10 Vs 11 Foot Ceilings . And ceilings in mechanical equipment rooms have to be at least 12 feet high. Why 9 foot ceiling instead of 10 foot. 8 Foot Ceilings Vs 9 from www.gradschoolfairs.com From a purely math standpoint, yes the total air volume, is harder to cool for a taller ceiling (depending on where the thermostat is placed). To read the full story 10+ foot ceilings for ceilings that are 10 feet or taller, a larger crown is necessary in order to make a visual impact.