HVAC Basics: HVAC Sizing
By Anne Fonda
It’s important to install a matched system that is the right size for your home. Whether you’re investing in HVAC replacement or building a new home, size matters. The Department of Energy (DOE) estimates that 31-93% of HVAC systems in the United States are oversized, while up to 9% are undersized.
The wrong system size could cost you
An improperly sized system can result in decreased comfort and increased energy costs. Who needs that?!
Too big
A system that is too large will cool or heat your house quickly, but you still may not feel comfortable. With an AC unit or heat pump in cooling mode, an oversized unit will satisfy the temperature setting on your thermostat before it can adequately remove sufficient moisture from the air, which is what makes you feel so sticky and uncomfortable in summer.
With an oversized gas furnace or heat pump in heating mode, an oversized unit that short cycles can leave you with hot and cold spots.
The stress of this short cycling (too many starts and stops) will shorten the life of your equipment and increase your heating and air conditioning bills.
Too small
An undersized HVAC system can result in excessive run times as the unit struggles to reach the desired temperature. This can lead to higher energy bills and decreased comfort.
The importance of a load calculation
The only way to know for sure what HVAC system size you need is to have a load calculation performed on your home. Any HVAC company giving you a quote on HVAC replacement should perform this calculation, also called a Manual J calculation.
The load calculation considers your home’s construction (stick-built, brick, stucco), the amount of insulation that you have, window efficiency (for example, single-pane windows vs double-pane), square footage, and your local weather to figure out what size system you need. Square footage alone is not a reliable indicator.
Your existing system has a good chance of being oversized. Even more so if you have upgraded your windows and doors or added insulation in recent years.
“Beware of HVAC companies that don’t perform load calculations and rely either on very basic rules of thumb or just want to replace your system with whatever size you currently have. Those are usually signs that you should find a better company.”
- Mark Woodruff, Senior Product Manager, Air Conditioners
They may also perform a Manual D calculation to help ensure that your ductwork is properly sized for your new system. This can be especially important with heat pump systems.
Once they have performed these calculations, they will recommend the appropriate AC unit or heat pump (in tons) and/or the appropriate paired furnace or air handler.
Proper installation and testing are crucial
Even the most energy-efficient and properly sized HVAC system won’t live up to its potential if it’s not correctly installed. According to the National Institute of Standards and Technology (NIST), improper installation could cause your heating and cooling bills to be 30% more than they should be.
Common installation errors include:
- Oversizing of systems
- Leaky ducts/failure to assess and seal or repair ductwork
- Improper ductwork size
- Improper refrigerant charge
At Trane, we strive to ensure that every system installation is perfect. We provide specific installation and commissioning directions for all of our HVAC equipment. In addition, we developed the Technician App, which uses AI to answer any question an HVAC technician may have during the installation process.
They have instant access to technical documents and verification reports to ensure that everything is done right. This can help ensure your system is installed correctly, giving you the enhanced comfort and increased energy efficiency you’re paying for.
Anne Fonda, Content Writer
A Content Writer with Trane Technologies, Anne Fonda researches topics and writes for Trane® and associated residential HVAC brands. She works in collaboration with Trane Technologies subject matter experts, offering easy-to-understand, informative content on complex topics. Her goal is to help consumers make informed decisions on the products and services they need.
She has written for HVAC and other service provider websites for over 16 years. Before transitioning to web content writing, Anne had a 14-year stint as an award-winning journalist. She graduated cum laude from the University of Missouri-Columbia School of Journalism.
When she’s not working, Anne enjoys playing word games, reading, gardening, spending time with family, and visiting gardens and museums.
Expert review by Mark Woodruff, Senior Product Manager, Air Conditioners
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