You want the longest axis facing south, whatever axis it is. You'll want to insulate everything that won't be getting a significant amount of winter sun with heavy insulation, preferably reflective to trap IR and give your plants extra light. You'll want at least double-layer clear on the rest. You'll want an auto-opening vent, probably with a fan unless it's a huge vent, for spring and fall (it's a pain to have to open and close it every day when the night temps are too cold but the day temps are too hot). As for heating, both electric and propane are valid options. Expect to use a good bit of energy either way. Propane is more efficient and provides critical winter CO2, but more difficult and expensive to set up. If you go electric, try not to make an airtight greenhouse so that your plants can get the CO2 that they need.

Isn't it a bit late in the season to be at the planning phase of setting up a greenhouse?

Thanks for the reply. Yes it is a little late. thought about getting an area ready for early spring building. I figured it would take me a while to learn what i need to know. I have been looking at kits, but homebuilt may be the better choice.

Hey if your a grower like us you might find that your building a g/h in January.....

Tbeardave,
The commonly recommended orientation for greenhouses in your area is indeed N/S. However, according to the University of Arizona-"Considering only the winter season, that is, the lowest light intensity and shortest day length period of the year, an E-W ridge orientation will gain more total light than a N-S orientation.". So, the decision would depend on when you plan on using your greenhouse. Also, the only way you will gain CO2 from using propane is with an unvented heater, which is not only unwise for some crops such as tomato, but illegal in some States.

Here is a link that might be useful: greenhouse orientation

TBD, good advice above. I would suggest that there are other considerations. First, the closer your GH is to square in shape, the less it matters which way it is oriented. Second, a N-S orientation results in a more even shadow distribution across the GH as compared to an E-W orientation. Third, and often ignored by the utilitarians among us, is aesthetics.

Mylu, where ya been?!?

quoting from that site:

"A taller greenhouse is better for improved climate uniformity. In gutter-connected greenhouses, a minimum of 3 m (10 ft) from floor surface to gutter, plus an additional 1.2 m (4 ft) from the gutter up to the ridge, is desirable. Tall greenhouses provide a large internal air volume, which reduces rapid changes of the greenhouse climate caused by the natural daily fluctuations of the outside environmental conditions."

Now the volumeteric heat capacity of gas is about 1kJ/m^3.K, compared with 4.2MJ/m^3.K for liquid water, i.e. 4000 greater. So claiming that tall greenhouse store heat better is clearly rubbish. I could get the same regulation of a 4m high greenhouse with a 1mm high layer of water on the plants. Tall greenhouses are better, but the reason must be something else.

When sites make big blunders like this, I wonder what else they have wrong.

There is no blunder of the reference. And, the reference does not claim "tall greenhouses store heat better". It simply and correctly states that "a taller greenhouse is better for improved climate uniformity".

Right. Off topic, here, but it is just the converse of what we're always saying about small greenhouses, that they heat up faster and cool off faster. Taller greenhouses are larger, so they'll heat up more slowly, cool off more slowly.

To get back on topic, here is a link from Alabama Extension that touches on orientation. The explanations here aren't as good as in the AZ Extension link above, but there may be some useful information here for you. I particularly like this link because it clearly states the proper steps in order: "Step 1: Decide what plants you will grow, what times of year you will use the greenhouse, and how a greenhouse fits into your lifestyle."

Here is a link that might be useful: AL Extension Link - Getting Started

A taller greenhouse IS better for improved climate uniformity.

It didn't say anything about STORING heat better.

I can keep my temperatures more uniform in my 16x20 hoop house better than I can in my 4x6 window box.

Nathanhurst, It sometimes appears you surf these posts just to be critical.

tbeardave, I have built hoop houses. Although I like them I much prefer a more solid structure. My wood or steel framed ones were easier to add vents, electrical, fans, etc.
Just my thoughts.

Tom

Thank You all for the wonderful response. my plans will mainly be for winter usage. but who knows it may be a year round venture. I will take all replies into consideration. It is wonderful how much help is available for the rookie that i am.

I am sure ill have more questions as days go on. thanks again

oregon_veg,
Critical thinking is the basis of the scientific method. Stating facts without justification or understanding is 'magic'. However, I think the time has come where I should move on, as we appear to have exhausted the possibilities of interesting discussion.

Cya peoples, it's been real!

Taller greenhouses should encourage a less uniform heat distribution, not a more uniform one. Heat rises. You're making convection have to do more work to circulate the air back. They also won't store more heat from the air, but the increase in plants, frame, soil, etc will store more.

[quote]Also, the only way you will gain CO2 from using propane is with an unvented heater, which is not only unwise for some crops such as tomato, but illegal in some States. [/quote]

Are you the person who said this in the other thread? Gas heating is the standard method used by industrial growers, so I don't know where you get off talking about how harmful it is. Some use unvented, some use vented. I recommend unvented. It's what I use, as do many other people on this forum. CO2 is typically the limiting factor to winter growth of plants -- even more than sunlight. You either need outside air brought in (or, usually, leaked in), hurting your efficiency, or exhaust CO2, if you want your plants to be able to grow.

