Last year, VAEEC member Nest partnered with the Colorado Energy Office to launch a pilot project for their Weatherization Assistance Program (WAP) to test the incremental energy savings Nest Learning Thermostats have on natural gas furnaces. One WAP agency installed Nest thermostats in 250 homes, approximately half of the homes that were weatherized from May 2016 throughout December 2017, to see its effects on gas savings. The primary purpose was to assess how well the technology functioned for the weatherization program and its clients in terms of installation logistics, acceptance, and operation. A treatment group received standard weatherization services plus a Nest thermostat and a control group received just the standard weatherization services.

Groups were assigned based on the following criteria:

• owner-occupied
• single family home — site built or manufactured/mobile home
• heated with natural gas provided by Xcel Energy
• only one thermostat in home
• customer was willing to have a Nest thermostat installed

Homes that received both WAP services and Nest thermostats saw a reduction of total gas use from 18% to 11%. Using the Weatherization Assistant National Energy Audit Tool (NEAT), the Nest thermostats were found to be very cost-effective, having Savings to Investment Ratios between 4.3-8.6. For homes that received a furnace replacement, the WAP+Nest group saved an average of 31% of total gas use (39% of heating use) compared to 14% savings (18% of heating use) for standard WAP homes. The incremental savings averaged 169 therms (17% of total, 22% of heating) in these homes. One of the more surprising results was that out of the clients that received a Nest thermostat, 81% had WiFi in the home indicating WiFi as a less significant factor on savings.

It should be noted that because there was no untreated control group in the analysis, the savings results are not adjusted for any trends in gas use beyond weather adjustment. This doesn’t affect the estimated saving from Nest, but it may affect the absolute levels of savings shown.

Overall, there was a strong correlation between the installation of the Nest thermostat and savings. Clients that received a Nest thermostat in addition to standard weatherization services saved an extra 58 therms of gas per year compared to clients that just received standard weatherization services. The total incremental savings equated approximately 7% of total gas use and 9% of gas heating. Based on these experiences, it appears that around half of WAP clients could be ideal candidates to receive Nest thermostats with their WAP treatments.