Portable AC Tips

In case you haven’t noticed, portable air conditioners are downright expensive!  And to make matters worse, they can be terribly confusing to compare, with all sorts of features and various components that can confuse even savvy shoppers.  As a result, we thought it would be useful to break the buying process down with these Portable AC Tips, and discuss some of the difference between models, and features that we think are key – or at least desirable.

How Much Power do I Need? Understanding Coverage Area

0912_btu_calculator1Determining how big an air conditioner is really needed is step one in the buying process, but is often poorly understood.  You first need to get an estimate of the size of your room – think floor space (LxW) for the moment.  If your room is not exactly square or rectangular, don’t worry, precision is not necessary.  Once you’ve got the area expressed in square footage, you can use this handy cheat-sheet to determine the BTUs you need.

However, please bear in mind that these figures assume fairly ideal circumstances.  In other words, it depicts coverage area for rooms that do not possess a number of “heat factors” that will make an AC unit work much harder.  Things like high (including vaulted) ceilings, lots of windows (especially sunny ones!), poor or little insulation, a bright sunny exposure, and the presence of heat generating equipment (cooking appliances, servers, etc.) can all reduce these coverage areas by a large margin.  So, when considering your square footage, err towards a more powerful unit if even one of these “factors” appear, and if multiple exist, then go to the next larger unit.  To illustrate, if I was looking for a model for my 250 square foot room that had two large windows, I’d immediately go for the 7,000 BTU unit rather than the 6,000 BTU option.  And, if that window also had vaulted ceilings, I would opt for the 8,000 BTU model to ensure enough cooling power for the extra “volume” in the room.

The whole point is obviously to match the power to the size of your room.  You may be thinking at this point that  you should just go for the strongest model you can afford.  This is not advised.  Having an AC unit that is too powerful for the room will cause the unit to cycle on and off too often.  Besides just being annoying, it prevents the unit for dehumidifying as it cools and can actually create muggy, stale conditions. As a result, while it’s best to err on the more powerful side, don’t overdo it and get a 14K model for a 200 square foot space!

Single Hoses Versus Dual Hoses

Perhaps more than any other concept, there is lots of confusion about venting portable ACs. Just about any model you will be using will need to vent to the outdoors, or some other venting system that connects to the outdoors.  Obviously, this is not an issue for window units, but many people forget this when getting their first portable AC.

But not only do you need to consider which window to exhaust the unit from; you need to decide how many hoses you want  – and fewer is not better!

Let’s back up a second.  Air conditioners are driven by compressors – compressors that need to be cooled off to operate effectively and efficiently. And this air has to go somewhere (outdoors of course) – but it also must originate from somewhere as well.  A single hose unit works by pulling some of the room air and passing this over the compressor, then exhausting it outdoors.  This works fine except for two things:  1) by pulling indoor air, it’s actually squandering a bit of the cooled air that you want to keep inside the room; and 2) by pulling indoor air a very weak (you can’t feel it) negative pressure is created, which is ordinarily filled by outside air seeping into the room around cracks and gaps around the vents, windows, doors, or anywhere else that’s not completely sealed off.  In both of these cases, the result is that additional heat load is placed on the unit, making it work harder to bring down and maintain the desired temperatures.

Dual hose units, on the other hand, have a dedicated compressor exhaust loop.  In other words, they bring in outdoor air precisely to blow over the compressor and then vent again outside – one hose brings in the air, the other expels it.  By virtue of this separate exhaust loop, none of your indoor (cooled) air is lost, and no negative pressure is created to encourage outdoor (hot) air infiltration.  The result is that dual hose units – assuming all other things are equal – cool a room faster and operate more efficiently than a sing hose unit.  The only downside is that dual hose units are slightly more expensive than a single hose system – and of course you need to make space for two hoses at the window, which adds a bit more bulk.  Nevertheless, as we discuss below, this is not that last word when it comes to efficiency!

Energy Efficiency and “EERs”

Besides the single versus dual hose consideration, the next most important factor when it comes to operating cost is the energy efficiency of the air conditioner.  Efficiency in this case is traditionally discussed in terms of the unit’s Energy Efficiency Ratio, or “EER.” While this all sounds fancy enough, it’s just the product of a model’s BTUs divided by its wattage  – that’s easy enough math, even for even me!

Given this relationship, the higher the EER the better, since what this means is that you are getting more BTUs (cooling power) for each watt of electricity expended. For example, a unit with an EER of “10.0” could produce 10,000 BTUs and draw a maximum of 1,000 watts.  Actually, an EER of 10.0 is quite efficient, and anything over this is excellent – again, the higher the better.  Most models fall somewhere between 8.0 and 10.8, although we do see the occasional 11 or 12 now and again. We suggest sticking with models with EERs of 9.0 at the very least.

Because EERs are not tied to the single/dual hose issue, you must consider them separately.  For example, some dual hose systems might have low EERs of around 8.0, while some single hose units have high EERs of 10.0 or higher.  As a result, the inherent inefficiency in a single hose system can be mitigated to some extent by a high EER.  On the other hand, a single hose system with a low EER is even more inefficient – so beware!  Again though, assuming similar or close EERs between two models, the dual hose option will usually always be more efficient for the reasons described above.

Size and Weight

Unless you’ve bought one before, you are likely to be surprised just how big portable AC units are. Indeed, most models between 10,000 and 14,000 BTUs will fall somewhere between 55 and 85 pounds, which is no joke, especially if you are responsible for dragging it up a flight or two of stairs!  The shapes of these things also vary widely, with some tall and slim, others squat and wide, and still others just all-around big and bulky.  Consequently, we highly suggest you take note of the dimensions and weight reported for each model to be sure it will be something that you can handle, and will fit in with your space.

Noise Noise Noise!

As with other compressor-driven appliances (e.g., dehumidifiers), the noise produced by portable AC units gets a lot of air-time in most user reviews.  Indeed, as we’ve discussed elsewhere, there is really no more subjective factor than this.  Some people expect virtually silent operation, while others will tolerate quite a bit of banging before they get bent out of shape.  In reality, however, most units these days tend to run somewhere between 50 and 65 decibels, which is around the levels associated with normal conversation.

To be sure, we are not trivializing this concern.  On the contrary, if you are intending to use the unit for sleeping quarters, you should definitely pay very close attention to it’s noise levels.  The only sticker is that noise ratings are not always reported and when they are they aren’t always done in a standard way.  Given this reality, we think you should instead give a careful read to the user reviews for each unit, while bearing in mind that virtually any air conditioner with more than a couple dozen or so reviews is going to have at least one person who complains about sound.  We suggest you disregard the stray comment and instead look for repeated complaints about noise – or the lack thereof.