The Best Portable Air Conditioner

A portable air conditioner is an inherently inefficient appliance.

Why? Because it puts a whole AC system – which includes both cold and hot components - inside of a single portable appliance.

The cold side is good – it cools air.

The hot side is a problem.

Specifically, a single hot part – the condenser- gets hot. It’s absolutely critical for the working of the whole AC system that the condenser is constantly cooled off.

Most portable air conditioners accomplish this task by constantly pulling cooled room air over the condenser and exhausting the heated air through a duct in your window.

The problem with this solution is that the air that’s exhausted out of the room is never replaced with fresh air.

This creates a “void” – an area of low pressure - inside the room. And this, in turn, creates a pressure gradient between the cooled air in the room and warm outdoor air.

This pressure gradient moves in only one direction – from high pressure to low pressure. Thus, warm outdoor air is constantly getting pulled into the conditioned room as room air (that was used to remove heat from the condenser) is exhausted by the portable AC unit.

The technical term for the warm air that’s constantly pulled into the room is “infiltration air”.

Another substantial inefficiency of a portable air conditioner is the fact that the large duct that is exhausting the warmed air (from the condenser) is completely uninsulated and inside of the room being cooled. The exhaust hose is usually made of a thin plastic that readily radiates heat back into the room.

Cooling Capacity Standards

In the past, portable air conditioners were tested in very favorable conditions:

• at indoor temperatures of 80° F
• at unspecified outdoor temperatures (single hose units)
• not fully accounting for major inefficiencies

The end result? Heavily inflated cooling capacity specifications – i.e. heavily inflated BTU specifications.

The US Department of Energy (DOE) recognized this issue and instituted new rules and regulations to combat it.

Their solution? Manufacturers are now required to give portable air conditioner cooling capacity in terms of a new standard of measurement called Seasonally Adjusted Cooling Capacity – SACC for short.

Here’s the equation used to determine SACC:

SACC = ACC₉₅ × 0.2 + ACC₈₃ × 0.8

Note how 20% of the SACC value comes from ACC₉₅ and 80% comes from ACC₈₃.

But what is ACC₉₅ and ACC₈₃?

ACC is simply Adjusted Cooling Capacity:

ACC₉₅ = Capacity_SD − Q_{duct_SD} − Q_{infiltration_95}
ACC₈₃ = Capacity_SD − Q_{duct_SD} − Q_{infiltration_83}

Thus, ACC₉₅ involves taking the overall cooling capacity of the portable air conditioner, still measured in BTUs/hr and still measured at an indoor air temperature of 80° F, but accounting for the heat added by ducting and infiltration air (outdoor air) at 95° F.

ACC₈₃ involves the same calculation but with infiltration air (outdoor air) at 83° F.

Thus, calculating SACC does not allow for testing at unspecified outdoor air temperatures. The minimum outdoor air temperature used for testing is 83° F.

This is the outdoor air temperature accounting for 80% of the SACC. 95° F is the outdoor air temperature accounting for 20% of the score.

You may be inclined to think that weighting the score in this way still makes for a higher overall value than if the weights were equal or even reversed. And you’d be correct. Hence why it’s not surprising that manufacturers have worked very closely with the DOE to compromise on this new testing standard.

The formal explanation for choosing these weights is that it represents the average seasonal use case – the DOE expects the average portable air conditioner to be used approx. 80% of the time at outdoor temperatures close to 83° F. And only 20% of the time in a heat wave with temperatures approaching 95° F.

Single vs Dual Duct Portable Air Conditioners

So far, we’ve primarily discussed single hose portable AC units.

Another type is dual hose.

Traditional dual hose units mitigate the pressure gradient problem by adding a second hose to the system. Instead of using cooled air from inside of the room to pull over the condenser and then exhaust out of a single duct, warm outdoor air is pulled into the system via a second duct. This warm outdoor air is cool compared to the condenser and so it can still remove heat from it. After it cools the condenser the heated air is exhausted via the first duct, much the same as heated air is exhausted in a single hose unit.

The end result is that the net volume of air in the room stays much more consistent than it does with a single hose system – the addition of infiltration air to the room is minimized.

