You are 100% correct. I have installed many Janitrols and others. I have had not had any more problems with Janitrol than any other brand. It is the installation that counts. The sizing of the unit and the ducting is of utmost importance.
The guy above who complained because the Janitrol wasn't keeping his house the same temperature is mistaken. His problem is in the thermostat. He replaced it with another piece of junk. I installed a janitrol in a customers house and he complained that before he had his thermostat set on 68 degrees and he was comfortable, now he has to set it on 72 degrees to be comfortable, he surmised that the janitrol furnace was junk because of that. I tried to tell this idiot that his problem was in the $12 thermostat he had. He would not spend any more money to have a good reliable thermostat. I told him that either his old thermostat was wrong or the new cheapo was wrong but he kept whining that the furnace was bad.
Just remember that a thermostat is nothing more than a temperature activated switch. Your furnace comes on when the switch calls for heat and shuts off when the switch is satisfied.