I called an ac company for a quote to install an HVAC system in my steel shop that's 1500 sq feet and 12ft high. The guy said on the phone it would need a 5 ton unit, but looking at the charts online they say only a 2.5 unit would be needed. Is he thinking the shop won't be insulated as well as a house? I plan on installing whatever the correct R value is needed for zone 1 which is Houston. I've heard companies frequently want to oversize units for some reason and this is a big problem.