A clever heating solution for challenging installations
Rinnai direct vent furnaces provide cost-effective comfort in a small package.
By Cheryl Weber
When Blossman Gas in Douglasville, Ga., went searching for fuel-efficient technology to heat its 1,360-square-foot showroom last year, several conditions guided the decision-making. One, the equipment had to install easily in a tight space, as the interior is built out with cabinetry and display areas for the gas fireplaces, space heaters, and appliances the company sells and services. The only available spot, says showroom manager Scott Weatherford, was next to the front door. Two, it had to be powerful enough to heat the open-plan, glass-front showroom and administrative offices, which occupy a metal-clad structure built in 1984.
The company's first choice was a Rinnai direct vent furnace. A retailer of the units, Blossman had installed them in countless building types and locations, including upstate New York and New England, and its technicians knew they could install it in a couple of hours simply by venting it through a small hole in the wall. Installing the technology in its own showroom allowed the company to experience first-hand how cost-efficient the units were. "After seeing how well it was performing, we turned off the gas furnace and used this exclusively to heat the showroom last winter," Weatherford says. "We were saving $125 to $175 per month."
Ductless and compact, the Japanese-made furnaces were originally designed for small houses, but about 15 years ago Rinnai began producing larger models for American residential and commercial markets. Here's how they work: The units, mounted against an exterior wall near the floor, have a modulating blower that disperses heat evenly throughout the building, including isolated rooms, provided there are wall registers or a two-inch airflow space under closed doors. While most furnaces blow hot air and then shut off, the Rinnai furnace's logic circuit constantly monitors the temperature and regulates the fan speed, radiating just enough heat to maintain the thermostat setting.
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Click to enlarge
"It's about comfort," says Rinnai product manager Tracy Young. "And without ducts, there is no heat loss. The U.S. Department of Energy says that up to 40 percent of energy is lost in the ductwork of a central forced-air system." That makes the direct vent furnace a good alternative to electric heat pumps, which push air through ducts.
In addition to maintaining consistent temperatures, the direct vent technology also offers some electricity savings over furnaces with big blowers. In a residential study conducted with CanmetEnergy's Renewables & Integrated Energy Systems Laboratory, the Rinnai furnace used approximately 9 percent more propane than a 91 percent efficient condensing furnace, but about 76 percent less electricity, while maintaining warmer minimum temperatures and eliminating the need for ductwork.
Rinnai's direct vent furnace is available in five sizes, from 8,000 Btu to 38,400 Btu; the largest model is powerful enough to heat a building up to 2,000 square feet. Multiples can be installed for zoned heating. "Our largest unit, the ES38, was installed in a 2,000-square-foot condo complex club house," Young says. "It heated the whole space, which had double-pane windows and good insulation. You have to do a heat loss calculation in order to size the unit correctly. On a three-story commercial building, for example, one would calculate the heat load per floor."
"After seeing how well [Rinnai's direct vent furnace] was performing, we turned off the gas furnace and used this exclusively to heat the showroom last winter."
In Blossman's case, the EX22CP direct vent furnace was connected to twin 100-pound propane cylinders with a changeover regulator. Weatherford says that the combined 50 gallons of fuel they supplied lasted a month. "There was a 2-degree difference between the unit thermostat and a wall thermostat on the other side of the showroom," Weatherford says. "I thought that was fabulous, given that the furnace is located next to the entry door." Their slow, evenly radiating heat and nimble installation make these units uniquely suited to a variety of commercial building types especially those with retrofit and spatial constraints.
To learn more about efficient space heating with propane, check out these Propane Energy Update articles: