Yeah one of the three HVAC installers I had over to provide quote told me this. Do your own research - it may not be a pervasive issue. Also the Mitsu ducted air handler is pretty big so it may not fit in every furnace replacement scenario. But it won't cost you anything to find out. Go to Mitsu's web site and call diamond contractors in your area and ask for a quote. And worst case is you can still do ductless mini split heat pumps if you can't put in a ducted a system. Honestly that is what most people do - I don't think tons of people are converting their whole house system like I did. Adding on some ductless minisplit units is also a pretty wise move if that's your only/best option.