Best Plumbing and AC Service & Repair

Best Plumbing and AC Service & Repair

AC unit for house

What Size of AC Unit Do I Need for My House?

Researching new air conditioning units for your home or office quickly reveals the size of this investment. That’s why buying the right sized unit is paramount in effectively (and efficiently) cooling your space. For most consumers, bigger equates to better, but that is not true for residential and commercial AC units. Buying a unit that is too large leads to uneven cooling and high utility bills while buying a unit that is too small lowers the life expectancy of the unit because it must work harder than it should over the years.

Nobody wants to get stuck with the wrong-sized unit, so here is information on the two ratings used to choose the right sized AC unit for your designated space: Seasonal Energy Efficiency Ratio (SEER) and British Thermal Units per Hour (BTUh). We will explain these ratings in more detail shortly. Other important variables include the quality of ductwork, home insulation, number of people living or working in the space, types of windows, and the square footage. With the cost of the unit and installation leaving no room for guesswork, here is some information and tips to get you pointed in the right direction in choosing the right AC unit size for your home or office.

Why a properly sized air conditioner is important?

To protect your investment and ensure many years of cooling from your AC unit, choosing the right size of the unit is one of the most important decisions you will make. An oversized or under-sized AC unit will not cool your space correctly and it will increase the amount of energy you consume and the size of your utility bills. A unit that is too small will struggle to cool your entire space and will run longer and much harder than it should. An oversized AC unit will turn on and off in short intervals causing unwanted humidity to build up and increase temperature in the space. Both miscalculations will lead to significantly higher operating costs and additional wear and tear and repairs over the years which is not ideal for any investment. This is why it is so important to choose the right size of AC unit for your home or office.

Determining the Right HVAC Size for Your Space

Determining the right size of an AC unit for your space can be calculated using a Manual J calculation (a very precise measurement).

Manual J calculation – It’s a formula that calculates a building’s HVAC capacity and is highly accurate because it considers various factors like square footage, ductwork, climate zone, style, number of windows, amount and quality of insulation, amount of sunlight, people utilizing the space, and heat-generating equipment. This calculation, however, is complex to calculate.

Our team of licensed HVAC technicians at Lantz’s Lakeside Plumbing & AC are experienced in performing this calculation and determining the correct AC unit sizes for our customer’s homes and offices, and a completed Manual J calculation will determine the correct BTU rating needed for a particular space. A BTU (or British Thermal Units) rating is the measure of an AC’s power and the energy required to remove heat from an area. Consequently, the higher BTUs an AC has, the more efficient it is to cool a bigger space.

Things to Consider When Choosing an AC Unit for A Home or Office

When evaluating your space to determine the correct sized AC unit to select, there are other considerations to account for through besides just square footage. Here are a few:

  • Ceiling height – Not all homes have Standard 8-foot ceilings with separated areas of a house. Many contemporary homes have vaulted ceilings and open floor plans so it is important to calculate the volume of your house – as more volume requires more BTUs to operate efficiently.
  • The number of stories – If you live in a two-story home, it is often recommended to install two separate units to help maintain an optimal temperature in all areas of your home – one unit for downstairs and one unit for the upstairs area.
  • Climate Zone – Climate also influences how many BTUs are needed by your AC unit to effectively cool your space(s). can give. The hotter the climate, the more BTUs are needed.
  • Ductwork – Quality ductwork is necessary to keeping your AC unit(s) effectively cooling your home or office. Inefficient or old ducts leak cool air and reduces the efficiency and effectiveness of the unit.
  • Number and Style of Windows – Windows are often a huge source of energy loss. Most single-paned windows allow heat to enter rooms much easier than double or triple paned windows so this might need to be calculated into the size of AC unit needed.
  • Natural Shade or Lighting – The BTU requirements of your AC will drop if buildings or trees shade your space.
  • The number of people using the space – Humans produce heat so it’s imperative to consider how many people will occupy a given space. Generally, it’s recommended to increase the cooling capacity by 600 BTU for every individual living or working in the space.

Do You Need a Second AC Unit?

A common concern among customers is a single AC unit is not effectively cooling their 2-story home. We commonly recommend two AC units for a space, especially for those living in large or 2-story homes. Here are several reasons why:

  • Balance of temperature – Two air conditioning units, particularly in the basement or garage, do a great job balancing the temperature in your living space. Usually, your single AC unit will struggle to cool the upstairs of your home. When you install another AC, it will not only balance the temperature in these difficult-to-cool areas but will also enhance efficiency in both AC. Let’s make this clear to you with an example. Suppose you have a bedroom upstairs that nobody uses during the day. You can set the temperature for the AC in it more than you would be able to do in the case of a single unit. It will enable you to keep the downstairs living room at a highly comfortable temperature range without any usage of energy to keep it that way.
  • Energy efficiency – Less energy is used when two smaller units are working in tandem to heat different parts of a space versus one large unit working too hard to keep up with the cooling requirements placed on it.
  • Redundancy – If one AC unit stops working, there is another unit that still works and can keep some spaces cool. Hot summer months is when lots of AC issues occur as units are running almost constantly.

A Second Important AC Size Rating to Consider – SEER (Seasonal Energy Efficiency Ratio)

A second AC rating important to consider when selecting the right unit for your home or office is a Seasonal Energy Efficiency Ratio or SEER Rating.

SEER Details & Calculation

SEER is a measurement that describes the effective usage of energy by your AC. A SEER rating is calculated by taking the cooling output of an AC during a usual cooling season and dividing it by the overall electrical energy output of the whole season. The higher the number, the more energy-efficient an air conditioning unit is which implies lower electricity usage and lower utility bills.

To determine SEER, use these simple steps.

  1. Determine the hourly BTUs of the AC unit. Reference owner’s manual.
  2. Find the watts per hour for your AC. Reference owner’s manual.
  3. Compute the BTUs needed in the summers. You can use 1000 hours which approximates 125 days, to represent the summer months. Now multiply the amount from step 1 by 1000. You’ll find the BTUs used in the summers.
  4. Calculate the number of watts/hours used during the summers – by multiplying the amount from step 2 by 1000.
  5. Last step – divide the BTUs used in the summers by the number of watt-hours utilized in the summer months to find the exact SEER rating.

Bottom Line

Every home is different, which means that there’s no one standard size of AC that’s right for everyone. Choosing a right-sized unit involves analyzing several important ratings and factors (that we have already addressed), and keep in mind these decisions doesn’t need to be made alone.

Lantz’s Lakeside Plumbing & AC has been serving the greater Austin community for over 50 years. We are a locally owned and operated HVAC expert, and our friendly and licensed technicians provide quality AC services, AC repairs, AC replacements, and AC installations. Our team of advisers offer free, in-home consultations where they will learn about your space (and your needs for that space) to provide a customized and economical solution for your home or office and will equip you with the knowledge you need to purchase an AC with complete confidence. They will also recommend the perfect AC based on factors such as room size, ceiling height, wall insulation, humidity levels, location, and number of occupants.

Lantz’s Lakeside Plumbing & AC serves residential and commercial customers in Lago Vista, Cedar Park, Leander, Liberty Hills, Marble Falls, Jonestown, Lakeway, and the greater Austin area, and offer flexible payment solutions that include fixed-interest financing so problems get fixed and upgrades get installed quickly. We have hundreds of 5-Star Reviews that show our commitment to quality and customer service, and are open 7 days a week, and open late until 9pm (Monday – Saturday). To schedule a service call, yearly unit maintenance, or free in-person consultation, call (512) 267-1188 or fill out a brief form here

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