How To Choose the Perfect AC Unit Size for Your Home’s Comfort and Efficiency
Your AC isn’t working right. It doesn’t cool your space evenly, constantly turns on and off, and seems to always be running, but never cooling your home.
Did you know having an AC unit that’s too large or too small for your home is a common problem?
Whether you’re needing to replace an old AC unit or purchase one for a new home, understanding how to choose the perfect size unit to optimize comfort and efficiency is vital.
Let’s dive into how to choose the right size AC unit for your home, important factors to consider in selecting a unit, and when to consult a professional HVAC contractor.
Table of Contents
- Why Choosing the Right AC Size Is Crucial
- How To Calculate the Right Size AC Unit for Your Space in 3 Steps
- Common Methods for Determining AC Unit Size: What’s the Best Option for You?
- Already Have an AC Unit That Isn’t Doing the Trick? Signs You Need a Bigger or Smaller AC Unit
- A Few More Factors To Consider When Choosing an AC Unit Size
- When To Consult a Professional HVAC Contractor
Why Choosing the Right AC Size Is Crucial
A unit that is too small will run constantly and still struggle to cool the space properly.
On the other hand, one that’s too large will cool too quickly without properly dehumidifying the air, leading to discomfort. It will constantly shut on and off, which is inefficient and can lead to system repairs being necessary sooner and more frequently.
You want to pick the right size system for three key reasons:
- Energy efficiency
- Comfort
- Cost savings
An HVAC professional can assist in determining what size AC unit you need, choosing the right size unit with consideration for the factors that impact performance, cost, and energy efficiency. In Portland, AAA Heating and Cooling is ready to help with an initial consultation of your home today.
How To Calculate the Right Size AC Unit for Your Space in 3 Steps
There are a few simple steps to determining the correct size for your home’s AC unit. AC units are measured in tons, and how many British thermal units (Btu) they can remove in one hour. Each ton of an AC unit can remove 12,000 Btu per hour. As a general guide, each ton can cover between 400 and 800 square feet of space.
Picking the right size unit also requires consideration of things like:
- Ceiling height
- Number and types of windows
- Sizes and number of west and south-facing windows
- How much shade your home gets
- Insulation
Step 1: Measure Your Room or Home
To determine the square footage of your house:
- Measure the length and width of each room in feet.
- Multiply the length by the width to get the square footage of that room.
- Calculate square footage for hallways and closets.
- Add up the square footage of all the rooms, hallways, and closets to find the total square footage of your house.
Step 2: Factor in Room Characteristics
Often, a decision about how many tons unit to get can fluctuate by a half-ton up or down depending on the room specifics, such as:
- Ceiling height
- Insulation
- Windows
- Sun exposure
- Shade
Homes with poor insulation, large windows, high ceilings, or lots of light may need a more powerful AC unit to compensate for heat gain. On the other hand, homes designed for optimal energy efficiency might not need such a large unit.
Step 3: Consider Climate and Local Weather Patterns
In hotter, more humid climates a larger unit may be necessary, while in cooler regions, a smaller unit may suffice.
A climate known for overcast skies and cooler temperatures, like we have in Portland and Western Oregon, might aid in maintaining cool temperatures in your home. On the other hand, areas with a lot of sun exposure and extreme heat might require the AC unit to run more consistently.
The best way to know for sure is to consult an HVAC professional, like the team at AAA Heating and Cooling, to evaluate your home and offer the best options for your unique situation.
Common Methods for Determining AC Unit Size: What’s the Best Option for You?
The Btu Per Square Foot Method: Quick and Easy
While many factors can significantly impact cooling system efficiency and usage, in general around 20 Btu are needed per square foot, or:
- 150-200 square feet: 4,000-6,000 Btu
- 250-350 square feet: 6,000-8,000 Btu
- 400-500 square feet: 8,000-10,000 Btu
- 550-600 square feet: 10,000-12,000 Btu
Manual J Load Calculation: For a More Precise Estimate (Requires a Pro)
For those who want to get really accurate, there’s a more detailed approach called Manual J load calculation. In addition to square footage, this method takes into account things like:
- Insulation
- Ceiling height
- Window size
- Shade
- The number of people who live in the house
Manual J load calculation is complicated and usually requires a professional to do the calculations, so this is where an HVAC technician comes in to help. Contact AAA Heating and Cooling, your Portland residential air conditioner experts, to have a qualified technician assess your home.
