Propane EE 

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    Gregg Walker
    Propane Education & Research Council

    Melissa Dohmen
    Swanson Russell


    Study Finds L.B. White Therma Grow Direct-Fired Heater System Is Fuel-Efficient and Plant-Safe 

    Propane-fueled, direct-fired heating system is up to 11.6 percent more fuel efficient than comparable models

    (Jan. 15, 2012) — A recent study conducted by the Ohio State University found that the L.B. White Therma Grow propane-fueled, direct-fired heater is a clean burning, more energy efficient system that saves fuel compared with some conventional indirect-fired heaters used in greenhouses.

    The study also concluded the Therma Grow system, which uses direct-fired technology, did not cause plant damage, a common concern among growers.  

    The study was funded by the Propane Education & Research Council (PERC) and conducted at the Ohio Agricultural Research and Development Center in Wooster, Ohio. The trial compared the L.B. White Therma Grow direct-fired model with a commonly used indirect-fired model using two separate 24-by-48-foot double-poly greenhouses.

    During the experiment, scientists monitored the greenhouse environment including fuel consumption, relative humidity, temperature, CO2, and ethylene. The study found that the house using the L.B. White system used 11.6 percent less fuel than the house with the indirect-fired heater.

    The reduction in fuel consumption is caused by the Therma Grow’s innovative heat combustion design which converts almost all fuel energy into useable heated air, allowing for an increase in thermal efficiency. While an average vented heater is able to convert only 80 percent of its given fuel into usable heat, the Therma Grow is able to convert 99.9 percent.

    “PERC is committed to engaging in new research and development projects to bring forth improved technology for the agricultural industry,” Mark Leitman, director of business development and marketing at PERC, said. “This research study is yet another example of how PERC is partnering with manufacturers to develop innovative products that are beneficial to producers and powered by a fuel-efficient, clean, and abundant fuel.”

    Along with monitoring fuel usage of the two houses, six plant varieties were tested during the study for signs of damage and overall quality: tomato, zinnia, marigold, impatiens, snapdragon, and petunia plants. Plants were monitored for symptoms of off-gas damage as well as pests, diseases, and signs of phytotoxicity (plant injury) throughout the experiment. No damage or other issues were reported while using the Therma Grow system. Although plants in both houses were “of very good quality,” the house using the Therma Grow system seemed to produce more compact growth, which can benefit growers.

    Historically, vented indirect-fired units have been used in greenhouses because the usable air is free from combustion byproducts such as carbon monoxide and ethylene that are unhealthy for plants and humans. However, this method can prove inefficient as energy is also expelled along with byproducts during the process, essentially causing growers to spend money on fuel that is going out the stack.

    “We’re confident that producers who switch to the L.B. White Therma Grow heater will save thousands of dollars due to increased fuel efficiency,” Leitman said. “The 11.6 percent reduction in fuel also benefits the environment and growers’ bottom line.”

    The study does not validate all other direct-fired heaters as being plant-safe. Rather, it’s the Therma Grow’s innovative combination of a clean-burning design and air management system that allows it to achieve lower-than-expected humidity and ethylene levels in the greenhouse so plants can thrive.

    Since the Therma Grow direct-fired heater is propane-fueled, growers can also enjoy the environmental benefis of using a clean, domestic alternative fuel. Nearly 40 percent of farms use propane for a variety of production purposes, relying on the fuel’s abundance to power their operations.

    For more information about the L.B. White Therma Grow research study, visit To learn about PERC and its ongoing research and development projects, visit