Cheapest would be more radiators in the basement. Is it baseboard, or a
mix of the two, between upstairs and down stairs. Large cast iron will
get you the most BTU. This is what happens when you don`t have a pro
do a load calculation and you are guessing. Best would be excess
capacity and a valve to allow you to manualy reduce flow-heat. Do your
floors have or will floor have carpet, that and foam padding will help a
little.