Your real problem is that unless you are planning to insulate the living H out of it, you are looking to heat what is in essence, just a very large tent. There are any number of options and it can be done, but beyond the cost of the heater itself, you should also consider the cost of the fuel or electrical power to operate it. If you want to operate a heated GH in winter, even in Z-6; to maintain a steady 50 deg. interior temp. 24/7, you might want to reconsider either the size and/or type of GH you plan to erect, or expect to spend a whole bunch of money to run the heater.

nathanhurst I'm not going to get into an electronics lesson with you, but you (with all due respect) are complete wrong on how amperage, wattage and voltage work. Real quick. Using your idea of connecting the panels to get 120V is not correct. Two problems with your scenario 1) the heaters we are talking about are 120V AC. Your method only provided DC current. While the elements can handle DC, the fan cannot. There may also be other electronics that are running off of a power supply thatÂs designed for AC. You need an inverter to change DC to AC. While there does exist inverters that will convert, say, 120DC to 120AC, this is not widely used in the Americas. 2) Parallel or SeriesÂ. That is the question. What you first need to understand is that in order to increase AMPERAGE, you need to connect the panels in PARALLEL. To make things simple, letÂs say that a single panel is 15 watts (thatÂs approx. 1 amp at 12V)  (which each panel is in the kit aboveÂ. 3 panels make 45 watts, which is approx. 3 amps at 12Volts). And also, letÂs use small numbers just to get the point across here. 1 panel producing 12V = 15 watts = 1 amp To product 10 amps at 12V, you connect 10 panels together in a parallel manner (positive to positive, negative to negative). Now, if you take those 10 panels and connect them in series (positive from 1 panel to negative on the other panel and repeat for each panel you end up with 1 positive and 1 negative when done). That would make 120V DC, BUT, it would be 120V at 1 amp only. To be clear: - Connecting panels in parallel increases AMPERAGE (watts) but the VOLTAGE stays the same. - Connecting panels in series increases VOLTAGE but the AMPS (watts) stay the same. So using your idea, in order to product 1,500 watts (which is approx. 12.5AMPS) you would need: 10 panels in series = 120V at 1 AMP (letÂs call this 1 set). To make the MINIMUM 12.5 amps (we are not including startup amperage or other necessary things to take into account when configuring a system)Â. you need to connect 13 "sets" (rounded off) of the above connected in parallel. ThatÂs 130 panels (individual panels). AND THEN, that would ONLY product the required amperage ONLY in direct, full sun (we havenÂt calculated for dimmer light levels). You still need an inverter here, which of course, also costs in amperage loss. Hopefully, you now understand how this works. Ok ok, so IÂve been a technician for over 30 years! LOL I just hope that I explained it well enough. I admit, itÂs difficult for me to put my knowledge into short words. LOL But like IÂve said before, itÂs better to use a water heating system for a greenhouse rather than solar electric panels.

Just a couple of impressions from scanning your post: I'm not sure exactly where you will be getting most of your light. None through the north wall, morning sun through the east wall, and the rest through skylights? Skylights will let through some ambient light, possibly a few minutes of direct sun depending upon the pitch of the roof and the angle of the sun, but the given amount of bright light on any square footprint of gh space (for plants) would be relatively small. Would your HOA object to twinwall polycarbonate for your roofing material? Compared with the expense of shingling and skylights, I think you'd come out way ahead, too. If you let in more light via a twinwall polycarbonate roof, those attic vents won't be enough. You said ~400 square feet...including peak I'm going to assume a 12-foot roof space. 20 x 20 x 12 = 4800 cubic feet. Cooling and airflow is going to be your greatest concern. You're going to need heavy-duty greenhouse exhaust fans, with a combined output of at least 6000 CFM. These will most likely be noisy -- don't know if that'll be a consideration or not. A method to reduce some solar gain is shade cloth, stretched over polycarbonate panels at a distance of about 6" or so. This is something else that might not be looked upon with favor by your HOA. It would have to be secured very tightly to make sure that one of your spring thunderstorms wouldn't carry them into the next county! Achieving the right balance between growing plants and storage is going to be your first hurdle. What you must do right now is decide what you want to grow, and how much space dedicated to that purpose, and then design the greenhouse around that goal. Trying to make a "bright grow space" work, after the fact, almost never produces the results you're looking for. For example, if your plan was to grow plants on the south side of your garage/gh, they wouldn't get enough light because of the wall. Adequate light would only be found in the center and north side. (If this is the case, then the south side could be your pathway to access items in your storage area.) If growing plants is not part of your plan, then forget everything I said above! -Bruce

I'm trying to picture it and don't quite understand the 4' x 4' window for the long side. Aren't the sides made out of the wavy plastic stuff too? You don't really need a window on one side or a screen for summer. The vents on the top of the short sides will be the best ventilation since the heat will rise. you could put a fan on one end to pull the heat out and that will pull fresh air in through the other end. If you open a large window in summer you will lose your humidity inside and that's one of the things you want to keep in the greenhouse if you are starting seedlings. I have found that seedlings didn't start so well in my greenhouse without heat mats under the flats and supplimental lighting real close to the tops of the flats. The seedlings also like a fan after they have germinated to keep them dry and make them strong, so you should try to plan for electricity in your greenhouse. Other than that, I think your greenhouse lean-to is a great idea.