I have gone through over $2200 in oil this winter in Germantown, Maryland. (And this has been a mild winter) So after much internet searching we have come to the conclusion that Geothermal is the way to go for us. After reading reviews, & other internet searches, we have decided that we would like to get a Waterfurnace 7 series. I went to the waterfurnace website & found certified installers in my area. So I got quotes from all ten of them. (I only work part time & I have lots of time to evaluate) Anyway I have narrowed my installers to 2 different companies. Company A is recommending a 3 ton unit. He say's that my 8" x 22" duct work can't handle the 1800cfm required (according to the installation manual) for the 4 ton unit. Company B installer is recommending a 4 ton unit. He said that company A was blowing smoke up my butt. According to the install manual the 3 ton requires 1500cfm airflow & the 4 ton requires 1800cfm. HOW MUCH CAN MY CURRENT 8" x 22" DUCT WORK HANDLE?