Selecting the right air conditioner for your home can be a daunting task. With so many different types, features, capacities and efficiency ratings to consider, it’s easy to feel overwhelmed. But having an AC unit properly sized and matched to your needs is crucial for comfort, energy efficiency and avoiding problems down the road. This comprehensive guide will walk you through the entire process step-by-step, from measuring your space and determining the required BTUs to choosing the best system type and brand for your home and budget.

How Does Air Conditioning Work?

Before diving into how to buy an air conditioner, it helps to understand the basic principles of how they work.

Air conditioners use a refrigeration cycle to cool air. This cycle involves four main components:

• Evaporator Coil: The indoor coil that absorbs heat from the air in your home. As warm household air passes over the coil, the refrigerant inside absorbs heat as it evaporates and cools the air.
• Compressor: The compressor pumps refrigerant through the system, moving it between the indoor evaporator coil and the outdoor condenser coil. This raises the temperature and pressure of the refrigerant.
• Condenser Coil: The hot refrigerant is pumped into the outdoor coil, where it condenses back into a liquid state, releasing heat into the outside air.
• Expansion Valve: The liquid refrigerant passes through the expansion valve, which causes it to turn back into a cool, low pressure gas so the cycle can start again.

By continually cycling refrigerant between gas and liquid states, heat is transferred from your home’s air to the outdoors, providing cool, conditioned air for your comfort.

How to Choose the Right Size Air Conditioner

Choosing an AC unit with the proper cooling capacity for your home is crucial. An undersized air conditioner won’t be able to cool your space adequately on hot days. An oversized unit will not only cost more upfront, but it will start and stop constantly, failing to remove humidity efficiently.

Step 1 – Calculate Square Footage

First, you’ll need to determine the square footage of the space you want to cool. This includes all finished living areas on the level(s) you plan to cool. Don’t include garages, attics, crawlspaces or unfinished basements.

To calculate total square footage:

• Measure the length and width of each room you want cooled.
• Multiply length x width to get square footage of each room.
• Add together square footage figures for all rooms.

This will give you your total square footage.

Step 2 – Factor in Key Details

In addition to total square footage, several other factors impact the required cooling capacity:

• Ceiling Height: Rooms with higher ceilings will require more cooling power. Add 100 BTU for every additional vertical foot over 8 feet.
• Windows: South and west facing windows with significant direct sun exposure will increase cooling needs. Add 100 BTU for every large sunny window. Consider window coverings to reduce solar heat gain.
• Occupants: More occupants means more body heat. Add 600 BTU for every additional person if your home will be occupied by more people than a typical family.
• Electronics: Major heat generating appliances like large TVs and computers can increase cooling load. Add 100 BTU per item.
• Insulation: Poor insulation makes your AC work harder. If insulation is limited, increase capacity by 10%.

Take these factors into account when sizing your unit.

Step 3 – Determine BTU Requirements

Air conditioner capacity is measured in British Thermal Units (BTUs). This represents the amount of heat per hour the AC can remove from your interior air.

As a rule of thumb:

• For a mild climate, multiply square footage by 20 to get minimum BTUs needed.
• For a hot climate, multiply square footage by 25 to get minimum BTUs.
• For a very hot climate, multiply by 30.

Check the BTU per square foot recommendations for your specific area too. Add any extras for the factors above. This gives your total minimum BTU requirement.

Example:

• 2,500 sq ft house
• Mild northern climate
• 12 ft high living room ceiling
• 3 south facing windows
• Family of 5
• Gaming computer

2,500 sq ft x 25 BTU = 62,500 minimum BTUs Add 100 BTUs for high ceiling
Add 300 BTUs for sunny windows Add 600 BTUs for extra family member Add 100 BTUs for gaming PC Total Recommended BTU: 64,600

Size up to the next available BTU unit for optimal performance and efficiency.

Choosing the Right Air Conditioner Type

Once you know the appropriate BTU capacity, the next decision is choosing the specific type of AC system. Key factors include configuration, placement, efficiency rating and your budget.

Window Units

Overview: Window air conditioners are single self-contained units installed in a window opening. All components are enclosed in a box that sits inside the home and vents hot air to the outside.

Pros:

• Low upfront cost
• Easy DIY installation
• Minimal ductwork needed – vents directly through window
• Zone cooling – add units just to rooms you want to cool

Cons:

• Visible window placement may be unsightly
• Efficiency can be lower than central air
• Only cool room they are installed in – no whole home cooling
• Can allow pollen, dust and noise in when window is open
• Require window location and installation space

Cost: $150 – $700 depending on size. Higher electricity bills than central air.

