Although the “bigger is always better” mentality applies to some fields, the HVAC industry usually isn’t one.
Many HVAC technicians will warn homeowners against drastically oversizing their HVAC equipment, as it can lead to various unwanted issues.
However, when it comes to mini-splits, do the same rules apply?
This article addresses this question in-depth, so continue reading to learn more!
Can You Oversize a Mini-Split?
Before we get into the ‘why’ of this question, let’s start by answering it.
Yes, you can oversize a mini-split.
If you’re familiar with the HVAC industry, you may be familiar with the adverse side effects of oversizing HVAC equipment. However, this brings us to the ‘why’ of our answer.
There’s a lot of truth to the dangers of oversizing HVAC equipment. If you drastically oversize it, there’s a good chance you’ll end up reaping the adverse side effects of this choice, such as short cycling.
With that said, slightly oversizing a mini-split air conditioner shouldn’t be an issue. The primary kicker is to use the system appropriately. Most of these units are variable capacity, meaning they can adjust to the necessary speed according to the demand.
So, if the temperature in the room is only slightly higher than the thermostat setting, the system can run at a slower speed to reach the desired temperature. This is great for a few reasons.
Firstly, it allows you to save energy. Instead of running the system full-tilt just to drop the temperature a few degrees, it runs only as much as necessary.
If you misuse the air conditioner and regularly use the remote to set the system to full blast, you’ll deal with the unwanted side effects.
But, this shouldn’t be a problem if you allow the system to automatically kick on and off to maintain the necessary temperature.
Why Oversize A Mini-Split?
There are several reasons why you may need to oversize a mini-split. For example, you may calculate the necessary size based on the square footage of the space. The room may be small enough that the required size isn’t even available in some cases.
Or, perhaps you have other factors included in your calculation. For instance, maybe multiple people spend a considerable amount of time in the space you want to cool.
Or, maybe it’s in the kitchen, where various appliances generate heat.
In that case, there’s extra heat in the space, and you’ll need a larger mini-split than the square footage of the space demands.
What Happens If You Oversize A Mini-Split?
A few things can happen when you oversize a mini-split. If you drastically oversize the unit, the system will short cycle, as it cools too quickly to run in a regular cycle.
This isn’t a desirable outcome since the unit doesn’t have enough time in its rapid cycles to dehumidify the air. So, you’ll end up in a humid, clammy environment.
Or, if you oversize a mini-split and constantly have the system running on full blast, you may deal with moisture and mold issues. Again, the same concept applies.
Objects in the space hold heat, like the walls, furniture, etc.
So, when the room cools dramatically in a short period, there’s still residual heat left in the walls. With the excess moisture in the space, there may be condensation issues. This creates the perfect environment for mold and mildew to take hold.
How Much Can I Oversize A Mini-Split System?
Based on Manual J and Manual S, if HDD / CDD < 2, You can at most oversize the mini split system by 30%. However, once the HDD / CDD > 2, the maximum mini split size is Estimated Cooling Load + 15000 BTU.
Using HDD(Heating Degree Days) / CDD (Cooling Degree Days) ratio is critical when deciding the the right oversized mini split system. Any other sources only give you a general oversized ratio , could mislead you to choose the wrong sized unit. You can check your HDD and CDD here.
In order to help you skip the calculation, we made a chart below.
Chart: Maximum BTU Size For Oversized Mini Split
| Estimated Cooling Load: | Max. Mini Split Size (HDD / CDD < 2) | Max. Mini Split Size (HDD / CDD > 2) |
| 1-Ton (12,000 BTU) | 15,500 BTU | 27,000 BTU |
| 1.25-Ton (15,000 BTU) | 19,500 BTU | 30,000 BTU |
| 1.5-Ton (18,000 BTU) | 23,000 BTU | 33,000 BTU |
| 1.75-Ton (21,000 BTU) | 27,000 BTU | 36,000 BTU |
| 2-Ton (24,000 BTU) | 31,000 BTU | 39,000 BTU |
| 2.5-Ton (30,000 BTU) | 39,000 BTU | 45,000 BTU |
| 3-Ton (36,000 BTU) | 46,000 BTU | 51,000 BTU |
| 3.5-Ton (42,000 BTU) | 54,000 BTU | 57,000 BTU |
| 4-Ton (48,000 BTU) | 62,000 BTU | 63,000 BTU |
| 5-Ton (60,000 BTU) | 75,000 BTU | 75,000 BTU |
Is It Good To Oversize A Mini-Split AC?
Oversizing a mini-split air conditioner isn’t necessarily a good thing. In many scenarios, it can end up being a bad thing.
However, some calculations don’t account for additional factors (poor insulation, large number of people in the space, appliances generating heat), so oversizing slightly is necessary.
You should never dramatically oversize a mini-split air conditioner, as you may contend with various issues, such as high humidity levels, uneven cooling, or mold.
Is It Better To Undersize Or Oversize The Mini-Split Condenser?
As a general rule of thumb, it’s better to slightly oversize the mini-split than undersize it. With an undersized system, you’ll run into different issues.
For example, the undersized unit will have to work harder for longer periods to bring the space down to the desired temperature.
In turn, your energy bills will skyrocket. In addition, the unit may not even be large enough to somewhat adequately cool the space, leaving you with a tepid, uncomfortable environment.
Conclusion
Although drastically oversizing your mini-split system is never a good thing to do, there may be some scenarios where slightly oversizing the unit is necessary.
If you have an awkward-sized space that falls between two mini-split sizes, it’s always better to somewhat oversize than undersize.
But, if you’re unsure of the best plan of action, reach out to a qualified HVAC technician for help!
