greenhouse ventilation

Hi. I'm just getting ready to build a greenhouse that will be attached to my screen porch. The greenhouse is a 10X15 Victorian made by Jensen's. It has four roof vents and I am putting a six foot sliding door, into the screened porch. I will also be putting in a 3 foot door. I can put the door in the southeast side of the greenhouse or the southwest end wall that is opposite the sliding door. I don't know which will be better or even if it matters. I also don't know if I will need a screen in the small door for the winter months. North Texas goes from 80 one day to 40 the next. Will I need to open the small door on warm winter days or will opening the slider and the roof vents be enough to cool the greenhouse? Any help would be appreciated.

Do you have fans in there? I'm not sure just opening doors and roof vents will be enough to keep the temps down on warmer days.

I'd asked hubby that. He's got a thermostat-controlled fan in his air compressor closet, says the same could be installed in my greenhouse.

Of course, it would have to be weatherproof. Any recommendations for suppliers?

There are many local factors which come into play...GH orientation, direction of the solid wall (if any), glazing, shading from trees (deciduous or otherwise), obstructions to airflow...all of these and more will affect GH temps.

Having said that, I would guess that no matter what, you will need an exhaust fan. Very generally, placement of the door should be determined by placement of the fan, and that placement of the fan would be determined by some combination of aesthetics, porch layout, and knowledge of the prevailing winds. Assuming prevailing winds go W -> E, if possible then you would want the fan on a eastern wall and a door or some other intake on the west.

I'm in zone 6a and I need to ventilate in the winter. We had a day just last week with a high of 60 and I had to put a fan in the open doorway to keep the temp at 82F. So in zone 7b, I would guess that you will need to do so as well.

A schematic of the layout would help...

Suppliers...many times you can go with farm store types of materials and you will pay a lot less. But my favorite greenhouse supplier is Hummert. Charley's is overpriced, generally.

SB,

We've got an older (commercial) Hummert catalog at work, and while I enjoy thumbing through it, I always thought their pricing was a bit on the high-side. Is this not the case? Do you drive all the way to Earth City? Or, do you order from their catalogs? (I'll admit, that when I drive by there, I always make a mental note to stop in some day, but as of yet I haven't)

Here's a Photoshop rendering my husband did, with South annotated. To be precise, the gated fenceline is about 160 degrees, you can see the deep evening shadows of this August photo.

At present, it looks like the best choice might be to mount a 24" shuttered fan above a Larson full-length door with slide-down screen. That'll give me a 140% air exchange per minute. While that falls a little short of formulae given for the greenhouse volume, it probably is OK to fudge a bit for 10% of my wall sfc being convertible to screen...

As for the planform, it's a simple 10'X15' rectangle.