Suitable For: Smaller homes, single rooms, supplementary cooling.

Portable Units

Overview: Portable air conditioners sit on casters and exhaust hot air through ducts vented in a window or sliding door, but are not permanently installed. Allow zone cooling.

Pros:

• Roll from room to room
• Do not require permanent installation
• Flexible zone control

Cons:

• More expensive than window units
• Still need window or sliding door
• Can be loud
• Tend to be less energy efficient

Cost: $300 – $700

Suitable For: Supplemental cooling, rooms without window access

Split Unit Systems

Overview: Split AC systems have an outdoor condenser/compressor and a slim ductless indoor unit mounted on the wall or ceiling. Allow zone control without windows.

Pros

• Quiet and energy efficient
• Zone cooling
• Mount on wall or ceiling – no window needed
• Unobtrusive appearance

Cons:

• Professional installation required
• Only cool rooms with indoor heads
• Multiple outdoor units may be required

Cost: $600 – $1,500 per zone

Suitable For: Homes without central air, supplemental cooling

Central Air Systems

Overview: Central air conditioners have an outdoor condenser linked to an indoor evaporator coil and blower which cools your whole home through ductwork.

Pros:

• Cool your entire home
• Even temperatures throughout
• Out of sight exterior unit
• High efficiency options

Cons:

• Major installation required
• Expensive upfront cost
• Does not allow zone control
• Can lose efficiency over time

Cost: $3,000 – $8,000 installed

Suitable For: Whole home cooling, new construction, major renovations

Choosing Efficiency – SEER and EER Ratings

Two key metrics indicate AC efficiency:

• SEER (Seasonal Energy Efficiency Ratio): Measures cooling efficiency in real world conditions. Minimum SEER today is 14. Higher SEER ratings above 16 provide better efficiency and energy savings.
• EER (Energy Efficiency Ratio): Measures instantaneous cooling efficiency at a fixed temperature. The higher the EER, the more efficient. 8-12+ is common.

Units with higher SEER and EER ratings cost more upfront but provide better performance and cut electricity costs over time. Weigh initial cost vs. ongoing savings.

Top Air Conditioner Brands

The brand and specific AC model you choose also impacts performance, features, noise, reliability and warranties. Consider these top brands:

Carrier

With 100+ years in the industry, Carrier is one of the most recognized and reliable air conditioner brands. Their central air units use quality copper coils and quiet, multi-speed compressors for excellent cooling, efficiency and durability. Units range from 13 to 21+ SEER ratings and come with up to 10 year warranties. Models with WiFi can integrate with smart home systems.

Trane

Known for innovation and quality, Trane central air systems provide whisper-quiet operation and superb energy efficiency with SEER ratings up to 20+. Trane’s XR series uses advanced components for optimal temperature balance and dehumidification. Units have durable fully-galvanized steel cabinets and 10 year warranties. Setup for smart controls is available.

Lennox

Lennox is another leading brand trusted for high-performing, quiet and efficient central air conditioners. The Elite and Merit series feature precision balanced air blades, multi-stage compressors and ratings up to 26 SEER. They offer advanced humidity control with the Humiditrol system. Units have corrosion-resistant cabinets, lowest sound ratings and 10 year warranties.

Amana

Owned by Goodman, Amana offers more affordable central air conditioners but still feature quality components. Performance series units are designed for longer life with copper tubing and rugged steel cabinets protected from rust and corrosion. Available in single and two stage configurations from 14 to 18 SEER. All come with a 10 year parts warranty.

LG

Known for electronics, LG makes highly efficient ductless and central air conditioners. LG’s Art Cool systems are slim, modern wall units providing zone cooling with SEER ratings up to 27.8. Their central air units have quiet designs, smart diagnostics via Wi-Fi and range from 16 to 20 SEER. All come with 10 year compressor warranties.

Key Air Conditioner Features to Look For

• Efficiency Ratings – Look for SEER 14+ and EER 11+ at minimum. Consider splurging for higher ratings to save long term on energy.
• Compressor – Units with two-stage compressors provide better temperature balance and humidity control than single stage models. Variable speed is even better.
• Coils – Copper tubing and aluminum fin coils provide maximum heat transfer and durability. Avoid cheaper aluminum coils.
• Fan – Multi-speed fans allow quieter, more even cooling than single speed fans.
• Filtration – Look for mesh filters that are easy to access and clean. Some units also accommodate advanced HEPA filters.
• Thermostat – Programmable and smart WiFi thermostats allow greater control over comfort and efficiency.
• Zoning – If cooling only certain rooms, zone control from mini-splits or multi-zone systems help optimize comfort and energy use.
• Warranty – 10 years on compressor and parts are ideal for added peace of mind.

