Jun 12, 2018

Is Bigger Really Better When It Comes To Your AC Unit?

Size definitely matters when it comes to choosing an air conditioner for your home, just not in the way most people think. 

A lot of people believe that an AC with a bigger capacity is always better when it comes to cooling your home. That, however, isn’t really the case. Oversized air conditioners can cause problems and cost you a lot of money in the long run. 

Oversized AC unit issues

The upfront cost is higher – Of course, bigger air conditioners generally cost more than smaller units. That means from the get-go, your air conditioning costs are already high even before you get the unit installed.

They use more energy – Oversized air conditioners almost certainly mean higher energy bills because they take up more power to cool your home. Since big capacity AC units cool your home rather quickly, they short-cycle more often, which refers to the way an AC’s compressor turns itself on and off in rapid intervals, which is not an energy-efficient way of operating. 

The unit’s lifespan gets shorter - The whole short-cycling thing that happens with an oversized air conditioner inflicts a lot of wear and tear on your unit, which will eventually shorten its overall lifespan.

Rising humidity levels and poor air quality - As we know, an oversized AC is prone to short-cycling, which means there would be extended periods where it’s turned off and therefore not doing its job of removing moisture, dust, allergens, and other particles from the air. So you can expect to be sneezing more often and feeling sweaty and sticky in your home.

The problem with undersized AC units

AC units that are too small for your home, on the other hand, present several issues as well.

Your home is never cool enough - It can try as hard as it can, but an undersized AC unit is always at a disadvantage when it comes to cooling an area that is too big for it. The best it can probably do is cool a certain area of the house, but leave other parts warm.

It will run continuously and lead to higher energy bills - Did you buy a small air conditioner because you think it will use less energy? While an AC’s capacity typically matches its energy usage, an undersized air conditioner will use more power simply because it is likely to run continuously, barely stopping for breath. A small AC will try its best to cool a given area, and if the area’s too big, it will just keep on running until it does that job, which it never really does.

The unit’s lifespan gets shorter - If oversized units suffer wear and tear because of frequent short-cycling, undersized units suffer the same wear and tear, but for the opposite reason: failure to go through healthy on and off cycles. The stress of the practically non-stop operation of your undersized AC unit leads to more frequent and costly repairs and lessens its overall lifespan. 

In air conditioning, sizing your unit right is extremely important. Only a properly-sized AC unit will run through healthy on and off cycles. It also won’t run non-stop at the expense of efficiency. When you right-size your air conditioner, you and your family will feel cooler and more comfortable, your energy bills won’t make you pay through the nose, and your air conditioner stands a better chance of lasting for as long as the manufacturer intended.

What is Air Conditioning Tonnage?

Whenever there is talk about right-sizing an air conditioner, the phrase “air conditioning tonnage” always comes up, and rightly so. After all, tonnage has everything to do with properly sizing your AC unit for your home.

In this context, “tonnage” does not in any way refer to the physical weight of your AC unit. In the air conditioning industry, the terms “tonnage” and “ton” both refer to the amount of heat an AC unit can remove from a given space or area in one hour.

Typically, the HVAC industry measures heat using the British thermal unit (BTU). The standard BTUs of air that a 1-ton AC unit can remove per hour stands at 12,000. It follows then that a 2-ton air conditioner removes 24,000 BTUs of air per hour; a 3-ton AC unit, 36,000, and so on.

How to calculate your BTUs

What size AC do I need? If you’ve been asking that question, then you would be pleased to know that you can determine the BTU needs of your home yourself.  By using a BTU calculator air conditioner sizing shouldn’t be so difficult.

While an AC unit size calculator is useful, there are more accurate tools. Ideally, a BTU calculator should only be used to make a rough estimate so you’ll have an idea what size air conditioner you’re going to buy. To get a better answer to the question, “how many BTU air conditioner do I need?”, it’s always best to have a reliable local HVAC company perform a professional BTU estimate. 

The first thing you need to do to determine your BTU needs is to calculate your home’s square footage. You need to get an accurate measurement of the entire space to be cooled. While most of us know the approximate square footage, others will have to break up each room into squares and rectangles for measurement and do as many of them as possible.

Using the inch as your basic measuring unit, determine the length and width of each separate area. You should then get the number of square inches in each area by multiplying the two figures. Divide the product by 144, and you’ll have the square feet of each area. You can then get the total square footage of the space to be cooled by rounding up the square feet of each area to the nearest whole number, then adding them all up. 

Choose your AC unit

With that rough estimate of your square footage, you can now start shopping for the right AC unit for your home. Take a look at the chart below and see which amount of BTUs corresponds to your square footage. Take note of the BTUs, and start looking for the right air conditioners, all of whom carry clear labels of the amount of BTUs they need.  

Square Footage

BTUs Required

100 – 150 5,000
150 – 250 6,000
250 – 300 7,000
300 – 350 8,000
350 – 400 9,000
400 – 450 10,000
450 – 500 12,000
500 – 700 14,000
700 – 1,000 18,000
1,000 – 1,200 21,000
1,200 – 1,400 23,000
1,400 – 1,500 24,000
1,500 – 2,000 30,000
2,000 – 2,500 34,000

So if you’ve been asking, “what size AC unit for 2000 square feet?”, then it’s 54,000 BTUs. The answer to the question, “what size AC unit for 2400 square feet?”, would be, is 60,000 BTUs or 5 Tons. It’s possible to fall between unit sizes, so if that’s the case with you, then you should choose the next higher size. That way, you can be sure that the AC unit can still cool a given area sufficiently. 

Other factors for right-sizing your air conditioner

Right-sizing your air conditioner takes more than just finding the exact square footage of the space to be cooled and determining the corresponding BTUs. There are also other variations and variables that need to be considered to make sure that the air conditioner size you’re purchasing is absolutely perfect for the area.

The number of people occupying the area to be cooled, for example, is an important factor. More people means more body heat, and more body heat means you’re going to need a unit with higher BTUs. There’s a general rule of thumb where you add 600 BTUs for every warm body in excess of an initial two people.

Even the appliances that give off heat in the space to be cooled have to be considered. So if you’re cooling the kitchen, add about 4,000 BTUs to factor in the ovens and stoves. 

The amount of sun or shade that your home is getting also needs to be taken into consideration. If your home or the room that needs to be cooled gets a lot of sunlight, adding 10 percent more BTUs should suffice. Conversely, a heavily-shaded room or house would require about 10 percent fewer BTUs to cool.

Ask the air conditioning pros

Then again, the what size ac unit do I need for my house calculator and the other factors mentioned above are just rules of thumb. While they have proven to be useful and effective, it would still be best to get a professional opinion to be absolutely sure your new air conditioner is perfectly-sized for your home. Give our Product Specialist, Ed, a call at 1-800-NEW-UNIT and we'll be happy to answer any of your more specific questions.