goods to a Philadelphia cafe. Brendle noticed 25 or 30 jugs of vegetable oil languishing in the alley. The cafe owner said that a removal service used to pick up the used oil, but pickup costs were getting to be too much. Brendle took the oil, thinking he might be able to put it to use. A former engineer and self-described “piker,” Brendle thought he might try the oil in the burners of his greenhouse.

He began tinkering with ways to run a burner off vegetable oil. He couldn’t install such a heater in the house – too iffy for the insurance company – so he installed his modified heater in one of his greenhouses. It worked all right, but with the maintenance it required to keep it clean and running, it was a headache.

After one heater exploded during the night and melted a 6- to 8-foot hole in the side of his greenhouse, Brendle bit the bullet and invested in two Clean Burn 350,000 BTU waste-oil burners, modifying them to burn vegetable oil. He installed them up in a greenhouse outbuilding and runs his hot water heating system from there. The burners heat the water, and pipes installed 4 feet underground (well out of reach of fluctuating temperatures at the surface) run the 180-degree water to the house, shop and greenhouses. The water constantly circulates so it doesn’t freeze. The exhaust, which is shimmering and clear, smells pleasantly of french fries.

Without crushing fuel expenses, Brendle is able to experiment with different crops. He has a permanent planting of rosemary in one greenhouse, which smells marvelously decadent. A 12-foot banana plant has been bearing bunches of tiny bananas every year. Kaffir lime, lemon and blood orange trees flourish in 50-gallon barrels cut in half. He owns a cardamom tree with wonderfully pungent leaves smelling “a little bit like bay.” People wrap fish in cardamom leaves before they cook it, “and it’s just superb.” Next, Brendle wants to get a Louisiana fig that is dark purple and half as big as a person’s fist. “I have a greenhouse anyway – might as well!” he laughs.

Brendle is able to grow heirloom tomatoes through the winter. In January he sells a limited number of tomatoes from the greenhouse, as well as baby beets, bay leaves, tender herbs, rainbow chard, and all kinds of greens. He also grows pawpaws, a small native tree that bears green-brown fruits in fall that taste something like bananas.

Lately he’s been growing a native South American crop called oca (Oxalis tuberosa), which is related to oxalis, or wood sorrel, “the one that’s the bane of greenhouse growers” because the weed reseeds like crazy and takes over greenhouse floors. But oca has potatolike tubers that come in a range of beautiful colors. “It has a funny season that’s out of kilter with everything else,” Brendle says. “It does well in greenhouses, it likes short days, and the tubers taste a lot like potatoes.”

Once a week, on a nondelivery day, Brendle goes into town to collect vegetable oil – an all day task. Some of the oil he picks up in 5-gallon totes, and some is collected from a special system that he helped popularize in Pennsylvania. This system plugs the restaurant’s fryers into a heated tank, and the oil is screened before it goes into the tank. When he comes around to collect the oil, he uses a hose with a 2-inch fitting to pump the oil into a 250-gallon tank. Altogether, Brendle gathers about 400 gallons of vegetable oil per week.

One challenge of using vegetable oil in a heating system is cleaning the oil to get all of the breading, flour and dirt out of it. When a vegetable oil burner runs on clean oil, it works pretty well. But if you use bad oil with junk in it, “it’s a fight to the death.” Fortunately, the special collection system makes the vegetable oil cleaner than the oil he used to get. Chefs no longer flush the fryer with water, and most have stopped using hydrogenated oils like Crisco. “That has helped our process quite a bit – there’s not nearly the waste we used to have,” Brendle says. The oil collected in the 250-gallon tank is clean and doesn’t need much prep to burn. However, the oil collected in the totes does. So, when Brendle arrives back home with the day’s haul, he dumps the oil into 50-gallon barrels along the inside wall of the waste-oil burner house. Once the gunk has settled to the bottom, he siphons the clear stuff off and filters it several times before using it in the burner. “It’s mostly a matter of being patient,” he says.

Brendle says that anyone could modify a waste-oil heater if he had a good knowledge of heating and cooling, or the willingness to learn. An easily obtained fuel source is just waiting to be utilized. “Here’s this wonderful source of fuel,” he says. “Everywhere you look, there’s french fries, and that’s generating oil.”


Melinda R. Cordell, a former horticulturist, lives in northwest Missouri with her family and two red hens. She is the author of the book Courageous Women of the Civil War: Soldiers, Spies, Medics, and More, available August 2016 from Chicago Review Press.