I guess I would have to patch up the HWF and install all the ductwork in the basement.

Run some ductwork and a furnace, scrap the metal and radiators, and never have to think about the pure evil known as water again.

Replace the carpet and furnace and either replace or at least clean the duct work.  

Did that and had plenum on top and no ductwork. 

Running duct work for 700SF may actually be cheaper than radiant - also look at baseboard heating.

They contracted to put in a new HVAC system with duct work.

I run into radiator/ forced air conversions all the time.I call my scraper- he removes all radiators, boilers, supply/return lines, oil/oil tanks for free, then I get my HVAC guy start running duct work--- Some of the boilers I've taken out were the size of a small car- not worth my time to deal with the little bit of scrap $$ in return.Find a good/clean scraper- they are an essential part of the team.

Many tenants are happy with window units which is the cheaper route but if the ductwork is already there I will usually spring for a new heat pump if that's all that is needed.

Also, that the duct work is too small and needs to be replaced as well.

HVAC, I planned to have a professional come in and do the duct work on one unit, then copy it for the remaining 3.