We don't have basements here in East Texas, so the two options are in the attic or in the house/garage. Seems like most new installs are going into the attic. I don't like this because it makes it very hard to maintain it. Seems like a lot of people don't realize that you need to add a little bleach to the drain line very month when you change your filter or the primary drain line will start to grow algae inside of the pipe and quickly plug it up. Then the water will fill up the pan and drain from the pan if there isn't any insulation or debris in the pan. A lot of the time that secondary drain is plugged and the water overflows the pan, causing damage to the ceiling. I get a lot of jobs repairing that damage!!!
Other issues with having it in the attic are having a path to get to it that does not disturb your insulation. I've built wood deck type pathways for clients to get to their units in their attic that is above the insulation. Most people have a path to get to their units in the attic that are completely devoid of insulation. Kind of like having a window in your ceiling. I have elderly clients that pay me to change their filter and pour bleach down the drain for them, but they tend to put it off to a couple times a year when they want me to do other things for them too. Sometimes the filter is at the return in the house, so nobody ever goes into the attic to add bleach, and nobody ever looks at it to see if their is a drainage issue.
In some higher end homes, they put the unit in an upstairs room that is built for this purpose that is easy to get to through a regular exterior type door that seals out the attic heat to some degree and it's all installed on a platform high enough above the joists to allow plenty of insulation. In those homes, there might be 3 units in that area, but usually two. One for upstairs, one for downstairs. If it's going to be in the attic, this seems to be the best way to do it.
I prefer to have it on the main living level of the house. When I built my parents house, I put it in their garage, kind off off to the side of where they park so it's never in the way of anything. The water heater is next to it and sits on the same wood platform. Filters and bleach are sitting on the platform too for easy access and a reminder to change the filter every month.
In my house, I have it in a small 8x6 room behind my garage that you have to go around the side of my house to get to it. There is a small porch over that exterior door, and lights with an outlet inside that room. My electrical pane, my water heater and my AC unit are all in that space, along with extra filters, bleach and drain hose in case I have to replace my water heater. This is also where my access to my attic is located.
My clients with their units on the living level of their homes have it in the hallway, or in their garage. Both areas are easy to get to, which is very important for the life of your unit. The filters have to be changed regularly, and the coils should be washed every year, two years max. I personally change my filters twice a month, but I have 4 large dogs and doggy doors that allow them to come and go when they want. Dust is a constant part of my life.
