As part of a large remodel of a 2200 sq.ft house, which involves re-insulating the interiors with green fiber, replacing all ducting and insulating with R6, new energy efficient windows, I am looking to arrive at the ideal configuration for my HVAC. I plan on dividing the single-story house into 3 zones based on occupancy and exposure to sunlight.
Based on the heat-loss calculations done by an energy consultant (see attached pic), it requires 46000 BTUH.
I have a HVAC quote for a 5-ton day&night furnace (92% AFUE, 100k BTU), 2000 cfm capacity to be installed horizontally in the attic, with 12 supply registers, 2 return air ducts, and 2 zone damper system with bypass, using 3 white rogers thermostats. I am not planning in cooling, but the system is going to be AC-ready.
Based on the calculations, for 12 vents @100 cfm each, I would only need a 3-ton unit at 60000 BTUH which would still have a 15-20% safety margin. Both my general contractor and HVAC contractor fee; 60k is too little especially when all vents are open. Also, the contractor does not recommend going with a 2-stage furnace due ECM motor reliability issues.
I think that the unit may be oversized and wanted your opinion on what should be the correct size. The ducting is already in place, and I have asked them to hold off on the furnace.