I recently solicited proposals for a geothermal system for my new home. I provided the house plans and other needed information so that both installers could run J calcualtions. There is nothing unique about the home design...ranch with a walk-out lower level, 3 bedrooms and about 3,200 sq.ft Both companies are well established, reputable players in the local HVAC marketplace. One quoted a 3 ton Waterfurnace system and the other a 5 ton Carrier system.

With the sophisticated tools available today and considering how long contractors have been doing these calculations, for the life of me I can't understand how the results can vary so much. I hate to think that I should be hiring a consultant to give me an unbiased and (hopefully) accurate analysis for what would seem to be a simple project.

Any tips on how to evaluate which installer's sizing I should trust, if either one?