When it is hot and muggy, air conditioners units lower the air temperature, remove air moisture, and filter the air within a room. Air conditioning needs vary greatly based on the home’s location, how it is used, the insulation, and other factors such as energy efficiency goals. When a fraction of the rooms in the home need to be cooled, supplemental units can offset the expensive costs of running a whole-house system. Supplemental units are also beneficial for providing additional cooling to some areas of the home that may be hot spots.
What is the size of the space that needs to be cooled?
How much power is available from the outlet for the unit?
Will the unit be installed in a window, through-the-wall, or portable?
If intended for the window, how large is the window?
How important is the energy efficiency for the unit?
Would it be beneficial for the unit to have more than one function?
Supplemental air conditioners can be window-installed, through-the-wall, portable, and multi-modal. Overall, supplemental air conditioning units provide supplemental cooling as well as cooling for specific locations where additional cooling is needed. Choose the air conditioner for your home based on size, installation, controls, special features, and its energy-efficiency rating.
Supplemental air conditioner units are frequently designed to provide additional cooling for a specific room. Units installed within the window allow the floor space to be free and clear of additional clutter. Conversely, some homeowners may prefer the unit be inside rather than partially outside the home’s facade. Recently, units now are more powerful and more energy efficient.
Relying on supplemental units is a popular way for a family to strive to lower energy costs for the home since cooling takes more energy than heating. While a whole-house air conditioning system is often a standard feature, the entire house does not need to be universally cooled regularly throughout the day and night. Energy savings can be achieved by using a combination of both a whole-house system and supplemental units.
Supplemental air conditioning units that are designed as permanent features in the home are most often through-the-wall units. These units are durable, powerful, and often come with specific control options. Through-the-wall units create significant benefits for homes located in temperate climates where a whole-house air conditioning system is not needed.
Through-the-wall supplemental air conditioners typically come as single units installed within a sleeve in the wall. Another type of through-the-wall unit is called a ductless mini split air conditioner. The single unit functions much in the same way as a window unit while the mini split system has two different types of mechanical units.
For ductless mini split air conditioners, the air handler unit is located indoors while the condenser is located outside. The condenser takes in fresh air and compresses it to make it cool through a mechanical procedure while the air handler blows the cooled air into the space. One to multiple zones is available where there can be several condensers per each air handler. A ductless mini split air conditioner is similar to a whole-house air conditioner, but is designed for several rooms in a very small home or apartment.
Through-the-wall units help to cool the occasional hot spot(s) with minimal energy consumption. Similar to the window-installed units, some homeowners are not in favor of the unit adding to the exterior aesthetics. Covering the area with smart landscaping can be a desirable option. In the winter, provide a sufficient cover to protect it against freezing weather.
The least-permanent options for supplemental air conditioning are the portable units. Portable units are a fairly new innovation that can be conveniently moved from room to room. The quality and the level of power for portable units are similar to the window-installed units. Portable units are ideal for the homeowner who likes the exterior of the home to be left as free and clear as is possible from additional mechanical equipment. Likewise, portable units are ideal for renting families that want the least-permanent option.
Portable units are also ideal for the home that has more than one area that needs occasional supplemental cooling. Portable units still need access to the outdoor air via plastic air intake hoods and flexible aluminum ducting. Some units can also be installed in the window if needed. The machines have castor wheels. When selecting the size, purchase a unit that is in the middle of the sizes of the rooms it needs to cool.
Multi-Modal Portable Units
Another type of portable supplemental air conditioning unit is one that can provide other indoor air features such as dehumidification, fan, heat, and air purification. Multi-modal portable units come in a variety of combinations, such as 3-in-1 and 4-in-1 units. A fan brings in outside air for natural ventilation. The heat acts is provided via a heat pump where electrical heat warms the air and it is then blown out by the fan. The dehumidifier takes humidity out of the air at a rate of pints of water per day.
Multi-modal portable units are ideal for the homeowner who may need any combination or all of these extra features on a somewhat regular basis. Purchasing a unit that can do more than one function can help to lower the cost and to reduce extra floor space from having several units rather than one. Units that provide the home with more than a fan and air conditioning will have shorter life spans if used continuously throughout the year.
Finding the right sized air conditioner unit for its associated space is based on several formulas and calculations. Keep in mind that if the air conditioner is too small, the space will not get cool quickly enough. If the air conditioner is too large, the space could cool too quickly. With units that are sized too largely, the humidity level will not be sufficiently lowered, which makes the room feel too damp and clammy.
Begin by calculating the room’s square footage. Square footage is calculated by multiplying the length by the width of the room. The cooling capacities of the units are rated in BTUs per hour. Units range from 5,000 to 25,000 BTUs. 15,000 BTU-units can be used for rooms up to 875 square feet and plugged into a 115 V outlet. Units that are larger than 15,000 will need to be plugged into a 230 V outlet.
