I think the first thing to do would be to get a max-min thermometer, preferably with a remote, so you can find out what the temps are. You might be surprised. I think a lot of folks would agree that it isn't the cold so much at night, as the heat during the day that can be a problem.

I'd also place it so it gets east / south sun, not west, which can be pretty intense.

I'm a bit suspicious of the automatic vents, more inclined to run out and open windows at 9:00 am and shut them at 5:00 pm.

First, congratulations! What a darling greenhouse - you're going to love it! And head over to the Greenhouse forum...those people gave me a ton of help this spring when I was just starting my first growing season in my greenhouse. I do want to say - you *think* it will be enough room now...but I thought that about my 6x8 too, and I'm going to be crammed into it once everything grows out this year! ;-)

You definately want a wireless remote thermometer...that was one of the first things I bought, and you'll be amazed at the high temps during the day. You may want to check around and make sure your fan isn't already solar powered if you don't have a power cord on it...and if it does need electrical power, you'll want to get a thermostat to wire it into at some point.

You'll also need a heater at night - the temps will indeed match the outside temps very quickly at night, and milk jugs of water won't provide enough thermal mass to hold the heat. I have a small oil-filled radient space heater in mine, just 1500 watts (I use it on 700 watts) hooked up to an independant thermostat to keep the temperature above 50 degrees at night. That works fine for mine, and yours will probably be more efficient since it's all glass (mine is polycarb panels). You can insulate it with bubble wrap on the inside (or a solar pool cover on the outside) to help cut the heating costs without giving up too much light.

With the thermometer, you can run out during the day and open the door/vents by hand until you figure out the automatic openers - I don't have any yet, because I'm cheap. ;-) You will need some fans in there to run 24/7 though - I have a couple of cheap wal-mart fans that keep the air moving all the time in mine. It makes all the difference for seedlings, especially when you can't get out there right away to open things up in the morning (my gh gets up to around 100 degrees by 10am or so on a sunny day, and since I work, I often can't get out there to open the door until my lunch break at noon).

In any case, get a thermometer, visit the other forum, and ask away! I don't know much (this is my first year with a green house), but I'll happily share whatever I know! :-)

Steve,
Okay Im going to have to stop reading your posts before I turn green with envy!!
First a magazine article and now your wife bought you a greenhouse?? You lucky duck!
Congratulations on both :)

Great Steve, you are in the groove now!

Automate. I have never used the automatic vent openers but one may be of help for you. If you had 2 vents (top and bottom of the greenhouse), they may be sufficient for daytime temperature control. But, I've always been the "automatic system" with regards to vents. It would be best if an exhaust vent opened well before an intake vent opened on a sunny Spring day.

And, that's what we are having here - a sunny Spring day! This week will be the 1st time that I turn on the greenhouse furnace. With lots of little seedlings, I'm carrying them back and forth, morning and evening, from the house.

6:42 am sunrise = 26°F outdoors, 16° windchill, 42° greenhouse

8:30 = 30° outdoors, 20° windchill, 61° greenhouse
>moved some seedlings out9:00 = 32° outdoors, 21° windchill, 80° greenhouse
>opened high vent9:30 = 33° outdoors, 23° windchill, 80° greenhouse
>opened fan cover, fan off12 noon = 37° outdoors, 30° windchill, 82° greenhouse
>opened door a crackIt's now 1 pm and the greenhouse is back to 80°. I don't want any more of that 30° air in there but may open the door another inch in an hour or so. The exhaust fan hasn't been turned on so far this year. There is an automatic fan on the furnace and it is set for "cooling" during the day. It will kick on about 82° but that fan doesn't do too much more than stir the air - which is okay since the outdoor air is so frigid.

If we ever get some high 50's temps (please!), I will turn on the exhaust fan but that's only because my ventilation system is so limited. And then, I really need that fan on a thermostat.

This is Spring, there are great, puffy clouds that can obscure the sun for an hour or more at a time. With that fan stuck ON, the temperature of the greenhouse will drop to whatever it is outdoors if the sun is behind a cloud for an hour or more. If it's 55° outdoors . . .

By sundown, it will be 40° outdoors and I will have worked backwards from about 3 pm on. Closing the door, fan cover, and vent. The temperature will probably be about 70° in the greenhouse by 7:07 pm sunset.

digitS'

Azura, I'm sorry -- I'm not trying to brag! And by the way, my wife "made the deal," but it still came out of my paycheck!

Sounds like I'd better get a good thermometer that will remember the max and min temps for me during the day and night and then figure out how to control it. I'm gone at work 35 miles away during weekdays and don't get home till 6 PM or so, so I won't be able to be the automatic temp control like you, Steve.

I've seen some solar fans online today, but they were pretty pricey, so I may just have to run a long, thick extension cord out there for now (after I figure out how to put a plug on the fan). Maybe I can figure out how to put an inline thermostat on the wiring for the fan, too.

If I run a little catalytic propane heater in there at night, should I have some ventilation open a little, or do you think it would be OK?

I do need to check out the greenhouse forum, as Jamie suggested.

Stevation, - Whatever ya do, don't let anyone bring in some potted plant from a shop / Walmart / Lowes / Home Depot / Friendly itinerant house plant salesman in there!!! because it will have white flies on it. Promise. And you haven't truly been anointed re greenhouses unless you have had a white fly infestation.

Also, don't glue it down just yet. My guess is you'll want to move it around a bit over this season, and maybe next, to see where it fits best.

Steve-
I dont think you are bragging at all. Who better to share your good news with than your fellow gardeners? I'm sure I speak for all of us when I say we are happy for you!
Argh... white flies. The rosemary I bought a few weeks ago came home with a complimentary batch of white flies just in time to infect my tomato seedlings. *sigh*
I cant even imagine the catastrophe that can be wrought in a greenhouse.

