This paper presents the package for calculation of energy and cost demands for heating, cooling and hot water. The package represents a new kind of approach to developing software, employing user (client) and server (program provider) computers connected by Internet. It is mounted on the owner server and is available to the whole world through the Web browser. The package was developed as a simplified tool for estimating energy use in four types of new and old houses, located in 900 US cities. The computing engine utilizes the database that was compiled by LBL in support of the'Affordable Housing through Energy Conservation'Project with over 10000 DOE-2.1 simulations. The package consists of 69 routines and scripts coded in four languages: HTML, Perl, C, and FORTRAN. The modelling, the programming, and the future perspectives of the new kind of computational tool are presented. The paper discusses further technical limitations, as well as suggestions for further improvements and development. Especially important is the problem of multi-user access, ways for its solution are proposed.