In six to twelve months we'll be adding 500 square feet to our home but my 12 year old 4 ton XL14 Trane Heat Pump was just diagnosed with a leak in the evaporator and a bad variable fan controller. Odd they both went out at once but we were going to remove the 4 ton that's support 1,900 sf and put in a 5 ton unit and convert to gas during the expansion to 2,400 anyway. My question is around the interim time while I'm still at 1,900 sf. I've been told by one contractor the 5 ton XL20i Trane is too large and will cause mold issues and that I have to sign a waiver about possible mold. I have another contractor saying if I go with a Lennox XC21 that I should be fine (because it's a two stage) while we prepare for the expansion. I know both are two stage but why the differing opinion? I'm in Dallas TX if that climate makes any difference.