I did a study the hvac guys call a "Manual J". You measure all the conditioned rooms, all the windows,type of windows and construction details like wall construction and insulation. Also your geographical location and temp swings. It tells you exactly what you need for sizes for heat and cool. Mine have been spot on. I gave the results to the guy that sold us our boiler because he doubted the results. He sold us what was recommended and it works perfect. Those units work well at maximum capacity as designed.