Definitely get a good 2 stage thermostat. It tells the furnace whether to fire on high or low based on the needs of the house. If you need a little heat, you get quiet, gentle low. If you need full capacity, you get it. With a single stage thermostat, high is timed on so you get high even if you don't need it. Doesn't make for the ultimate in comfort.

I think you can. Connect the AC to the Y2 connection and change the swing setting to 0.4 degrees. The second stage AC (Y2) will activate at twice the swing setting which would be 0.8 degrees. If the set point is 75 degrees, then the AC will turn on at 75.8 degrees, and turn off at 74.2 degrees.

What part of Texas? (It's huge--- I'm in Katy, Texas area) Certain areas of Texas are more dry than others. (Less humid) Certainly any area can have bouts of high humidity here. So sometimes this is a more difficult decision. What is important to you? Humidity reduction is achieved when the AC is running. A single stage AC main function is to drop temperature. While you will get some dehumidification from that it's primary function is to drop temperature. Because we live in a hot climate people are more prone to wanting a larger AC unit thinking that will work better, when in fact it will make things worse. -------- 2 stage AC --- It will run upwards of 90% of the time in 1st stage AC mode or more or less dehumidification mode. However, this systems short comings become abundantly clear in the shoulder seasons of our Texas climate. Because 1st stage is approximately 70% of the capacity of the machine -- in the shoulder season that first stage is often times over sized and does little to combat high humidity that certain areas of Texas are prone to. ------- Variable Speed AC --- not all are created equal here. In some cases the system in question may be limited to 5 stages, if paired with legacy controls it may be no better than the 2 stage AC unit above. A true variable speed AC will excel at a number of things - depending on the brand / model chosen could have as many as 75 speeds. In this realm it's more about 'load matching' the structure. Because of the ability to ramp very low gives this kind of AC unprecedented dehumidification. By reducing humidity a mere 5% will make you that much more comfortable than merely dropping temperature alone. It may become 'too cold' than what your current setting makes you think you are comfortable at. So if that happens, you raise the set point on the thermostat. Which will reduce your electric bill on top of the very high efficient Variable Speed AC unit. ---------- Is it for everyone? no. A variable speed AC will cost more up front. Over time it will pay for itself... how fast will depend on a wide variety of factors. If you plan to sell your home soon, it could help you sell the home sooner. But you may not recoup the investment. I recently installed a Variable Speed AC at my home in Katy, Texas. I service the Katy, Texas area.

Has anyone had any experience controlling this unit with an Ecobee 4 Thermostat? Seems when the fan wire (G) is connected the Thermostat seems to reset periodically. Does the Cooling system require the Y2 lead? (Product Man. p.76 makes no reference to anything other than G and Y1 for running the cooling system). Anyhow would be much appreciated. Thanks.