I set up a spreadsheet much like the sunnyjohn calculator, and ran some numbers for my climate, Edmonton, Alberta. I came to the conclusion that in this climate I needed to double the depth of the layers. E.g. 6-8 foot deep. This starts getting awkward, as they don't rent ditchwitches that do a narrow trench that deep. Ballpark calcs: The worst case is a 'frozen fog' weather cycle. Cloudy days, so minimum heating, coupled with temps of -20C (-30F). Given an R2 greenhouse (typical for 2 layers of poly with an inflation fan, then every square foot of surface has a 90 degree temperature differential across it. Because of the sides of a hoop house, I am going to make the approximation that there are 2 square feet of outer envelope for each square foot of ground. This is pessimistic. It's somewhere between 1.57 (pi/2) for a very long green house and 2. So each square foot of greenhouse floor has to store heat for 2 square feet of R2. With a 90 degree F temperature differential, it takes 45 BTU/hr x 2 square feet = 90 BTU per hour. Again, being pessimistic 5 day operation = 120 hours. So 90* 120 = 10,800 BTU The heat capacity of dirt is about 1/3 that of water on a volume basis. Call it 20 BTU/cuft/F If we are willing to let the greenhouse temp drop 20 degrees, then each cubic foot can store 400 BTU. That would mean 25 cubic feet of dirt per square feet of floor. Ouch! If we are willing to go 2 days, it's easier. 2/5 as much heat = 10 feet. Saving grace: If we are are going for long term heat storage, the tubes can be further apart. Sunny John estimated on the basis of storing 1 days heat, so his pipes were a foot apart. If you want 5 days heat, you can put them further apart. It starts to make sense to drill vertical holes instead. E.g. Drill a 1 foot diameter hole 20 feet deep every 5 feet. Each one gets a loop of pipe going down and up. This does make for a less efficient heat exchanger, as the air going down will transfer some heat to the air coming. Worst case, the air out will be the average of the ground temperature and the air going in. E.g. With 50 degree ground, and 80 degree air, you will get 65 degree air coming out of the ground. This ignores the latent heat factor. You might be able to get better efficiency with concentric pipes, but this makes the plumbing complicated. A cheaper way to do this may be to dig a pit 3 feet deep over the entire interior space. Put barrels in the space, filled with water, with a bit of space between them. Put in a lightly insulated floor. (R4 should do.) Barrels are about 22 inches. Put in a 2 inch space, and you have 1 barrel for 4 square feet. A barrel has 480 lbs of water. A 20 degree temperature variation is 10,000 BTU, plus whatever heat goes into the ground below the barrels. But that's for 4 square feet, so it's 2500 BTU/sqft Would do for a day and a bit of our worst case. Lets look at a different solution: Natural gas. Winter gas prices are about $6/GJ and a GJ is about a million BTU. So our one day worst case is 2000 BTU/sqft. That .002 GJ will cost us about a cent a day. How much digging are you prepared to do to save 3 bucks a year? That's worst case too. It's not always that cold. Actual greenhouse operations are worse than this. When plants are actively doing their photosynthesis thing, they will use up the CO2 in a greenhouse in about 10 minutes. So you need an air change, or another source of CO2 every 10 minutes. Air has about the same specific heat as water on a weight basis. A cubic yard of air is about 2 lbs. Your square foot of ground with a 15 foot ceiling has about a pound of air to heat. Heating from -30 to +60 takes another 90 BTU. Every 10 minutes. So the air heating load is 6 times the building heating load. However, no sunlight, no photosynthesis. And when there is sun, it's providing even in winter about 600 W/m2 which is 200 BTU/sqft/hr One greenhouse operator near here heats water in the day, pipes the CO2 into the green house to help the plants, does an air exchange every few minutes on top of that, and uses the stored hot water at night. They claim energy costs of $3.50/square foot. Conclusion: It's a cool idea. If you are off grid, it's a great idea, especially if you have sunny winters. Is it practical as a 'best solution' at current energy prices for a cold climate? I don't think so.

Lucent bought out the old Biltbest factory in Ste. Genevieve, MO. Biltbest was in business for 60 years as a wood window manufacturer, but they were acquired by a company just before the economic downturn and didn't survive it. While I don't know about the quality of Lucent windows I do know that many of the former Biltbest team are employees and that they are in the old Biltbest factory. Hope that helps. Here is a link that might be useful: Article about Lucent

Sounds expensive. I'm in the middle of pricing for a San Francisco Victorian and looking at Marvin wood double hung (or wood with exterior Al cladding) and for 36x77, low-E 366, they are retailing at $730 a window (and qualify in the set-in, but not the sash-pack). Even with San Francisco's obscene labor rates of $400-500 a window, you're still only looking at $1250 a window or so. I don't know how pricing on casements compare to double hung, but sounds like Pella is far too expensive. They are about the only window that doesn't look completely out of place in a Victorian that I know of and the only one I've seen that doesn't shout "fake" from 100' away (I'd love to hear of others). I can also get custom sashes made here and installed for less than the cost of "factory" windows, even with the 30% tax rebate on the windows themselves. Something to consider if your climate isn't energy-intensive.

Not yet, but I did just join today after lurking for a while! I'm hoping zipdee will tell me where in NC she lives? (Sorry if that's a bad thing to ask; I've tried to learn all the rules before posting.) I want to hire her to be my interior designer! Anyone else in the Triangle area in NC? lisa_a, we spent last Christmas in Sherwood OR. (LONG but great story, if there's a place to tell it elsewhere on here.) In a nutshell, our baby had been born in Hillsboro the day before we left (Dec. 21... Happy Birthday, Baby!), so we went to get her and stayed in a house on the highest point in Sherwood. Took us 36 hours to get to the hospital because of the awful weather. Wonderful experience though! I'd love to go back in the summer. Thanks for being so willing to share all your kitchen experiences! We are getting ready to pull the trigger on a reno right after Christmas. I'm nervous!