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PostPosted: Sat Sep 25, 2010 11:24 pm 
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Since I'll be filling up a greenhouse full of plants and only have a paraffin lamp that only has enough power to raise the temperature by about 5F would metal halide lights put out a significant amount of heat? My goal is to keep the greenhouse over 32F all throughout the winter so that I can leave all my tropicals in there, and perhaps other non-bamboo plants too. Kerosene heaters, even the ones with the lowest BTUs tend to produce too much heat.

Has anyone ever used metal halide lights?

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PostPosted: Sun Sep 26, 2010 1:54 am 
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Why not use an electric heater with a thermostat? Last year I used a DeLonghi ceramic heater, and kept my greenhouse at 70+ all winter. It has an anti-freeze setting too. Much safer than relying on light bulbs and buckets of water.


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PostPosted: Sun Sep 26, 2010 2:13 am 
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The electric heaters as well as kerosene heater that I have looked into seemed to be over-kill as far as heating a 12X7X7 space especially since the goal is to just keep it above freezing in there which should benefit all the plants however still give them a dormancy period. Do you know of any heaters that are something in-between a paraffin lamp and space heater?

My concern about metal halides is that the humidity in the greenhouse can be near 100% at any given time and I don't know if they can handle that type of moisture. With my current paraffin lamp turned on, the lowest it has dropped has been 24F and none of the pots have ever frozen over last year, but we also didn't see sub-zero temperatures either.

The benefit I see in a light is that it can supplement the 8 hours of winter daylight we get during the middle of winter and hopefully add several more degrees of heat for extremely cold nights.

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PostPosted: Sun Sep 26, 2010 2:32 am 
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Metal halides can handle the humidity, we have been running halides over our saltwater aquariums in a closed hood with only an exhaust fan for ventilation for about 5 years now with no problems. They are only about 4 inches above the water and at night when the lights are out, they collect condensation on the bulbs but it goes away quickly when the lights come on in the mornings.

I can't say for sure how many watts of heat are given out but they get very hot, you can't get within a few inches of the bulbs and not feel the radiant heat. Maybe you have a pet store near you that you could check out their lighting systems for saltwater aquariums, live coral requires intense light. Don't buy the bulbs there though, they are way overpriced for what you want to do, you could get by with industrial high bay light bulbs from your electrical supply house, just use the pet store to see how much light and heat actually comes off of a MH bulb.

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PostPosted: Mon Sep 27, 2010 12:49 am 
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Thanks for the info.

I'll shop around and see if I can find something with a decent price because a 400 watt light should both heat up the greenhouse a bit and have some benefit for the plants inside that do not get that much light in the winter. Does 400 watts sound like enough though?

There will be approximately 100 1-5 gallon plants in there nicely packed together for the winter.

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PostPosted: Mon Sep 27, 2010 10:04 am 
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HPS - High pressure sodiums ... will give more heat per watt - but both aren't cheap to run!

- try using 250's instead. MH would be better tbo ... as it's blue end spectrum ..... HPS tend to be better for flowering plants!


Laz


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PostPosted: Tue Sep 11, 2012 11:57 pm 
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I just got my 400watt metal halide for $20 off of craigslist, and turned it on. According to my camera, at a distance of around 3-4ft, the strength of the light is equivalent to daylight at around 9-10AM at this time of the year. 36,000 lumens is not bad. It definitely generates heat after having it on for a while so I won't be placing it inches within any plants, but this light is far superior in brightness in comparison to any of the cfls, leds, or other household lights that I have seen. I can tell based on the brightness setting on my camera.

I do plan on sticking this in my greenhouse, and turning it on once in a while, and definitely if it gets too cold in there. One thing I'm wondering is whether or not something like this means that I won't need to turn on the paraffin lamp which is basically equivalent to around 25 burning candles when it is turned up all the way. Maybe I'll find a way to over-winter tropicals in a greenhouse without having to invest in a heating system.

I guess this would also work very well in germinating seedlings in the spring to prevent them from etoliating. It produces a very bright clean white light so I think it should be good for foliar growth.

