Air source heat pumps don't make sense in areas where winter temps frequently fall below 32 degrees. Once you get below freezing, you will be running the auxillary heat a lot. If you decide to go the air source route, you will want a second stage gas fired auxillary heat. I live in the mid-atlantic region in the mountains and selected GT. That choice was coupled with a blown cellulose insulation package. My other choice was a propane heat/electric AC with a foam insulation package. Both options were roughly the same install cost. Both would have provided similar energy efficiency. At the time we selected, propane was 3.75 a gallon and rising (with no end in sight) so we went with GT. The delta cost for the GT system (above the cost for a HE propane heat and electric AC system) was $15,000 for the heat pumps and loop plumbing (including pumps) plus $17,000 for digging the pit. The pit excavation should not have cost as much as it did but it is a 12 ton system and the hole was gigantic (120' x 48' x 6'). We live on a mountain and hit a bunch of boulders that required special equipment to get out. Rocky soil also required a 1' base of stone dust to cover the loop piping. The total cost for the GT HVAC system including all ducting was $50,000 plus the pit excavation cost of 17K. It is a large investment and I would only recommend it if you plan to live in the house a very long time. My heating bills are great - maybe 300 dollars maximum a month during peak winter for an 8500 square foot home (5900 living and the rest a condiitoned but unfinished basement). Make sure that whatever equipment you choose can be maintained by more than 1 very qualified HVAC company who has many years of GT experience. In my area there is only 1 GT company who has over 20 years of experience but I am stuck with them for maintenance. There have been times when I wanted to fire them but cannot. Local competition is a good thing. Also - if you build a tight home make sure that you consider ventilation and dehumidification in the HVAC design. I wound up adding both a whole house dehumidifier and energy recovery vent after we moved in becuase we had basement moisture issues as well as stale air in the winter. Tight homes are great for energy efficiency but can create health issues too. It is easy to deal with as long as you plan for it. Good luck with the build.

The XL15i is Trane's highest efficiency single stage system and a very nice unit overall. In your case, for a new build, your primary focuses should be proper equipment/ductwork sizing and a quality installation. A properly designed system with good ductwork will help ensure year-round comfort. A 2-stage, variable speed system is an upgrade. The 2-stage system will provide better comfort throughout the home with longer runtimes (hence the need for a properly sized system, single or 2-stage) and therefore more dehumidification. I recommend a variable speed indoor air handler regardless of whether you choose the XL15i, XL16i or XL20i heat pumps (or other). While their summer dehumidification benefits may not be as important to you, one of the main advantages is the blower's ability to maintain a constant cfm (airflow) across varying duct conditions. This means that if the ductwork is less than adequately designed, or if your filter gets dirty and total system pressure drop increases, your airflow won't decrease and the motor will work harder (increase rpm) to meet the required airflow (up to a point, typically 1" external static pressure). This protects the equipment and maximizes performance and efficiency. I would first get a full load calculation (Manual J) to determine equipment sizing, followed by proper ductwork sizing (Manual J). Once you know where you stand, you can make a better decision on equipment selection. If you cover the right bases in terms of system design and installation, you should be comfortable regardless of which type of outdoor unit you choose to install. The XL16i Trane typically runs around 75% capacity on low stage, whereas the XL20i typically runs around 50% capacity on low stage for a greater split. If you decide on a 2-stage system I would look strongly at the XL20i (the system I chose my for home). The dual compressors are outstanding for part-load conditions, dehumidification, and more even temperatures throughout the home.

Short cycling occurs when the AC has much more capacity than the heat load of the house. The AC turns on and cools the house very quickly. Quickly could mean 10 - 20 minutes. The short amount of time does not allow the AC to lower the indoor humidity. You feel cool but your are still sweating. It becomes a problem if you live in an area which has high humidity. The 5 ton capacity refers the size of the condenser. The blower in the air handler is adjusted to work with various condenser sizes. Your handler may be able to work with a smaller condenser. I don't have a good feeling about the installation contractor. He has done a poor installation and appears to be avoiding you. What type of warranty does he provide? Make sure you document the problems and stay on top of him.

Tigerdunes, Thanks for the prompt feedback! I'll ask the contractor about the heat strip. (Our winters are very mild so I was more concerned about the A/C.) I agree, the utility company should not dictate size, but what can I do about it? Do you think I should instead go with a 2.5 ton unit and forgo the $400 rebate? The contractor agrees though that a 2 ton unit would be fine. My house is in the shade from post oaks, all the way around all summer long. Perhaps that is why the old system lasted so long(?) and the contractor thinks 2 tons would be OK. I asked him about the lineset (after reading about it on the forum). I forgot to write down whether he was going to flush them or replace them. I'll ask again. Should I ask that he replaces them? For the last decade he has mostly installed Rheem systems and tells me he has had excellent results. Thanks again.