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Mechanical systems, including HVAC equipment and water heaters, have undergone rigorous upgrades in recent years to improve their efficiency and longevity. But despite those improvements’ contributions to green building, the International Energy Conservation Code (IECC) has not recognized mechanical systems as components that contribute toward a home’s code compliance — until now.

The IECC, an internationally recognized set of building standards aimed at conserving household energy through high-performing products and materials, posted its most recent revision in 2015. Newport Partners, an agency that regularly consults on code matters, analyzed the latest update to the energy code and found that it offers newfound flexibility to builders: a new compliance path called the Energy Rating Index (ERI). The ERI allows builders to earn credit for mechanical systems, such as energy-efficient propane furnaces and water heaters while making effective trade-offs by scaling back in other efficiency measures.

How the ERI works

The ERI requires a third-party computer model to generate a Home Energy Rating System (HERS) score for the home. The HERS Index benchmarks a “standard” house with a score of 100, accounting for everything from HVAC and hot water to lighting, appliance, and electrical loads. For each 1 percent of energy savings in a new or remodeled home, the HERS score drops by 1 point, so a 35 percent energy savings would translate to a HERS score of 65 — the lower, the better. Builders can use a combination of mechanical, structural, electrical, water, lighting, and appliance upgrades to lower the HERS score to within 2015 IECC code requirements, which vary based on the location and size of the home.

“Taking advantage of the Energy Rating Index pathway for the 2015 IECC is a differentiator coming into the market, and will be an attractive way for builders to distinguish their products from older homes.”

The addition of mechanical equipment into the compliance rubric offers new flexibility for builders to meet the 2015 IECC criteria, says Mike Moore, a professional engineer and technical consultant with Newport. But going this route requires some strategic thinking. “It’s not easy to get to this point with the Energy Rating Index,” Moore says. “You still have to apply a lot of energy-efficient measures, and it’s about thoughtful building, not just building as usual. It creates opportunities for trade-offs in construction.”

Newport’s analysis of the ERI compliance option and its impact on builders found that installing high-efficiency propane equipment can allow builders to avoid other costly design changes, such as thicker insulation. For example, a home in a mixed climate like St. Louis, Missouri, would requires a HERS score of 54 to comply with the 2015 IECC. Rather than requiring the expense and design challenge of upgrading to 2×6 framing with extra insulation to achieve HERS 54, the ERI could allow for standard 2×4 framing, giving the project credit for a high-efficiency propane furnace, a propane tankless water heater, better windows, and improved air sealing and ventilation options.

Moreover, “high-efficiency propane equipment can actually come at a lower installed cost, so you’re getting two for one”—that is, both code compliance and lower construction costs, Moore adds. The cost savings is thanks to less expensive labor and materials associated with direct-vented propane equipment, compared with that of constructing a chimney that would exhaust standard equipment through the roof of the home. Builders and their customers will also appreciate the more open floor plans that can be achieved by removing that chimney stack through the house.

Cost-Benefit Analysis

For builders worried about costs associated with energy modeling to generate a preliminary HERS score for their homes, Moore says the investment comes with benefits beyond the HERS number.

“When you’re working with a HERS rater, they’re acting as a consultant to you — not just as someone who comes in and does the testing,” he says. “They can help get you into compliance faster and help ensure that homes will pass inspections without getting caught in noncompliance situations around the home.”

Additionally, homes with a HERS rating can benefit builders’ reputations by offering home buyers a better understanding of their home’s energy efficiency. Many make the analogy that HERS scores act like a vehicle’s miles-per-gallon rating. Buyers will appreciate having the HERS score as an easy-to-understand reference point for efficiency as they consider which builder to work with.

“If you Google ‘HERS index’ or ‘HERS score,’ you’ll see a lot of big builders that have their own labels out there with a graphic related to energy-efficient construction and how they relate to other builders,” Moore says. “Taking advantage of the Energy Rating Index pathway for the 2015 IECC is a differentiator coming into the market, and will be an attractive way for builders to distinguish their products from older homes.”

The full analysis by Newport Partners is available in a new fact sheet, “Propane offers builders design flexibility for code and beyond-code homes.” Download the fact sheet for examples of ways builders can utilize high-efficiency propane space heating and water heating systems to meet the requirements for the IECC and other green building programs.

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Lauren Hunter