Consumer Reports and the U.S. Environmental Protection Agency (EPA) agree: The average home needs 20 BTUs for each square foot of living space. If you’re in the market for a new air conditioner, heat pump, or heater for your Gilbert, AZ home, BTUs are one of several critical factors to consider. The international standard for HVAC equipment sizing, BTUs denote the heating and cooling capacity of HVAC units. But what is a BTU, and why is it relevant to your selection?
The British Thermal Unit and Its Purpose
BTU is short for British Thermal Unit. Although there’s no final consensus on its exact origins, the term is believed to have been coined by either James Prescott Joule, Thomas Tredgold, or Nicolas Clement in the mid-19th century. No matter which scientist can lay claim to its beginnings, the overarching goal of the BTU is to compare a quantity of fuel used to a quantity of heat extracted or added. In essence, the BTU rates heat transfer.
What Is 1 BTU?
A single BTU is the amount of heat necessary for raising or lowering the temperature of 1 pound of water by 1 degree Fahrenheit. It takes 1,055.6 Joules of heat to accomplish this. One BTU is the equivalent of burning one match. According to the EPA’s recommendation, you would need to burn 20 matches per every square foot of living space in your home to raise your indoor temperature by a single degree.
Why BTUs Are Important
BTUs have a direct correlation to the amount of energy that HVAC systems use to create or extract heat. Although they aren’t efficiency ratings, they do have an important hand in determining whether any AC, heat pump, boiler, or furnace will work efficiently in your home. Lacking the right cooling or heating capacity for their service areas, even the most efficient HVAC models consistently underperform.
Why Getting the Right BTUs for Your Home Is Essential
When correctly sized, central heaters, heat pumps, and air conditioners provide uniform heat distribution or heat extraction. They run 10 to 15-minute heating or cooling cycles approximately two to three times each hour. They also have a limited risk of overheating and sustaining undue wear. With adequate capacity for creating and maintaining the temperatures that homeowners set at their thermostats, properly sized units function exactly as their manufacturers intended.
What Happens When HVAC Systems Don’t Have Enough BTUs?
If you install an air conditioner that’s too small for your home, it will run longer, less effective cooling cycles and more of them. In fact, on the hottest days of the year, an undersized air conditioner or heat pump might run all of the time. The extra stress that undersized ACs are subjected to can also result in problems like icing, overheating, short cycling, and shutdown.
Undersized air conditioners have shorter-than-average lifespans, and they experience more-than-average problems along the way. Unfortunately, getting undersized cooling equipment is a common issue among homeowners who shop for ACs or heat pumps by visiting local big-box stores.
What Happens When Homeowners Install Oversized HVAC Equipment?
Oversized heaters, ACs, and heat pumps experience similar problems. However, rather than running longer-than-average cycles, these powerful units cycle on and then rapidly cycle back off. With short bursts of heating or cooling, oversized units don’t have a major impact on indoor temperatures. They also have far less of an opportunity to extract excess humidity. This can leave building interiors feeling muggy or clammy. It can also create the perfect conditions for mold and mildew formation. Like undersized units, oversized models have shorter-than-average lifespans and experience frequent breakdowns.
What’s the Best Way to Calculate Your Heating and Cooling Needs?
When recommending 20 BTUs per every square foot of living space, both the EPA and Consumer Reports cite specific factors or conditions that must exist to make this recommendation effective. For instance, as per the EPA, this recommendation only works well for average-sized homes with good insulation and limited sun exposure. You might need slightly more or fewer BTUs per every square foot of living space based on the R-value of your home’s insulation, the size and location of your windows, and more. Hiring a licensed HVAC company to both source and install your new heating or cooling equipment is always the best way to ensure accurate sizing.
The Problems With Using BTUs and Square Footage Only
When shopping for their own heating and cooling equipment, homeowners often use online charts that recommend BTU amounts according to the square footage of buildings. Even when carefully matching BTUs to the square footage of homes, there’s always the major risk of getting oversized or undersized units.
The listed square footage for your home accounts for all areas within the building. This includes spaces that won’t be serviced by your HVAC system, such as utility closets, basements, attics, attached garages, crawlspaces, and pantries, among other things. For this and other reasons, when BTUs and square footage are used alone, homeowners aren’t accounting for many important building and household-specific factors.
How Do HVAC Companies Size HVAC Equipment?
HVAC companies also account for square footage and the recommended number of BTUs per usable area, but they leverage highly sophisticated software to run a complex calculation known as the Manual J Load Calculation. The Manual J Load Calculation accounts for things like:
- Ceiling heights
- Building layouts
- Ventilation
- Household sizes
The Manual J ensures that all service areas are properly accounted for even as it excludes closed-off and remote spaces that don’t require central heating and cooling. It also considers solar heat gains, heating and cooling loss, and added heat resulting from residents’ movements and activities.
Are BTUs the Most Important Factor to Consider When Choosing HVAC Equipment?
BTUs are the most important factor to consider when shopping for HVAC equipment. If you choose an AC, heat pump, or heater with too many or too few BTUs, its efficiency rating won’t matter. However, square footage should never be the sole factor that consumers use to calculate their heating and cooling needs. Sadly, when people buy new HVAC units in big-box stores, there aren’t any resources for factoring in everything that’s considered by the Manual J.
Choosing Equipment With the Wrong Amount of BTUs Can Void Its Warranty
Installing properly sized heating and cooling equipment is also a prerequisite of most HVAC equipment manufacturers’ warranties. Buying a unit that’s too large or small for your home won’t just result in higher energy bills, a shorter lifespan, and more than normal performance problems. It will also leave you paying for all necessary repairs out of your own pocket.
We help residents of Gilbert and the surrounding areas choose the perfect HVAC equipment for their homes. We offer expert heating, air conditioning, and plumbing services. We also provide ductwork, energy recovery ventilators, and advanced indoor air quality improvements. For help sizing your next AC, heat pump, or furnace, get in touch with A/C & Plumbing Doctors today.
