There are a few things to consider when deciding whether to place your HVAC unit in an attic or crawl space. One is the climate. If you live in an area with hot summers and cold winters, it may be beneficial to put your unit in the attic so it can better regulate the temperature in your home. Another thing to consider is the height of your ceilings. If you have high ceilings, putting your unit in the attic may be the best option so that it can evenly distribute heat or cool air throughout your home. Finally, you should also think about access and maintenance. If you need to frequently access your unit for maintenance or repairs, it may be easier to do so if it's in a crawl space rather than an attic.