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Did you know that in the U.S., space cooling made up 16% of residential electricity consumption in 2022? Space heating accounted for 14%, bringing the total to 40%.

That’s a lot, especially if you live in Oklahoma City.

After all, the average residential electric bill in OKC is 5% higher than the U.S. average. So, if you pay $230 a month for electricity, over $90 goes toward heating and cooling alone. It may be even higher if you have the wrong size HVAC system.

That’s why you must learn how to size an HVAC system correctly. We’ll tell you why and how to do it properly, so read on. 

Why the Right HVAC Size Matters

The size of an HVAC unit determines its ability to heat and cool your home efficiently.

Adequately sized systems improve indoor temperatures without using more energy than necessary. They’re also effective in controlling humidity levels, making them essential for comfort.

By contrast, oversized and undersized HVAC systems are inefficient and waste energy. 

Oversized HVAC Systems

Oversized HVAC systems can heat and cool indoor spaces faster. However, they do so by using more energy. This reduces their energy efficiency, leading to higher energy bills.

A too-big air conditioner also performs poorly in terms of humidity control. It’s more prone to short cycling, wherein it turns on and off too rapidly to complete a cycle. As a result, it can’t extract as much moisture from the air as it should.

Indoor air that is too humid can make your home feel stuffy and uncomfortable. It can also promote mold and mildew growth, impacting indoor air quality. This is a big problem in Oklahoma City, as it has a humid subtropical climate.

It’s even more crucial to control indoor humidity if you or a family member has a mold allergy. It affects 10% of people in the U.S. and can cause symptoms like nasal congestion and headaches.

Oversized HVAC systems are also more prone to early wear and tear due to short cycling. They’re also noisy. Besides, their upfront and operating costs are higher. 

Undersized HVAC Systems

A too-small HVAC system lacks the heating and cooling power to support your comfort needs. For example, it won’t be able to heat your home adequately during cold days. Neither will it provide sufficient cooling during warm days.

As a result, your inefficient system may force you to raise or lower your thermostat settings. This can lead to higher energy consumption, increasing your energy bills. 

Undersized HVAC units also have to work harder to heat and cool spaces too large for them. This places undue strain on their components.

All that extra stress can cause premature wear, tear, and breakdowns. As a result, you’d have to call an HVAC technician more often for professional repairs. Worse, the more often your system breaks, the more likely you’ll need to replace it early. 

How to Size an HVAC System

Before, many people, including contractors, calculated HVAC sizes based only on floor areas. They used to install AC units that could provide one ton of cooling for each 400 to 500 square feet. One ton is equivalent to 12,000 British Thermal Units (BTUs).

That method is no longer viable today, as it’s incomplete and inaccurate. It doesn’t account for factors such as local climate and home insulation.

Instead, today’s reliable HVAC professionals use the Manual J calculation. 

The Manual J Calculation

Manual J is a technique designed by the Air Conditioning Contractors of America (ACCA). The U.S. Department of Energy recommends this HVAC sizing method. The DOE even says homeowners should insist their contractors use it.

A good enough reason is that this sizing method is far more accurate. It considers the following variables:

  • The size of the heating and cooling area
  • The local climate (in this case, Oklahoma City’s)
  • The type of home insulation you have
  • The number of windows in your home
  • How high your ceilings are
  • The availability and condition of ductwork
  • How many people live in your home

After determining those factors, HVAC professionals can factor in equipment capacity in BTUs. They also assign BTU values to the variables listed above. 

Sample HVAC Size Calculation

The Manual J method has standard rules for the variables used in its HVAC size calculation. For example, it assigns a value of 100 BTUs for every occupant and 1,000 BTUs for every window and exterior door.

Suppose your home has three occupants, ten windows, and three exterior doors. In this case, you’d need to factor in the following when computing your HVAC size:

  • 3 occupants X 100 BTU = 300 additional BTUs
  • 10 windows X 1,000 BTU = 10,000 additional BTUs
  • 3 (exterior) doors X 1,000 BTU = 3,000 additional BTUs

Next, add all the products of the variables, including the BTU for your home’s size. You can then choose an HVAC system based on the total you get.

Alternatively, you can use an online HVAC load calculator to calculate things easily. These tools will ask you to input the values for the variables above.  

But for the best, most accurate calculation, hiring a licensed HVAC company is the way to go.

A local HVAC specialist is your best bet since they’re from Oklahoma City, too. This means they have in-depth knowledge of the city’s climate. As mentioned above, local climate conditions are vital for proper HVAC sizing.

HVAC experts also use specialized tools for accurate system sizing. They’ll use this while conducting their in-depth, on-site analysis of your home. You can also expect them to recommend the best HVAC models for your needs. 

Stay Comfy With the Right HVAC Size

Now that you know how to size an HVAC system, you can avoid buying one too small or too big. You don’t want an oversized or undersized unit, which can affect your comfort and health. The wrong size can also spike your energy bills and put you at risk of unnecessary repair costs.

Are you still unsure which HVAC size is right for your home in Oklahoma City? Then our team of experts here at Advantage Plumbing, Heating, and Cooling can help. Call us now, and we’ll be happy to discuss your options!

Stillwater Sapulpa