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Air Conditioning / September 22, 2020

Is Your Air Conditioner the Right Size? The AC Terms You Need to Know

What is the right size air conditioner for your home? A one-size-fits-all AC approach can cost you money in inefficiency, energy loss, and repairs. Before you buy a new system, take a look at the top size-related terms you need to know.

British Thermal Units

Also known by the abbreviation BTU, the British Thermal Unit is a standardized measurement used to quantify the heat content of an energy source. A BTU equals the amount of heat needed to raise one pound of water by one degree Fahrenheit.

Even though your air conditioner cools, and BTUs measure heat, you may see this measurement used for an AC system. In air conditioning terms, BTUs refer to power or energy used of the AC unit. The higher the BTU number, the more powerful an air conditioner is.

Air conditioner BTUs typically range in the tens of thousands of units. While this may seem high, one BTU is a small unit of energy. According to the U.S. Energy Information Administration (EIA), Americans used 100.2 quadrillion BTUs of energy (in total across the country) in 2019.

Manual J Calculations

It may seem like a higher BTU number is better for your home’s cooling needs. But this isn’t always true. A qualified HVAC contractor will evaluate your home’s square footage, building material makeup, wall position, insulation, ductwork, sun exposure, and other related issues to calculate size and power requirements. These factors are part of the Manual J load calculation.

The load calculation allows the contractor to help you choose the just-right AC system for your home. An oversized central system may cause short cycling problems, while an undersized AC unit may never reach the desired indoor air temperature. Both sizing problems can result in energy loss, poor cooling, comfort control, and excessive wear and tear.

Air Conditioner Short Cycling

Short cycling is a common AC issue that has several potential causes. In relation to size and installation, short cycling can result from a mismatch in needs. Again, an oversized unit is often the culprit behind this air conditioning issue.

A too-large or too-high BTU unit quickly cools the interior air. Even though this may sound desirable, short cooling times may not completely remove the humidity from your home. Residential central AC systems won’t only cool the indoor environment. Along with cooling, the system also dehumidifies the air. Quick cooling won’t allow the air conditioner to effectively combat indoor humidity.

The leftover sticky, humid air forces the air conditioner to quickly turn back on after it shuts off. The repeated on and off pattern is known as short cycling. This AC issue can increase energy needs (and the related costs) and damage the system. If your air conditioner was not sized correctly and short cycles, contact an HVAC contractor to evaluate the issue.

Climate Zones

The International Energy Conservation Code (IECC) climate zones refer to the geographic areas and designations for temperature and humidity. When an HVAC contractor sizes your central air conditioning system, they’ll need to factor in the climate zone as part of the size and energy use calculations.

Different regions have different types of climates — and different cooling and dehumidification needs. California and New Hampshire homeowners won’t need the same level of cooling power (under typical weather circumstances).

Insulation R-Value

The R-value measures the insulation’s effectiveness. A higher R-value equals a higher degree of insulation. Before the HVAC contractor can recommend a specific sized product, they will need to assess your home’s existing or expected insulation — if you plan to add more insulation in the near future. Does your home need a new air conditioner? Contact Mauzy Heating, Air & Solar for more information.

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