When we say “roof top air conditioner,” your first thought is probably any old machine bolted to the roof and blasting air into your building. This is only partially correct. There are specialist systems designed to be roof mounted and regular systems which simply can be roof mounted. The difference is sort of like a big rig versus a regular pick up. They’re both trucks and both can haul a trailer, but only one of them was built to only haul trailers for it’s entire service life.
Roof Top Units
The easiest way to think of these is as a packaged system. A roof top unit is a fully self contained air conditioner and heating system, in one mass of hardware, that will blast air of an arbitrary temperature into your ductwork. In some ways this makes things easier. You don’t need to have separate systems, you have a single, bolt in system that does all the work in one place.
Units like this take advantage of being pre-assembled at the factory. Everything about them is optimized from the start for the best possible performance. There can be tighter tolerances in assembly because it was all built at the factory. It’s also likely to never be seen by a customer, being tucked away on the roof, it won’t take up indoor space either, except for the duct work. It’s a really attractive idea for a business to consider.
There are some challenges though. Installation will require your installer either own or rent a crane. Even a small roof top unit will physically weigh over a thousand pounds and be about the size of a large table. It won’t fit through any doors, much less be moveable by a contractor or two… or six at once, without heavy equipment.
This also means your building needs to have a sturdy and easily accessible roof. If you’ve recently bought a 1950s vintage, gently used warehouse, you’ll need to have it inspected to find out if it can take the weight of a new system.
Roof Mounted Units
The opposing concept is a roof mounted air conditioner, which isn’t a packaged system, just a regular condenser unit that just so happens to be sitting on the roof. This is a viable option, but it throws out many of the advantages of a packaged roof top unit and adds more heavily to the cons. You’re not picking up any significant advantage except putting the unit out of sight and it’s now a bit harder to get access to. This is especially a challenge in buildings with multiple evaporator coils and indoor components, sending contractors up and down stairs all day, rather than working in just one place. These regular condenser units might not handle the weather as well either. When they’re mounted on the ground, they’re at least a little better protected from wind and rain by the nearest side of the building. They’ll also get more attention and be more likely to have a protective cover put on them for the winter. And on top of all that, you’ll probably still need a crane to get it on the roof in the first place. Even a regular, consumer-grade condenser is back-breakingly heavy when assembled.
What’s Right for YOU?
What works for you is going to depend on your situation. If you have a newer building, want to replace an existing packaged system, or are out to replace your entire HVAC set up with something entirely new, then the roof top mounted systems are a really enticing idea. If you just need a new air conditioner and there isn’t much ground space to hide your condenser coil, then your roof might be a viable place to put it, if it’s easy enough to access and sturdy enough to support the unit. You just have to remember to stay on top of maintenance, because out of sight, out of mind, is a real issue with these systems.