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.

I would (at least) go with flushing the lines out, adding a 2 way liquid drier and a suction drier. pull a micron vacume to 400, lock the system in the A/C mode and run it a week, then replace the liquid drier and remove the suction drier. Was the cut in the aluminum coil? A repair kit for that will be permanent. I don't know what you mean by damage to the "condensor"- that is the outdoor coil section. It is possible the system ran while it was raining (heat mode) and if a lot of moisture is suspected, checking the oil in the compressor would help make the desicion on which course to take. Many american standards have a 10 year warranty on the compressor and coil, so doing the above first would be my choice. If the unit needs replacing because of moisture contamination and it's that bad, the best route may be to replace the whole system for the long haul. Green oil and clumpy oil in the compressor or lines will indicate this extreme moisture contamination and installing filters driers won't work.

A heat pump is a central a/c unit that also produces heat in the winter because it can reverse the refrigerant flow. Heat pumps produce cheap heat. They require aux heat when outdoor temps get to 32F or so. You can install a heat pump and still keep your fairly new (only 3 years old) oil furnace as back-up or auxillary heat when needed. Or you can get a new gas furnace to go with the heat pump. Either option is dual-fuel. Keeping the fairly new oil furnace, even though oil is at an all-time high, saves you the upfront cost of the gas furnace. Lots to consider. Good luck.

Tigerdunes, After going crazy about finding an uncased ADP coil, which I can't seem to find, I think the 4TON Rheem cased coil will work with minimum fabrication to get it to work... The Rheem RCF4821STAMCA, is one of the coils Rheem recommends for it but I have one issue with it... The suction side is only 3/4" on the coil, not the 7/8" like on the condenser side.. I guess this would be ok, or they wouldn't have done it, but which side should I put the reduce on? .. I guess I'm asking should I use a 7/8" line to the coil and use the reducer there or should I use a 3/4" line and use the reducer on the heat pump side? I'm kind of shocked that Rheem has setup the HP for 7/8", but 3/4" on the coil side... Rheem RP1442AJ1NA 3 1/2 Ton, 14 SEER, Single-Stage Heat Pump Rheem RCF4821STAMCA 3.5 Ton to 4.0 Ton Cased Multi-Position Evaporator Coil Thanks!