New homeowners in San Marcos may not understand how much goes into the decision-making process of selecting a new furnace. Not only do you need to consider the climate zone, and type of furnace you want, but you also need to consider the BTUs needed to heat your home comfortably. While you can buy any unit you want, it is important to choose the right furnace for your home so you get optimal efficiency and avoid wasting money paying high-energy bills. If you feel overwhelmed deciding which size furnace you need, consider seeking the help of a trained technician from Oak Island Heating and Air Conditioning. This blog will discuss several factors you should understand so you can choose the best-sized furnace for your home.

Establishing the Square Footage of Your Home

The first step in sizing a furnace is determining the square footage of the home that you want to heat. Many homeowners will know this value offhand because they were made aware of it when they purchased or constructed the home. If you do not know the number, you will need to find it or calculate it. You can often find it on closing documents or on the various paperwork filed with the local municipality. If you need to calculate it, then what you want to do is essentially organize your home into a series of rectangles. Measure the square footage of each rectangle. You can then add the values of all of these rectangles to achieve the total square footage for the home. You may also opt to have a professional measure it.

Understanding British Thermal Units

In order to evaluate and size a furnace, you will need to understand BTUs, which stands for British Thermal Unit. You do not need to understand the finer details of it as a metric, but it is important to understand that it is a unit of heat and that it is used to rate furnaces in the United States. Most furnaces on the market range between 80,000 and 100,000 BTUs. Nevertheless, since the U.S. is a large place with many different climates and heating needs, you can find furnaces as low as 40,000 BTUs in addition to furnaces that generate 200,000 BTUs or more.

Assessing BTUs Within the Context of Energy Efficiency

What can be a little confusing is that a furnace rated for 60,000 BTUs does not actually generate that much in practice because there is no such thing as a 100% efficient furnace. If it were a high-efficiency model rated at 90%, then it would produce 60,000 * 0.90 = 54,000 BTUs per hour. Furnaces have an AFUE rating—annual fuel utilization efficiency—that indicates this percentage. You can find modern furnaces with an AFUE rating as high as 99. However, paying for a high-efficiency model may not be worth it for the average homeowner. The minimum AFUE available is 80 and the average home in the U.S. does just fine with a furnace that has an 85 AFUE rating.

Identifying Your Climate Zone

The next step is to determine how many BTUs you need per square foot. Homes in the U.S. generally need between 30 and 60 BTUs, but determining a more precise number requires identifying your climate zone. There are seven climate zones in the U.S. The first zone is the hottest, and the seventh zone is the coldest. Most of our service area is in climate zone 3, which requires 40-45 BTUs per square foot. If you happen to be in climate zone 4, then you will need 45-50 BTUs per square foot.

Calculating the BTUs Required for Your Home

The average home in our area is about 2,000 square feet, so we will use that value for our example. If you are in zone three, you need 40-45 BTUs * 2,000 square feet = 80,000-90,000 BTUs. If you are in zone four, then you need 90,000-100,000 BTUs. As mentioned in the introduction, this is not an exact science, which is the reason that we work within a range. We will adjust our target to one end of that range or the other based on a number of other factors that we will discuss in the sections ahead.

Furnace Tonnage

So far, we have discussed furnace size in terms of the BTUs they produce. You may also encounter the concept of furnace tonnage, which refers not to the weight of the furnace but how much energy it can expend. The general rule to determine the tonnage required is to divide the BTUs by 12,000. In our above zone 3 example, the calculation is 90,000 / 12,000 = 7.5 tons. Not coincidentally, the general recommendation for a 2,000-square-foot home in the U.S. is a 7.5-ton furnace. Our trained technicians at Oak Island Heating and Air Conditioning can recommend the best size furnace to heat your home.

The Insulation Factor

The overall size of a home is the most important factor in heating it, but it is not the only factor. A modern well-insulated home can get by at the lower end of the BTU range and you will enjoy a lower monthly heating bill. If you have an older home with inadequate insulation, then you will need a furnace at the higher end of the range and perhaps even higher. In fact, insulation is extremely important so you may want to consider installing new insulation before getting a new furnace.

The Natural Ventilation Factor

Natural ventilation is a factor too. We may use that term to refer to an open window on a comfortable day, but it also refers to unintended ventilation such as drafty windows and cracks in the foundation. Modern homes tend to be well sealed to the point that mechanical ventilation is a focal point. Therefore, a well-sealed home could get by with fewer BTUs as well. If you have an older home, you may want to consider having it sealed when you have new insulation installed.

Other Factors to Consider

Another factor to consider is the size and type of ductwork in your home. Unless you are willing to replace the existing ductwork, you will need to select the new furnace to work with the old ductwork. Other factors can include ceiling height, the type of windows and doors in your home, sunlight, and wind, as they are specific to your particular lot.

Your Local Furnace Pros in San Marcos

Oak Island Heating and Air Conditioning is a family-owned and -operated HVAC company that has served San Marcos and the neighboring communities since 1988. Our company installs, maintains, and repairs furnaces, heat pumps, and all manner of other heating equipment. We install, maintain, and repair air conditioners, too. Our team has the skills to install ducted and ductless equipment, including electric units and those that run on natural gas. Other services we provide include indoor air quality, smart thermostats, humidifiers, dehumidifiers, and air purification systems. Contact us online or call us today to learn more about the many services we offer!

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