While units are often listed based solely on square footages, there are other factors to consider before choosing the right size for the space. Natural Resources Canada provides a free air conditioning calculator online The size calculators factors in the total window area, level of sun exposure, insulation value, and the room’s use.
The following chart contains rough estimates that can help guide the homeowner to the right size unit for the space.
|Capacity Needed |
(BTU per hour)
100 - 150
150 - 250
250 - 300
300 - 350
350 - 400
400 – 450
450 - 500
500 - 700
700 – 1,000
1,000 – 1,400
875 square foot room
Open L- or T-shaped spaces
Based on square footage. It is likely these types of spaces will need two units.
Based on square footage plus 4000 additional BTUs.
2+ People Capacity Rooms
Based on square footage plus 600 additional BTUs.
Based on square footage plus 10% of the square footage calculation.
Based on square footage minus 10% of the square footage calculation.
*Square footage recommendations provided by Energy Star.
Supplemental air conditioners are all given an EER rating, or an energy efficiency rating, that is listed on the unit. The EER is derived from taking the cooling capacity and dividing it by the electrical power required to run the unit. The EER rating usually ranges from 8 to 12. If the EER is high, the energy efficiency is better, monthly electric bills are lower, and greenhouse gas emissions are reduced.
15,000 BTU-units typically have an EER of 9 or 10. Units with an EER of over 10 are considered to be extremely efficient. While higher EERs are better, these units also cost more. Keep in mind, however, that there is always a trade-off in a reduction of operating costs for the unit if used over a longer period of time. The cost for a more expensive unit could balance out or end up being cheaper than paying for more expensive electrical costs.
Energy Efficiency Tips
The air conditioner controls are operated either via fan speed or via digital, programmable temperature controls. Programmable temperature controls can improve the effectiveness of the unit because the room will turn off when it reaches the user’s desired temperature or will continue to blow until the right temperature is reached.
Programmable or adjustable thermostats help the homeowner to control the temperature consistently throughout the day and night. If the space can be kept fairly cool during the day, when many homeowners are at-work, the unit will then be spared from working hard to cool the space during the evening hours.
Digital / Electronic Controls
Digital or electronic controls offer the user more precise control. The exact temperature is programmed into the unit rather than “LOW,” “MED,” OR “HI” air conditioning modes.
Timers provide a preset schedule for turning power “on” and “off.” Timer controls simply control the time the unit turns “on” and “off.” Timers are a more affordable option to conserve energy than programmable thermostats.
Units that come with a fan-only feature allow the unit to draw in cool air without using extra electricity for operating the compressor. In addition to features that allow the user to turn the compressor “on” and “off,” further cooling controls can be achieved through multispeed fan options. Three-speed options are the most common, but two-speed are also available. Turning the unit onto its lower setting saves energy costs.
The amount of noise emitted from the air conditioner is equal to the fan speed. Therefore, the higher the speed, the louder the unit becomes. Programmable temperature fan controls can optimize the noise reduction of the unit. Since supplemental air conditioners are commonly installed within bedroom spaces, a sleep mode is useful for keeping the unit on a low and quiet setting.
While controlling the temperature is key to operating an air conditioner, there are some options that go above and beyond temperature controls such as digital controls, fan speeds, and noise levels.
Air conditioners have controls located on the top, bottom, or on the sides. The location of the control affects where the unit can be installed within the home. If the controls are on the top, then it is better for the unit to be installed at waist level. If the controls are on the bottom or on the sides, then a through-the-wall unit installed at shoulder or head-height would be ideal.
Remote control devices are designed for convenience. Remote controls may be more useful if the unit does not have a programmable thermostat or a timer.
The energy-saver option turns off the compressor, fan, and all other energy so that it will not continue to draw electricity while turned off.
Filters need to be cleaned every few weeks during the cooling season. When shopping for a unit, find out how easy it would be to access the filter and to clean it. The easier it is to find and access the filter, the more likely it will be cleaned as recommended. Clean filters will increase the efficiency of the unit. Replace filters when they are dry.
Since keeping the filters cleaned regularly is important for indoor air quality, washable filters help to lessen the maintenance hassle. These filters are also often easily accessible.
Adjustable louvers allow the blowing air to be directed in at least two different directions. Adjustable louvers are especially needed for larger spaces.
Adjustable slide-out chassis allow the window-installed air conditioner to fit snuggly within the window’s opening. Slide-out chassis also help to easily block out extra outside air.
Portable air conditioning units allow the homeowner to use the machine in any room. While ductwork still needs to be set up within the window opening, the window’s opening is much smaller. These units are great for adding extra cooling in a least invasive manner.
Through-the-Wall Unit Step-by-Step
Below is a generic step-by-step installation procedure.
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