Howdy folks, found this site from a solar energy site. After reading some of the posts, you folks seem to know your water boiler systems, so I'd like to ask for some design advice. I'm planning to build a new house sometime in the next 2 years or so, and intend to use hot water for all my heating needs. I'm in Oklahoma, so we don't see the super cold days the folks in the north do, and our cold snaps normally last less than a week before we see a couple days break with sunny days in the 60 degree range. The coldest I've seen here ever is about 6 degrees. The house itself will be a dry block construction with blocks exposed to the inside and heavily insulated on the outside, with approximately 2000 sq ft of living space. More likely it'll be smaller, but I'm using this for a planning number for now. Insulation will wrap the entire house, including under the slab. The idea will be to bring the house to a specific temp, then use the thermal mass of the walls to help maintain that temp year round. Heating and cooling will be done with an central heat and air system that uses hot water to provide the heat. Saw it on a This Old House episode where they retrofitted a 3 story house built in the 1900s with an HVAC unit using hot water. The HVAC will also incorporate a fresh air exchange and an active humidity control. I'm willing to fork over a little extra for this seeing as I'll be building the house itself with my own hands for a HUGE labor savings. The only part I'll have to hire out is the slab, plumbing, wiring, and cabinetry. What I'd like to do for providing hot water is build a solar collector shed that will heat a large, heavily insulated storage tank, and here's where I start to become unsure about my design. My current plan is to build a 2000 - 3000 gallon tank, and fill it with a water/antifreeze mix. This water will be pumped through the solar collectors for heating, and will be pumped directly into the house for heat use. There will just be the one loop from the tank to the house. Inside the house the loop will split into two. One loop will put hot water into a heat exchange loop to heat the potable water, the other loop will provide hot water to the HVAC system. I also want to have an emergency backup since the sun can go away for days at a time, and I intend on a third loop that only runs through a wood fired boiler for this. All the pumps in the system will be operated by a solar power system with generator backup, off the main house grid. What I need to clear up is: - Would it be better to pump the antifreeze solution (fluid) directly from the tank to the solar collectors or would it be better to use a loop to keep the collector fluid separate from the storage fluid? I'm pretty good about keeping track of antifreeze conditions and will be using a non-toxic antifreeze (want something I can just drain on the ground if necessary, not that I would unless it was an emergency) with anti-corrosion protection. - How large of a storage tank do I need? Once I get the water up to temp, I'd like for it to be able to go 2-3 days in the winter before needing to fire up the boiler, if necessary. I also want to be able to maintain a constant 79 degrees in the winter, and be able to run 6 people through the shower every morning before the sun comes up. This is a worst case scenario, as the house will be occupied by 2 people and we tend to keep the house cooler than this. I've already gleaned some pretty good ideas from this site, for example I now plan to put the storage tank against the house next to the garage, and have the tank room vent into the garage in the winter to use the radiated heat to keep the cars warmer than they might be otherwise. Be more comfy on the morning drive to work, less warmup time for better fuel efficiency, ect. I'm also planning to use a few more inches of insulation around the tank than I was, and am going to reexamine the flat plate collectors instead of the evacuated tube collectors. I was going to go all evac tubes since they actually collect light instead of heat so can heat water with no direct sunlight, but now might either go for a mix or when I install the evacs build them inside of a flat plate style case along with a straight copper pipe to heat the case and help melt snow quickly. I figure a single pane of glass with no UV blocking qualities would heat up quickly once the water from the tank started pumping through, and I'd be able to get right on collecting sunshine earlier without having to sweep snow every morning. OK, be brutal with this plan, I'd much rather get a little grief now before I've set the first block than find out when the place is done that it won't cut the mustard. Any other ideas for this are welcome too, other than in-floor radiant heat. I just don't like the idea of running water through the floor inside of a plastic tube, because if the line is broken for whatever reason the floor has to come out and there's an instant multi-thousand dollar bill. Thanks.