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What is a Load Calculation?

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What is a Load Calculation?

Have you ever wondered how we know what size HVAC equipment your home needs? Okay, maybe that’s not top of mind for you, but it is for us. Many homeowners think it’s fine to just replace their old equipment with a new version of the same size. But over the years, things change! Maybe you have renovated or you’ve finished out an attic. And most everyone has more electronics in the home than they did even 10 years ago. That’s why our Comfort Advisors will calculate your home’s heating and cooling load before we provide an estimate on a replacement.

Simply put, a load calculation is how HVAC professionals know what size heating and cooling unit your home needs. There are some rules-of-thumb for this calculation, but those are not a sure way to make sure your HVAC is large enough to keep your family comfortable year round. 

With a comprehensive load calculation, our team determines sources of heat transfer into and out of a building. Load calculations are the only sure way to know that the unit selected to provide you comfort is adequate to handle whatever weird weather comes Austin’s way.

Sources of Heat Transfer in HVAC Loads

First rule of heat transfer: heat flows from hot surfaces to cold ones. Just touch any cool surface and you experience that heat transfer first hand (pun intended). Sources of heat transfer come in many forms.

Envelope HVAC Load

Envelope heat transfer is the heat that flows through the walls, roof, and windows of a building. That means that during the summer, heat flows into your house and in the winter, heat flows out of it. This is why good insulation and high efficiency windows are essential. Insulation decreases the amount of heat that can flow through the walls leading to a smaller required HVAC unit saving you money upfront and lower energy bills saving you money in the long run.

Lighting HVAC Load

Year round, heat from your home’s lights are adding to the heat load from your house. During the colder winter months, that extra heat may be welcome. But come summer, no one wants their home to be any hotter. Since Austin is dominated by its cooling demand, decreasing sources of heat is essential. Switching to LED lighting where possible can help reduce your lighting heat load.

Equipment HVAC Load

Other sources of heat around the house come from televisions, computers, washer and dryer, dishwasher, stove, microwave, coffeemaker, blender, etc. Basically, if it consumes electricity or gas, it will produce heat. Not only do some of your home’s equipment add heat, but they also add moisture to the home (think dishwasher, washing machine, stove…). Your air conditioner is both cooling and dehumidifying your home, so considering moisture-producing appliances is important in a load calculation.

People HVAC Load

Humans (and their pets) also contribute to the heat load of a building. After all, a normal body temperature is 98.6F – and since that’s probably warmer than the temperature inside your house, heat is actively transferring from your body to the air in the surrounding spaces. And not only do humans contribute heat to the home, they also contribute moisture through breathing and evaporation from the skin.

Why You Need an Expert for HVAC Load Calculations

HVAC loads take into account all the variables: 

  • sources of heat in a building
  • the location of the building and the climate
  • the orientation relative to the sun
  • overhangs or other objects that cast shadows on the building
  • the pitch of the roof
  • the color (darker objects absorb more heat) of the shingles
  • the color of the brick/siding
  • the efficiency of the windows
  • if there are blinds or curtains in use and their color
  • the number of people typically in the home and what time of day they are there
  • the number of appliances that are likely to be in use at a given time

… you get the idea. These factors (along with some very fancy HVAC load calculation software) are used to determine the heating and cooling load of your home. 

Here’s the thing: if all the sources of heat are simply added together, the HVAC unit will be terribly oversized. And in the case of a HVAC system, bigger is not better. If we skip some of these items, your HVAC unit will be woefully insufficient. 

It takes an experienced professional to balance all the factors to arrive at the right solution for a home. 

What Makes Austin HVAC Load Calculations Unique

Most of Austin is classified in the 2A Climate Zone, according to ASHRAE. It sits just below the Warm-Humid Red Line and is right next to a different climate zone.

This makes Austin one of the most unique climates to calculate an HVAC load. The climate mimics those in more coastal locations like New Orleans and Orlando while retaining the inland characteristics of Dallas and Fort Worth. Getting the HVAC load calculations just right is a delicate balance.

Contact Austin’s Locally Owned McCullough

McCullough Heating & Air Conditioning is an Austin local with the expertise to perform an intricate HVAC load calculation on your family’s home and repair or replace your HVAC system. We have been around since 1977 and are one of the last remaining locally owned contractors in the area. We look forward to helping keep your family comfortable year round. Call on us for your HVAC system repair and replacement.

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