The study by Newport Partners, LLC, “Whole-House Analysis of Energy Efficiency Upgrades for Existing Homes,”evaluates dozens of energy efficiency measures (EEMs) for their energy, economic, and environmental performance at 10 locations across five climates zones. The study provides a credible performance analysis to help prioritize competing EEMs, with added focus on the performance of propane systems.
Building energy simulation models require dozens of inputs to be able to characterize the interrelationships of building systems, so the study used a “typical” reference home based on historic housing data that defines standard characteristics of existing homes. The study then evaluated dozens of household upgrades, or EEMs, and categorized them as elective (building envelope upgrades or renewable energy systems, for instance) or non-elective (systems that would require immediate repair or replacement, such as mechanical systems or lighting).
Each measure was evaluated in terms of its payback — how much time it takes to recoup the net first costs of a system, based on annual energy cost savings — and by the annual CO2 emissions savings. The study also identified the savings-to-investment ratios (SIR), a metric used by weatherization programs to evaluate the economic value of an energy efficiency measure. The higher the SIR, the more attractive the measure is from an economic standpoint.
The study’s final report provides extensive detail on the findings by climate zone for each EEM evaluated. But the study identified 10 systems that are worthy of consideration throughout most of the country.
- Air sealing consistently had the best payback across all five regions, at one to four years. This measure assumes that a 30 percent reduction in air infiltration could be realized through typical air-sealing efforts.
- Attic insulation had the second-best payback across all regions, ranging from three to five years.
- Aerosolized duct sealing paybacks ranged from four to seven years in all climates except the Northeast, where boilers were the most typical means of winter heating, reducing the impact of ductwork on space conditioning.
- Replacement windows were found to offer paybacks of 10 years or less in all climates except the Northeast, where survey data has shown existing windows to have considerably better thermal properties than in other climates.
- Propane fireplace inserts were economically attractive in the two colder climates, with a payback of six to seven years.
- Lighting. Replacing existing incandescent lighting with high-efficacy fluorescents was a consistently strong performer with paybacks of one year or less in all climates and annual emissions savings of 0.2–1.2 tons of CO2.
- Clothes dryer. Selecting a propane clothes dryer over an electric clothes dryer showed the most attractive payback in the three colder climates, with paybacks between four and six years.
- Space heating. The economic and efficiency performance of space heating EEMs were highly dependent on climate, but a consistent performer across all climates was a high-efficiency propane furnace in lieu of a standard propane furnace. The high-efficiency furnace offers a one-year payback in mixed-humid, cold/very cold, and Northeast regions. The associated annual emissions savings are 1.9–3.4 metric tons of CO2 — higher emissions savings than any lighting or appliance EEM analyzed across all climate zones.
- Dual-fuel systems, composed of a high-efficiency air source heat pump working in tandem with a high-efficiency propane furnace, also performed well. When replacing a furnace in all climates, they had simple paybacks of four to six years and showed high emissions savings, with over three metric tons of CO2 emissions savings in all climates when chosen over a standard forced-air furnace.
- Water heating. In the Northeast, specifying a propane tankless unit over an electric tank has a payback of five years and annual emissions savings of 0.6 metric tons of CO2, while also offering longer life expectancy and delivering hot water at nearly triple the hourly rate.