Installation and Maintenance Tips

Proper installation and regular maintenance helps ensure your AC runs reliably and efficiently for years to come.

Installation Tips

• Have a professional install central air systems – improper ductwork can reduce performance. Get multiple quotes.
• Carefully measure window units before buying. Seal gaps with caulk for efficiency. Angle units slightly outward for drainage.
• Make sure portable and window units are securely supported and plugged into dedicated outlets.

Regular Maintenance

• Change filters every 1-3 months, more often if you have pets or allergies. Clogged filters reduce airflow.
• Clear debris and overgrowth away from the outdoor unit. Allow 2 feet clearance all around for airflow.
• Clean coils regularly with a brush and hose – avoid damaging the fins. Dirty coils reduce performance.
• Check refrigerant levels yearly and recharge as needed. Refrigerant eventually leaks out over time.
• Inspect drain lines for mold or clogs which can cause water damage if blocked.
• Have a technician do a full tune-up and check components before each cooling season.

Following a proper AC sizing calculator, buying an energy efficient unit and taking care of your air conditioner will ensure ideal comfort and costs for years to come. With this guide’s tips in mind, you can make the best decision for your home’s comfort.

Frequently Asked Questions About Air Conditioners

Are portable air conditioners any good?

Portable air conditioners can be an effective cooling solution in the right circumstances. They are easy to move from room to room and only require a window or sliding door to vent hot air outside. However, they are not as efficient or quiet as permanent split or central air options. Portables work best for supplemental cooling in spaces without permanent AC installations.

How long do central air conditioners last?

The average lifespan of a central air conditioning unit is 15-20 years. However, AC compressors typically last only 10-15 years before needing replacement. With proper maintenance like regular filter changes, cleaning coils, recharging refrigerant and tune ups, you can maximize the functional lifespan of your central air system.

Is it cheaper to use window air conditioners?

Window air conditioners are less expensive to purchase upfront than central cooling systems or ductless splits. However, they are generally less energy efficient so your energy bills may be higher in the long run. They also only cool the room they are installed in rather than your entire home. For whole home and more efficient cooling, central air or ductless splits are a better investment.

Should I get a two stage air conditioner?

Two stage air conditioners provide better comfort and efficiency than single stage models. They run at a lower capacity most of the time, only temporarily ramping up to higher capacity at peak times. This allows for more even cooling, lower humidity and quieter operation. The added efficiency makes the higher upfront cost of two stage AC units worthwhile over time.

What SEER rating should I get?

Experts typically recommend getting an AC unit rated at least 14 SEER for adequate efficiency. Higher SEER ratings above 16 provide even greater energy savings. However, the higher the SEER rating, the more the unit will cost upfront. Find the right balance for your climate and budget. Mini splits can have SEER ratings up to 27+ for maximum efficiency.

How much does it cost to install central air?

The average cost to install a new central air conditioning system ranges from $3,000 to $8,000 including the unit and professional installation. Prices vary based on the brand, efficiency rating, home size, necessary ductwork modifications and complexity of the installation process. Get multiple quotes to find the best deal.

Should I get a smart air conditioner?

Smart air conditioners with WiFi connectivity offer convenient control and added benefits that may be worth the upgrade cost. With a smart AC, you can adjust temperatures and modes from your phone and even when away from home. Advanced monitoring provides maintenance reminders, tracks energy use and can diagnose problems automatically. Smart systems also easily integrate with other connected home devices.

Case Study: Choosing the Right Air Conditioner for a 3 Bedroom Home

To understand how to select an air conditioner in a real world situation, let’s walk through an example scenario:

The homeowners in this case have a 2 story, 3 bedroom house with the following details:

• 1,800 square feet of living space
• Located in Virginia, hot and humid climate
• 2 large windows facing South
• Standard 8 foot ceilings
• 3 occupants – married couple and one child
• Attic and walls well insulated

Sizing Calculations

• 1,800 sq ft
• Recommended BTUs per sq ft in Virginia: 30
• 1,800 x 30 = 54,000 minimum recommended BTUs
• Add 200 BTUs total for the 2 sunny windows
• Add 600 BTUs for extra occupant

Total minimum capacity needed: 54,800 BTUs

Given the humidity in Virginia, a 2 stage or variable capacity central air unit would provide better moisture removal. They decide to go with a Trane XV18 variable speed central AC with up to 18 SEER rating for the best comfort and efficiency.

