What Size Furnace Do I Need to Heat My Home?

Modern furnaces are designed to last for up to 20 years. For this reason, most Houston homeowners may only need to shop for a furnace once or twice. It can come as a surprise to many that furnaces come in a variety of sizes and models. This begs the question, what size furnace is needed to heat your home effectively? The following are some factors to consider when deciding on the right furnace to suit your needs.

What Are BTUs, and How Do They Impact Sizing a Furnace?

The right furnace size is critical for comfort during the late fall, winter, and early spring. If your furnace doesn’t keep your house warm enough during the winter, your pipes could freeze and burst, and you could find yourself paying high energy bills even though your home does not feel comfortable.

British thermal units are the measure used to gauge your furnace’s capacity. One British thermal unit is the equivalent of the amount of energy needed to raise the temperature of one pound of water by one degree Fahrenheit. This standard is used to gauge the size of furnace units. The more BTUs the furnace has, the more powerful it is.

A single BTU is small when compared to the energy needed to heat your home. It is estimated that in 2021, in the U.S., houses used approximately 97.3 quadrillion BTUs of energy.

How the Size of Your Home Determines the Size of the Furnace You Need

The most significant factor when sizing a furnace is the square footage of your home. The easiest way to find your home’s square footage is to look at its blueprint or closing document. If you can’t get access to this information, measure the length and width of each room in your home. Multiply these two numbers by each other, and then add the totals of all the rooms in your home to get your home’s total square footage.

As a general rule of thumb, HVAC contractors allocate 20 BTUs for every square foot of your home. To properly heat a room that is 200 square feet, you will need a minimum of 4,000 BTUs. For a larger space between 800 and 900 square feet, you will need a minimum of 30,000 BTUs. The typical home in Houston is about 2,000 square feet, requiring a furnace that can produce 115,000 BTUs to heat it efficiently.

How Does Climate Affect Sizing a Furnace?

While the most significant factor in sizing a furnace is your home’s square footage, the climate will also play a large role. In Houston, winters are relatively mild, with temperatures staying in the high 40s to low 50s Fahrenheit. In colder climates, like those found in Wisconsin, Minnesota, and Michigan, homes require an additional 30 to 60 BTUs per square foot.

The United States is broken into seven climate codes. Zone one, including places like Florida and Texas, is the hottest. Zone seven, including states like Wisconsin and Minnesota, is the coldest. In colder climates like Wisconsin, a furnace is a must. Some homeowners in places like Houston choose not to use a furnace but instead control the temperature of their homes using a heat pump.

Insulation Can Affect Furnace Sizing

Insulation is designed to help your home maintain its existing temperature. During the summer, it keeps your home cool, and during the winter, it helps maintain the heat produced by your furnace.

In areas like Texas, Arizona, and parts of California, it is recommended to observe the 3 – 5 – 10 – 20 – 60 rule. Homes should have insulation with an R-3 rating for under the windows, R-5 for under slabs, R-10 for above-grade foundation, R-20 for above-ground walls, and R-60 for the attic. If your Houston home is well insulated, you have reduced energy bills because your furnace does not need to work as hard. However, if your space is poorly insulated, cold air infiltration will force your system to work harder to reach the desired temperature. This typically means needing a more extensive system to get the job done. Do you have questions about your home’s insulation and how it impacts sizing the right furnace? Contact our technicians at The Lee Thompson Co., and let us help you evaluate your home to determine the correct size furnace for your needs.

How the Age of Your Home Affects Furnace Sizing

In an older home, the windows may not be as well insulated as those in a newer home. Modern windows are designed to prevent air penetration and escape. Additionally, if your home has a lot of windows, there is a greater chance that hot air will be lost. This is especially true if your windows are damaged or have broken seals that lead to air leaks.

Gauging the Furnace’s Efficiency Rating

AFUE, Annual Fuel Utilization Efficiency, is the standard used to measure your furnace’s efficiency. This standard measures the percentage of energy input that gets turned into BTUs. The higher the percentage of energy input the transforms to BTU output, the more efficient a furnace is.

For the last few years, the government has required furnaces to have an 80% efficiency rating. If you purchase a new high-efficiency furnace with an ENERGY STAR rating label, you can expect the furnace to operate at between 90% and 98.5% efficiency. Superefficient furnaces have two heat exchangers in the sealed combustion chamber. This allows any escaping gas to be burned in the second exchanger, thereby increasing efficiency. Older furnaces that have a continuous pilot light are typically lower in efficiency. They may operate in the 56% to 70% efficiency range.

Newer furnaces are typically labeled with two numbers, the input rating in BTUs and the efficiency rating. The best way to determine how many BTUs your furnace will put out when operated at peak efficiency is to multiply its BTU input by the efficiency rating.

For example, if your furnace has 100,000 BTU input and is 95% efficient, it should have an output rating of around 95,000 BTUs. Of course, if the unit is not properly maintained, its energy efficiency will decrease as it ages.

It’s recommended that our technicians at The Lee Thompson Co. service your furnace at least once yearly. Regular maintenance helps us find minor issues that could impact the unit’s performance and fix them before they become more significant over time.

Trustworthy Commercial and Residential HVAC Services in Houston

At The Lee Thompson Co., we have been serving the Houston area for over 50 years. We take pride in our work and take the time to ensure that our customers are happy with what we do before we leave. We guarantee 100% satisfaction, offer our clients peace of mind, and are proud of our outstanding reviews and A+ Better Business Bureau rating.

Our services include residential and commercial HVAC installation, maintenance, and repair. We install ductless and mini-split systems and perform indoor air quality checks. We install air filtration and purification equipment, dehumidifiers, and HVAC zoning systems, and we’re proud to provide emergency HVAC repair service. Contact us at The Lee Thompson Co. today, and see why we are one of Houston’s most respected names in the HVAC field.