To get the tax credit, you need to buy a fairly expensive, efficient unit. Efficiency is good, but it may or not pay for itself in the short-term. Long-term, probably. If the fan motor is shot, that may not be all that expensive in the scheme of things, and the furnace could last another 10-years or more. In my limited experience, the bearing may be the thing shot, and if it is a bronze one, if you can free up the shaft, and put some oil on it, it could last another few years. But, it may be fairly inexpensive and just replace the whole thing. If the system is applying the proper voltage, but the motor rotor is locked and can't turn, eventually, the motor will burn up or if it has a fuse, the fuse might blow. Not sure how much of that assembly has to be replaced as a unit. You'd need the parts breakdown drawing. Keep in mind that federal thing is a tax credit, so depending on your bracket and deductions, it may not mean too much. Unless you changed your withholding starting now, you won't see it until you file your tax return next year (remember to change it back at the end of the year or you may be subject to penalties for not taking out enough next year). The credit is 30% of the qualifying PARTS (not labor, and not all parts qualify) up to $5000 (which gives you the max $1500). A new furnace parts cost probably isn't that much, but labor could exceed that for total cost.