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RED Calc Free Online Tools

Residential Energy Dynamics (RED) offers innovative software solutions for energy professionals through free building science calculation tools called RED Calc.

RED’s mission is to provide the best software tools and information available so that residential energy-efficiency professionals can maximize the effectiveness of their work. RED wants to make buildings healthier and less costly places to live, while helping protect the environment outside and inside of dwellings. 

What are RED Calc Free Tools?

RED Calc are free online tools for building diagnostics that cover topics on ventilation, moisture, air leakage, insulation, and domestic hot water systems.

Here is a listing of the RED Calc Free Tools that are currently available:

Ventilation Tools

This bundle of tools includes all you need for your ventilation design and analysis. The Department of Energy (DOE), the Building Performance Institute (BPI), and RESNET are requiring design and analysis of residential ventilation systems. These ventilation tools will help you get your work done fast, accurately, and with professionalism.

ASHRAE 62.2-2013
ASHRAE 62.2-2010
Electrical Usage
Pitot Tube Airflow
Box Airflow

Moisture Tools

This bundle of tools includes all you need for analyzing moisture issues in buildings, including dew point temperatures, vapor pressure, humidity ratios, and much more.

Moisture Metrics
Wood Moisture

Air Leakage Tools

This bundle includes tools for determining natural air leakage (infiltration) rates and the resulting sensible heat loss or gain. The dependency on building leakage, building height, flues, leakage distribution, sheltering, terrain, and weather conditions can be explored. The calculations use the same, powerful infiltration model, AIM-2, that was used to calculate the weather and shielding factors for the ASHRAE 62.2-2013 ventilation standard. These tools are a part of our ongoing work to bring the wealth of knowledge and capabilities that exists in our national labs to our users.

Air Leakage Metrics
Design Infiltration
Advanced Infiltration

Insulation Tools

This bundle includes tools for determining R-value, the number of bags of insulation, and insulation density. These tools will help you get your estimating and analysis done fast and accurately.

Dense Pack
Loose Fill
Heat Transfer
Infrared R-Value
Parallel Path R-Value

Domestic Hot Water Tools

These tools help you analyze hot water use, allow you to compare hot water systems, and guide you through the procedure of determining flow rate from a fixture.

Systems Comparison
Average Daily Usage
First Hour Rating
Instantaneous Sizing
Volume per Use
Water Flow Rate

Weather Data Tools

These tools report and analyze weather data. Often it is useful to use these tools with other RED Calc tools. For example, it is useful to use the Weather Station Data (TMY) tool to find your closest weather station before using the ASHRAE 62.2-2013 Ventilation tool.

Weather Station Data

Who Uses RED Calc Free Tools?

  1. Home performance analysts
  2. DOE weatherization energy auditors and quality-control inspectors
  3. Energy auditors
  4. HERS raters
  5. Design professionals
  6. HVAC analysts and installers
  7. Building inspectors
  8. Architects
  9. Engineers
  10. Building science researchers

Navigating RED Calc Free Tools

Learn how to navigate among the Residential Energy Dynamics (RED) free building diagnostics calculation tools and their companion User Guides.

To learn more about and to use the RED Calc Free Online Tools, visit their website at


  Energy Efficiency
  Renewable Energy


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