Note that certain dual hose units may still use a small portion of cooled indoor air to contribute to cooling the condenser. And so, air infiltration is never completely eliminated.

It’s not surprising then, to see that the equations used to calculate ACC for dual hose units still account for infiltration air at different temperatures.

The equations for ACC for dual hose units are as follows:

ACC₉₅ = Capacity₉₅ − Q_{duct_95} − Q_{infiltration_95}
ACC₈₃ = Capacity₈₃ − Q_{duct_83} − Q_{infiltration_83}

Recall that the equations for single hose units are as follows:

ACC₉₅ = Capacity_SD − Q_{duct_SD} − Q_{infiltration_95}
ACC₈₃ = Capacity_SD − Q_{duct_SD} − Q_{infiltration_83}

Note that while the Q_infiltration variables in both sets of equations are the same, the Q_duct and Capacity variables are slightly different. This is only to account for the fact that single hose units have slightly different parameters set when measuring cooling and duct heat transfer because they have only one hose instead of two.

This raises an important point: while the addition of a second hose in a dual hose unit does make for one major advantage over single hose units – that being that they create much less of a pressure gradient and therefore minimize the introduction of infiltration air into the room – the addition of a second hose does create a few disadvantages in the process.

These include:

These disadvantages are likely why very few manufacturers still make dual hose portable AC units today.

The Dual Hose Myth

Contrary to what you may have read or seen elsewhere online, it’s incorrect to make the blanket statement that:

A dual hose unit is always the superior option to a single hose unit simply because it’s a dual hose unit.

The primary factor that should be driving your purchase decision is real world cooling capacity – in other words, the unit’s Seasonally Adjusted Cooling Capacity.

SACC fully takes into account the inefficiencies of both single hose and dual hose units at lower and higher outdoor temperatures.

Remember, the equations for SACC and ACC are:

SACC = ACC₉₅ × 0.2 + ACC₈₃ × 0.8

Where, for single hose units:

ACC₉₅ = Capacity_SD − Q_{duct_SD} − Q_{infiltration_95}
ACC₈₃ = Capacity_SD − Q_{duct_SD} − Q_{infiltration_83}

And for dual hose units:

ACC₉₅ = Capacity₉₅ − Q_{duct_95} − Q_{infiltration_95}
ACC₈₃ = Capacity₈₃ − Q_{duct_83} − Q_{infiltration_83}

These values account for any advantage (and disadvantage) a dual hose unit might have compared to a single hose unit: namely, the contribution of heat from infiltration air and ducting. They also take into account these effects at lower and higher outdoor temperatures – 83° F and 95° F.

If a single hose unit has a higher SACC than a dual hose unit, it will be able to cool faster. It will be able to cool a larger room. Conversely, if a dual hose unit has a higher SACC than a single hose unit it will be able to cool the room faster and cool a larger room as well.

SACC is the differentiating factor between two units – not whether one or the other is a dual hose unit or not.

Our testing showed high SACC single hose units greatly outperforming one of the highest SACC dual hose units on the market, even in extremely hot outdoor conditions.

Why? How? The number of hoses involved had nothing to do with it. The high SACC single hose units simply had a higher SACC than the high SACC dual hose unit.

SACC Compared to Traditional Cooling Capacity

With this information in mind, let’s take a look at the current lineup of the most popular portable air conditioner models on the market, sorted by SACC.

Note how SACC varies dramatically even among units with the same traditional BTU specification.

For example, the Midea Duo (MAP14S1TBL), a 14,000 BTU unit, has a SACC of 12,000 BTUs. The Black + Decker BPACT14WT, also a 14,000 BTU unit, has a SACC of only 7,700 BTUs.

We see the same variance in SACC - a number that's much more representative of actual cooling capacity - in other traditional BTU size classes (12,000 BTU, 10,000 BTU, and 8,000 BTU size classes).

For 12,000 BTU units, for example, SACC varies between 6,500 and 10,000 BTUs (SACC).

*Units marked with a * in the table above have a higher SACC now than they did in the past. For example, the Whynter ARC-14S we tested for review only had a SACC of 8,900 BTUs. The newest version of this model now has a SACC of 9,500 BTUs.

