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Author Topic: Heating a greenhouse on a budget??? Ideas?  (Read 710 times)

D-Grower

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Heating a greenhouse on a budget??? Ideas?
« on: January 01, 2018, 10:27:39 PM »
Hello all! Just getting settled at my new zone 8 location. Have erected two greenhouses but not of the greatest resistance to the 20s F nights here right now. Many of my prized plants have gotten cold burnt already but most my important ones still live and could perhaps make it through at this point. However the 20s are here to stay for another week or so at night...

Right now I've strung up my best plants with old incandescent Christmas lights and also covered them with sheets even inside the greenhouses. Hopefully that will help get me through the week...

However outside what I've done with my little buget at the moment is there any tricks up your all's sleves? I don't have huge barrels for the water heat retention and radiation at night thing. Probably cost way too much to put a space heater in thin plastic greenhouses and could be even more a fire hazard than what I've currently done...

One greenhouse is 20'10'10' and the other 10'10'10'. Did double plastic them too on the top at least and the long sides on the biggest one.

Any suggestions?

Thanks! DG
Trying to grow it all!

Isaac-1

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Re: Heating a greenhouse on a budget??? Ideas?
« Reply #1 on: January 01, 2018, 11:33:34 PM »
My suggestion would be a propane heater, perhaps one of those $100 patio style radiant heater that hold a 20 pound propane tank in their base.  Or even one of these https://smile.amazon.com/Mr-Heater-Single-Outdoor-Propane/dp/B004W7SIUG  On low they will run for about 16-20 hours on a tank of propane, a 20 pound tank typically cost around $17 at one those propane tank exchange cabinets that can be found in front of all sorts of stores (hardware, grocery, dollar, etc.)
« Last Edit: January 01, 2018, 11:36:12 PM by Isaac-1 »

KarenRei

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Re: Heating a greenhouse on a budget??? Ideas?
« Reply #2 on: January 02, 2018, 04:08:19 AM »
Once upon a time I lived in Iowa and built a greenhouse. I had a choice between propane and electricity. I chose propane.

I chose poorly.  Go electric.  Propane is an annoying chore for a greenhouse. Even though I went with a 30 pound tank to reduce the frequency of trips, and kept the greenhouse super-cold (wasn't growing true tropicals back then, just "garden plants"), the periodic replacements were a drain on my life.  Also note my caveat further down in this post about propane heat.  Now, you're certainly in a warmer climate than I was in Iowa! But you're also surely not wanting to keep your greenhouse super-cold either.

Now, when I say "go electric", am I saying "add electric heaters"?  NO!  Add electric lights!  Your plants will lack light in the winter (even if you do what I did and put reflective insulation on the north walls); mine sure hated it. Ideally go LED if your budget supports it; even with LED, most energy that goes in is wasted as heat, but you get a *lot* more light out than you do with incandescent for a given wattage.

Do black-painted water barrels help?  A little.  But not as much as you'd hope.  Also note that the water inside will steadily get ucky, and if you add chlorine, it'll shorten the barrels' lifespan.  Better for heat storage would be - if your budget allows for it - running tubing underground and hooking up a blower (or a water system, so long as you're sure it won't freeze).  I had an idea for a "low budget" version at one point involving an auger and doing pairs of 45 holes that meet at the bottom, then fitting PVC tubing through them forming a zigzag network. But I never implemented it.

Some other things:

Do yourself a favour and run water to your greenhouse; hauling buckets of water is tiresome work.  And don't do what I did and manually dig a trench with a garden hose in it; get a proper trenching tool so that it'll be deep enough to not freeze, and have a plumber connect a water line to the *inside* of your house.  Or if you don't want to do that, then find an electric heating solution for where the hose is exposed outdoors on its way into the ground. Insulation alone isn't enough to keep that from freezing.  And on the greenhouse end, make sure that the hose comes up *inside* the greenhouse, not outside as I foolishly did in my first iteration.