Hi Steve,

I just want to agree with Jamie on getting and using one of the oil-filled radiators to heat it. From my experience with catalytic heaters (assuming yours doesnÂt have much of a temperature control), I think in that small of a space you may find it produces way, way too much heat. The electric radiators have quite a wide range of temperatures and I bet putting it on one of the lower settings would give you plenty of heat at this time of year. YouÂd want to keep the temps on the cool side overnite anyway so the plants donÂt grow too quickly yet at this time of year, and so they spend more time producing a good root system without getting all leggy on top. IÂve had one of these heaters for over 15 years now, and theyÂre really great for heating whole rooms. And when I was commuting to SFO and had a "crash pad" room in someoneÂs house, they gave me one of these to keep it warm (I donÂt have a clue why people in San Fran even put furnaces in their housesÂthey NEVER turn them on!). It was a pretty big bedroom, and I had to keep the heater on the lowest setting or it got too warm.

Check out the link below. I noticed the DeLonghi one even has an automatic switch that turns it on if the temp gets down to 44. I think you can buy fancier models with timers to turn them on and off for you, but I donÂt know where or how much theyÂd cost. But I really do think youÂd be very happy with it if you decided to use one of these.

Oh, and I concur with everybody about sticking a remote high-low thermometer in it soon too. TheyÂre not all that expensive these days, and youÂll be SO glad you have it so you can keep an eye on the temp without constantly running out there.

In any eventÂhave fun playing in your new GREENhouseÂas if you wouldnÂt!

Skybird

Here is a link that might be useful: Oil-filled radiators

I just got my energy bill for this month, in case you're interested (since your gh is only a couple feet smaller than mine). It cost me an extra $30 to heat the greenhouse with the oil-filled radient heater, so about a dollar per day, and that's even with 4 days worth of no extra insulation (while I was still putting bubble wrap and such up). So not too bad...I keep it around 50-55 at night.

Just a note on greenhouse heat loss:

It's good to have "rules of thumb" as long as they have some basis in reality. There's been a few studies done, generally rather casually, on greenhouse coverings. At the same time, there are quite a few outrageous claims.

The rule of thumb that seemed to gain wide acceptance was that most any material (glass, film, polycarbonate) cuts out 10% of available light. Light is critically important to Winter operation but not so much to Spring growing and, not so much in places where there is little cloud cover and a higher angle of the sun.

Okay, what that means is that it doesn't always make sense to put too many layers between your plants and the sunlight. As important, it doesn't always make sense to spend extra $$ on fancy-smancy products. The UV light that "kills" construction grade film is mostly blocked by any greenhouse cover - so, even if it doesn't make sense to put it outside, it probably makes a lot of sense to put cheap film inside.

Now, all that being said -- greenhouses are notorious for leaking air. Plug the holes!

Finally, a heat sink doesn't need to be things like bottles of water or whatever taking up room. The important direction for sun exposure is SOUTH. An insulated north wall makes infinite sense.

digitS'
who fired up the greenhouse furnace last night after the cat scratches were patched and now cringes at the thought of his natural gas bill showing up in the mail box. Cat Scratch Fever?

When I first started off with mine, I too tried to keep the night time temps above 55º - at considerable cost. I then spoke with someone who does this professionally in the 'hood, and she said 40º was just fine for 99% of the plants. I bought some special thermostat thingies that are set to come on at 40º, and that cut my electricity bill in half.

Ditto what Digit said about insulated north walls.

Now that I've got David agreeing with me on the north wall idea, I'll complete my thought. (He can beat me up for it later.)

With the sunlight shining from the south and coming thru the greenhouse, the light energy can be absorbed by the north wall. I have placed reflecting insulation board on the interior of my "sunshed" but sometimes I wonder if it wouldn't have been better to paint it black - probably so. My original plan was to use the sunshed right thru the Winter when maximizing light was critical to getting plants to grow.

How that might work for your new greenhouse, Steve, I'm not sure. But obviously, the light passes entirely thru a structure that is 4 feet deep.

digitS'

I would imagine that a greenhouse with all glass windows would be much tighter at the frame than my polycarb one. I have bubble wrap up on the inside, not just for basic insulation, but also because I have it taped together in a single layer, so it helps seal off the spaces in the frame I may have missed. Nothing is growing "leggy", so I assume it still lets enough light through. I plugged up all the larger holes with "great stuff" foam, and the bottom 1 1/2 to 2 feet I have foamboard insulation on all around, except the south wall (bubble wrap all the way down on that one). I also have 3/4 of my north wall covered with foam board insulation.

My temps did drop into the 40's a few times earlier in the month (when the temps outside dropped into the teens), and everything survived, but they do seem to grow better/more steadily when it stays above 50 in there, for me at least. I think it probably depends on what you're growing as to what temp you'll want to keep it at. Part of the reason I want mine at least 50 degrees is to minimize the temp swings from day to night, since it does get so warm in there during the day.

More to think about...overwhelmed yet, Steve? :-)

I think the reflective stuff would be better than painting the northfacing wall black. But I guess that depends on whether the north facing wall will release it's heat back into the greenhouse or into the room behind the wall.
Because I'm cheap I would go with the reflective stuff then use gallon jugs(found free on CL) filled with water to release the heat they stored over the night. I tried painting them black with a little success, but am looking for something I can use to dye the water black.
I agree with jamie as to keeping the night time temps at least to the 40's and only had to use the oil filled heater a couple of times when the temps were getting too low and I couldn't bring in all the non cold tolerant plants.