You have several options as a buyer to consider when installing a new air conditioning system in Los Angeles. Your decision will depend on your needs and budget. Installing Ducting is a big variable in the installation cost. If your home doesn’t have any ducts, adding new ducting will double the budget- it can cost $5,000 to $6,000 to add ducting (Ducting works best in Attic because heat rises, but is also effective from the crawl space if there is no attic) so if you already have that you can minus that from installation cost. Another Variable is the home’s size. The larger the house the bigger the AC unit you will need to cool it, or in two-story homes, you may consider having dual zones, which means installing two sets of HVAC equipment. The general rule of thumb is about 1 ton for every 300 to 400 sqft of living space. Another variable is the brand. Carrier is the first air conditioning company and they are considered the industry gold standard, but they also have a 20% premium on the price as compared to other brands and require installers to get special certification which is why some AC companies do not have their product.
Sometimes it can be tough to find a good place to put the condenser (that is the unit on the outside of the house) because building code requires at least a 3-foot setbacks from the structure on the ground- the AC is not allowed to be in the side yard setback, or if you are putting on the roof you may need roof reinforcement if the weight of the unit exceeds 400 lbs which means getting a structural engineer involved.
I would caution Flat Roof homes from putting HVAC on the roof- it can be done and often is, but the ducts usually heat up in the sun which lowers the system’s efficiency, and also it makes a lot of roof penetrations which will require resealing every 5 years and greatly increases the chance of leaks. For flat roofs, a lot of owners put in the Split system on the sidewalls. This may be an adequate solution if the home isn’t very large, but like wall furnaces, ductless split systems reach is limited to 15 to 20 feet. This means you usually need to install at least 2 if not 3 ductless AC units (one in the living room, one in the master bedroom typically) to get adequate coverage.