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A properly sized residential heating and air conditioning system is one that closely matches the capacity of a home on a typical design day for the city or town that the home is located in.

Oversizing a system will result in the home being cooled faster, but it also means that the system will not run as long. Turning on and off frequently (known as “short-cycling”) not only decreases the expected life span of the equipment, but it also decreases the system’s ability to dehumidify the air since the indoor coil does not remain cold long enough to cause condensation.

Furthermore, a condenser consumes the most power when the compressor is first started (up to 700% more!), with a maximum efficiency being achieved after approximately 10 minutes of run-time. Optimally sized systems will result in longer-run times and lower utility bills.

In order to determine the size of the air conditioner required, a load calculation must first be performed on the home. A load calculation is a complex set of mathematical equations that are used to determine the sensible cooling, latent cooling, and heating BTU values required to deliver maximum comfort and efficiency.

The first step in performing a load calculation is to calculate the net surface area and orientation of all walls, ceilings, floors, and glass that are exposed to unconditioned spaces. This can be done with a traditional tape measure or a laser distance-measuring tool sold at most home improvement stores.

The second step is to inspect and identify the type of building materials used in the construction of the home, including style of windows, skylights, doors, roofing, flooring, and siding. This information is used to obtain the equivalent R-values, u-values, and solar heat gain coefficients (SHGC) needed in the final load calculation.

The final step is to combine the surface areas and building material info to calculate the sensible, latent, and heating loads for all opaque panels. The opaque panel loads are then combined with the duct, infiltration, ventilation, piping, and internal loads (from occupants and appliances) to determine the total load.

This final step can be done by hand using reference tables or using sophisticated software.

There are two primary calculation methods used to determine the HVAC load of a home. The simplest method is to perform a “block load” assessment (also known as “whole house”), which only looks at the opaque panels and glass exposed to the elements. A more complex method known as as “Room-by-Room”, breaks down the load to each room. Room-by-Room calculations are more accurate and also allow the practitioner to determine the cfm requirements for each room.

The most widely accepted method to perform whole-house or room-by-room calculations is to use the ACCA Manual J process. An ACCA approved manual J uses well-documented tables and building codes to determine the heating and cooling requirements for the home.

Many utilities and building inspectors will only accept an ACCA approved Manual J (version 8) for rebates and permit applications. Since performing an ACCA Manual J by hand is very tedious and can take several hours, the preferred method is to use an ACCA approved software solution. Only approved software listed here has gone through ACCA’s rigorous testing process and has been qualified as accurate.

ACCA Manual J Book

Cool Calc revolutionizes the Manual J process by completely automating the surface area measurement and building material gathering processes required to perform a load calculation.

Our proprietary software allows the user to trace a home from Google Maps and then uses complex algorithms to determine the surface area and orientation of all walls, ceilings, floors, and windows.

Next, the software accesses public property tax data to determine the age of the house, and then cross-references that data against the building code for that year and region to determine the most likely construction materials used.

From there the software generates a detailed ACCA approved Manual J Report complete with and Adequate Exposure Diversity (AED) chart that can be used to identify when zoning or variable speed equipment is recommended.

Instantly produce Manual J load calculations from any computer or tablet, anywhere, anytime! Projects are stored in the cloud and can be accessed from any browser.


Cool Calc Manual J Responsive Design
% Tracing Accuracy
mins Time Required
million Successfully modeled homes
% Improved efficiency
Professional Reports

Cool Calc produces 100% ACCA approved Manual J version 8 reports, including all detailed worksheet calculations. These reports are required in many locations to pull permits or qualify for local utility rebates.

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Sample Manual J Report
Our Philosophy

I don't create companies for the sake of creating companies, but to get things done...Any product that needs a manual to work is broken.

Elon Musk Founder of Paypal, Tesla Motors, Solar City, and SpaceX

Cool Calc ACCA Manual J Software
Manual J Load Calc
Free - No Really
Unlimited Users Unlimited Load Calcs Block Load & Room-by-Room Manual J Reports
Cool Calc ACCA Manual S Software
Equipment Selection
Coming Soon
Unlimited Users Operating Cost Manual S Reports Rebates (Limited Markets)
Cool Calc API
API Integration
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Load Calculations Recommended Equipment Operating Costs Building Footprint Info
Why is Cool Calc Manual J free when others charge?

We are not a software company. The Cool Calc suite of tools were developed by HVAC distributors to help facilitate the sale of heating and air conditioning equipment.

Can I use Cool Calc Manual J for new construction?

Yes, a user can skip the tracing step and enter all lengths and building materials manually. Similar to how other Manual J programs on the market.

Can I integrate Cool Calc Manual J into my website?

Contact us to discuss possible API integration opportunities.

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Do you sell homeowner information?

No, we do not share or sell homeowner information. However, we do track user behavior and encourage users to read our full privacy policy.

Can I use your software on Apple and Android devices?

Cool Calc Manual J is web-based and therefore works on all devices including Windows, Mac OS, Android, iPhone, etc.

Do you offer technical support?

Because our software is offered at no charge, there is limited technical support. We will address software bugs, but users should refer to our youtube videos and Knowledge Base for training.

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