Although you probably don’t need to learn exactly how to size an AC system before having new equipment installed, understanding how the process works can be helpful.
The calculations used to make this determination – and the industry-specific terms used to describe the process – can be confusing for anyone who isn’t well-versed in HVAC technology. Consequently, calculating how many tons your system should be or what SEER rating is best for you can seem like learning complex mathematics in a foreign language. But we are here to help uncomplicate the process for you.
Multiple factors go into determining the appropriate size and type of air conditioning system you need. The best place to start is by defining some of the most common terms used in the industry, and then learning how those influence AC installation.
What Does “Size” Mean in Air Conditioning Systems
When we talk about size in terms of home improvement projects and systems, most people think in terms of dimensions or volume. For example, even though you might not know the precise dimensions, you can safely assume that a 60-gallon hot water tank holds and heats about 60 gallons of water at a time. You can reliably assume that a 36” door is going to fit in an opening that is about three feet wide.
So, shouldn’t that mean a 5-ton AC system weighs 5 tons? As you probably realize, the term does not refer to weight in this case.
What Is AC System Tonnage?
The way AC systems cool your home is by removing hot air. So, when we refer to “tons” in the residential HVAC context, we are referring to the system’s capacity to remove heat from the home. But, again, we aren’t talking about the weight of the hot air.
A ton in this case refers to one ton of ice. Melting one ton of ice in one hour requires 12,000 British Thermal Units (BTUs) of heat. What is a BTU, you ask? One BTU is the amount of heat generated by one burning kitchen match. (As silly as this unit of measure might seem, remember that we still rate our vehicle engine sizes based on how many horses it would take to move 550 pounds one foot per second. Don’t even ask why we rate carpet by weight or insulation by R-value…)
Units are rated between one and five tons. So, a 3-ton unit has the ability to remove the heat it would take to melt 3 tons of ice in an hour…at least theoretically.
What Does the AC SEER Rating Mean?
Systems are rated between 10 and 23 and again use BTUs. A unit with a 10-SEER rating produces 10 BTUs for every watt-hour of electricity consumption. The more BTUs a unit can produce per watt-hour of consumption, the more efficient the unit operates. Hence, a higher SEER rating indicates a more efficient system.
Why Does an AC’s Size Matter?
Ensuring that your air conditioning system is sized correctly is important for several reasons. The system must have sufficient capacity for your home; otherwise, your home won’t cool properly. If the system is too large or too small, you will use more power than you would for a correctly sized system – and you’ll feel the financial effects of higher energy bills for the life of the system.
As for the life and health of the equipment, installing a unit that is correctly sized helps ensure the maximum possible lifespan of the system. If the equipment is the wrong size, it places additional wear and tear on the system, leading to unexpected breakdowns and the resulting repair bills. The additional strain on the equipment will also shorten its life.
It is important to note that installing an AC system that is too large for your needs can be just as problematic as one that is too small. Oversized systems cool the home too quickly, cycling off before the system can adequately remove moisture (humidity) from the air – this is known as short-cycling. The beginning of each cycle draws the most energy and, as a result of shorter, more frequent cycling, your power bills will soar. You will experience more wear and tear on the equipment, shortening its lifespan and causing more component failures.
Cooling Load Calculation Factors
Now that you know the technical terminology, let’s look at the factors that go into calculating the correct size of your system. These factors combine to identify heat gain, which is the rate at which heat enters the home.
- Cooled square footage,
- Number of floors (stories),
- Physical Orientation, (which rooms get morning and which rooms get afternoon sun)
- Are there trees or nearby structures that provide shade
- Ceiling height,
- Wall insulation,
- Attic insulation,
- Roofing material
- Home design.
- Number and type of windows
Should You Use an Online AC Size Calculator?
You might come across online calculators that claim to provide the information you need to size your central air conditioning system. These calculators typically consider only the most basic factors, such as geographic zone and square footage. It’s best not to place your faith in the accuracy of these automated tools. Without the rest of the information necessary to make an accurate calculation, you’re not likely to get the answers you need.
Contact a Local Air Conditioning Contractor for Help
Although you don’t necessarily need a mechanical engineering degree to calculate a correct central AC system size, you do need to have extensive training, knowledge and experience in the industry.
Presidential Heating & Air has been helping Maryland and D.C. homeowners with their HVAC needs since 1982 . Our highly trained and experienced technicians understand the importance of correctly sizing the furnace or central air conditioner you need, while keeping your costs as low as possible. Contact us today to request a free consultation and cost estimate for air conditioning installation in Gaithersburg.