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What Size Furnace Do I Need?

A furnace is a vital tool for many households during winter since it helps maintain the right indoor temperatures. Although these units look very similar at a glance, they differ significantly in terms of capacity. If you have no experience, you will most likely choose the wrong furnace size, which creates temperature inconsistency throughout the house. It’s, therefore, vital that you seek professional help.

An undersized furnace won’t heat your home adequately. You will need additional space heaters to achieve the required temperature. Again, a smaller furnace continuously runs to meet the heat demands, which wastes energy and drives utility bills higher.

On the other hand, an oversized furnace produces more heat than required since it has a higher capacity than your house needs. As a result, it consumes more energy, leading to a spike in utility bills. Still, a larger unit cycles on and off frequently, which increases the chances of wear and tear, shortening its lifespan. Look into the following factors to guide you in selecting the right furnace size for your house.

1. Your Home’s Square Footage

The size of your house helps your technician determine the exact furnace capacity required. For most people, finding out their home’s square footage is a pretty easy task. You will only need to look at the lease, appraisal, listing, or any other paperwork you received when you purchased the home. If you fail to find it in such documents, you can also ask your Realtor.

Alternatively, you can choose to measure it by yourself. Take the length and width measurements in each room and multiply them to get the square footage. Add them, but remember to exclude the rooms you don’t intend to heat up, like your sunroom or garage.

Not all rooms have a rectangular shape. If you have a circular room, measure the radius, distance from one wall to the center, then calculate the area. For a triangular space, multiple the length and width and then divide the figure by two. If you have irregularly shaped rooms, divide them into sections and measure each separately.

It’s also worth noting that most furnace size charts assume that the ceiling should be around 8 feet high. If your house is different, remember to adjust your measurements accordingly.

2. Consider Your Climate

Next, you need to find out the climate zone that you live in since it influences what strength of furnace is required. Climate affects how much heat you will need in the house and how often you will run the unit.

Zone 1 mostly covers areas in the USA’s southern region, including Houston, Miami, and New Orleans. Such places have a recommended heating factor of between 30 and 35 BTUs. On the other hand, coastal California, Atlanta, and Little Rock lie within Zone 2 with a 35 to 40 BTU heating factor.

Additionally, Zone 3 begins from Virginia, extending to Missouri and Kansas with 40 to 45 BTUs. Zone 4 covers New York, Chicago, and Boston and has a 45 to 50 BTU heating factor. Lastly, Zone 5 includes the northern part of the continent, covering cities like Minneapolis and Buffalo, and has a heating factor between 50 and 60 BTUs.

3. Calculate BTU Output

BTU stands for “British thermal unit,” a standard value for measuring the heating output quantity in a system. An average furnace falls between 80,000 and 100,000 BTUs. To calculate the necessary BTU for your furnace, multiply your home’s square footage by the BTUs required in your climate region.

The higher the BTUs, the more heat a unit can produce. However, before buying the furnace, you also need to consider its efficiency rating. The annual fuel utilization efficiency (AFUE) rating represents the furnace’s percentage of energy converted into heat. It’s derived by measuring the amount of heat produced by a furnace in relation to the amount of fuel used in a year.

Note that two furnaces can have the same heating capacity but varying efficiency. For a natural gas furnace, the USA’s minimum AFUE rating is 80%, but higher models can go up to 98.5%. If you buy an 80% efficient furnace of 100,000 BTUs, the unit will deliver 80,000 BTUs of heat, and the remaining 20% gets lost throughout the flow.

When buying a new furnace, check for its AFUE ratings on the Energy Star logo. You need to choose the highest energy-efficient unit within your price point. It helps keep your bills as low as possible and your home adequately warm.

4. Insulation Variables

If your house is well insulated, the furnace will need less power. You can therefore get a smaller unit that falls within your total square footage. Similarly, if you have poor insulation, you need a larger furnace. Additionally, the number and rooms within your house also affect the size of the unit you choose. The larger your home is, the more energy it requires. If you live in a two-story house, you might need fewer BTUs since the second floor and the downstairs areas act as extra insulation.

Also, if your home has larger, older windows, more heat is likely to escape, so you need to choose a furnace in the upper end of your heating factor range. However, newer windows have better insulation. Generally, older homes have multiple areas through which heat can escape, and you may require more BTUs to stay warm. Further, if your house has a long and narrow shape, the numerous exterior walls lose more heat. As a result, you will need more BTUs than a square house with similar square footage.

5. Other General Factors

The number of occupants in your house can also affect the size of the furnace required. Naturally, the human body dissipates heat; hence, if you have a large family sharing a space, consider buying a furnace with slightly fewer BTUs. If you have considerably high ceiling heights, you need more BTUs to heat your home to comfortable levels. Additionally, if you have ceiling fans, it helps improve air circulation, lowering BTU usage.

Consult a Professional

Even after knowing the requirements, correctly sizing your furnace can be a daunting task. There are several calculations, estimations and considerations involved. Opting for DIY fixes might not create a long-lasting solution, but instead, you will end up spending too much money and time. It’s therefore essential to consult a qualified professional to prevent unnecessary costs or further damage. If you have difficulties figuring out the right size of furnace your house needs, you can always reach out to We Care Plumbing Heating and Air.

We have advanced tools and the knowledge to assess your home’s insulation level, window sizes, ceiling height, duct size, and other considerations that affect the size of furnace you require. With over 20 years of experience, we provide high-quality services in Murrieta, CA, and the surrounding areas.

Our company installs, repairs, services, and maintains air conditioners, furnaces, central air units, and various heating systems. We also offer drain cleaning, re-piping, humidity control, air purification, high pressure jetting, toilet repair, and installation services. We care about your comfort, and our team of experts is always standing by to help provide emergency services upon request. To schedule an appointment, call us now.

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