Are you in the market for a new air conditioning system, either as a replacement for an older, ailing AC unit or as part of your new home? It’s important to have HVAC professionals involved in the process from the very beginning, not just for the actual few hours of work required to put the system in place and hook it up. You’ll want them to take the proper measurements, so you can be sure you have the correct size of unit for your home. If the air conditioner is too small, it will not provide the cooling your home needs. If it is too large, it causes its own set of problems.
No doubt you’ve heard the expression “bigger is better.” While this may be true for steaks, trucks, birthday cakes and yearly bonuses, it is not true for air conditioners. Selecting the wrong size air conditioner leads to many problems that are not easily fixed.
How HVAC Contractors Determine the Size of An AC System
The first thing your HVAC technician will need to determine is how many British Thermal Units (BTUs) your home requires. A BTU is the amount of heat needed to raise 1 pound of water 1°F. A BTU describes the size of the air conditioning unit in tons —12,000 BTUs equals one ton. Larger air conditioning units will be rated in tons rather than BTUs.
These are some of the steps needed to determine the square footage of your home, which will help determine the size you need:
- With a square room, multiply the length by its width.
- Multiply length by width and divide by two in a triangular-shaped room.
- For a room with more complicated shapes, break the room up into squares and triangles. Apply the above formulas.
- For each area multiply the square footage by 25.
- In an area like the living room, where there might frequently be a number of people gathered, add 400 BTUs for each person you know will use the room regularly.
- Add a thousand BTUs for every window in your home.
- The final number will tell you the minimum number of BTUs your air conditioning unit must supply for you to be cool and comfortable.
Problems With an Oversized Air Conditioner
At first, it might seem like it’s impossible to put in an air conditioning system that is too powerful. Isn’t it simply better to be on the safe side of too much cooling rather than too little?
The answer is no. An oversized air conditioner presents a number of problems that can be crippling and result in needing to replace the unit years before its time. You’ll also be wasting energy during the short period when it does run. Problems with an oversized air conditioner can affect your family home for many years and be costly to replace or fix:
An air conditioner has two jobs. It cools the air in your home, and it takes out moisture from the air. To remove the moisture, the air has to pass over an evaporator coil, which is a very cold surface. When the air passes over that coil, the air temperature can drop by as much as 20°F. When the temperature of the coil is below the air’s dewpoint, water vapor condenses on the surface of the coil.
However, with oversized air-conditioners, the air conditioning unit makes the room cooler faster. As a result, it runs a much shorter period of time than an air conditioner that has been properly sized will. This means the water cannot condense on the coil and is carried back into the room. So while your room may be cooler, an oversized air conditioner results in that “sticky feeling” you sometimes get in air-conditioned houses.
As a result of this increased level of moisture produced by an oversized air conditioner, the air quality in your home can deteriorate. This is a problem for anyone with asthma or any other respiratory disease.
Dust Mites and Mold
Too much humidity makes it easy for dust mites and mold to grab a foothold in your home.
We’ve all been in homes or buildings where the air conditioning unit sounds like a freight train when it turns on. That’s a sure sign the air conditioning unit is too big for the space. A properly-sized unit makes very little noise, and in some cases, it will almost run silently. You do not want to spoil the enjoyment of your cool house on a warm summer’s day with having to listen to a very noisy air conditioning unit.
Oversized air conditioners run much less efficiently than their appropriately-sized counterparts. They may turn on and off several times throughout the day. This costs more in terms of energy use, money and wear and tear on the machine
Wear and Tear
This point builds on the one we just made. An oversized air conditioner has many more stops and starts during a normal day than a properly-sized air conditioner. Greater use means more repairs and more money out of your wallet.
This is especially true in parts of the country where air-conditioning helps deal with a lot of moisture in the air. Since an oversized air conditioner does not remove enough moisture from the air, it can have very serious consequences for your home. Wood products, paint and drywall can suffer from too much moisture.
Do You Save Money?
The difference between a properly-sized air conditioner and an oversized air conditioner only adds about 2% to your actual energy bill. When you do buy a properly-sized air conditioner, however, you are definitely saving money on the upfront costs. You will also save money in terms of repairs and replacement parts. Properly-sized air conditioners last much longer, are more efficient and need fewer fixes than an oversized unit.
How to Tell If You Have an Oversized Air Conditioner
We mentioned some of the best ways to determine if you have an oversized AC unit above. But without a doubt, the best way to determine this is the moisture level in your home. If your home feels cool but “wet” and too humid, that is a sure sign you have an oversized air conditioner.
If you notice mold in your home or paint beginning to peel in rooms where it feels particularly sticky, you should consult an HVAC technician to determine if the problem is an oversized air conditioner. If you’re sneezing or coughing a lot when the air conditioning is on, this could be another sign. This is also the case if someone in your home has asthma and you notice they have trouble breathing during periods when the air-conditioning is running.
