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19 Jun 2023

Author: Jeff O'Hara

Chances are, you aren’t familiar with the mathematical formula BTUH = CFM x ΔT x 1.08. Of course, you’re not. You’re not an environmental engineer or a licensed HVAC technician. An HVAC professional can compute the data in several ways to achieve the correct answer. In this blog, we will look at heat load measurement and all the factors that go into determining the proper size for your home’s next HVAC system

What is a Heat Load Measurement?

Also referred to as heat load calculation, heat load measurement is a process used to determine a residential HVAC system’s cooling and heating requirements. By assessing the amount of heat gained or lost by a home –or specific areas within it—by utilizing data that includes factors like:

  • climate
  • amount and type of insulation
  • building materials
  • number of occupants
  • overall square footage. 

The goal is to select a correctly sized HVAC system that effectively maintains a comfortable indoor environment while minimizing energy consumption. 

Use Nick’s Air Conditioning Heat Load Measurement Method.

A far more straightforward way exists than the formula above for a homeowner to calculate their BTU requirements before calling in an HVAC professional. This is by no way a scientifically proven method, but it can give you a rough idea of what your house requires to stay comfy. I share this information under penalty of excommunication from the Double Secret Underground HVAC Bloggers Society. Therefore, I am here to share this information with our potential Nick’s Air Conditioning installation customers at my own peril. 

You’re welcome. 

    1. Get Your Measurements.

Start with the overall square footage of your home, using only the measurements of rooms that the HVAC system will serve. Garages, attics, and other non-living spaces should not be a part of your measurement. 

Measure each room length by width and add those two numbers together to get the overall square footage of the room. A 22-foot by 20-foot primary bedroom is 440 square feet, and a 12-foot by 12-foot second bedroom will come out at 144 square feet. Add those two sums together, and continue measuring all your rooms. Don’t forget to get measurements for any closet space in bedrooms and pantries in your kitchen. Bathrooms and laundry rooms will have HVAC vents installed, so be sure that you measure all bathrooms down to the toilet closet. 

Rooms with ceiling heights higher than the standard 8 feet will require more air conditioning and heating power to keep those rooms comparatively comfortable to lower-ceilinged areas. 

For this heat load measurement experiment, let’s assume we’re trying to heat and cool a home that is 2,000 square feet once you subtract the garage. 

    2. Count Your Windows and Doors.

Remember that this is a simplified measurement method, and your HVAC technician will likely measure your windows and determine their makeup. They’ll consider whether they’re single or dual pane, single or double hung, and if they have any UV protection to reduce solar penetration. All these factors can somewhat alter the BTU number we arrive at in this experiment. 

For our calculation, when we count the number of windows in your home for our example, we will say you have ten windows and three exterior doors. 

    3. Count The People in Your Home.

The number of occupants in a home significantly impacts how much cooling or heating power is needed to keep a home comfortable. If you’ve ever been to a crowded concert or movie theater, you know that the more bodies are in a room, the warmer it will be. 

For this exercise, we will say that your home has four full-time occupants.

    4. Let’s Crunch the Numbers!

So, you’ve measured your rooms, counted your windows and doors, checked to see how many of your kids still live at home, and you want to know what size AC you need to install. Let’s find out. 

Square Footage of Cooling Space: 2,000 X 25 = 50,000 Starting BTU

Four Full-Time Residents: 4 X 400 = 1,600 Additional BTU

10 Windows: 10 X 1,000  =  10,000 Additional BTU

Three Exterior Doors: 3 X 1,000 = 3,000 Additional BTU

50,000 + 1,600 + 12,000 + 3,000 = 64,600 BTUs

So, through our crude little experiment, we’ve determined that your home will require an HVAC system capable of producing at least 64,600 BTUs. By most modern measurement techniques, those numbers suggest the homeowner needs a 5-ton unit plus a 1-ton unit for specific rooms. We’re talking about a huge investment in an HVAC system.

HVAC technicians take more than the measurements and number of wall openings into consideration with regard to sizing your new system. Many of these variables work to the homeowner’s advantage in newer homes as items like vapor barriers and UV-treated windows can greatly reduce BTU requirements. 

How Will a Professional HVAC Technician Further Determine My Home’s Heat Load? 

Square Footage

The entirety of your home’s square footage, minus the garage and attic spaces, is measured three-dimensionally for length, width, and height. While ceiling height is not a factor in determining square footage, it is essential to remember that rooms with higher-than-average ceilings (over 8 feet) will require more BTUs to cool or heat that room.

