But there is more to upgrading your home a/c unit with higher SEER unit. One of the biggest mistakes made when replacing a unit with higher efficiency unit is not taking the duct work size into account.
The higher efficiency units have larger coils which typically require a higher airflow. If the duct work is not enlarged to accommodate this you are missing out on a big part of your potential savings.
any companies will simply replace a unit with a newer, higher efficiency unit and call the job complete. It is very likely that your utility bill will drop. This is because you are replacing a 10 or 15 year old unit with a newer one. But unless the proper amount of airflow is there you are leaving the larger potential savings on the table.
Typically, the return air grill will need to be enlarged. This is dependent on where the grill is, mostly. In other words, if the air handler is in a closet and is utilizing louvers through most of the door as a return the it should be sufficient. However, if it is a ceiling mount return air grill it will likely need to be enlarged.
It is also possible that you may need to add an additional supply air grill as well. It is best to add this to the furthest area away fro the air handler. This will allow the maximum benefit for cooling. If it is placed to close to the thermostat or return air grill it may return to the coil without fully realizing the full potential of the cool air. Likewise, if it is placed too close to the thermostat it may satisfy the thermostat before the entire house is cooled to the desired temperature.
The additional cost enlarging the return air grill and possibly adding a supply grill will quickly be negated by the additional savings on the electric bill.
A thorough and qualified contractor will check the duct work size prior to quoting for a replacement system. In the course of checking the duct work, it is hopeful that he or she will also notice any deficiencies in the duct work, such as holes, kinks or damaged insulation.
So remember, when you are ready to replace your system with a high efficiency system be sure to have a qualified contractor look at the entire system, not just submit a low bid in order to get the job. The real savings will come for years to come if the new system is designed and installed properly.