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What Size Air Conditioner or AC Unit Do I Need?

Are you wanting and/or needing an air conditioner for your home? Brand, size, efficiency and available rebates are all factors that you should consider. Though brand and efficiency are important, it is crucial that you pick an air conditioner that is the right size for your home. The brand and efficiency won’t matter if the air conditioner is sized incorrectly. Incorrectly sized air conditioners are inefficient and can raise your utility bills no matter how great the brand or energy efficiency. 

Undersized air conditioners won’t cool your home to a comfortable level. The AC unit won’t have enough capacity to cool all the square footage of your home. It’s worth spending the money on a larger unit that is correctly sized for your home so you have even cooling avoiding hot spots in your home.  

Oversized air conditioners run more than they need to resulting in higher energy bills and lower energy efficiency. Humidity could also be a problem as oversized air conditioners. Ultimately, your oversized air conditioner is keeping your house cool, but it is costing you more and you may experience more humidity in the home.

You may asking yourself what size AC unit do I need? In order for your air conditioner to be sized correctly, the HVAC contractor giving you the quote will need to do a heat load calculation. Best practices indicate that HVAC contractors should always complete a heat load calculation for your home before providing you an estimate on an air conditioner. You may be able to determine your own heat load calculation using some tools that we will discuss below.

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How to Pick the Right Size Air Conditioner

Learn how to pick the right air conditioner vancouver wa for your home based on your air conditioning vancouver wa needs. This will help to avoid future air contionining repair vancouver wa.

Now that you know how important it is to pick the correctly sized air conditioner for your home you may be asking yourself, “How do I calculate what size air conditioner I need ?” There are a number of factors that impact what size of AC you will need for your home. These factors include, but are not limited to:

Size of Your Home

As you may expect, the size of your home greatly impacts how large of an air conditioner you need. It’s not only the amount of square footage you have in the home, but also the number of stories your home has.


The climate and weather of the city you live in will also impact your home AC size. If you live in a dry and hot climate, you will need more tonnage in your air conditioner in order for it to keep your house cool and comfortable. If you live in a more moderate climate like the Pacific Northwest, you can probably get away with less tonnage in your air conditioner.


Do you know what type of ductwork you have? What is the age of your ductwork? Is your ductwork properly sealed? If your ductwork is old, not of good quality and/or not sealed properly conditioned air will escape through holes and cracks in your ductwork. This will cause you to need a higher tonnage air conditioner in order to compensate for the lost conditioned air.


Do you have a lot of windows in your home? If so, you may need a larger air conditioner. Windows can be a source of energy loss. This especially depends on the types of windows in your home. Single-paned windows have the highest energy loss when compared to double-paned, or triple-paned.

Sun Exposure

As we discussed with your home’s windows, the amount of sun exposure your home gets will impact the size of your AC. It’s important to consider how much sun exposure versus shade exposure your home gets in the summer.


Insulation helps keep outdoor heat from entering your home. If you have newer quality insulation, you may need less tonnage in your air conditioner. Where your insulation is located and how much insulation you have also will impact your air conditioning needs.


How many people do you have living in the home? The more people living in the home translates to higher air conditioning needs for the home.

Home Appliances

Did you know that your home electronics and appliances impact your air conditioning? Electronics and appliances generate heat when in use. The biggest culprits are your lights, tvs, dishwasher, refrigerator and stove.

An HVAC contractor Heat Load Calculations take most of these factors into account. These calculations can be a bit complicated to determine and are best left to the professionals. We will provide some general guidelines to go by that will help to determine the size of an air conditioner you will need.

AC Air Conditioning in States Like Washington and the Pacific Northwest

Learn how to pick the right size air conditioner vancouver wa and air conditioning vancouver wa.

If you live in the Pacific Northwest, you generally will not need air conditioning as often as other parts of the country. Mostly you will just need it during the warmer summer months. However, it’s still extremely important that you size your air conditioner Vancouver WA correctly so when you do need air conditioning Vancouver WA it works correctly and your home stays comfortably cool.

Since our climate is moderate, heat pumps are a great cooling and heating option for those of us in Oregon and Washington. Heat pumps are a split system with both an indoor unit and an outdoor unit. They are designed to be able to cool in the summer and heat in the winter. Though they are more expensive than air conditioners, they are generally more energy efficient and get your more bang for your buck since they can cool as well. Heat pumps work best in 40-70 degree weather, which is the climate in the Pacific Northwest most of the year.

