Hi
At last someone with my problems lol I'm in 10 florida so the climate is a bit different . I think your cold fronts are of longer duration .But I'm familiar with heatlol
Have tried your method for two years I heated the lily pool and a 150 gallon aquarium with circulation between the two as well as a seep wall to distribute heat.
Worked perfectly until temps fell below 35. Could not keep up below that even with a total of 1100 gallons of water. Kept the water warm and did raise the air about 10 degrees. That was the low for that winter so have no resultes from colder or longer than 3 hours duration.
This spring the tank developed a leak so was not functional except to heat the pool . had great hopes for it lol Wouldn't you know it had the coldest winter in 30 years lol
I suspect that 150 watts would not be enough but since you could warm it above 80 (without fish and plants )Preceding a cold front you might have a chance.
How long a duration and what are normal air temps ?? What are your ideal temp goals??
My main problem is that after a cold front passes there is blazing sunlight which overheats a lot during the day .
Not sure how the fronts behave in your area. gary

Hi
So, did you try this method and what were the results??
gary

I had to make a couple of assumptions about your gh type and covering (I estimated a 5-foot sidewall and 6-mil plastic), but I did the calculations and came up with a requirement of 2,772 BTUs to maintain a +10F differential. This is equivalent to 812 watts.

Your 150-watt aquarium heater puts out 512 BTUs, or enough to give you slightly less than +2F in your gh.

-Bruce

Hi Bruce,

Thanx for the reply & info., I appreciate it...

Honestly, I wouldn't even know where to began on how to calculate all that??? LOL...
Thanx for taking the time do so...

Eric

Bruce
i figured there was a way to calculate that but not by me.
As I mentioned I keep a heated pool and aquarium with a total gallonage of 1100, I use 3 300 watt heaters nmaintained at 70 min. It worked until around 35 .At this point the heaters could no longer keep up. I chickened out and covered the pool and aquarium with bubble wrap so didn't find how effective it was. Warmed the air with an electric forced heater..
So my question is would stepping up the wattage make it more effective and if so by how much.?? I would like to keep both the air and the water at least 55 regardless of outdoor temps. I'm in 10 so overheating is ten times more of a problem than cold. Of all the systems I've tried over the years this seems to answer the most problems on a year around basis. If you could steer me in a direction on how to figure this out ??? Thanks very much gary

Hi Gary --

I seem to recall that your setup is more of a shadehouse than a greenhouse. In order to make an accurate BTU determination, your structure needs to at least be airtight. Then, what sort of design is it? Quonset? Standard? Lean-to? What are the dimensions: length, width, height at peak, and sidewall? And finally, how well insulated...and what sort of covering?

You stated that you want to maintain 55F, so that's another variable. The additional number you need to know is your lowest possible outside temp. You mentioned above that you can have temps falling below 35F, so that would require at least a +20F differential.

Once you know these variables you can set to work figuring what your BTU needs are, and what sort of heater would deliver.

Each of your 300-watt heaters has a 1,024 BTU output. There is some storage capability from your pond and aquarium, but as has been discussed elsewhere, passive tanks simply do not radiate quickly enough or with enough efficiency to be of value when there is a large temperature differential to be maintained.

Just to give you an idea, a standard 10x14 gh with a nine-foot peak and eight-foot sidewall, covered with 6-mil plastic, would require 12,420 BTUs to maintain +20F. A single 1500-watt electric heater puts out 5,120 BTUs.

-Bruce

Hi
Thanks for your thoughts on this !! In this location unacceptable lows total about 40 hours per year and never for an entire day.. Too hot about 300 days per year but only if you block the air flow, wide open reduces this to less than 30 days. have found no covering that addresses both problems. Went back to vinyl lattice with vines pruned back during winter. The aquarium and lily pool are functioning as such Obviosly I have to keep the aquarium above 55,added heating to the lily pool as an experiment to see what would happen ,no problem keeping at desired temps. Added a waterfal mostly to distribute heat during summer but noted the warming effect during winter. Magic number seems to be 35 at which point the heaters can't keep up with the heat loss. I guessed at the 300 watts x3
What it absolutely does is provide a frostproof area above the pools and tank but does not heat the air to desired temps on a temporary basis. So was wondering if greater wattage would increase the effect and if so how much?? Obviously I can't preheat the tanks to above 80 due to the fish and plants.
In the last go round the low was 33 to 40 in 3 hours total.Daytime high was 58 to 45 for 8 hours. As you can see blocking air flow would create excessive temps .
So is there any way to guesstimate ??
Might add that the 33 was a record low but the alltime record low was 27 which has not happened in 33 years.
Thanks for any guidance you can give me !!! gary

My suggestion would be to not waste the effort and energy pumping more BTUs into your tanks. The energy transfer rate from a static water source is simply too inefficient. Now, if you're talking about the slow-moving water through the Fakahatchee, that's a different matter. The temperature-moderating effect of the water in the swamps is huge, but that's as a result of the extraordinary mass.