Using SACC to Buy the Right Model

So, how do you choose which model to buy? How do you match the SACC of a particular model to the size of your room?

Here we have to dispel our second major myth of the day: Using BTUs to properly size a portable air conditioner for a room is a fool’s errand.

Take a look at the box of this LG portable air conditioner. Notice how it matches a particular room size in square feet to a particular BTU specification.

Other boxes on other portable air conditioners have a similar table. Portable AC manufacturer websites use a similar table. Many other consumer guides for portable ACs use a similar table.

What is the major problem with this table? First of all, it uses traditional BTUs – not SACC  BTUs - to specify area of coverage. We just showed how one 14,000 BTU unit has at least 50% more actual cooling capacity – i.e. 50+% higher SACC – than another 14,000 BTU unit. Wouldn’t it logically follow, then, that it would have a 50% greater area of coverage? Still, almost all area of coverage tables you find printed on product packaging and online specify area of coverage in terms of traditional BTUs and not SACC BTUs.

This, however, is only the tip of the iceberg when it comes to exposing the true area of coverage for a particular portable AC unit.

The truth of the matter is this: there’s only one size portable AC unit you should buy – the highest SACC unit you can afford.

Any area of coverage table, no matter if it’s in terms of traditional BTUs or SACC BTUs, fails to take into account all of the factors that will impact the true area of coverage. That’s because it’s impossible for it to do so.

And many of these factors have a tremendous impact on the overall cooling ability of the portable air conditioner, regardless of its SACC.

Here we’re talking about factors like:

1. The surroundings - i.e. the climate the unit will be used in

The same sized room located in a climate that rarely sees temperatures over 90° F requires a unit with a much different cooling capacity than the equivalent sized room in a climate that frequently sees temperatures exceeding 100° F.

2. The room itself

3. What’s inside the room

4. How you use/install the AC unit

It’s impossible for a BTU calculator or chart to take into account this many complex factors that affect portable air conditioning sizing.

Our Testing Shows Minimum Requirements

Our own testing revealed a quantum leap in performance going from a sub 9,000 SACC BTU unit to a 9,000+ SACC BTU unit in an approx. 150 sq. ft. room.

9,000+ SACC BTU units cooled the room extremely quickly and to a much colder temperature.

Sub 9,000 SACC BTU units took much longer to cool the room and couldn’t reach as cold of a room temperature.

And so, at a minimum, we recommend a unit with at least 9,000 SACC BTUs.

One More Factor to Consider - Energy Efficiency

Portable AC units draw a lot of power. So much so that you'll eventually spend more to power one (on power bills) than you will to buy the unit itself. For this reason, energy efficiency is of paramount importance when buying a portable AC unit.

EER vs CEER vs SACC/watt

In the past EER (Energy Efficiency Ratio) was used to describe a portable AC’s energy efficiency.

Let’s take a look at the equation used to determine EER:

EER = BTUs per hour/Watts

For example, a 14,000 BTU model that draws 1,400 watts of power on maximum settings would have an EER of 10.0 as 14,000/1,400 = 10.0.

A 14,000 BTU unit that draws 1200 watts of power would have an EER of 11.67 as 14,000/1,200 = 11.67.

Taken at face value, this looks like a good and proper metric to use for energy efficiency. The lower the power draw (watts) compared to the cooling capacity (BTUs/hr), the higher the EER. And the higher the EER, the better the energy efficiency.

Thus, if we were to look at the EER of the two example units above we could easily say that the second has better energy efficiency because it has a higher EER – 11.67 compared to 10.0.

However, taking into account what you’ve learned so far about the old method used to determine cooling capacity (standard BTUs) vs the new method used to do so (SACC), you should be able to spot one major problem with EER. That’s right. It uses standard BTU’s – yes, the old BTU metric – in its equation.

The Department of Energy also recognized this issue with EER and acted accordingly by instituting a new metric by which to determine a portable AC unit’s energy efficiency.

That metric is called CEER – Combined Energy Efficiency Ratio.

