I bought a 2300 square foot bi-level in Philly suburbs built in 1964 for investment/rehab and am converting from oil heat to gas. I am a carpenter and figured I could handle doing a heat loss calculation to size a new gas boiler using the calculator at www.crownboiler.com/Support/Education/Boiler-sizing. It calculated 56,000 BTU heat loss but the existing oil boiler a New Yorker APU 690U bt4 has a DOE heating capacity 129 MBH. Does my BTU calculation sound too low for this house or is the existing boiler oversized? Was it oversized due to DHW? Or am I misreading the rating numbers? The house is 4 bedroom 2 1/2 bath, 25' x 47', lower level uninsulated brick veneered conc. block and upper level is frame with 2" batts in walls and 5 1/2" loose fill in attic. All new double glazed mid quality windows and doors. ODT= 13. I am looking at Crown mod con BWC070 rated 70,000 BTU. Any thoughts on if this might do the job?