GROUND UP TO U: (vs. in-ground) Since 1980: about 7,ooo btuh [separately in a ditch] in damp clay as described below can be extracted from 52-deg earth with every 500 ft of 3/4" Poly-Black tubing and circulated easily [up to 5-3/4" pipe runs with a header to 1.1/4"] hdpe pipe 160 psi thicker sdr-9 www.geothermal-pipe.com www.flowcenterproducts.com on one 1) 1/6 hp (B&G pl 33) if the loop is ~ 35 degrees (chilled) by/on www.hydro-temp.com (ARKANSAS) a heat-pump, having ~ 18% methanol antifreeze by volume ~20% glycol, for usable(net) output per the following: if at a depth of ~6-to-7ft, lower piping runs (back-in-bottom-of-ditch-tightly-packed) x ditch length of 245 ft, up to 3-pipes in 2ft ditch and on the bottom of the ditch, up to 5 piping runs (2 ditches) on 1) pump 1/6hp damp clay soil, and returns back in same ditch as follows: RETURNS are on top at a depth of ~5ft (4.1/2 settles to 5ft in backfilling~) like a 'hair-pin over under design on side view... each ditch may support a "2-TON" Hydro-Temp, which is equal to others' 2.2/2-"ton" rated units that use higher than normal blower speeds, or water:water with over pumping to just get "high" ratings... LOOK at COMPRESSOR labels: they should have a 19,000-24,000 btuh compressor IF VERY WET, 52-DEG SUPPORTS A 30,OOO COMPRESSOR IN THAT DESCRIBED DITCH FOR RATINGS @ "3.0-TONS" YOU GET ONLY ~85% OF ANY COMPRESSOR ON ~34-DEG LOOPS... Directly GeoLoops : ECL's (Earth Coupled Loops) are generally producing only ~ 4,200 btuh at 40-degrees/avg and high volumes of ~ 3.1/2 gpm per 3/4"pipe and no antifreeze keeping things obove 38-degrees (ie @ 37 entering ECL, from loads applied/ with or without a heat pump... )

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.

Hello solargary, Thanks for that counterpoint. The reason why I'm not 100% sure about solar water heating to heat the water used for a radiant heat system is because of the weather. (I want to like solar water heating but I'm not sure...) Generally speaking, the west side of San Francisco needs heat the most in Nov, Dec, Jan, and Feb. During these months, I see the least amount of sunshine (as verified by the PVWatts calculator). Often times, we see very little direct sunshine during these months as it is raining. During these conditions, I don't think I'd be generating any heat with solar heat collectors (I'm guessing - I have no direct experience with solar heat collectors - I'd love to be proven wrong). Consequently, I might be in a position where I need hot solar water to use in my heating system the most during the time that I don't have it. However, given that there is *light*, I could certainly be making electricity, hence my query on a electric tankless water heaters. While the PVwatts link shows that a DC 5KW PV system generates 420 KWh AC electricity a month in mid winter, it also shows the over the course of the year, it could generate about 600 KWh per month. The beauty of a grid-tie system is then (I'm assuming) is that the utility company calculates your balance on a yearly basis - so the energy deficit that I'm have in the winter (since lights, computers, etc would eat up most if not all of that 420 KWh) would be balanced by an energy surplus in the warmer months (where I could be generating around 710 KWh per month) The issue with gas tankless water heat for the radiant heat for me is venting. I need to figure out a way to vent the water heater - I live in a rowhouse so its not easy to find a hole on the exterior surface. I'd probably have to vent the thing on the roof .... which would make it difficult for me to place the unit 2 or 3 stories below the roof. An issue with solar water heat for the radiant heat system for me is finding the room to store all that heat - I would be extremely hard pressed to find space for a 200 gallon tank or even a 100 gallon tank for that matter. Actually, I *could* find the space - but that would be 3 stories down from the roof - which would then make it difficult to vent a gas fired heater.... So many constraints.... Thanks

I have no idea whether the photovoltaic panels could produce enough energy enough of the time to offset the small cost disadvantage of electricity, but your numbers are right. Rather than using an electric resistance water heater (the standard type) have you considered a heat pump water heater? This would be two to three times as efficient as a standard water heater, so you could give yourself a huge cost advantage over gas. Then you could use the power from the PV panels for something else. I am not sure about the heat recovery rates of this type of water heater, so in many places I don't know how well it would work for space heating, but since it's not too cold in San Francisco, it might be worth considering. Here is a link that might be useful: Heat Pump Water Heaters