My exhaust fan is a 10 inch model from Farm Tek ($85-350 cfm). They have larger models if desired. It is connected to a hard wired fan thermostat from Charleys, $22. The wiring was actually easy. Works great.

Use this link to figure what you need
My experience has been that you need more fan than what this calculation shows so go bigger NOT smaller
You will need 5000cfm or more depending on where you live.
Instead of one monster fan I Would use two or three smaller ones that would make it more flexible
A single 12 inch fan would not even be noticeable the temp would not drop a bit you will need some serious fans in a GH of that size.

Here is a link that might be useful: FAN CALCULATOR

Many thanks for your responses and links! Just when I think I have the GH up and running, there's another expense. My fault for not doing my homework up front. Hubby wants to take off for a few days and not be tied down 24/7. :)

That's going to be our problem next year when my husband retires. It looks like we'll also have that expense or wait until summer to go anywhere overnight. But then we have the problem of who's going to water them while we're gone. One of my acquaintances suggested I switch to all cacti and succulents. But what do I do with everything else including my beloved orchids?!?!?!?

In addition to the exhaust fan a motorized intake louver is a good idea. Otherwise you'll need to prop a door open to allow for makeup air. Leaving a door open on cold nights is not a good idea either.

If you purchase a 2-stage thermostat you can have the louver open a few degrees before the fan kicks on. Often I notice on cool days that the louver will open and then close without the inside temperature ever reaching the point where the exhaust fan needs to start.

If you run a 12-3 (14-3 may work) electric wire thru the louver (or fan) recepticle to the thermostat and continue with 12-2 to the end fan (or louver) then you won't need to run multiple wires. I have a switch below the thermostat to allow the fan to be manually on or off for special reasons which is a good idea.

greenhouser - you may consider a mister or sprinker system for your orchids. I also have some, along with staghorn ferns and mostly tropicals. I only water once a week, so that gives us 7 days away.

Great idea about the motorized intake louver. Thanks for the info on thermostat and wiring!

Here in sunny PHx I am setting up a new HFGH to run mostly on solar. The cooling is the big power draw of course and eventually will be a combo of house current and solar panel energy if my plans work. I have found that dead air caused by corners and peaks (don't use the roof vents here) create quite a differential that I need to account for with smaller fans in odd areas. I have a swamp cooler rated for 8-1200 sq ft and it looks like it may work to keep the temp at 90 when it is 110 out. Wish all I had to do was open a window and turn on a fan! :-) Our houses here typically are the inside of a swamp cooler with lots of shade screen.

Oh golly- here I go again. The ceiling fan lady. But gosh darn it- they work!

I'm sorry now that I even wasted my money on a wall mounted exhaust fan. The powered intake vents- absolutely, but with the big ceiling fans pulling air up from the floor and out the roof vents, the exhaust fan served no purpose other than to make noise, take up space on the wall and prevent the heated air from being drawn up to the roof. So I turned it off and even when the outside temps hit well into the high 80's, the ceiling fans coupled with the low, north facing intake vents kept the GH under 75.

Okay: aluminet shadecloths too.

Use whatever method works best to chill the floor of a GH and if you can pull air up from it and out the roof, the entire space will be cooled.

jan22

Because of where our water comes in from the road, we can't run water to our GH. It would be cost prohibitive. Leaving pressure on a hose and being away can be catastrophic if the hose splits - and the best of them can and do. There are so many plants in both GHs that I would really need a dependable and knowledgeable person to come in and water ever other day. There is no one like that, that we know of.

If you have room outside, you could create a reservoir for the water storage and a timed pump to water, mist while you are away. Maybe some plastic barrels or even a much bigger type? Then it would be a matter of timing and adjusting each emitter on the drip system, not the prettiest setup but could be effective.

The drip systems works without a doubt and it is not that expensive anymore. The big box stores all had some of it so you can pick and choose. I used to use it in FL on my heather beds.

1eyedJack and the Dawg

solar_gh

Doesn't each plant need a water tube to it's own pot? I have so many plants in my Rion GH it would be a mass of tubes everywhere. And not all plants need the same amount of water. While one went thirsty another would be rotting away. Setting up each plant to it's needs wouldn't work as there is no way to know the weather beforehand. They want more water when it's sunny than when it's overcast. More when the heater runs longer etc. A fully automated system to cover every condition and plant would be beyond what we could afford.

I already have extra water pumps because of my ponds. It's the running of hundreds of tubes off a mainline and adjusting them all to the ever changing conditions that's not possible.

Well them you will have to stay at home. If you want all the little children you have to be prepared to take care of them. U really ought to start looking for a new neighbor or friend to help you when you want to go away or you are going to be stuck. Put on your best Southern Girl Accent and hit Wally World or the Big K mart and hang out in the garden center. Check out local garden clubs in your area. If push comes to shove you might have to join a local church. Those guys always want to help you out unless you REALLY need help and then they are GWTW.

Time to hit the sack. I have been sick all day with a high fever and it has finally broken.

1eyedJack and the Dawg