Size Matters — Industrial “Shortcomings”

This article was written by Jennifer Manzo, an HVAC technician and the founder of HVA-Chicks Coalition. You can find her on social media as @HVAChicksjennifer. Thanks, Jennifer!

It’s no secret that the HVAC industry is in the throes of an oversizing epidemic. Instead of stating the obvious, I wanted to take a deep dive into the when, why, and how of this country-wide virus.

Let’s start off with a little bit of history: The first residential comfort heating and cooling systems were MASSIVE! AC systems, which first hit the market in 1914, were 7 feet tall, 6 feet wide, and 20 feet long, while the only “furnaces” were coal-fired coal boilers with cast iron radiators heavy enough to fall through a second-story floor! My point is, there was just no such thing as properly sizing these beasts!

Luckily, with knowledge comes technology, and humanity is a race of infinite growth. By the 1960s, central air had become much more available for typical family dwellings, and for decades, the HVAC and engineering communities grappled with new ways to size them. One thing everyone agreed on was that comfort heating and cooling was NOT a one-size-fits-all situation, and by-hand calculations just weren't cutting it.

Finally, in 1986, ACCA and Wrightsoft released the very first version of Manual J Software (Right-J), which allowed the contractor (if they cared enough) to accurately size a home's HVAC system, revolutionizing the relationship between the home and its comfort equipment.

End history rant, back to the task at hand…

In terms of residential HVAC, load calculation as we know it today is just a teeny, tiny baby. We’ve had less than 30 years of properly sizing systems for residential comfort, and within that short time, we have made advancements in the science of it that no one thought possible. So why today, in 2024, are we still swimming in oversized equipment, and what can we do to change that now?

The Why:

There are many reasons that oversized systems are still plaguing the HVAC and building science communities, but I’d like to start off with one of my least favorite reasons: Turn around. 

Don’t get me wrong; there are companies in this country that are repair-driven, honest companies run by great people with honor and integrity. Unfortunately, they are the minority. So many companies see an old system as a cash cow and just can’t wait to replace it as quickly as possible to net a profit worthy of a king. The most effective way to reach that goal is to simply swap it out with a system of equal or lesser value, ton for ton. Laziness and greed are by far the worst catalysts for this illness, in my humble opinion.

Some “whys” are less sinister, such as the following: lack of training. It's as if we, as an industry, spent so much time perfecting the cure that we forgot to tell anyone it existed! I've found that company owners and lead techs have often never heard of Manual J—or load calculation at all, for that matter. Sizing isn’t taught in trade school in any tangible way. Social media and internet advertising are so new, especially when it comes to this trade, that those who have heard of it have no idea what it means or how to gather that information on their own.

Last but not least comes good ol’-fashioned fear. The trades are such a prideful space where developments that threaten to change the fundamental values of the sequence of a job from start to finish in any real way are feared and slandered. We see it all the time in our field, whether it be sizing, measuring airflow, evacuation procedures—I could go on forever listing advancements that truly make our workmanship better but are so hated and bashed that even younger technicians who know better are afraid to use them. Whatever the case, this problem needs a solution, and it’s up to us to change it for the next generation!

So what can we do? 

Well, I’m no expert in how to reweave a tapestry that’s hell-bent on staying ripped, but I do have a few ideas that may just help start that needle on the right path.  

  • We can start by utilizing and appreciating the tools and technology we were given. We live in an era where we can reach a mass of people at the click of a button, and it’s time we use it to our benefit as tradesmen. You just read an article that designs a really great process or equation for sizing? Post it! You, yourself, just designed the perfect system for a customer in need? Post it! Heard about a tool that makes sizing a breeze and a foolproof process to go along with it? That’s right, POST IT!
  • Within our own companies, we can make the promise to seek out proper training, continue to research and learn best practices, and lead our technicians in the best possible ways to promote retention. 
  • Share ideas! It’s hard in some locations to sell load calculation and duct sizing/design to our customers. Sharing the “pros” and quality-of-life fixes that come with properly sized equipment will impact the greater community while educating the public on this service’s necessity. 
  • Last on my list, but certainly not least: head over to! Sign the pledge and register your company to always live up to the #betterhvac promise! Bill Spohn has created a community within a community for applying the best possible standards to help us someday see a better HVAC world! 

There are many social media groups and resources to follow for more information, so don’t be afraid to dive deep! Help each other! One of us may not be able to change the world, but many of us implementing the same practice will at least someday forge a cure for the oversizing epidemic, which will greatly optimize OUR world. 

—Jennifer Manzo



To continue you need to agree to our terms.

The HVAC School site, podcast and daily tech tips
Made possible by Generous support from