Because heat pumps are so energy efficient, utility companies offer rebates for local residences who chose to install  heat pumps in their homes. In our area, Clark PUD, Cowlitz PUD and Energy Trust of Oregon all offer rebates for heat pump units that meet their qualifications. Make sure to ask your HVAC contractor what rebates would be available to you if you decided to go with a heat pump instead of an air conditioner. Often manufacturers offer season rebates on their energy efficient heat pumps as well. The utility rebate plus a manufacturer rebate can greatly help bridge the gap between the cost of an air conditioner and a heat pump.

Miller’s Heating & Air is located in Vancouver, WA and has been serving the  local Vancouver, WA and North Portland communities for over 70 years. Our heating and air conditioning Vancouver WA experts can answer any question or concern that you have regarding air conditioning. It is the policy of our Comfort Advisors to always complete a heat load calculation for your home before offering any estimates for  air conditioning Vancouver WA. We pride ourselves on making sure your air conditioning is sized correctly so we take our time and our through. This is our process whether we are performing a heat load calculation for a traditional AC unit or a heat pump so that your system works effectively and efficiently. If you do have any problems down the road, we have 7 professionally trained technicians ready to help with your air conditioning needs such as air conditioning repair Vancouver WA and air conditioning service vancouver wa. 24/7 Emergency Services are also available for your convenience; we understand emergencies often happen once your office closes and our work day ends.

Do It Yourself – How Do I Calculate What Size Air Conditioner I Need ?

Learn how to pick the right size air conditioner vancouver wa and air conditioning vancouver wa using some basic rules of thumbs and formulas.

Option 1

You can get a general idea of what sized air conditioner Vancouver WA you need for your home by using a couple formulas. First, you will need to determine the necessary tonnage of the AC unit for your home based on the square feet of your home. The measurement of “one ton” equals the ability of an air conditioning unit in an hour to cool to 12,000 BTUs.

In order to determine what ton air conditioning unit you will need, use this formula:

(Square footage of your home times 30 divided by 12,000) -1= Tonnage Needed

Let’s do an example using the formula above. Let’s say that you have a 1600 square foot home. You would plug the square footage into the formula:

(1600 x 30/ 12,000) -1= 3 tons

In this example, you would need a 3 ton air conditioner for your home. However, this does not take into consideration factors that a HVAC contractor’s Heat Load Calculation would. Quality of ductwork, insulation, number of windows, etc. can have a impact on what size air conditioning unit you need.

Option 2

Another way to generally determine the size of the AC unit you need would be to use an online BTU calculator. Click here to view one. You simply input information about your home such as size, room ceiling height, and lowest outside temperature. This formula accounts for more factors than the square footage calculator, but still doesn’t account for everything such as number of windows, quality of your ductwork and insulation.

Option 3

Lastly you can use a climate zone map to determine roughly how much tonnage your air conditioner will need to be using the square footage of your home and the climate zone it’s located in. For us located in the Pacific Northwest, we will need less tonnage in an air conditioner Vancouver WA than someone with the same size house in the Southwest region of the United States. This is a very general rule of thumb to go by.


how big of an ac unit do i need , how do i calculate what size air conditioner i need

Professional Calculation for Your Home Air Conditioner AC Needs

Learn how a professional HVAC contractor can help you determine the right size air conditioning vancouver wa and air conditioner vancouver wa that you need.

As previously discussed, the best way to determine “How big of an AC unit do I need ?” is to have a professional HVAC contractor perform what is a called a Heat Load Calculation or Manual J Calculation for your home. This calculation and the estimate on an air conditioner should be completely free. In order to determine this calculation, the HVAC contractor will need to determine the square footage of your windows, doors, net walls, ceiling, and floor. In addition, they will need to determine the total inflation/ventilation in the home and the heat gain from your duct work. After determining all of these factors, they will be able to find out how many BTUs your home needs. This process does take a bit of time, but well worth it so you can get a professional assessment of what AC size your home needs.

At Miller’s Heating & Air, we take our time to tailor your air conditioning Vancouver WA system to your home and your family’s needs. Our Heat Load Calculations and air conditioning Vancouver WA estimates are completely free. Our Comfort Advisors will spend 1.5-2 hours in your home doing a thorough assessment of your existing system and home while also discussing your families cooling needs. Then the Comfort Advisor will give you several best air conditioning options for your home for you to choose from. Available rebates, both manufacturer and utility rebates, will be presented with these options as well.

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It is crucial that you pick an air conditioner that is the right size for your home. The brand and efficiency won’t matter if the air conditioner is sized incorrectly. #AC #HVAC #size @millersheatingair

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