I am installing a packaged unit for my new residence. If there is enough room in the attic, can I install the unit there? Do I have to get engineering done for any load calculations if I install the unit in the attic?

A package unit needs to be installed outside

The package unit has to be installed outside like esquire1 said above. It has to have ambient air to pass over the condenser coil or it will not condense the freon. In the attic it would be re-circulating the same air and it would only get hotter and hotter. Now about any load calculations, you have to have some idea of how much heating and cooling you are going to have to have for your house. A good guess is better than nothing.

It would only be in your best interests to have a load calculation done before installing any equipment, the extra effort put forward now to determine the correct size equipment will save money later by being more efficient and still get the job done, some states require this load calculation for approval. There are many options to installing a heating and air conditioning system, you might want to look at horizontal systems that could be installed in your attic. Good luck, Mike