Room Size and Cooling Capacity (BTU)

Cooling capacity is typically measured in BTU (British Thermal Units). The BTU number indicates how much heat the unit can remove from a room per hour. Matching BTU to room size is one of the most important steps in selecting the right air conditioner.

General room size guidelines:

• Up to 150 sq ft: 5,000–6,000 BTU
• 150–250 sq ft: 6,000–8,000 BTU
• 250–350 sq ft: 9,000–12,000 BTU
• 350–450 sq ft: 12,000–14,000 BTU
• 450–550 sq ft: 14,000–18,000 BTU

Factors that require adjustment:

• High ceilings increase cooling load by 10–20%.
• Direct sunlight or west-facing windows require higher BTU.
• Multiple occupants add heat; add ~600 BTU for each person beyond two.
• Kitchens or electronic-heavy rooms may need additional capacity.

Why sizing matters:

• Too large a unit cools the room quickly but removes less humidity, leaving the space cold yet sticky.
• Too small a unit runs constantly but still fails to reduce temperature, increasing energy use and discomfort.

Correct sizing ensures the unit runs efficiently, maintains steady comfort, and controls humidity properly.

Energy Efficiency Ratings (SEER and EER)

Energy efficiency determines how much electricity your air conditioner will use. When comparing models, two common ratings appear:

• SEER (Seasonal Energy Efficiency Ratio): Used mostly for split and central systems, measuring performance across a full season.
• EER (Energy Efficiency Ratio): Used more for window and portable units, measuring performance at a fixed temperature.

Higher SEER/EER ratings indicate a more efficient system. Although high-efficiency units cost more upfront, they often lower long-term energy bills.

Tip: Check for ENERGY STAR certification. This confirms that a unit meets established efficiency standards and may help reduce overall operating costs, especially in hot regions with frequent AC use.

Noise Level and Comfort

Noise matters most for bedrooms, nurseries, study rooms, and home offices. An air conditioner’s noise level is measured in decibels (dB).

Typical noise ranges:

• Split system indoor units: ~25–45 dB (very quiet, ideal for bedrooms)
• Window units: ~45–60 dB
• Portable units: ~50–65 dB

If you are sensitive to noise:

• Choose models with a “Quiet” or “Sleep Mode” setting.
• Consider variable-speed (inverter) compressors, which avoid sudden loud cycling.
• For long-term comfort, split systems are usually the quietest option.

Installation Requirements: Window, Portable, Split, or Central

Different air conditioner types are suited to different living situations.

Window Units

• Best for cooling single rooms.
• Affordable and easy to install.
• Takes up window space and may be noisier.

Portable Units

• Good for temporary or rental situations.
• Requires a window for venting.
• Generally noisier and less efficient.

Split (Ductless) Systems

• Quiet and energy-efficient.
• Allows room-by-room control.
• Requires outdoor unit space and professional installation.

Central Air Systems

• Best for cooling entire homes.
• Works with ducting and often provides consistent whole-house comfort.
• Higher installation and maintenance costs.

Before choosing, consider whether you have:

• Permission to mount units (important for renters)
• Suitable exterior wall or balcony space for outdoor units
• Electrical capacity (some larger units require dedicated circuits)

Climate Considerations

Climate influences how well an AC performs and what features matter most.

Humid climates: Dehumidification is as important as temperature control. Properly sized units or units with strong moisture removal capability provide better comfort.

Dry climates: Focus on cooling power and efficiency. Humidity control is less critical.

Seasonal climates: A heat pump (a type of split system that provides both heating and cooling) may offer year-round efficiency and reduce the need for separate heating equipment.

Air Filtration and Health Needs

Air conditioners influence indoor air quality, especially in homes with:

• Allergy or asthma sufferers
• Pets
• High outdoor pollution levels

Filter options:

• Basic filters: Trap dust but offer minimal allergy protection.
• HEPA-level filtration: Captures fine particles; often available in higher-end models or as separate purifiers.
• Activated carbon: Helps reduce odors and certain chemicals.

Regardless of filter type, regular cleaning or replacement maintains performance, efficiency, and healthy air.

Budget vs. Long-Term Cost

The cost of an air conditioner includes more than just the purchase price.

Consider:

• Purchase cost
• Installation fees
• Electricity usage over time
• Filter replacements and periodic maintenance
• Expected lifespan (often 8–20 years depending on the type)

A unit with higher energy efficiency may cost more initially but save money in annual energy use. If you run your AC frequently, it is often more economical to invest in higher efficiency.

Quick Buying Checklist

• Measure your room’s square footage.
• Match BTU to room size and adjust for height, sunlight, and occupancy.
• Compare SEER/EER ratings for energy efficiency.
• Consider noise level, especially for sleeping or working areas.
• Choose installation type based on living situation and space.
• Check whether dehumidification or air filtration matters for your climate and health needs.
• Evaluate total lifetime cost, not just the purchase price.