We use air conditioners to lower indoor temperatures. Usually, they are needed most when it’s hottest outside. A reasonable thing would be to look into the relationship between outside temperature and the AC unit. Namely, does outside temperature affect the air conditioner?
In one word: Yes.
Of course, the outside temperature affects the air conditioner. How the outdoor temperature affects the AC unit, however, is another matter entirely.
It is generally cited that air conditioners can work at outdoor temperatures between 14°F and 115°F. What happens if the temperature falls below 14°F or, even more troublesome, rise above 115°F?
Most energy efficiency metrics like EER and SEER rating are measured at an outdoor temperature of 95°F. This is the optimum temperature for most AC units. The outside temperature affects the air conditioner the most when:
- It’s hot or extremely hot outside. We will start seeing these effects at 100°F but they become significant (and troublesome) when outdoor temperatures reach 120°F or more. Using an air conditioner sun shield (to shade the unit) is a very good idea when it’s extremely hot.
- It’s cold or extremely cold outside. What outside temperature is too cold for an air conditioner? If the outdoor temperature is too low, the air conditioner will stop working effectively. Luckily, we mostly don’t need air conditioning when it’s cold outside.
Running an AC unit at very high or very low outdoor temperatures can lead to a number of negative effects. These include higher cooling costs, the lower lifespan of AC units due to increased wear-and-tear, indoor temperature fluctuations, longer cooling times, increase in accumulated water accumulation, AC units being louder, and so on.
Note: Besides the AC units, the other key factor that affects the indoor temperature levels is insulation. During high outdoor temperatures, good insulation will reduce the transfer of heat from outdoors to indoors. On top of that, it will help to keep the cool air indoors as well.
To understand why AC units behave differently at different outdoor temperatures, we need to look into how air conditioners work in the first place:
Why Does Outdoor Temperature Affect Air Conditioners?
Here is the basic working principle of every air conditioner:
- Accumulate heat from indoor air.
- Expel the accumulated heat outdoors.
This principle is underpinned by a refrigeration cycle. This has all to do with the expansion (indoors) and compression of air (outdoors).
Now, the key to understanding how does outside temperature affects air conditioners is this:
The ability of AC units to expel accumulated heat is determined by the temperature of the outside air.
Example: Let’s say that an AC unit accumulated indoor heat and wants to expel it outdoors. The temperature of the air they are expelling (blowing out of the outdoor unit) is let’s say 100°F.
Here is how easy or difficult it is for an AC unit to expel this heat:
- At 100°F outdoor temperature, the AC will have no problems expelling heat outdoors.
- At 110°F outdoor temperature, the AC will start to have problems with expelling heat outdoors.
- At 120°F outdoor temperature, the AC will struggle to expel the heat outdoors.
- At 130°F outdoor temperature, the AC will have problems expelling heat outdoors.
- At 140°F outdoor temperature, the AC will have serious problems expelling heat outdoors.
- At 150°F outdoor temperature, the AC will hardly be able to function anymore since the difference between the expelling airflow temperature and outdoor temperature is a full 50°F.
At very low temperatures (below 14°F), we have similar problems with air conditioners that are also able to provide heating (heat pumps). If the temperature is extremely low, we will start seeing less efficiency (higher heating costs) and less effectiveness (slower heating) from these heat pumps.
Let’s focus on high outdoor temperatures since these are the ones that cause the most problems with air conditioners.
Here is a list of problems that running an air conditioner in extremely high outdoor temperatures causes:
1. Higher Cooling Costs At Higher Outdoor Temperatures (Lower Energy Efficiency)
Modern AC units are very energy efficient. However, these energy efficiency metrics – like EER rating and SEER rating – are measured at 95°F outdoor temperature. What happens if the outdoor is above 95°F?
Well, the air conditioner will have more problems expelling the accumulated heat outdoors. That is simply because the outdoor temperature is already very high; it’s harder to remove heat into a 130°F atmosphere than into a 100°F atmosphere.
As a result, the air conditioner will not be able to remove the heat effectively. This will increase its energy efficiency and thereby increase the electricity bill.
At hot outdoor temperatures, we can see this air efficiency fall by 10%, 20%, or 30%. However, at 140°F or higher, the loss in energy efficiency will be more than 50% which will double our cooling costs.
2. Slower Cooling Due To High Outside Temperatures
We know that a 3-ton AC unit will provide 3 tons of cooling output, right? This is true at normal conditioners.
However, in case of high outdoor temperatures, the cooling output will drop. In effect, we will see our 3-ton AC unit providing only 2 tons of cooling output, or even less at extremely high outdoor temperatures.
