a correctly sized unit is best for any house. with foam throw all rule of thumb sizing out and get manual J for sizing of unit s&d for sizing of ducts and design. rule of thumb sizing is 500 sq ft per ton. while I avoid this wag form of sizing, when it comes to foam houses 700+ sq ft per ton is the better wag/rule of thumb. 3 small units would at least be 1.5 tons each (very uncommon) more likely 2 tons each which would be 6 tons. or you could use one unit with different zones. invest in the load, duct sizing & design calculations, they are worth every penny. just make sure that inputs are correct. I recommend foam sheating on exterior of walls, sealing sole plates, conventional insulation in walls and air tight drwyall for wall construction. foam sheathing on exterior of walls will stop air movement (tape all seams, seal any holes) from outside to inside walls, air tight drywall stops interior air movement. this allows the insulation in stud bays to perform. save your foam dollars for creating an unvented attic. we make far too many holes in ceilings that don't get sealed. make sure that the R-value of the inches of foam meet code in your area. faces of rafters should be covered, and foam should not belly in and out. should be fairly smooth between rafters. when we put mechanicals and ducts in the attic unvented is worth the upcharge. best of luck.

Maybe it is this? http://www.hvacpartstore.com/product_details.php?products_id=14 Or perhaps this one: http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=260419514629 This is an interesting article/response to a somewhat similar problem. Though for the life of me I can find no little white button to temporarily save the day: >>>> http://www.askmehelpdesk.com/heating-air-conditioning/hvac-split-unit-heat-works-fine-c-compressor-fan-off-364882.html Old Jun 14, 2009, 12:01 PM #2 Joshdta Ultra Member Joshdta is offline Joshdta's Avatar Join Date: Apr 2009 Location: West Virginia Posts: 1,802 Joshdta See this member's comment history on his/her Profile page. Send a message via AIM to Joshdta sounds like your fan center relay has went bad. pull the little white botton on the fan limit intill you get one and you should have ac the rest of the weekend. >>>>

Quote #1 does not include increasing the size of the ductwork which needs to be done because you are replacing a 2 ton with a 3 or 4 ton (depending on the quote) and a 1.5 ton with a 3 or 3.5 ton. Quote #2 also includes zoning equipment/controls. There is a VERY large discrepancy in size of existing units vs. proposed units(both quotes) Did any of these contractors do a heat loss calculation? You should ask to see a manual J, which will determine the proper size system for the home. I understand the size needs to be increased due to the additions to the home, but what is the proper size? I would not sign any contract without a heat loss calculation first. That is the basics. Post back and we can continue this. Or email me @ woody22478@yahoo.com. I can forward you info and links to help explain better.

Will you post some pictures, please? Even though I haven't seen your basement, I imagine you'll need/want to build a mechanical room around the furnace to separate it from the rest of the space.