Note that's for the whole home $10K rebate only. For the per-ton rebate, you can leave the existing fossil fueled appliance installed and connected. (It's also new for 2024; the 2023 rules allowed you to leave the appliance in to be used for supplemental heat during extreme cold or during an equipment outage. https://www.masssave.com/-/media/Files/PDFs/Save/Residential... )