Blog

In order to make sure your home is comfortable year-round, it's important to have the right-sized HVAC system. Having accurate measurements for your home is critical for recommending the appropriate-sized HVAC system. Understanding air conditioning sizes can help you make informed decisions for your home's comfort needs.

Oversized air conditioners cause short cycling, higher electricity costs, temperature swings, uneven cooling, and wear and tear on your system. Undersized air conditioners take longer to cool, which causes discomfort and high electric bills. This is why finding the right size for your home is so crucial. With our help, you’ll be able to determine the appropriate size AC unit for your needs.

The Basics of Air Conditioner Sizing

BTUs

A BTU, or British Thermal Unit, is a measurement that indicates how much energy your air conditioner needs in one hour to remove heat from your interior air. You should calculate the BTU of your HVAC system using the square footage of your home, insulation quality, temperature zone, and ducting.

AC Size vs. Space

An oversized air conditioner can cause discomfort by cooling the air faster than it can dehumidify the space, leaving you with a humid and sticky environment. Additionally, oversized units cost more to purchase and run—and they require more repairs. They don't filter the air as well as properly-sized units, resulting in less removal of pollutants like dust mites, mold, allergens, and viruses. On the other hand, an undersized AC unit will run constantly and increase your energy bills.

Factors Affecting AC Size Requirements

Room Size and Layout

The square footage of the area you plan to cool influences the size of the AC unit that you need. Exclude the spaces you don’t intend to cool, such as corridors and sunrooms. Treat rooms that cut through to each other as single rooms, like an open kitchen without a door, for example.

Different room shapes also impact the total square footage of the area you plan to cool. Rectangular or square-shaped rooms, triangular rooms, circular rooms, and multidimensional homes all have their own formulas for calculating square footage.

Climate and Location

Your local climate plays a factor in the size of your air conditioner. A home in a mildly hot region will have different cooling requirements than one in a hot and humid climate. If you reside in a hotter area, your HVAC system will work harder to achieve and maintain the proper inside temperatures than in a home residing in a cooler region.

Insulation and Windows

You may be able to downsize your air conditioner thanks to efficient insulation, which keeps heat out in the summer and in during the winter. To maintain a reasonable temperature in a home with inadequate insulation, a larger unit is required. To keep your area cool, you'll need more cooling capacity the more windows you have, especially if they're larger and less energy-efficient. The largest effects are from windows facing south and west.

Ceiling Height

AC size estimations are typically made for 9-foot-tall ceilings, which are normal for most modern homes. Taller ceilings increase the volume of air that has to be cooled, sometimes needing an air conditioner with more BTUs.

Number of Occupants

People produce their own body heat. This means the more people living in your home, the more BTUs are needed to offset the extra heat.

Heat-Generating Appliances

Large appliances such as dishwashers, washers, and dryers tend to generate a lot of heat when in use. You’ll need to compensate for this by increasing the number of BTUs in your home.

How to Calculate the Right Air Conditioner Size

Step-by-Step Guide

1. Measure the square footage of your room or home.
2. Use a BTU calculator or chart to calculate the needed cooling capacity.
3. Make adjustments for specific factors like insulation, climate, room orientation, windows and doors, and regular home occupants.

AC Size Chart

• 100-150 sq ft: 5,000 BTUs
• 150-250 sq ft: 6,000 BTUs
• 250-300 sq ft: 7,000 BTUs
• 300-350 sq ft: 8,000 BTUs
• 350-400 sq ft: 9,000 BTUs
• 400-450 sq ft: 10,000 BTUs
• 450-550 sq ft: 12,000 BTUs
• 550-700 sq ft: 14,000 BTUs
• 700-1,000 sq ft: 18,000 BTUs

Common Sizing Mistakes to Avoid

Oversizing or Undersizing

Oversizing HVAC systems can lead to increased utility costs from short cycling and installation costs, as well as a shorter lifespan due to wear and tear from repeated cycles. Undersized systems may struggle to maintain a comfortable temperature with inefficiency and inadequate cooling, leading to frequent repairs and early system breakdowns in severe weather conditions.

Ignoring Specific Home Factors

In load calculations, the heating and cooling needs of your house are evaluated according to climate, insulation, and square footage. Ignoring these factors can cause inaccurate estimates and lead to an incorrectly sized system.

Not Seeking Professional Help

A professional HVAC technician uses industry-standard calculations to accurately assess the design of your air conditioning system, which ensures the correct fit for your specific needs.

Recap

Deciding on a new AC unit needs a lot more thought than “How much will it cost me?” You need to consider the size of your space, how powerful the unit is, and other unique factors of your home. Even if you’re on the right path, we recommend you hire professional HVAC technicians like the ones at T. Webber. We provide the Hudson Valley with comprehensive air conditioning services, including installation, maintenance, and repairs.

Contact T. Webber, your local HVAC professional, for a consultation.