I took a couple of surplus 110v muffin fans, built 1' long wooden boxes around them, and hung them from the ceiling pointed down. They do a great job destratifying the air and only take about 15W each.

I found that muffin fans were a lot less efficient than big bladed sorts. A 30W ceiling fan can move something like 30000cfm, compared with maybe 500cfm from a muffin fan acting as an inductor. They're also noisy :-(

I wasn't asking about the TYPE of ceiling fan so much as IF they are beneficial.

From your responses, it would seem so, but the only type I would use would be the kind made to be used outdoors.

We have one on the ceiling of a covered, open sided porch that gets pretty wet in a windy rainstorm. It's held up for 5 years so far, and was fairly inexpensive.

Thanks for the input.

The big problem you'll have in a greenhouse is the condensation. That can quickly destroy electrical devices. Rain is harmless by comparison, particularly as you'll be operating your fan while it has water in it, whereas you wouldn't operate your existing fan in the rain.

Ideally you'd start you fan by running a little current through it to warm the insides up first. But that's probably hard to achieve. A small lightbulb inside the mechanism that you switch on a few minutes earlier (or leave on if you generally need to heat your greenhouse) will reduce the problem considerably.

If you want to be fancy, start the fan with a light bulb in series inside the case which won't provide enough current to rotate the fan, but warm the coils. Then short out the bulb and the fan will spin up.

Alternatively, find a properly rated fan, but they could cost big $. One advantage of 12V muffin fans is that they are brushless and thus avoid these problems. If you could get large DC-brushless fans that ran off the mains you'd be set.

I have a 52 inch ceiling fan with three speeds and on high it moves over 30000 cfm.I run it on high blowing up in the summer it pulls cool air in the bottom and blows it out the roof vents. when heating you run it on low blowing down and in my 10x12 it circulates the air really good making uniform temps everywhere in the GH. The motor is magnetic drive no bushes and sealed bearings. It runs on 30 watts and is not affected by water but when you are heating the air is dry anyway. Another plus is it is quiet when you run it on low you can't even hear it running.
Compared to the fans that most use the ceiling fan cost less runs for less makes far less noise moves more air and is impervious to water. I like mine.

nathanhurst:

I am confused by your comment, but perhaps misunderstood it.

I do understand that electrical motors ought not be operated if wet, but the casing on our outdoor ceiling fan, intended for outdoors use, runs perfectly regardless of the wet.

I believe it has a sealed motor, but will accept your caution. However, it would also be used mostly when the heater is running.

In the hot months, the 2 intake vents set low on the north wall and the exhaust fan, set high at the south, will surely provide cross ventillation?

I ordered my GH with roof vents too, so I'm actually less concerned about the summer as I am the winter, as I plan to operate my GH year round and want to get the most bang for my nat. gas bill as possible.

That's why I thought about using ceiling fans, to keep the warm air from the heater in constant circulation from ceiling to floor.

Regardless; all of your input has persuaded me that ceiling fans would be beneficial, so now I'll start reading the specs on what is available.

I want to make my decision before we erect the GH, to eliminate the need to retrofit electrical work, but do know the fans would be mounted above the lights.

We installed some ceiling fans in our barn aisle and didn't think about the flush mounted ceiling lights, until we turned on the fans and the flickering light through the moving blades not only gave me headaches, it drove the horses nuts.

Yes, the muffin fans are noisy (newer 12V ones are very quiet now, but the 110V ones move more air), but are also very reliable. Mine have been running 24/7 for 9 years now -- hot and humid in the summer, just plain humid in the winter.

The problem is if there is a path for air to get into the motor and to any electrical brushes, terminals or other steel surfaces then you will get dew forming. This is a different problem to rain, which is simply a matter of avoiding drips. Think instead of whether you would be willing to turn the fan on under water.

When you first put on the heater you may make the problem worse, as the inside will still be cool and thus get more condensation.

I suspect that modern high efficiency fans are brushless anyway, and may even have fully water proof insides, which means they will be fine. You can get fans with a light built in the base.

Thank you for the explanation, Nathanhurst. I will look for a fan with a sealed, brushless motor.

But what is a muffin fan?

like a computer fan.

Thank you again Nathanhurst.

Computer fan? Surely larger?

I never thought about one of those in a (larger size?) but do know they will operate in wet. I use small ones to cool some of my fish tanks and they operate even when accidentally splashed.

But I am pleased to report that after checking out our 52" porch ceiling fan, we determined that it is indeed, brushless, with a sealed motor.

Now I can only hope that Home Depot still sells them. They have become fairly popular, so I have high hopes.

Thank you again for your follow ups to my perhaps foolish questions.

I have been wanting a GH for so many years, but admit that I really know nothing about how to fit one out.

Thanks to the kind people on this forum, I'm learning.

We're all learning, birdwindow. Your questions are not foolish, indeed it suggests my original post took too much for granted! My latest greenhouse is now half complete, and I'm just writing up a blog entry about it. I too am wondering about fans. I'd be interested in how much ceiling fans cost over there.

What I'd like to do is run my destratification air through an air-water heat exchanger (probably a spiral of polypipe) to transfer the excess heat at roof level to my thermal store. A ceiling fan and large spiral might work quite well, and be cheap. That way I can save up considerable heat for release during the night.

I don't think you can buy a ceiling fan that is not brushless. They are powered by magnetic drive.
Mine is a 52 inch and I bought it on sale at LOWES for $49.00

Most likely they are squirrel cage or shaded pole motors. All commercial electric motors are 'magnetic drive' :) I've repaired ceiling fans for people and they've had brushes (the brushes were what needed replacement) which is why I thought it important to check.

Ok, so probably $80 here. Cool, just gotta work out how I can put one in without lopping my head off.

Nathanhurst:

Thank you for the kind words of encouragement and I've finally figured out what you meant when you wrote about the cost of wet location ceiling fans "over there."

You are an Aussie! Yes? Lucky you. You live in one of the truly Great Places in the world: hope you appreciate it.

I expect that you can buy just about any fan there as we can here, but to give you an idea of what's available, check out the following:

http://www.ceilingfanwholesalers.com/category.aspx?uid=137-10

I just typed "outdoor ceiling fans" into my search bar, and this is one of the sellers that displayed, but I liked how they listed by wet or damp UL ratings.

UL here, means the US Underwriting Labs. They test and rate electrical devices for different applications and uses, and their labels are accepted as assuring that the the widget meets specs.

At least; that's what I have always understood it was all about and I can't believe you haven't the same there, even if under another name.

A problem with living in australia is that we have a much smaller population, which means less crazy people like me who have a greenhouse... Also, our climate is generally warm to hot (Melbourne, on the southern end of australia is about the same latitude as san franscisco - everything else is more tropical). Despite this, I've never seen fans advertised as 'wet area'.

It is currently 9C, after week of around 5C, so things are cooling down now, and I need to finish putting the walls on :)

Things are often marked as UL here too (presumably it's easy to just get UL rating and let the rest of the world use the same standard).

I certainly appreciate where I live, and I plan to stay here as long as possible :)