Are you able to cover at all -- or is the lattice and vines your only protection? If you can throw some kind of tarp over your structure (maybe have it rolled up on one side of the roof), then I would go with a 1500-watt electric heater. I wouldn't mess with those oil-filled types, or a radiant-type. Just grab one of those Holmes heaters for $17 from WalMart.

I suspect that you have more cubic feet than one heater can manage comfortably. If you can run an extension off another circuit (using 12-gauge wire), get a second one. With the two running you'll have a bit over 10,000 BTUs, which should be enough to maintain the 55F you're looking for. Then again, as I re-read your post, you said that you can maintain 55F as long as outside temps are above 35? If that's the case, then maybe you can get away with a single heater.

As you've discovered, the rate of cooling and heat loss from your structure is well beyond the capability of the water to moderate. The electric heaters are much more efficient, and not that expensive to run.

They say that our cold weather might be done for this winter. Keep your fingers crossed...

-Bruce

Hi
Kind of wish it had failed lol.Down to 40 it kept the water warm and moderated the air below that the heaters could not keep up. So I chickened out and shut down the water fall and covered the tank and pool. The thermostats were functioning properly and circulation was kept at 1600
gph. When I did this the water bounced back to 70. So even though it did not keep the air warm it worked fine for the water. What was most impressive about it was what it didn't do. Overheat ,drop the humidity.or take up a lot of room in reverse it's very useful during summer. I still feel I'm moving in the right direction.. What would have happened if I was able to keep the water at 70? Last winter was misleading as the low was only 42.
I've generally used electric heaters in the past. Have two VERY serious drawbacks. Gets way too hot directly in front and drops the humidity. both more serious than drop in temps at least to a point. They also require constant attention.
have used all kinds of covers in the past. The best was
UV stabilized plexiglass. But since I only have a 10 foot ceiling overheating was a terrific problem addressed by removing for 9 months. Where do you store those suckers?? lol
My last attempt at covering was on a temporary basis using frostcloth , christmas lights. Very limited usefullness. I'm now using vines on the lattice only ,have even removed the shadescreen. Have kept the 1/4 hardware cloth because I keep freeflight birds in it but I doubt it's moderating the climate at all. Sensitive plants are moved into the house birds are provided with "Warm boxes"
and of course the aquarium is heated.
Anyway, thanks very much for your thoughts. At this point I still feel that this is the best all around system but stepping the heaters up from 300 watts is getting into serious bucks lol. gary

I have never experienced humidity loss as I run my electric heaters, which, from November through March, is frequently. Since my gh is fully-enclosed, the humidity is always higher inside than outside.

You also mentioned them getting too hot directly in front. The dimensions of my gh are 8W x 9H x 14L, and I have a 30" walkway down the center with orchids on either side, and hanging above. I place both heaters at either end of this walkway, such that the fans blow towards each other. (Hanging orchids above are four feet or so over the heaters.) When temps aren't expected to go below 40F, I just run one heater. Lower, and both get turned on. Placing the heaters as I have, I have never had burn issues. I turn them on in the evening, then go out in the morning at 7:30am and turn them off. They've always worked flawlessly for me, over the many years I've grown orchids outside.

If your plants are tighter than mine, you may want to try the following, which I did when I lived in Vero Beach: I took a tub of water, and made a frame around and above it so that I could hang a wet towel as a wet curtain...with the bottom in the water. The heater was placed on a low stand, and blew into the wet towel. Before turning on the heater, I'd dunk the towel, and it would still be damp in the morning. In retrospect I didn't need this as the hot air dissipates in 2-3 feet or so, but it may be something for you to consider.

During much of the year you are warm and reasonably humid, but I think you'd solve some of your winter issues if you at least enclosed three sides of your structure -- leaving the roof and front open. (Success in growing orchids is determined by how well you moderate extremes, and if you fail to plan for extremes, you'll have headaches!) This will also prevent wind from blowing through, and drying mounted plants out too quickly, etc. I use the gh fabric linked below. It's like iron, and would be much easier for you to store than rigid panels (and could potentially make a tighter seal around edges as well). It's reinforced with fibreglas "tapes" sandwiched between the plastic, and a hurricane couldn't rip it open.

-Bruce

Here is a link that might be useful: FarmTek 5.2-ounce fabric

Hi

Have tried every covering known to man and don't like any of them lol. . Wide open answers the most problems most of the year lol believe me. If interested I'll bore you with long lists of failures
It serves as an enclosure for some tropical birds though it's stuffed with plants. The aquarium was added because I needed a reservoir for a waterfall so decided to serve two functions. added a heater because I wanted more EXOTIC fish lol Needed more reserve water because of evaportion. so heated the pool also.
Anyway started noticing the cooling ,heating, effects of all the water. Seems worth exploring.
I do keep orchids in it but mostly cool dry rest dends. Brassidiums Catts Phals are moved into the house as I keep a warm room for the fish anyway. Those outdoors are either covered or left to mother nature lol.Now you know somebody who grows orchids as annuals lol.
The prize plants in the shadehouse are the understory palms along with the lace plants and they require a winter cool down anyway.
Thanks very much for the suggestions but I think at long last I'm finally heading in the best direction lol gary