The most valueable and comprehensive tool for calculating Passive Houses is the Passive House Planning Package (English Version) developed by the Passivhaus Insitut in Darmstadt, Germany. PHPP

There are some other tools which deal with certain aspects of energy efficient buildings like THERM. With THERM, you can model two-dimensional heat-transfer effects in building components such as windows, walls, foundations, roofs, and doors, and thereby calculate the effects of thermal bridges. THERM is FREE!

WUFI is another excellent tool to calculate hydrothermal performance of multi layer building components. As a result of WUFi calculations you get the combined heat and moisture transfer of any component once you've edited it. A film will be created that shows the performance of this component during the next couple of years. You can thereby foresee the future (if only the future of a wall, roof or slab - but: that's a start!). The North America version is FREE! There is a free R&D version also on the German website WUFI.de.

More to come soon.