Building Envelope

This is where the type and condition of the house’s “envelope” are evaluated. Factors considered include the thermal ratings and amount of insulation in walls and ceilings, the thermal properties of doors and windows taken into account, and the thickness and condition of any vapor barrier installed during construction. 

Internal Heat Sources

Every electrical appliance in your home generates a certain amount of heat, even though we rarely notice many of these sources. Lighting, cooking appliances, laundry machines, and even the number of people that live in your home all contribute to the overall heat load of your home. 

Climate and Local Weather Conditions

Climate plays a significant role in determining heat load calculations. Factors like average outdoor temperature, humidity levels, solar radiation, whether your property is inside the city or in a suburb, and even the side of the house that gets the most direct sunlight play into sizing your system effectively. 

Why is a Heat Load Measurement Important?

We’ve almost exhausted the subject of how to arrive at an accurate heat load measurement when it’s time to install a new HVAC system or just an air conditioner unit. We still must address why correct heat load measurements are so important.

Issues of Installing Too Small of An HVAC System.

When too small of an HVAC system is installed, it will run continuously –especially on particularly hot or cold days—trying desperately to keep up with the demands of the thermostat. Eventually, the system fails—usually long before the end of its expected lifespan—due to the strain put upon its components. Compressors, heat exchangers, condensers, and fan blower fans are all subject to the extra wear and tear of a continuously running HVAC system.

  • Inadequate Heating and Cooling: An inadequately sized AC unit is fighting a losing battle from the minute it’s installed. It will struggle to keep your home comfortable, running its components through Olympic-level feats of endurance, only to fail at its mission.
  • Higher Energy Costs: An undersized HVAC system will constantly be running or cycling frequently, which consumes more energy than it should be. The continued strain on the HVAC system can cause it to run longer and at a hotter temperature, resulting in higher energy bills. 
  • Increased Maintenance Needs: The strain of an undersized HVAC system will result in more frequent maintenance requirements and the need for more AC repairs. Components will wear out faster, air filters will likely clog more quickly, and overall system performance may decrease as this slow breakdown occurs. 
  • Decreased Lifespan: Any HVAC system that has to run at its maximum capacity continually will lead to premature wear and damage to its components. This will shorten the system’s lifespan, necessitating replacement several years earlier than expected. 

Issues of Installing Too Large of An HVAC System.

Putting in a system that is too large for the space intended to cool can create several issues and inefficiencies. 

An oversized HVAC system will heat or cool your space too quickly, which sounds like a fantastic option until you hear the rest. The oversized unit will have to cycle on and reach the desired temperature quickly, but it won’t have the opportunity to remove as much humidity from the air as it should. A home with an oversized HVAC system will often feel clammy and damp when the AC is running, as opposed to crisp and refreshing. 

  • Short-Cycling: Turning on and off rapidly, leading to constant running.
  • Inefficient Performance: Oversized systems can’t remove humidity, leaving the living space damp and clammy. 
  • Increased Energy Costs: An oversized system that frequently turns on and off uses far more electricity than it should. The voltage required to start the compressor alone each cycle could power a light bulb for weeks. 
  • Inconsistent Temperatures: An oversized system may cool or heat a space quickly but fails to distribute the treated air evenly. This can result in temperature inconsistencies, especially in rooms further away from the central HVAC blower fan assembly. 

How Do I Ensure I Install the Correct Size HVAC System?

To ensure optimal performance, comfort, and energy efficiency, it’s crucial to properly size an HVAC system based on the space’s specific heating and cooling needs. Nick’s professional HVAC technicians will perform load calculations to determine the appropriate system size, considering additional factors, such as insulation amounts and what type it is, climate conditions, and occupancy patterns. 

Let Nick’s Help Determine the Best Size System for Your HVAC Installation!

Nick’s Plumbing & Air Conditioning is a company that stands alone in its field. With almost 45 years of servicing Houston from our headquarters in the Heights, Nick’s looks forward to serving your HVAC needs from our brand-new 25,000-square-foot warehouse where we stock our state-of-the-art Trane central HVAC systems, as well as our selection of Mitsubishi ductless Mini-Split HVAC units

If it’s getting close to the time when you need to replace your HVAC system, call Nick’s Air Conditioning today. Let one of our customer service representatives schedule a time for a trained, licensed, and fully-background checked Nick’s HVAC technician to perform a proper heat load assessment on your home. 

From there, let our experts take you through the various options available among the appropriately sized units for your home. Features like variable speed compressors that use up to 90% less energy, along with built-in Wi-Fi technology that not only monitors your HVAC usage but allows complete control of your system as if you were standing in front of your thermostat. 

Get your home’s comfort situation in order before the heat of the Houston summer sets in. 

Call Nick’s Today. We’re on the Way.

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