Your best bet is to get an HVAC technician to inspect your home. They will give you an honest answer about the cooling power of your system.
Why Are So Many Oversized Air-Conditioners Installed?
There are a number of factors that industry experts have observed over the years as to why installing too big of a unit is an issue. HVAC contractors tend to “think big” about air conditioning units. A good HVAC technician uses the measurement methods we’ve outlined above to determine what size unit you’ll need in your home. If a contractor says to you that they determine the size of an air conditioner based on the size of your home without making any measurements, find another technician.
Some other reasons include
- Technicians Are Afraid of Undersizing the Unit: Very few homeowners complain if their HVAC system is too big. That’s because few homeowners understand the kind of problems that can be caused by an oversized AC unit. Many people will complain, however, if the unit is too small. So many contractors will err on the side of caution rather than deal with angry homeowners.
- They’ve Always Done It That Way: In past years, air conditioning technicians used “rules of thumb” to determine the size of an air conditioning unit. But with the improvement in high-performance homes and additions like better insulation and windows, these rules of thumb just don’t work anymore.
- They Don’t Double Check Measurements: When you’re considering upgrading your air conditioning unit or purchasing one for your new home, it’s very likely that you’ll ask for estimates from a number of companies that sell air-conditioners. Since they haven’t actually gotten the job yet, too many contractors use worst-case scenarios to come up with an estimate of the size needed. Once they get the job, not many will go back and perform the measurements mentioned above to check their original figures.
- Homeowners Go With the Lowest Price: Many homeowners will automatically go for the lower price, allowing their desire for a cheaper deal to overwhelm their need for the long-term comfort and safety of their home. An HVAC contractor who only uses best practices will consistently submit bids that will be higher than competitors. That’s why when you find a contractor who models best practices, stick to them like glue. You will save valuable dollars in the long run.
- Builders Are Hired Who Aren’t HVAC Specialists: As much as homeowners may not understand the calculations needed to determine the proper size air conditioner for their home, the same can be said of many builders. As a result, many homes get outfitted with an oversized air conditioner because the builders want to “play it safe.”
- Technicians Lack Proper Training: Much of the curriculum materials that are developed for apprentices who are learning how to be HVAC technicians have been created by people who are largely unfamiliar with the needs and nuances of high-performance homes. As a result, even newly trained technicians tend to lean toward air conditioning units that are too big.
What to Do About an Oversized Air Conditioner?
There are fixes that you can make to solve the problem of an oversized air conditioner but the main one is quite expensive: Replace the unit with a smaller one that provides more efficient cooling and moisture control.
If that is a solution that is financially difficult for you at the moment, there are a couple of temporary options you can try:
- A Whole House Dehumidifier: The recommended humidity level for most modern homes is 45% to 55%. Oversized air conditioning units can often drive this up to 60% or higher. One way to resolve this issue is to use a whole house dehumidifier. It monitors the air and turns on automatically when the humidity in your home goes above that 55% level – or at whatever level you set the system. Normally, you attach a whole house dehumidifier to your central air conditioner and it provides dehumidification for your entire home. But if you only have a problem with humidity in one of your rooms you can purchase standalone dehumidifiers that work just as well.
- Cool a Larger Space: When you increase the amount of space an oversized air conditioning unit is cooling, it stays on for a longer period of time and can reduce some of your moisture issues. It is a controversial method, though, because it upsets the air conditioning balance in the rest of your home. It also leads to higher energy bills. However, it’s a reasonable temporary solution if you are unable to purchase a new unit at the moment.
Oasis Can Help With Your Air Conditioning Needs
Oasis Heating, A/C and Refrigeration, Inc. has been in the business of providing quality air conditioning installations and service in Northern Virginia since 1998. When you work with us, you can be sure you’re working with a contractor you can count on.
All our knowledgeable and experienced technicians are NATE-Certified. When you’re looking to upgrade your current air conditioner or if you’re building and installing a new one, our service is comprehensive and impeccable. It is very important to us that you have the proper-sized air-conditioning unit in your home. We want to make sure all of our customers have equipment that works efficiently and effectively all year long. We know homeowners often have important budget concerns, and we will work with you to ensure a new system doesn’t overextend your budget.
If you would like to learn more about how we can help you install a new system or upgrade an older one, or if you need repairs to your current system, call us today at 703-339-3877. You can also visit our contact us page and let us know all about your air conditioning needs. We look forward to helping you and showing you the best service possible.
It’s easy to avoid an oversized AC: call on professionals for the job. OASIS Heating, A/C & Refrigeration, Inc. can provide you with an excellent air conditioning installation in northern Virginia.