The unit at 65,000 BTUs will have adequate power to cool their home even on the hottest days. This system will give them:

• Even, consistent cooling in every room
• Advanced humidity removal
• High energy efficiency to save on bills
• Zoning control with multiple thermostats
• 10 year warranty plus optional extended coverage

Installing the Trane system will cost around $6,500 with installation. But the peace of mind and lower operating costs for years to come make it a worthwhile investment. Going with a quality, properly sized AC unit improves comfort while adding value to their home.

Expert Tips for Air Conditioner Installation and Repairs

I spoke with heating and cooling technicians Mark Thompson and Luis Ramos to get their expert insights on installing and maintaining air conditioning systems. Here are their top tips for homeowners:

On AC installation:

“Carefully examine your home first to understand your needs and layout. This will determine the best system type and specifications before purchasing. Always get multiple quotes from licensed contractors too.” – Mark T.

“With central air, the details matter. Ensure your contractor properly sizes the ductwork, registers, refrigerant lines and condensate drainage for maximum comfort and efficiency.” – Luis R.

“Don’t just default to the cheapest bid. There’s huge variability in skill level and quality of installations. A little extra upfront to hire a reputable pro is worth it in the long run.” – Mark T.

On AC maintenance:

“The number one thing is to change your filters regularly. I recommend every 1-3 months, especially during heavy use seasons. This prevents poor airflow leading to problems.” – Luis R.

“Keep the outdoor unit clear. Overgrown plants or debris crowd the condenser, reducing performance. Give it at least 2 feet clearance all around.” – Mark T.

“Don’t neglect annual tune-ups. A technician can spot and fix minor issues before they become major repairs. It also keeps your warranty valid.” – Luis R.

“Monitor refrigerant levels and recharge when needed. Low refrigerant reduces cooling capacity and overworks the compressor.” – Mark T.

On AC repairs:

“Many issues like frozen coils or leaking refrigerant lines require a trained pro. Don’t try DIY repairs unless you’re an HVAC specialist.” – Luis R.

“Replace your central air system once it gets over 15-20 years old. Repairs tend to pile up and efficiency declines with age.” – Mark T.

“Be proactive to avoid being stuck without AC during hot weather. Schedule spring tune-ups to ensure your system is ready for summer.” – Luis R.

Their experience proves that properly sizing, installing and maintaining your air conditioner is essential to providing comfort, savings and avoiding costly repairs down the road.

Interview with an HVAC Contractor

To gain more firsthand advice on choosing air conditioners, I interviewed Tony Molina, owner of Comfort Zone Heating and Air Conditioning in Austin, Texas. Here are Tony’s tips:

On sizing AC units:

“Take the time to accurately calculate the cooling needs for the specific rooms you want cooled. Oversized units cost more upfront and operate less efficiently. Undersized units can’t keep your home comfortable on hot days.”

On types of air conditioners:

“Think about your goals. Window units offer inexpensive zone cooling for single rooms. Ductless splits also provide zone control without major installation. Central air cools the whole home evenly but at a higher upfront cost.”

On efficiency ratings:

“Don’t just look at the minimum SEER rating. In hot climates especially, investing in a higher efficiency unit above 16 SEER can pay for itself through energy savings within 5 years.”

On brands:

“Stick with proven brands like Trane, Carrier and Lennox. Check that key components like compressors and coils are high quality. Also confirm the warranty period for peace of mind.”

On maintenance:

“Don’t neglect regular maintenance. Things like frequent filter changes, clearing debris and annual tune-ups prevent more serious issues and keep your system running at peak performance.”

On installation:

“Hire a licensed local contractor, not a friend of a friend. Pay a little more for a certified technician who will do the job right the first time, protecting your investment.”

On repairs:

“Don’t delay needed repairs. Small issues can quickly compound. Be proactive about maintenance and you’ll avoid most major repairs and added costs.”

Tony’s insights reinforce the importance of proper sizing, an efficient unit, quality installation, brand reputation and ongoing maintenance when selecting your ideal air conditioner.

Conclusion

Choosing the right air conditioning system involves careful calculation of your needs, climate and budget. While the process may seem complicated, this guide provides you with clear steps to select the ideal central, ductless or window air conditioner for maximum comfort and cost savings.

Accurately measuring your space, correctly calculating BTUs, choosing an energy efficient unit, shopping top brands, allowing proper installation and practicing regular maintenance gives you the best chance for staying cool for years to come. With these tips in mind, you can make an informed decision on the perfect air conditioning solution for your home.