Boston Standard removed oil tanks and oil furnace, and then rearranged the ducts to serve the second floor separately from the first floor. Then installed two natural gas furnaces in the basement, one for each floor, along with a heat pump in the basement to serve the first floor. So this was a difficult job, but everything looks good so far. They put in a lot of time and effort, which is much appreciated.
UPDATE (9 SEP 2023): Thank you to Tony Selamaj of Boston Standard for coming this week to tune up our system for the coming year. This was very helpful.
