pushindirt I think he meant a separate gas heater just for the GH. For that matter a small electric heater may also work. Moving heat from a woodstove 2 rooms away would take some duct-work and fan to move it there. The fan can be run on a thermostat. Kkontrols.com has good prices in these thermostats.

Laura- I'm hoping to put a greenhouse on my remodel, too. It's been called an 'orangery' on another post, but it's just a fancy greenhouse. There will be one door from the mudroom and one window, from the pantry. This part of the home is the only place we're adding on...so we could use brick or some other material for the greenhouse wall, if that would help. I think sinking the greenhouse will be even more trouble, when the snow melts. You'd probably have to do french drains and other things to try to take the water around the greenhouse. I think your temperature could be more easily regulated (and more affordable) with some heavy shades for night and maybe even a little heat from the house...or a baseboard heat. I believe plants will still be fine at about 55 degrees (maybe even a little cooler). Good luck with your research and please let us know what you find. I'm still getting ideas and working out a few details, too :) Oh, and my greenhouse is just for plants...not a breakfast room or family room, which is often a concern on the forums.

It's been a awhile since I have worked with vinyl siding, but I would be concerned with the max temps your GH will reach in the summer warping the siding. Even if you ventilate it will likely hit upper 90's to 100F air temps, and depending on the color of the siding it could get quite a bit hotter on the siding itself. It might be safest to remove the vinyl siding from inside the GH when you add the attachment struct for the GH. Also textured vinyl lap siding tends to have lots of grooves, hollows, and spots to collect mold, etc, so you might want a better surface in there regardless of the heat issue, and a white one to reflect maximum light back to the plants. I would think that if you are putting a long 2x4 (or whatever) up along the upper attachment point with connections into each stud along its length, that would be adequate. Of course it will depend upon the snow and wind loads you get. You could check with a builder or civil engineer. If you could put a room on the size of your GH and the wall would hold, then it should be fine with the GH. Although you will likely need to use similar attachments for the GH as one would use for a room extension (remove siding under the attachment members, nail/screw into existing garage framing, adding it inside if needed). One concern may be frost heaving. If your gh "foundation" will be nothing more than some timbers laying on the ground, then it is likely that it will move as the ground freezes and thaws over the winter. That will cause added stress to GH where it attaches to the not moving garage. Something to consider. As far as insulation goes, if you don't insulate the garage wall to the GH, then you will loose/gain more heat thru it. If you were planning on using the garage as a heat sink that might be OK (although you'd probably need the rest of the garage insulated to hold that heat). But in general it is probably easier to insulate the GH-garage wall and put in fans/vents if you decide to use the garage as a heat sink/store. If you know how cold the garage gets at night and what the GH temp and outside temp is, you can do a quick calculation of the heat losses thru each surface. That would give you guideline as to whether insulating that wall would be worth it or not. Depending upon the numbers, you might find that insulation there gets you some additional above freezing time at each end of the season.

I have no experience but spent some time researching and designing ideas. I think it would be pretty easy to heat in the winter using solar hot water. Maybe $200-400 in materials and no running cost. A tank or pond inside holds the water mass which heats up in the day and releases heat at night. Plus you can grow fish in the water. I've seen these used in the far north. We only have to get the temp up a little in winter so I think these are great. You can have plant tables and walkways over the top of the pond so there's no loss of floor space. City water goes into the pond and you water the plants from the pond. This helps keep the pond clean, fish healthy and the water is better for the plants. Some of the nurseries here use swamp coolers. They're they're pretty simple. One end wall is the media the water flows over and air is pulled thru with a big fan. I think they build it themselves. Work good. I think maybe more for raising humidity than lowering temp although the temp was lower when I've been in them.