Circulating fans

[Carolina girl]

I'm trying to figure out what I should get for circulating fans in my greenhouse to ensure good air movement in the winter. It's been up for less than a year, and so far I've relied on some old box fans. But as I add more plants I know I'll need something more.

It's relatively large for a hobby greenhouse, 14' x 24' with 10' roof height at the center.

So far, after visiting 3 websites I have 3 different figures for the cfm rating I need for an overhead circulating fan, ranging from 1000 cfm to 4000 cfm. (!) I suspect the lower figure is closer to correct, since the third number I have is 1200 cfm.

I've seen advice to use two fans in diagonal corners (above the plants) to create an oval air circ pattern, which is similar to what I've seen in large production greenhouses. Also advice to aim fans up or down to break up stratification of warm air at the roof in the winter, but nothing on placement of fans for that.

Does anyone have good information on air circulation fans, particularly for use during the cooler months?

Thanks!
Ann

[raybark]

Ann,

I have the two opposite corners setup, and they are oriented horizontally, blowing down the long walls of the greenhouse above the benches, right at the roof line. They create enough turbulence that stratification does not seem to be a problem.

One thing I did do - not on purpose; just got too good of a deal - is buy fans with larger capacity than I really needed, and then added a fan speed controller. I basically have the fans operating at fairly low speed most of the time to give me a nice, tumbling breeze, but if I water and the humidity is so high outside that the plants aren't drying rapidly enough, I have the capability of cranking them up to accelerate the process.

Another option you have is ceiling fans blowing down.

[Hingecek73]

Thanks again for the replies.

I think Ill investigate the gloves and maybe bar ends to give another option for hand position.

Cheers

John

[IanRodgers]

Ann,

I'm coming very late to this, and you may well already have decided what to do, but have you considered the type of fan which draws in air from high in the greenhouse and uses a flexible tube to blow the air out near ground level? This ought to promote an efficient mixing.

Regards,

Ian

[Carolina girl]

Ian,

The horizontal circulating fans turned out to be so heavy and difficult to mount in my setup that I did end up

going with two small fans in diagonal corners directed downward into the aisle. Charlie's Greenhouse has this

type for sale -- about $75 if I remember correctly. But we just took two small fans we had on hand and hung

them with wires. I figure this is a $0 investment trial to see how this works over the winter. The ones with

the flexible tubes might be nice, if the tubes hang out of the path of traffic. Standing under the downdraft of

the ones I have now is not very pleasant.

Ann

[Darbege09]

I purchased a prefabricated vinyl indoor greenhouse to grow my Nepenthes and other cps in. I have had this greenhouse for about 1 week. I was not using a fan and developed some black mold on some of my Nepenthes leaves. It was suggested that I wipe off the mold and use a fan to prevent this. I had been leaving part of the greenhouse open to help with circulation, but this obviously did not work.

I have not been able to find a small fan to use in this indoor greenhouse. The greenhouse is 28"Lx19"Wx5H. I currently am using a small clip on desk fan for circulation. This is the same one I had blowing onto the greenhouse, but it has now been moved inside and turned to low speed.

I have read that computer cooling fans can be used, but local suppliers are out of the 120V fans at this time.

What other types of fans are people using to circulate the air in their terrariums and greenhouses?

[EdM-in-TN]

Virtually any type of small fan can be used. The only caveate is that you must be sure to keep any water off of them. UL listed greenhouse fans are protected from water damage, shorting out, and electrocution but these cheaper fans are not. They will work great but if you choose to use them you take on the risk of fire or electrocution. I personally use the cheap box fans in my greenhouse but I hang them in areas where they are not exposed to water.