A: The sizing of the equipment is very important to the equivalent performance as you use it— it has to be the right size. A common misconception is, as with other things, is that bigger is better.
However, when sizing equipment to your home, it’s more like sizing your shoes. Too small in capacity and your system is going to run all day and never achieve the setpoint. That is going to run your bills high and not perform as efficiently as it’s designed to.
If you put an oversized system in your home, that system is going to short cycle. Meaning it’s going to achieve the setpoint so quickly, it’s not going to have enough time to remove humidity. The comfort level inside the home is going to go down. So, you want to make sure your system is sized properly.
What we do is we provide a heat load calculation on a home where we calculate based on what heat sources are. We also consider the size and type of windows, type of insulation in the home, the size of the area being cooled.
All of these things go into the mix that results in an accurate heat load calculation. That calculation will then give you the exact size system you need for your space.
Whether you’re buying a new air conditioning unit only, or you’re replacing your entire system—getting the right size system is crucial. You can make a critical mistake and buy too small or even buy too big—yes, too big. As Marcelo mentioned, most people seem to think that bigger is better—especially here in Houston. As it turns out, when it comes to Houston HVAC—that’s not always true.
Calculating The Right Size For A Houston HVAC System
Buying the right size air conditioning unit for your home comes down to science—literally. Your installer needs to do a load calculation on your home. This calculation is based on a scientific formula that considers several factors. Contrary to what many might think, it depends on a lot more than just how large or small your home is.
In fact, square footage is just one of the many factors to determine the load calculation for your home. Ah, but first we should probably explain to you what a load calculation is right? It’s pretty simple. A load calculation is a simple number that dictates how much cooling and heating is needed to keep you comfortable. Getting that number, however, is not that simple. For example, HVAC system requirements are going to be different by region. What you need in hot and humid Houston will be different than hot and dry Phoenix, AZ.
Overview Of A Load Calculation
There is a standard calculation method that is most often used in Houston air conditioning companies and others nationwide. This method was designed by the Air Conditioning Contractors of America (ACCA) decades ago and is mostly done by computer these days. The load calculation helps ensure that you have a proper size system that will cool and heat efficiently without wasting resources. The load calculation process goes like this:
Step One:
Get the square footage of your home. If you have blueprints for your home, then this is going to be pretty easy. However, if you don’t, no worries, you’ll just need to do a little legwork. Start by measuring the length and width of each room and multiply those measurements to get the square footage for that room. After you’ve covered all the rooms just add up the square footage of each and you have the total square footage.
Step Two:
Now that you have your square footage you need to account for variables that affect insulation. First, you want to check the insulation itself. What grade is it? Is there an ample amount of insulation coverage? Are there any gaps or uninsulated parts of the attic?
Then, you want to consider those factors that can affect the effectiveness of your insulation. Even the best insulation is negated by other structural vulnerabilities. Look for things such as poorly insulated windows, gaps in doorways or exterior walls, and sun exposure. Some other common factors that you need to account for are:
- Each occupant in a home: add 100 additional BTUs
- Each exterior door: add 1,000 additional BTUs
- Per window: add 1,000 additional BTUs
Step Three:
You also need to consider how the living space to be cooled is being utilized. For example, a kitchen is going to generate a lot more heat than a bedroom. A bathroom will be more humid than the living room. Consider how many appliances that produce heat will be in each room—computers, ovens, TV’s, etc. All of these appliances generate heat to some extent and will affect the cooling requirements of the home. Also, think about how many people at once will occupy each room. The more people in a room, the more cool air needs to flow through to keep it comfortable.
Cooling Load Calculation Scenario
Let’s take a look at an example scenario to bring this all together so you can understand how it works. Let’s calculate the estimated load calculation for a Houston HVAC client we are doing an install on next week. This particular home is 1,675 square feet, has 11 windows, 2 exterior doors, and is occupied by 3 people. We simply plug the numbers into the following formula:
- 1,675 x 25 = 41,875 BTU: The base BTU requirements before considering the below factors
- 3 people x 100 = 300 BTU
- 10 windows x 1,000 = 10,000 BTU
- 2 exterior doors x 1,000 = 2,000 BTU
- 47,875 + 300 + 10,000 + 2,000 = 51,175 BTU This is the adjusted BTU requirements for a Houston air conditioning system
So, in this case, a 4-ton unit like the Lennox Signature Collection XC25 would deliver high-efficiency cooling*.
Why A Proper Sized Houston HVAC System Works Better
As mentioned before, you can compare two similar-sized homes in two different climate regions and need differently sized units. Not having the right sized system for your home can leave you with a bunch of problems.
Everything in Texas is better bigger—that’s the rumor, but going too big on your HVAC system is not good at all. You hear it all the time from people in Houston on a summer day, “It’s the humidity that makes it bad, not the heat.” One, that’s just a big lie. However, in the terms of cooling your home—it’s gospel.
What happens when you cool a room too quickly with an oversized system is that it does too good of a job—at cooling. However, the second task of a Houston HVAC system is to remove excess humidity from the air. The result is sure, you feel cool but you also feel sticky or clammy. This can lead to mold growth and other damage related to excess moisture, such as drywall rot.
On the flip side, this is the more obvious issue that most people know about—you can buy a unit that is too small for your home. That is pretty self-explanatory but let’s get into it briefly.
An undersized unit unlike the oversized unit that runs hard and short, is going to just run constantly. It does this because it can never catch up and cool to the desired temperature. It simply cannot move the volume of air required to maintain that temperature very long. The result is a unit that wears out very quickly and never really gets your home cool—only tolerable.
Get the Champions of Houston HVAC And Get It Done Right
It’s always better to go slightly undersized and we mean very slightly, rather than oversized. However, the best way to avoid extremes of either direction is to call one of our comfort consultants. At Airteam we are in the service industry, not the upsell industry.
We present the options we have for the size of the home you are wanting to cool. We don’t do high-pressure salespersons that read from a script. Our technicians and consultants have nearly 30 years of combined experience.
Contact us today and experience the AIRTEAM difference!
*AIRTEAM is a licensed and authorized distributor of Lennox HVAC systems. (TACLA704C, TACLA26649E)
