Thanks again for all of your comments and ideas - the give and take of your posts provide us with great insights and ideas which will help us eventually choose the right system for our situation. Hubby found the DYI attachment interesting, but as an overworked aerospace engineer he just doesn't have the heart to tackle a DYI project of this size. (Over 1000 hours of overtime last year, similar amounts for the previous five years, and no end in sight! We joke this is our dream house money.) We did a major remodel of our own master bath four years ago, which included installing electric radiant heat, and it took two years, partially due to hubby's lack of time and partially due to the fact his engineer training meant every thing had to be perfect! Slows everything way down! :-) (Our current plan is to have the shell of the home, plumbing, and wiring done for us, and then we'll tackle as much of the interior work as we can ourselves, over time.) The JAGA site has some beautiful options (I love the scrolled radiator), but had my heart set on in-floor heat since this will be a small home with small rooms and would prefer to keep our wall space open. Just out of curiosity why is clay soil considered not good for geothermal? (I can't remember where I had read clay soils were preferred over dry, sandy soils.) I want to make sure I'm fairly well informed if and when we start to talk to geothermal installers. We may rule that option out entirely if it appears to be a problematic option for our property. Right now I'm really leaning towards the soapstone/masonry fireplace idea, and a combination of electric radiant in-floor heat (in tiled places where we might like heat year round, like the bathrooms) and hydronic radiant heat in rooms with wood flooring. Just need to figure out what will be the best way for us to heat and circulate that water. (If we use the fireplace to partially heat the water will we need a boiler or could a tankless or regular water heater handle the load?)

Quick follow up: We have Natural Gas - we are planning on using a Polaris condensing tank water heater for both the domestic hot water and the heat source for the Hydronic in floor heat. We will use a heat exchanger. Currently we are looking at 1 zone for downstairs with 5 circuits or loops. If we did go with radiant hydronic baseboards upstairs there are 3 walls under windows that would never have furniture on them. Also, I thought it might be possible to run the 3 baseboards upstairs as separate zones with pex, then if we wanted to upgrade to under-floor heat in the future we could do so pretty easily...we are planning for a floating floor upstairs (laminate or engineered)

Thanks for all of the replies. I'll give some more background info. The first layer is the existing subfloor which is real wood, it looks like a 2x4, but the size is actually about 3/4" x 3.5". The subfloor has 1/4" or so gaps between each board. The second layer on top of the subfloor is the existing wood floor, which is real wood. It looks like oak and must be regular cut, but not entirely sure. It has alternating widths of about 3/4" x 3" and 3/4" x 5". It currently has some gaps between most boards about 1/8" or so wide. We plan to install real wood flooring on top of that, but not sure what species yet. Are there certain species that won't work? It sounds like I may have to get a certain type of cut. Do you think it will be okay to install the new wood floor over the existing wood floor, or is the old wood floor likely to buckle underneath if it expands too much?

@Millworkman Thanks. That thought about adding another layer (and maybe getting less heat) did cross my mind. I'm not too concerned about it though as we cook a lot and are generally hot natured people (we keep our heat pretty low in the winter). Plus the kitchen is fairly small (less than 200 square feet and that includes a broom closet and small walk in pantry). I'm sure the proper way to do it would be to rip it all out but I worry about damaging the heating system. Is a little heat better than the risk of no heat? Ha!