Use an Online Calculator: Simple and Convenient
Online calculators can help you get a ballpark estimate of the right AC size based on your room’s square footage and a few basic details.
You’ll input your room size, ceiling height, window type, the direction your home faces, and other factors impacting your cooling system’s capacity. From there, you’ll receive guidance on the necessary equipment for your space.
Which Method Is Right for You?
Consider these factors to determine which of these methods is best for you:
- If you’re just cooling a small room and want a quick estimate, the Btu per square foot method will do the job.
- For larger homes or spaces with special factors like high ceilings, poor insulation, or big windows, contacting a professional to do the Manual J calculation is likely your best option.
- For a quick online estimate, try one of the many free calculators to get a rough idea.
- For the most thorough option, start with a Btu square footage calculation and/or an online calculator, then reach out to the professionals at AAA Heating and Cooling to confirm your estimate. Our expert technician can make recommendations and provide a quote for the installation.
Already Have an AC Unit That Isn’t Doing the Trick? Signs You Need a Bigger or Smaller AC Unit
If you already have an AC unit that is not functioning properly, there are a few options:
- Consult a professional for a maintenance check and tune-up of your system. Some issues are simple to fix and not indicative of a larger problem or the need for a different system.
- Check the age of your system and begin to research on your own whether it might be too large or too small for your space.
- Consider whether changes to how you use your system might impact its overall efficiency.
Symptoms of an Undersized AC Unit
Here are some things you may notice if your AC is undersized for the space in your home:
- Poor cooling
- Longer cooling times
- Uneven cooling of different parts of your home
- High electricity bills
If you observe these symptoms, consult with a professional about whether a larger unit could cool your home better and more efficiently.
Symptoms of an Oversized AC Unit
Bigger is not always better when it comes to AC systems. There are some signs that your AC unit could actually be too big for your home, including:
- A system that turns off too quickly
- AC that frequently turns on and off throughout the day
- Inconsistent humidity levels
- More frequent than recommended maintenance
- Increased wear and tear on your unit due to short cycling
A Few More Factors To Consider When Choosing an AC Unit Size
There are additional factors you might want to learn a bit more about to decide on the right size AC unit for your home, including:
- The type of air conditioning system. This will likely depend on the size of the space that needs to be cooled and your budget (central, window, or portable AC are all options).
- Your Home Energy Rating System (HERS).
- The Seasonal Energy Efficiency Ratio (SEER) and the energy-efficient units and technology available in your market.
- Noise levels. Window units are generally the noisiest, followed by central systems with ducts.
- Your budget. Be sure to consider both the upfront cost and ongoing maintenance costs for different types of units.
When To Consult a Professional HVAC Contractor
You can generally get a good idea of the right size AC system for your home using a simple formula and online calculators that consider other factors.
A professional HVAC contractor can confirm your research and help with complex load calculations, selecting the best system, and proper installation.
Getting multiple quotes and checking qualifications before hiring a contractor is always a good idea. Choosing the right HVAC company can lead to years of good service and low ongoing costs, versus huge headaches and unexpected costs down the line.
Let the Experts at AAA Heating and Cooling Help You Choose the Right AC for Your Home
At AAA Heating & Cooling, our mission is to provide reliable, high-quality HVAC products and services to residential and commercial clients in Portland. As the region’s premier heating and cooling contractors, we’re committed to keeping your home and business comfortable and climate-controlled while improving your indoor air quality.
We have an A+ rating with the Better Business Bureau and provide top-of-the-line heating and cooling services. Licensed and bonded since 1961 as a certified heating and cooling contractor, AAA Heating & Cooling has installed over 30,000 residential and commercial units throughout Portland.
Our family-owned business looks forward to answering your questions and keeping your family comfortable year-round.