My old greenhouse is basically beyond reparable so I just ordered another one from eBay. I literally had to sew the little windows shut on my old greenhouse to prevent cold drafts from getting in so it is much simpler to get one with no air vents.
http://www.ebay.com/itm/Outdoor-10x6-6x ... 43a928118d

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PostPosted: Thu Sep 13, 2012 12:24 am 
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Stevelau have you checked out any passive heating systems like solar water heaters to use for your green house. Been investigating solar water heaters for suplimenting my house waterheater and ran across many referances to using them in cold country like yours maybe You can adopt one for your green house. Oh I am installing one in my green house but I only need a few degrees to keep from freezing here.
MarCat


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PostPosted: Thu Sep 13, 2012 2:29 am 
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I've looked into it, but those solar systems which can warm a heat sink cost hundreds of dollars. There is also no guarantee they will work when there are only 8 hours of daylight, and barely any sunny days during the coldest parts of winter. Sunny days are very rare through the winter, especially the colder ones. I know my 70 watt fish tank heater can keep the GH right at freezing, but if the metal halide alone is enough to get the job done, then I won't need to use both.

I also use a lot of insulation since the WNE sides will be lined with reflective bubble wrap, and if it is really necessary, I can add a plastic tarp over the entire greenhouse so the heat doesn't escape the greenhouse. I know a metal halide heats up pretty well, but I have no idea if it heats up enough warm keep the greenhouse unfrozen over the winter.


One Idea I have never tested is Brad's idea of double layering which prevents heat conduction, and this can be achieved by simply laying a large tarp over the entire greenhouse over a very cold stretch. I have no idea how much more it holds in the heat, but there are usually no more than 5-10 nights in a typical winter where that would be necessary.

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PostPosted: Thu Sep 13, 2012 1:03 pm 
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I think if the light was pointed toward a heat sink (rocks,sand,water jugs) it may be more effective. They will definitely radiate heat, but the larger and taller the greenhouse the harder that light will have to work to heat.

Also, cops.are.drawn go the heat signatures oh hilide bulb from what I eheard

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PostPosted: Thu Sep 13, 2012 1:31 pm 
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If 70W aquarium heater did the job, 400W MH will definitely do the trick. I think it produces at least two times more heat than aquarium thingie. You can always add the heater in case light isn't enough.

Black piping in vacuum tubes can generate unimaginable amount of heat even without direct sun. I think investing into solar heater would be far better investment than metalhalide light which ends up quite expensive - when you receive your power bill. :drunken:

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PostPosted: Thu Sep 13, 2012 2:48 pm 
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That was my other thought tarzanus.... ID rather spend say, 1000 bucks on a set of solar cells and batteries, then 1000 bucks every few months for hydro :S

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PostPosted: Thu Sep 13, 2012 3:30 pm 
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We run 2 hp sodium halides on the main floor of the barn. They are on from about 9am til 9pm. Since installing them the propane furnace rarely comes on. Had we know they threw so much heat (though it's not sop apparent) we could have gone with a much smaller propane stove, it's really well insulated on that floor though - like a styrobox really.

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PostPosted: Thu Sep 13, 2012 4:32 pm 
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johnw wrote:
We run 2 hp sodium halides on the main floor of the barn. They are on from about 9am til 9pm. Since installing them the propane furnace rarely comes on. Had we know they threw so much heat (though it's not sop apparent) we could have gone with a much smaller propane stove, it's really well insulated on that floor though - like a styrobox really.

johnw



Do you know how much 400 watt metal halides consume as far as electricity per month if I did happen to run it for 12 hours every single night?

I don't plan on using it unless I really find it to be necessary, but I thought that using a light would kill 2 birds with one stone in that it can also provide the plants in the GH with supplemental light on top of the heating effect, especially if it got cold enough outside for me to put a tarp over the entire greenhouse.

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PostPosted: Thu Sep 13, 2012 8:33 pm 
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Steve - I can find out for you at work tomorrow.

I would only rely on them for some heating effect in a well insulated structure; in a greenhouse set-up once the lights go out there would be little heat retention. We cover the glass on the north side with thick styro from December till March and still go through $500 of propane. Once we get hooked up to natural gas and have someone dig by hand a trench out to the ghouse we'll switch but will need a new stove, still with electric back-up.

john

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