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.

"Wait a minute, David, I think the only thing changing the air's relative humidity is the temperature rise, not the method used to warm the air. Whether the rise is caused by a warm air furnace, a hydronic furnace, a radiator, sunlight shining into the room or a space heater, if the air temp increases from (say) 50 degrees to 70 degrees and the air volume is otherwise sealed off from outside, the ending relative humidity is going to be the same. " When you heat (or cool) a small quantity of air that is then dispersed into a larger volume the RH changes tend to get exaggerated by the extra heating (and cooling) in the small quantity of air the system operate on compared to the total volume of the space being conditioned. Add to that that the outside RH is usually lower during heating season, heating the air up further lowers the RH, and the higher temp air from the vents is even lower RH until it mixes. You have to keep in mind the difference between RH and absolute moisture content also.

Thanks for the replies! I've got rolls of R-30 fiberglass ready to roll out, just waiting until I figure out what to do about air sealing. The house was designed in 1910 to be comfortable in the summer without A/C, so it has deep eaves and great ventilation. Downstairs is comfortable except on the very worst days. It's only upstairs that has a heat problem in the summer. (If money were no object, sure, I'd pop for cooling right away for both floors.) Good catch on the 5 ton vs. 4 ton unit, that was sloppy of them. http://www.energyvanguard.com/blog-building-science-HERS-BPI/bid/53540/Keep-Your-Elbow-Rigid-A-Lesson-in-Flex-Duct-Installation agrees that at least the places where ducts bend should be metal, and the guy who came out mentioned they would be. I was disappointed to not see that spelled out in the estimate. The past two years of energy use were: 2013 heating degree days: 1501 2013 electric, gas use: 16960 kwh / $5,235.29, 1334 therms / $1,600.88 2014 heating degree days: 1037 2014 electric, gas use: 11609 kwh / $2050.43, 948 therms / $1,259.44 Electricity use declined because a) I started paying attention and turning things off when not in use, b) I replaced about 70 (!) light bulbs with LEDs, and c) I stopped using an electric space heater. My previous solar house had 4.5 hours of full sun on average over the year (i.e. its 8kw array generated 36 kwh/day on average). This one has slightly more shading so I'm guessing it'll get 4 kwh/kw on average, or 32 kwh/day. The price after subsidies is about $18,000, or about $720/year over 25 years. (Net metering is truly a sweet deal.) My goal in partly switching from natural gas to solar electricity is not to save money, but rather to reduce my carbon footprint. Supposedly all new residential houses in California are supposed to be zero net energy by 2020; I wanted to see how practical that was for my historic house. I'm still figuring it out.

New construction should have a heating and cooling load (aka Manual J) calculation. Your builder should not be suggesting sizes. The size needs to be calculated four your house and location. I also suggest identifying equipment built for coastal applications. Wall insulation of R19 is good. You could upgrade the R13 to R15, but only if it is at a reasonable cost. Is the R30 in that attic blown in insulation? If it is, then see how much it would cost to upgrade to R40. Blown in insulation is often not uniformly installed, and will settle over time. I would put more money towards better windows than insulation in my opinion.