Square Footage: 2,050
Year Built: 1962/1963
Concerned with the impact of fossil fuel usage on the environment and climate change, the homeowners wanted to take advantage of the surplus electricity their solar PV array was providing. They had been heating with natural gas. They decided to replace their existing furnace with a cold climate air source heat pump matched with a new high efficiency gas-fired furnace to reduce their gas use.
Installation and Energy Details
Prior Energy system: Natural Gas furnace
New Energy System: Cold climate air source heat pump / 96% efficient natural gas furnace
New Insulation or Sealing: Air sealing, insulation, as well as installation of high efficiency windows and external doors
- Bosch 20 SEER 3.5 ton air source heat pump
- York LXTM9Y Series 2 stage natural gas furnace
- 6.4 kW roof-top array installed in 2012, 2016 & 2019
Net Zero? No. Natural gas is still utilized, although at amounts significantly below their most efficient neighbors, according to National Grid reports.
- Overall, the Wirths are very pleased with the outcome. Their home is comfortable, cost effective, and more environmentally friendly. The cold climate heat pump serves as the primary heating system down to a temperature chosen by the homeowner – currently 30 degrees F outdoor temperature. Below 30 degrees, the system switches to the furnace. The cold climate air source heat pump could provide heat even when the outdoor temperatures are as low as -4*F. The Wirths are monitoring the system to identify whether or not the current solar PV will cover their annual electricity use at this temperature set point. If, at the end of the heating season, they are still producing excess solar power, they will lower the set point temperature for system switchover from the heat pump to the furnace. Replacing heating operation by the natural gas furnace with the air source heat pump powered by solar energy reduces their greenhouse gas emissions. The Wirths intend to continue to improve the building envelope performance as well as add additional solar panels with the hope of getting the home close to net zero. The utility bills to operate the house are very low and significantly below their most efficient neighbors, according to their utility.
Motivation for Heat Pump Technology
- Over the past 10 years, the Wirths have been making various energy efficiency improvements to the home, including air sealing, insulation, as well as installation of high efficiency windows and external doors. In 2012 they installed 4.6 kW of solar PV to generate the majority of the electricity utilized by the home, and later added more panels to generate a total of 6.4 kW, providing them with extra solar generated electricity. The Wirths wished to utilize this extra solar capacity to offset some of the home’s natural gas useage associated with the home’s heating system as well as add cooling to the home. Motivated by this desire, a concern about climate change and the various incentives/rebates, they decided to install a cold climate air source heat pump matched with a new high efficiency gas furnace.
Case Study: Wirth
|Cost Category||Initial Cost||Incentives||Final Cost|
|Air Source Heat Pump/High Efficiency Furnace||$11,674||NYSERDA rebate: $4,550||$7,124|
|Solar PV System||$30,249||NYSERDA Rebate: $8,174||$10,538|
|30% federal tax credit: $6,537|
|25% NYS tax credit: $5,000|
|Grand Total||$41,923||$24,261 (58% of total)||$17,662|