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Getting the best new cooling system for your home requires planning along with expert advice and precise load calculations. Your new air conditioner represents a big investment. With your budget and long-term home comfort on the line, making an informed decision is critical. You can’t begin to choose a new system until you know what size you need. 

Load calculation basics

Load calculations are the keys to the system sizing process. Load calculation formulas determine how much air conditioner your home needs to be efficiently and evenly cooled. Here in the Sarasota and Bradenton areas, we rely on our A/C systems for much of the year and have quite a bit of humidity to deal with. These factors make it all the more important to size and choose new equipment wisely.

Using detailed measurements and specific information about your home and your family’s usage patterns, your HVAC contractor will do cooling load calculations to learn what size system will best fit your needs. If you hear any talk about “rules of thumb,” it’s time to find another contractor. Rule-of-thumb estimates are not acceptable for system sizing purposes. There are clear industry standards that your HVAC expert should follow to ensure the accuracy of load calculations. The proper method is set out in Manuals J and D published by the ACCA, or Air Conditioning Contractors of America.

The consequences of mistakes and shortcuts

The outcome of the complex ACCA formula tells your contractor what the cooling capacity of your new equipment must be. Neither a too-large nor too-small A/C system will do. An overly large system will cost more upfront than is necessary. A too-small system will be stressed to its limit trying to cool your home and without success. An incorrectly-sized system can cause multiple problems, including:

  • Noisy operation
  • Energy waste
  • High utility costs
  • Inadequate or uneven cooling
  • Poor humidity control
  • Frequent equipment breakdowns
  • Shortened system life

What about skipping all this load calculation stuff and just getting a new system that’s the same size as your old one? That’s a good way to end up with an oversized air conditioning system. The cooling load your home requires today may be much less than in the past. Over time, it’s likely that insulation and other energy-efficiency improvements have been made to your home. Sealing air leaks and adding energy-efficient windows are also common efficiency upgrades that may have decreased your cooling load.

It’s also possible that load calculations done before installing your existing system were simply done incorrectly years ago. Calculations were certainly much less precise back then and are therefore likely to be inaccurate. Getting a current load calculation is the only way to properly size you new system. 

Load calculation factors

Your cooling loads are unique to your home and family. Just getting an air conditioning system in the same size as a neighbor with a similar house won’t do. Your system’s sizing and load calculations depend upon all these distinct variables:

  • Climate information
  • Elevation
  • House size
  • House layout – Is it compact, spread out, two-story, etc.?
  • Position on the lot, including how much direct sun you get, etc.
  • Airtightness of the home, which affects the cooling load and humidity or moisture retention
  • R-value, or thermal resistance, of insulation materials
  • Number, type and size of windows including U-value (amount of heat transmission)
  • Number of residents and ages
  • Number and types of appliances, lighting, etc. These items give off warmth and increase cooling loads.
  • Amount of ductwork running through unconditioned and uninsulated parts of the home

A well-trained HVAC contractor will gather all this information in a variety of ways, including asking questions, measuring rooms, inspecting ductwork and perhaps performing a blower door test for airtightness.

Integrating with the duct system

Once load calculations are done, your contractor will use the ACCA’s Manual J methods to ensure proper airflow, air circulation and distribution in your home. Some retrofitting or enlarging of ducts may be necessary so that they work with the new system. Air return registers and connecting ducts (called jump ducts) may be added to increase and balance airflow throughout the home. Duct sealing is recommended to minimize energy loss and duct cleaning may be advisable in some cases. 

Need help with load calculations before choosing a new air conditioner for new home construction or as an upgrade? Contact the experts at Aqua Plumbing & Air. Visit our website for valuable home comfort advice, energy efficiency tips and new product information or give us a call. 

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