Unfortunately, CEER is a lot more complicated than EER. The new energy efficiency ratio could have simply involved taking SACC and dividing it by maximum power draw on cooling mode in watts. But the DOE decided that the equation needed a little bit more nuance than that. Let’s take a look at the end result:

CEER_SD = ACC₉₅ × 0.2 + ACC₈₃ × 0.8 divided by AEC_SP + AEC_T ⁄ k × t

Note: this is the equation for single hose units. The equation for dual hose units is even more complex.

We’ve already shown how

SACC = ACC₉₅ × 0.2 + ACC₈₃ × 0.8

Thus, the top half of the fraction (the part that goes before "divided by") in the equation can simply be replaced by SACC.

The bottom half of the fraction (the part that goes after "divided by") simply equates to power draw under specific conditions.

CEER combines the power draw of the air conditioner on all of its different modes over a set period of time; hence the name – combined energy efficiency ratio.

More specifically,

AEC_SD = annual energy consumption in cooling mode
AEC_T = total annual energy consumption attributed to all modes except cooling
t = number of cooling mode hours per year, 750.
k = 0.001 kWh/Wh conversion factor for watt-hours to kilowatt-hours.

Thus, the denominator for this equation involves accounting for power draw during cooling mode on top of certain other modes for a certain number of hours with “k” being nothing more than a conversion factor.

We can therefore say that

CEER = SACC/watts (but on all modes; NOT just on cooling mode)

Note that

1. the other modes involved here – standby (when the unit is plugged in but not on) and fan only (when cooling isn’t necessary and the desired temperature has been reached) - draw very little power compared to cooling mode. Thus, their impact on the CEER equation above is minimal

2. Furthermore, most models on the market draw roughly the same amount of power on these two modes – standby and fan only - which further minimizes their impact on the CEER equation above when comparing one model to another

Most models we tested do draw a few watts of power on standby (plugged in but not powered on) but they all draw very little power and roughly the same amount of power (1 or 2 watts).

Most models draw little power when only the fan is activated and most draw roughly the same amount as well (about 50 watts or so on max. fan speed).

The bottom line: the “other modes” that CEER takes into account (other than cooling mode) don’t really matter.

What does matter – cooling mode

When cooling mode is fully activated maximum power draw does vary. It tends to correlate with the old standard for measuring BTUs/hr. High BTU (14,000 BTU) units tend to draw about 1200 to 1400 watts. Lower BTU (8,000 to 12,000 BTU) units tend to draw about 1,000 to 1,200 watts.

So, in summary:

• power draw on fully activated cooling mode is important. It does vary.
• But on other modes – standby and fan only - power draw is minimal and essentially the same for different models.

This means that we can further simplify our evaluation of portable AC unit energy efficiency by simply looking at:

SACC/watts

Which only considers energy efficiency on cooling mode with maximum power draw.

Furthermore, you can make things even simpler by only using:

SACC

Since maximum power draw is so similar between units in the same traditional BTU size class, you really could just focus on SACC.

The higher the SACC, the better the unit’s energy efficiency (in most cases).

In other words, if energy efficiency = SACC/watts and watts are essentially equal in the comparison, then the higher SACC, the greater the energy efficiency.

Indeed, when we look at a table for 14,000 BTU units - all with similar power draw - we see the trend that higher SACC units have better energy efficiency (better SACC/watt ratios).

We see the same trend when we compare 12,000 BTU units, 10,000 BTU units, and 8,000 BTU units – higher SACC units tend to have better energy efficiency (better SACC/watt ratios).

Putting It All Together - General Recommendations

Accounting for

• The fact that portable AC units are inherently highly inefficient
• All of the complex factors that impact portable air conditioner sizing (factors like the insulation of the room, whether it's on a second floor or not, etc.)
• Our own test results which show high SACC units greatly outperforming low SACC units even in 150 sq. ft.
• The fact that higher SACC units are more energy efficient

We generally recommend you buy a portable AC unit with as much cooling capacity (SACC) as possible.

Buying a portable air conditioner with as much SACC as possible is the only way to ensure you will have a reliable portable AC unit that will be able to cool any size room no matter how difficult it is to cool.

With this in mind, these are the top 3 options currently on the market: