Q: Hello, we are having a new home built (3300sf) and the home is split into (2) zones. Zone 1 (bedrooms), 1727sf has a 1.5 ton installed and cannot keep up with Zone 2 (living) 1555sf, 2.5 ton. We have told them our concerns that the unit may be undersized. The A/C company has provided (4) calculations all with different final loads/numbers. The A/C company states” the calculations are correct”. I’ve hired a 3rd party A/C company and he has said the unit is undersized and duct work does not meet code. He has even following up in emails and I have given copies to the builder and the A/C company, but with no luck. The builder is trying to have us close in two weeks. My 3rd party A/C company says I should file a complaint with TDLR. We are at our wits end dealing with this issue. Do you have some info or suggestions for the next step I should take?
In our opinion:
New homes are built more efficient allowing less heat into the home. A Manual J load calculation is used to help figure out the size of the air conditioner for the load. Air conditioning equipment is engineered to remove dry heat; humidity is removed by condensation when the air moves across the evaporator coil. Air (moves in and out of your home through opening and closing of doors, windows) infiltrates into the home naturally, the amount of grains of moisture in the air depends on the region you are in.
Mold or mildew is a great concern, getting the air conditioning right matters. Here is what you may have with the home builder’s strict adherence to the Manual J without regard to total air flow:
An under size unit will run longer, not necessarily costing you more to operate, the longer run times means better humidity control. This is a plus.
On the other hand with an undersized unit, during peak load cooling conditions it will not have enough total cooling capacity for maximum cooling performance. With high ceilings or large open areas, a smaller system will not be capable of producing the airflow CFM needed to push air for proper circulation in the space. This is a big problem regarding your comfort in the space.
Today, most of the manufacturers systems are lower on total BTU (relates to tonnage) capacity, which may also prevent maximum cooling performance during peak load cooling demands. We suggest you find a mechanical engineer to run an independent load calculation to calculate the CFM needed from each supply duct to distribute the air across the rooms based on 98 or 100 degree cooling load conditions. We also suggest you contact the TDLR for help.
We highly recommend that you look at inverter technology cooling systems as they have varying capacities that range from 40% of total cooling capacity for more aggressive humidity control and can rise to 115% of total capacity for maximum cooling performance.