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Manual J Load Calculations

RESCheck and Manual J Combine for Maximum Compliance and Savings


When determining the energy efficiency and code adherence of new residential construction, the days of back of the envelope calculations are over. The help couldn't come at a better time, as homes and additions are coming under increasingly more scrutiny for their energy usage.


The International Energy Conservations Code (IECC) is being adopted at the state and local levels. With this adoption comes standardized methods of proving your project meets very nuanced code. That’s where REScheck and Manual J come in.


REScheck vs Manual J. Differences and Similarities


REScheck The REScheck software created by the Department of Energy gives homes a simple pass/no-pass score. By taking in multiple details about things such as windows and insulation, tradeoffs can be made to come up with a score that either fails, meets, or exceed the IECC’s guidelines.


Your building’s REScheck score is a simple statement on how well your home is designed for energy efficiency, taking into account its location, orientation, window coverage, construction and many other factors. REScheck measures the suitability of your building’s insulation envelope against your local climate zone and gives you a pass or fail score.


REscheck does not merely consider mechanical systems you use to heat and cool your home. The rationale is, just because your home is designed well with adequate insulation, triple-paned windows, and proper overhangs doesn’t mean your heating and cooling systems won’t waste energy. HVAC systems need to be right sized to heat the specified space, to cool no more or less than needed.


Manual J steps in to make that happen


Manual J Created by the Air Conditioning Contractors of America (ACCA), “Manual J8 Residential Load Calculation” or “Manual J” for short, is a tool that provides detailed requirements for producing residential load calculations for single family residential homes. Those load calculations are then used to get the correct size heating and cooling equipment into the home.


Window measurements, insulation, roof design, local climate, and many more factors are used to determine the HVAC equipment needed to condition interior spaces without wasting energy.


When You Need Each


REScheck is quickly becoming a default standard to meet energy code requirements across the country. Most states and local authorities are requiring proof of compliance. The fact that REScheck has the stamp of approval from the federal government has made it ubiquitous. As with all things related to code, it’s worthwhile to check with your county building office to make sure a REScheck score will suffice. Here is a list of states currently allowing the use of REScheck to show compliance with energy codes. (


Since the advent of the Energy Star Version 3 Residential Program at the federal level, states are adopting the voluntary guidelines and turning them into requirements. It’s only a matter of time before all 50 states demand IECC and Energy Star compliance.


Manual J is being widely adopted by local building authorities as the gold standard in meeting Energy Star compliance. With Version 3, HVAC companies will have to raise the level of their game significantly. It’s no longer enough to install efficient appliances. They now must help choose the correct sized systems for the home and environment. Manual J is the tool that can help them. 


To see which states are requiring Energy Star ratings, click here. (


More Than Just Code Compliance


Even if you are not undertaking new construction, and only replacing your outdated HVAC system, you'll still benefit from a Manual J load calculation. Older HVAC systems (10 years or older) are often unreliable and are less efficient than newer systems. If any of the following are occurring, a Manual J calculation could be needed to determine if it’s time to replace an outdated or poorly designed HVAC system:


  • Clients are complaining of discomfort during hot weather 

  • Clients are complaining of the inability to control indoor  

  • The equipment is short cycling  

  • Capacitors and compressors are experiencing repeated failures


It is the first step in diagnosing potential issues in comfort and system performance. National surveys have determined that well over half of all HVAC contractors do not size heating and cooling systems correctly.

A newer HVAC system can vastly improve efficiency, comfort, and lower maintenance and operating costs over the life of the new system.


HVAC companies tend to install overly large systems, figuring that “bigger is better.” But oversized systems ca create more problems than they solve.  Issues include:


  • Higher installation costs

  • Inefficient operation leading to higher utility bills

  • Faster breakdown and increasing maintenance costs

  • Humidity buildup leading to mold and clammy air


REScheck, Manual J, or Both


The future of code compliance is putting a heavier burden on the homeowner, architect, and builder to prove that minimum standards are being met. The complexity and quantity of regulations make it difficult to know where to start. Fortunately, REScheck and Manual J options are becoming industry and government standards.


Call us today to see if which code compliance tool best fits your needs.

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