Cricket,
What size house are you building?
I have a 1900sf house and we have a 2ton heat pump unit (lennox)(2 stage) and we have a fully encapsulated house with spray foam on the rafters, in the walls, and the underside (house is on stilts).
Our house gets FRIDGID, as the wife likes it at 68 inside..
4 Ton is way to much unless your house is over 3500sf.. You need to make sure the proper Manual J calculation is done.. Also, there are some other things to consider when doing spray foam... 1 penetration for plumbing vents, sealed eaves, no vents etc etc
Thomas
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