The sewer line replacement costs is classified as a land improvement and depreciated over 15 years under the MACRS GDS depreciation schedule. See IRS Pub 946 at https://www.irs.gov/pub/irs-pdf/p946.pdf on page 97, item 00.3 - Land Improvements.
The furnace, since it becomes "a physical part of" the structure, is classified as Residential Rental Real Estate and depreciated over 27.5 years. See https://www.irs.gov/pub/irs-pdf/p946.pdf on page 108 middle column, section "Structural Components".