Look at it this way: natural CO2 levels are ~0.03% of the air. Of that, less than a third of it ( 3 CO2 + 4 H2O), one cubic meter of air has the capability to hold 70 grams of carbon in CO2. Now, you're not going to burn through all your oxygen (nor would you want to come even close). Rather, this simply means that, as a base value, 1/700th as much air needs to leak in/out to produce the same level of CO2 influx in the greenhouse as you would need with electric heating, since the much more common O2 gets converted to CO2. And the actual value is much better than that 1/700th number, since your plants will be producing O2 (just not at the rate that it's being consumed, in most situations).

Picture what leaking 1 cubic meter of air into your greenhouse will do to your temperatures, just to provide one tenth of a gram of carbon for your plants to share among each other. To most people, this level of leaks is simply inacceptable. Hence, they seal to the point that there's a CO2 shortage in the greenhouse, limiting plant growth.

Yes, there are plants sensitive to ethylene, a potential hazard to plants from propane use. Most plants aren't that susceptible; I only know of two (tomatoes and carnations) that are. They use it as a hormone, so if it reaches about 50 ppm, you can get growth deformities. Often, such deformities aren't even noticed, but occasionally they can be problematic. With a proper propane setup, you don't get ethylene accumulation, so even tomatoes and carnations should do fine. Basically, if you're not getting carbon monoxide problems, odds are good that you're not getting ethylene problems, either, as the incomplete combustion that will vent ethylene will also vent CO. Another reason why it's good to have a carbon monoxide detector in your greenhouse. :) They're only $10-20.

Also, a propane leak can also leak some of the ethylene impurities in the propane itself. However, it'll also leak the mercaptans that scent the propane. Just like with natural gas, if you smell it, there's a problem.

At least some of the information in the post above is incorrect. My information as to unvented heaters is correct. There was no mention in my comments of how harmful gas heating was,as it obviously is not if properly used. Most commercial greenhouse operations use natural gas or propane for heat. Most do not use unvented heaters for the reasons I gave. There was no mention in my comments about CO2. Levels of CO2 in most greenhouses are below optimal for good plant production. Specialized CO2 generators are commonly used in commercial greenhouses. For a hobby greenhouse, the best method to increase inside CO2 is to increase ventilation. In the winter, this will require more heat after the ventilation.
Regarding ethylene, the above note stated "Most plants aren't that susceptible; I only know of two (tomatoes and carnations) that are. They use it as a hormone, so if it reaches about 50 ppm, you can get growth deformities.". The actual number that starts to damage plants is 0.02 ppm.(Utah State University- www.usu.edu/cpl/research_ethylene.htm)
The list of greenhouse grown vegetables susceptible to ethylene damage is somewhat longer than 2. So that forum members can check the background of my comments, please check the following web site.

Here is a link that might be useful: ethylene effects on greenhouse plants

That was a typo; it was supposed to be 50ppb, as stated here:

http://www.ces.ncsu.edu/depts/hort/greenhouse_veg/more_info_/stress2.html

"Ethylene levels less than 0.05 ppm (parts per million) can make leaves droop downward even though they are not wilted (epinasty). With chronic exposure, stem thickening, increased branching, flower bud abortion (Fig. 3) or flower malformation (small, slightly distorted petals) and general plant stunting can occur. These symptoms may be very subtle, and hard to diagnose at low exposure levels, especially if no plants grown in clean air are available for comparison. Symptoms will also depend on exposure time, concentration of ethylene, stage of plant development, and temperature."

I've seen pages report higher:

http://www.sorbentsystems.com/epaxtech.html

It calls 100ppb the plant threshold, and says that 200 ppb won't even ripen bananas.

Note that I said "aren't THAT susceptible" (stress added). Most plants are less susceptible to ethylene than tomatoes and carnations. As the page mentions:

"The main problem is diagnosis and detection. Tomatoes are so sensitive that they are considered an indicator crop."

Looking up, I find some other plants that are moderately sensitive: wheat, rice, geranium, petunia, snapdragons, orchids, and fuscias. However, I can't find any crops that get the sort of loss of yield that you get in tomatoes (as much as 95% at 100ppb@15C, not that much lower at 50ppb. Higher temps help...). Can you?

Again, I'll reiterate: it's not that most plants *aren't* susceptible to ethylene. It's that most are more tolerant than tomatoes and a few other plants. Also, I should add that simply enclosing plants puts them at risk for having too much ethylene. They produce it on their own. In the outside, recirculating air pulls it away. It doesn't take a propane leak or incomplete combustion for that to occur.

[quote]For a hobby greenhouse, the best method to increase inside CO2 is to increase ventilation. In the winter, this will require more heat after the ventilation. [/quote]

It takes more ventilation that most home GH owners are willing to provide because of the increased heating costs. That's why you see so many people on this forum talking about how to plug up every little crack. One person even suggested an airlock. ;)

What I'd like to see most would be an affordable ethylene scrubber. I've read that potassium permanganate denatures it, slowly, and I know that I could get ahold of some, but I'm unfamiliar with the reaction rate, and I'd need air circulation. Probably not worth it when I haven't seen any signs of ethylene poisoning in even my tomatoes.