I could use some insight on heat sources for my radiant setup. I originally intended to go with DX Geo, but the cost at this point in my build would blow my budget. I'm also skeptical that my heating load requirements would require such a setup. House is a single story 1008 square foot Ranch with ICF foundation (another 1008 square feet) (R30), SIPs with EIFs walls (R40) and raised heel roof trusses with (R70) foam/ cellulose mix. My limited knowledge of passive solar design included the following. House is oriented close to true south with triple paned Thermotech fiberglass windows optimized for passive solar gain on the south side with about 8% coverage. The main floor is 1/2 Soapstone tile with wonder board and thin set while the basement is acid stained concrete. The radiant is set up with 7/8 PEX tubbing 16" on center in the slab and the staple up with aluminum plates. Two zones currently setup as an open setup (I know, I know) Know I've got to decided on if I want to add the heat exchanger and change it to a closed system and what I'll be using for my heat source. If I remember correctly the BTU load calculations are about 18,000 per zone. I only have two practical choices LPG or electric. I live in an area with some of the highest electric rates in the nation, so that is a consideration. But I also would rather not put any more holes through my standing seam roof, SIP/EIF walls or the foundation. I've looked at mod/cons, tank and tankless until I'm blue in the face and I still haven't the foggiest idea on which way to go. Could I get away with a large electric tank heater like this one? http://www.lowes.com/lowes/lkn?action=productDetail&productId=161857-135-EE3Z80HD055V

GOT wood? wood gasification furnaces, renewable energy source, clean burning

A 36K of heat load (2 x 18K zones) for that type of construction would be and extremely high estimate in my neighborhood (central MA, ~6800HDD base 65F heating season.) What is your design day temp, and what did you use for the calc? (Or maybe you live in Yukon?)

Even if it were correct, you are right that Geo would likely be far outside the payback equation, and your installation method is likely not able to function at appropriate geothermal temperatures anyway, assuming you did the joist at 16"o.c. like the slab.

Your heatload may be at little as half of what you estimate, but depending on how effective your passive solar is, you would likely want propane, either a tank heater if you don't need much heat on a yearly basis... IF water temps are adequate in all areas with your installation method, which I would say probably is but you're using a fairly weak setup so I am not sure... or a small mod/con boiler such as a T50 Munchkin or a Triangle Tube Prestige Solo 60. If your electric rates are high, even if you don't need much heat, you probably don't want to use it for heating.

In short: depends on where you are, how much you expect to get from solar, and what your final water temperature requirements are. One more hole shouldn't make this decision either way; you can seal a hole.

Short answer is no. There's plenty of downed trees that would work great for something like this. However they are not on my property, they are on the in-laws. Think Hatfield-McCoy. I wouldn't want to purchase, store and deal with the mess of wood.

House is constructed in Upstate New York. The BTU estimates came from the online radiant company I used. I gave them the building envelope information and they used that calculate the requirements. I think the Geo guy calculated something like 12k a zone. I'll have to see if I can find the info I had and get back to you.

Rob, I was hoping you would respond. This whole experience is new to me. I hope that the tight shell along with the passive solar will cover most of the heating needs. However since I've never built a passive solar house, I'd much rather have a system that puts out a little too much instead of not enough.

I was told the recommended temperature was between 120-135 degrees. My well water will be pretty cold in the winter.

The electric rates are high in this area, but the rest of my house will also be very energy efficient including LED/CFL lighting and the most energy efficient rated appliances. The rest of the house is all electric, including the cooktop and oven.

This means that I'd have propane only for heat and hot water. Some time in the next few years I plan on adding a 5-10KW solar PV array and possibly solar hot water.

One of the local plumbers I consulted suggest a gas tankless, but I'm concerned with the hard water reducing the efficiency. Plus I'm not sold on tankless heaters.

Am I right in thinking that a tankless would not be the best for this job? As far as a standard off the shelf water heater. There's the Polaris, AO Smith Vertex, a standard off the shelf gas heater and possibly the 80 gallon electric whirlpool I posted earlier. The Whirlpool is 5.500 watt. That's about 19,000 BTU. Do you think that could do the job without running constantly?

As far as the small mod/cons you pointed out, which one would you recommend? Also what to do about the domestic hot water? Small fired indirect (30) gallon or so?

Please keep in mind I'm also on a budget.

My other heat loss analysis was 25k Btu and even that still sounds a little on the high side to me.

I am not aware of any internet copmanies using 7/8" pipe that actually calculate heat load. I am aware of more than one that do "energy calculations" that involve "energy factors" and are basically a "structured guess", not a calculation. You need a real load calculation.

12,000 per zone sounds an awful lot like a ballpark as well. Your basement load is probably not the same as your first floor load. Maybe... I've seen it before... but it's not common. That said, 10 to 12 BTUs/sq ft is efficient, though not amazingly so.

without knowing your real load, preferably along with your expected passive solar contribution on a yearly basis, it's hard to answer this. If I had to guess blind I would go Solo 60 with an indirect for hot water, though the indirect sizing would have to take into account the smaller burner it was working with. That would not be the cheapest, but I believe the solo 60, with a bronze or stainless system pump, would withstand the oxygen in your system since you're probably not using barrier pipe.

If electric makes any sense for you, on a fuel cost basis, not assuming PV will do your heat... then small electric on demands with a heat exchanger can make good sense just be aware of the draw (you can break 100 amps pretty easy).

How about a pellet stove boiler? I believe they're available and pellet energy will probably be less than electricity.

ModCon high efficiency boiler and indirect fired water heater sized to the load by an experienced designer (which excludes most online venders.