Coul you possibly build a small unheated entry over and around your existing north door; sort of like they have in some stores to block the cold air? It wouldn't have to be very large; then have the door to it face another direction out of the prevailing winds. Just a thought. It seems running another fan would just add to the electrical bill.

Wind isn't my problem. The issue for me is simply cold air and the need to prevent, as much as possible, sudden, sharp drops in air temp. in the GH.

Perhaps my large gas heater and ceiling fans are really all I need. I honesty don't know, so am hoping for some insights from others who operate a heated GH in areas that can have more a few 0 degree days every winter.

Not that constructing a winter use GH with an air lock isn't a great idea, and ought to be given more consideration in GH design for cold climates, but it's not a viable option for mine. Thank's for the thought anyway.

BW, I worried a lot about this, since my GH door is on the north wall. In reality, it doesn't seem to be a big problem. I don't put any really sensitive plants near the door, and I don't swing the door wide open when going in or out.

SB

Thanks stressbaby; that makes me feel better about how I sited my GH.

It isn't pretty, but you could try something like what I did last winter; I do think it helped cut down on heat loss: From the excess solar pool cover material, I cut several wide strips long enough to reach from the top of the door frame just to the floor and hung them, overlapping, just inside the door. The one that overlapped the opening edge of the sliding door frame was taped to the frame. This made the entry and exit a little less convenient, but I felt it was worth it and will put them up again this winter.

Or ... you could get a little HFGH and use it as an "airlock". Now there's oneupmanship ... a greenhouse with a foyer.

Diane.

Or ... you could get a little HFGH and use it as an "airlock". Now there's oneupmanship ... a greenhouse with a foyer.

Already got that on my grand plan :) Desert plants in the airlock greenhouse, moist climate in the greenhouse proper.

Diane:

An air lock on a cold climate heated GH is actually quite sensible. I wish I'd thought about it before I ordered what is in fact, a custom built GH. Alas, I didn't.

I'll see how it goes this winter. But I'm still waiting for one of the clever gurus to come in to tell me if blowing warm air at the door might make a difference. Floor fans really don't use that much electricity.

All I know for sure, is that once I set up baby fish grow out tanks in my GH, the door will be opened no less than 12 times daily, regardless of weather. It's the price I'll pay to get the unceasing noise of the big air compressors out of the house.

BTW: I don't know what upsmanship is in GH's, but in the world of the aquarist's, it's at least one 2,000 gal. tank. The ultimante "up" is +10,000 gal., and reef sharks.

I am NOT in that league. :)

coincidently I was reading this:
http://www.cichlid-forum.com/articles/diy_1700g_tank_1.php
yesterday. Does that count?

re blowing air at doors; that sounds like a way to waste a lot of heat - you're reducing the boundary layer on the wall, reducing the insulation rating. I would a) make sure the door is well sealing b) heat the middle of the room c) not use fans to spread heat, but have enough insulation that you don't need to spread the heat around. Natural convection should be adequate to maintain an even air temperature.

It doesn't take much insulation to make a big difference - putting an extra layer of plastic film on might be all it takes, and you could have that done in a few hours with caulking gun and a roll of shrinkwrap film.

Nathan:

Okay, I understand now.

No fan.

More insulation.

In my greenhouse,in zone 7b,During the day the heater Does not come on.The sun heats it.Now at night,the heater runs quite a bit.My door is not totally sealed.I need some frsh air for the ventfree propane heater.When do you expect to be entering the greenhouse the most?If it's during the day,it would not cause a problem.

trigger:

I'll be in/out of the GH no later than 8 am, and no earlier than 10 pm, many hours after the sun has gone down.

Please understand, that what works in your climate doesn't, up here. When a strong Canadian front comes whipping down and across our flat Illinois cornfields, it can drop our temps from a balmy +40, to -10, in hours, then settle in for 0 to +10 deg. days that can linger.

My first winter with my GH will be as much experimental as for intended use, and while I'll have tanks out there, it isn't won't be fish at first, just plants. If an aquatic plant dies down to it's roots, it will come back, but once a fish bellies up, it's premanently dead.

Nevertheless, I have learned so much from communicating with so many different people here on the GH Forum, and as result, believe I've avoided many mistakes that would have been impossible to mitigate without tearing it all down and starting over; a dreadful thought.

Which makes me wonder how many backyard GH's have been abandonded, simply because their owners didn't have access to so many different ideas and experiences, from so many others who have made their own mistakes, learned from them, and have come here, to share their knowledge.

I really am, very, VERY grateful.

If you're collecting a fair amount of sun (Moline gets 1.6 kWh / m^2 on the ground, 2.9kWh/m^2 tilted to your latitude) you might find that your tanks store enough to make the heater mostly superfluous. It all comes back to insulation vs insolation.

I think you might well be right about derelict greenhouses. They are a bit subtle to own and maintain and many people would just give up, I think.

http://rredc.nrel.gov/solar/old_data/nsrdb/redbook/sum2/state.html

Here is a link that might be useful: moline's solar data

Nathan:

I'd be interested to learn if your solar research has revealed any measurable differences between Molene, and Chciago Heights, IL, which are at near identical latitudes.

But one is located in a riverine valley 160 miles inland, and the other but 15 miles from the shores of Lake Michigan and "lake effect snow".

The Great Lakes make their own weather patterns, so it would be interesting to learn what, if any difference topography and proximity to huge bodies of water make to the amount of sunlight any given point will receive in winter, because the position of the sun may not be as relevant as the amount of cloud cover.

I honestly don't know, but while those Canadian fronts often bring bitter cold, it's often with clear skies. When the east wind blows in winter, we may not receive enough sunlight to percieve a shadow.

I suppose that for GH heating, they do balance things somewhat, as in my area, very heavy snows usually mean higher temps.

Comment?

I think you are pretty much right on the money. I posted the link for the redbook, which gives all that data for molene and chicago, summarising to an average kWh/m^2 (which includes the clouds and everything).

Nathan: I used the link you provided, but admit I don't know how to inturpret the data to a language I really understand.

Some everyday English, understood by us non-scientists, would be appreciated.

If my observation about topography and massive bodies of water is, as you say, correct: could that be another reason why so many gardeners in the same plant "zone" experience so many different results, even with the same soil types and gardening techniques?

If so, it explains a lot, and establishes a need to consider ALL factors for a GH, not just zones, and average temps.

I see that chicago is consistently less sunny than moline.

"I see that chicago is consistently less sunny than moline."

Yes, that's what I've been trying to explain to our friends in the sunny South.

That's why I was concerned about heat escaping as my GH door is opened, because there will be weeks without sunlight to warm it, so every bit of heat that is lost, will need to be replaced.

Hopefully, my desire to address the need to both prevent that loss and maximize the best use of both natural gas and electricity, might now seem more rational.