Mini Split Sizing

Here is a more in depth guide.

Sizing Your Mini Split Air Conditioner: What’s the Right BTU Rating to Effectively Cool or Heat Your Room?

When buying a ductless mini split system, getting the right size matters—a lot. Keep in mind that size, in this respect, means capacity or BTU rating. While many other things have to be considered prior to a purchasing decision, making sure that you have chosen a properly sized unit should be on top of your checklist. To err on this aspect will have a huge impact on the level of comfort that you’ll be getting from your mini split unit and the amount of money that you’ll be paying for your energy bill in the long-term. Suffice to say, the correctness of the size, capacity, or BTU rating of the mini split system that you use determines the success or failure of your space cooling project. To help you make a smart buying decision, this article discusses the important things that you should know, consider, and be aware about when it comes to proper sizing of a mini split air conditioner.

AC Size Also Means Cooling Capacity

When it comes to mini split air conditioners, size refers to the capacity of the unit to heat or cool a specific space or room. Now, here’s what you need to know: The size of air conditioners is measured based in tons or expressed in British Thermal Units (BTUs). To better understand these concepts, it is best to take note of the following: 

BTU is a measurement of heat, which by definition really means the amount of energy that is required to increase the temperature of water by one degree Fahrenheit.

One ton is equal to 12,000 BTUs per hour

Basically, when we’re talking about tons, what we mean is the amount of heat (or BTU) that an air conditioner can remove in a space every hour.

Based on the statement, it follows that a 1-ton air conditioner can remove in a span of one hour an amount of heat that is equal to 12,000 BTUs. Meaning to say, if you have a 5-ton mini split air conditioner at home, for example, you can be assured that your unit will be able to remove an amount of heat that is equal to 60,000 BTU per hour. We can safely deduce that the bigger the ton means the bigger the BTU; and the bigger the BTU that an air conditioner can remove every hour, the bigger an air conditioner is considered in terms of size.  Click here to view our most popular 12,000 BTU System.

All Ductless Mini Splits Are Built with a Specific Size

Air conditioners, including ductless mini split systems, are built in different sizes. Each unit is practically made for a specific size of a space. With ductless mini splits, the indoor and outdoor units have varying sizes or rated capacities. Knowing the size of each unit will guide you to properly install a correctly sized system. When installing a ductless AC solution to your home, your sizing consideration should factor in the size of the room for single-zone application or each of individual rooms for a multi-zone configuration.  To put it simply, your outdoor unit may have a different but enough size to complement the size of each indoor air handler that are installed in different rooms inside the house. Because it’s more likely that each room in your home may have different sizes, the size or rated capacity of individual air handlers may also vary.

Bigger Size Doesn’t Always Mean Better

Contrary to popular belief, bigger doesn’t always mean better when it comes to air conditioners. This means that having a unit with a higher rated capacity or higher BTU rating doesn’t assure you that you’re actually getting the right size. The truth is, the size of your unit must be proportionate to the size of the space. So, when choosing a ductless mini split, it is important to make sure that its BTU rating is suitable to the size of the room where you will install the system. The rule of thumb is, the larger the space means the bigger size of a unit is required; conversely, the smaller the space, the smaller size of the unit that is needed. The key is just to make sure that your chosen mini split system is properly sized for the specific space that you need to heat or cool.

Why Proper Sizing for Your Mini Split Unit is Important?

Because your comfort and energy-savings are stake, it is imperative that your mini split system is properly sized for the room that you will heat or cool. To put this another way, it is important that your system is not too big or too small for your specific space. Now, what would happen if you installed a mini split with a BTU rating that does not match the size of the room? What would happen if the system is oversized or undersized?

Well, let’s say that your air conditioner is too big for your space. Based on what was discussed earlier about tons and BTUs in relation to the size of an air conditioner, this could also mean that your air conditioner packs more tons than necessary to cool a smaller space. What happens is your oversized air conditioner might quickly cool your home or a small room inside your house. The problem is it might undergo a process called short cycling, which is bad. In short cycling, your oversized air conditioner turns itself on, blows some good blast of air, then quickly shuts down only to run again. This cycle continues because your system, in this case, is trying to maintain the temperature that you specifically set in the thermostat. With your air conditioner turning itself on and off means it is only running for a short period of time. The immediate result is discomfort because the humidity from the air will not be sufficiently removed. Worse, short cycling forces your system to use more energy and sustain stress. When kept this way, your system will only be using more energy than necessary and the extra wear-and-tear can result to system breakdown. Obviously, wasted energy and system malfunction can translate to higher energy bills and maintenance costs.

Now, what if your air conditioner is too small? Again, take this in the context of tonnage or BTU as units to measure the size or your unit or determine its capacity. Using an undersized air conditioner to cool a big space would not make any sense. It is downright impractical because it would not even be able to cool much of the space in your home even if it runs longer. The wasted energy, in this case, would be substantial and you can expect your electricity bill to skyrocket. So, what’s the best size for your air conditioner to achieve more efficiency? Obviously the right fit is always the best fit.

Your Mini Split System Sizing Guide

Determining the size of a space to figure out the right BTU rating of the unit to be used is usually done by taking into consideration the square footage of the room. But there’s a caveat. While you can accurately measure the size of the room based on the square footage, determining the right size of a mini split would be a little bit challenging due to several factors, such as the height of the ceiling, insulation, the climate in the area, and even the level of the room’s exposure to sunlight.

The aforementioned variables normally affect or influences the size of the unit that you need to use. So, what does this imply? It means, that the BTU ratings are just general estimates, which are determined based on these factors. This doesn’t mean, however, that proper sizing cannot be established. By considering the environmental or external factors, we can still effectively determine the right size of a mini split unit that is needed for a specific space. While the requirements look a bit too much, it’s not as hard to handle as it looks. In fact, sizing guides are now very common.  

For your guidance, here’s a sample of a sizing chart that you can reference when shopping for your mini split system:

When the external factors are present, the amount of BTU that is needed are normally increased to compensate for the extra strain or energy needed to cool or heat the space. For accurate sizing, you can always tap the help of an HVAC expert who will calculate your cooling or heating requirements and determine the right size of the mini split air conditioner for your home.

Sizing Means Load Calculation

Sizing an air conditioner or a mini split system is conducted through the so-called load calculation. Calculating the load means determining the correct amount of cool or warm air that is needed to establish a comfortable temperature or maintain that desired that temperature inside the room. When HVAC experts conduct a load calculation for a specific space, what they normally come up with is the estimated amount of BTU that is needed to cool or heat the room. This is the same data that is used to determine the right BTU rating for the unit that will be used for that particular space.

When sizing for a multi-zone application, you want to select each air handler in a size that can handle the square footage for each room.  Once you have done that, you'll want to make sure the system is built with a condenser that can handle the entire load.  Some manufacturer's allow sizing combinations that don't exactly make mathmatical sense.  These are allowable because with some applications, you wouldn't need full capacity out of each zone 100% of the time.  

For example, if you have a 12,000 BTU air handler in your living room, a 18,000 BTU air handler in your kitchen, and a 9,000 BTU air handler in your master bedroom, you may be able to build this system with a 30,000 BTU condenser.  Even though the air handlers add up to 39,000 BTU's, the odds may be small of a time when you need full capacity out of the bedroom and the kitchen at the same time. 


For more help with sizing out your multi-zone system, please call our product experts at 855.337.0001.


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