You don’t have to be a rocket scientist to understand that a 3-ton AC unit now turned 2-ton AC unit will cool our home slower.
Less cooling output is not the main issue. If your air conditioner is still being able to lower the temperature to our set temperature, that’s not all that serious.
What is serious, however, is that the high outdoor temperatures affect your air conditioner so much that it will be deemed undersized.
An undersized air conditioner will not be able to lower the temperature adequately, despite running at 100% output all the time.
This struggle many air conditioners suffer at high outdoor temperatures will inevitably result in:
3. Shorter Lifespan Of Air Conditioners Running At High Outdoor Temperatures
Needless to say, if you run an air conditioner at harder-than-average, its lifespan will shorten. You can check how long do air conditioners last (on average) here.
Now, if you have an absurdly high temperature for a day or two, this won’t affect the durability of the AC unit significantly.
However, if you are dealing with week-long summer heatwaves with 120°F temperatures or higher, you will likely shave a year or more from your air conditioner lifespan.
4. Indoor Temperatures Fluctuate With Fluctuating Outdoor Temperatures
As we have seen, the ability of air conditioners to provide cooling is affected by outdoor temperatures.
That means that the AC unit will have different effectiveness at different outdoor temperatures.
In some cases, especially with high-temperature swings and undersized AC units, this may lead to temperature fluctuations in our home.
At hot but not extremely hot temperatures, an AC unit will still be able to do its job adequately. That means it will be able to achieve the temperature you set on the thermostat.
However, if the outdoor temperature is too high, the AC unit won’t be capable to cool your rooms sufficiently. As a result, the indoor temperature can stay above the set temperature.
If the outdoor temperatures swing between let’s say 130°F during the day and 100°F during the night, the indoor temperature will likely swing as well. Not as much as 30°F but you may see swings between 72°F and 76°F, for example.
5. Other Problems Running AC At High Outdoor Temperatures Will Cause
As we have seen, the outdoor temperature impacts air conditioner in various negative ways. The majority of these effects are caused by the AC unit having to work harder (closer to 100% cooling output) than at lower temperatures.
Other related problems you will likely face are:
- Higher dehumidification rates. Higher outdoor temperatures usually mean that the AC unit will have to drain more water. This lower the energy efficiency even further and can lead to AC leaking problems in limited cases.
- Noisier air conditioner. Both the indoor air handler and outdoor unit (with compressor) will generate more noise if they have to operate at higher cooling output levels. This is not ideal.
- Outdoor unit will produce more heat. If the outdoor temperate is already high and you are running your AC hard, the outdoor unit will produce much more heat. It will be hotter to the touch and the airflow from it will be hotter as well. A hotter outdoor unit can equal to lower lifespan as well.
Let’s look at what you can do to reduce the effect high outdoor temperature has on your air conditioner:
How To Minimize effect Of Outdoor Temperature To An Air Conditioner
There is little you can do when the summer heatwave kicks in. It’s not like we can control the weather.
Nonetheless, we can do two things to minimize the effect of outdoor temperature on an AC unit during hot summer:
- Shade the outdoor unit. If the outdoor unit is directly exposed to the sun, it will get hotter. The air surrounding the unit will also be hotter. The easiest way to protect your AC unit in high outdoor temperatures is to put it in the shade. If that is not possible, use an air conditioner sun shield. This is basically an air conditioner umbrella that shades your AC unit.
- Set the thermostat to
72°F78°F or even 80°F. By increasing the indoor temperature you can partially minimize the effect outdoor temperature has on the AC unit. If the AC unit doesn’t have to cool your home to 72°F, it has a lower cooling output. By increasing the thermostat temperature to 78°F, for example, you can at least take a bit of stress off your air conditioner. Of course, you will have to figure out how comfortable you are with higher indoor air temperature.
- Install a ceiling fan. A ceiling fan working in a clockwork direction in the summer can give you a feeling that the indoor air is 4°F colder than it actually is. With a ceiling fan, you will be more comfortable increasing the thermostat temperature to 80°F and thereby helping your AC survive during extremely high outdoor temperatures. You can check the best ceiling fans to use here.
All in all, the outdoor temperature definitely affects air conditioners. Almost all the effects on the performance, lifespan and cooling capability are negative.
Nonetheless, you need your air conditioner the most when the outdoor temperature is the hottest. There is little you can do to help your AC unit but having the outdoor unit positioned in the shade and setting your thermostat a few degrees higher will take at least some stress off your AC unit.