Calculates the thermal transmittance (U-factor), solar heat gain coefficient (SHGC), and visible transmittance (VT) of a window, curtain wall, skylight, or other fenestration product. FENSIZE greatly simplifies and speeds up calculation of overall window performance by combining thermal performance of glazing, spacer and frames and calculating overall performance on the fly.

FENSIZE is capable of configuring fenestration product of arbitrary complexity. FENSIZE has direct interface to WINDOW and SPACER programs for convenient import of frame and glazing performance data. FENSIZE is a powerful tool for company's engineers, sales and marketing people to quickly and effectively calculate thermal and solar-optical performance of their products whether it is done in the field while talking to a customer, or in the office while deciding what is the best option for a project, for which windows or any other fenestration products are being specified. The calculations are compliant with the NFRC 100 and 200 and AAMA 507. Code compliance and Energy Star compliance of individual products as well as overall project are calculated automatically based on the project location. Targeting feature allows users to quickly locate all glazing and spacer configurations for a particular product that will meet code requirement or Energy Star criteria. Standard project and product reports, including handy chart for use in the field are generated and are available for printing or pdf file generation. Screen Shots


fenestration, solar heat gain coefficient, thermal transmittance, visible transmittance, windows, skylights, code compliance


Compliant with NFRC 100, 200 and AAMA 507.

Expertise Required

Moderate level of computer familiarity; Knowledge of heat transfer and fenestration products helpful.


More than 20.


Engineering, sales and marketing professionals working in the area of thermal analysis in fenestration industry, architect/engineer firms, consulting firms and research organizations.


Fenestration product size, framing, glazing, and spacer selection, number of products, product configuration, project details including project address.


U-Factor, SHGC and VT for overall project and individual products at NFRC and custom sizes; Customized product and project reports, List of glazing and spacer information from the database to meet Energy Star or IECC code requirement for fenestration. Standard reports.

Computer Platform

Windows 98/NT/2000/XP with Pentium processor, 128MB of RAM, 50MB of hard disk space.

Programming Language



User friendly window based interface. Quick and effective calculation of overall product performance. Database driven library of window cross-sections, glazing configurations, product lines and product families. Powerful filtering technology. Automatic code and Energy Star compliance. Expandable for future calculations of structural and acoustical performance.


Does not have direct interface to the THERM program.



DesignBuilder Software


18 Tanglewood Road
Amhert, Massachusetts 01002
United States


+1 (413) 256-4647


+1 (413) 256-4823






Company wide enterprise license is $4,500. Check web site for price and ordering information.