Im looking to put a new propane furnace in a 2250 sq ft property. Is a 125k btu unit too big?

The property is in central PA, has a brick exterior and was built in 1900. There is currently R-19 insulation in the walls and R-11 doubled up to make 22 in the ceilings. I found a 125k btu gas furnace 3 years old, like new condition, runs fine, for 400 dollars. I feel like buying this used unit could save me 1k if I dont let it p me by. Any suggestions?