You can set up an automatic watering system to save you from having to go outside in the cold, but be careful.  You have to keep your electronics from getting wet first off.  But secondly, don't make my ultimately fatal mistake.  I had a painted-steel framed kit greenhouse (which I heavily adapted over time).  My watering system *dramatically* shortened its lifespan, and ultimately rusted it away after just several years.  The thing actually collapsed on me while I was inside. Now, my heavy insulation that I added on the north wall sure didn't help things any (lots of extra weight), but it was fine until the steel rusted; by that point, a windstorm would have taken it down regardless even if the insulation weight wasn't there.

If you don't have them, install vent openers and/or fans.  Leaving the door open all the time in the summer may be fine, and always closed in the winter, but in spring and fall it's a twice-daily task of opening and shutting them manually.  And if you screw up?  Hello scorched plants.  Or more accurately, goodbye scorched plants.  I did implement an improvised solution that did actually work (solar panels hooked up to fans on a small vent in the roof - it vented when the sun shone, and stopped at night), but a proper opener would be better.

Oh, remember that caveat about propane heat that I mentioned above? Here it is: the heater Isaac linked is NOT AN INDOOR HEATER.  At least as far as I can tell from the ad.  It could kill you if you use it in the enclosed space of a greenhouse.  And FYI, your plants can be poisoned by carbon monoxide as well.  You need an *indoor* propane heater.  There are two types, indoor-rated unvented heaters, and vented heaters.  The former - even though its rated for indoor use - will still worsen your air quality (buildup of ethylene is the biggest one for plants).  And if the greenhouse is too well sealed, it'll keep hitting its oxygen cutoff.  I used an indoor-rated unvented heater because I thought the extra CO2 would be worth it, but it wasn't. I'd recommend an outdoor, vented heater if you go propane (or natural gas).

Concerning indoor air quality: you may want to seal every gap, but greenhouses need to breathe.  Even without a propane heater, an overly sealed greenhouse will suffer from ethylene buildup (plants give it off on their own), and ethylene is toxic to plants at much lower levels than carbon monoxide is to humans.  One of my DIY projects which I *was* happy with was my DIY heat exchanging ventilation system, which brought in fresh air while heating it up with outgoing air.

Ultimately, though, after my greenhouse rusted, I didn't rebuild.  Since I no longer had a greenhouse, I began starting my seeds indoors.  And they kept taking up increasing amounts of space.  And needing more and more light.  And then it got to the point of, "hey, I have all this light here, I can grow plants that I never would have been able to otherwise, and just never move them outside".  And so bit by bit began my bad habit of obsessively culturing exotic tropicals indoors  ;)
« Last Edit: January 02, 2018, 11:57:49 AM by KarenRei »
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KarenRei

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Re: Heating a greenhouse on a budget??? Ideas?
« Reply #3 on: January 02, 2018, 04:16:58 AM »
Oh, and as for the "double plastic" thing: sounds like it's a film greenhouse.  I had that too.  Hope you realize that you need to change that film regularly.  If it's a good (but conventional) greenhouse film, say, PVC, it should be once every two years, maybe three as a stretch.  If it's something not rated for outdoor use, change it annually, if even that late.  It'll fog and get brittle.  Even PE designed as greenhouse film is generally replaced annually.  And if it's not a proper greenhouse film, you're probably losing more light than you realize, even when it's not visibly fogging.  And light matters a huge amount. 

Again, I really can't recommend doing a "greenhouse on a budget".  Build a proper greenhouse, or don't build one.  I know that sounds harsh, but seriously, picture how you'd feel if after a few years you decided that the thing you built was turning out to be a giant PITA and/or was killing your plants, and all that money and labour you poured into it was for naught.  You don't want that to happen, do you?

If you want a film greenhouse, there's now some ETFE ones out there on the market (expect to pay a lot more for ETFE film than PVC or PE), and ETFE actually does last for decades (UV doesn't degrade it). On the small scale, however, polycarbonate panels are probably the best choice.  You'll have to replace them after 10 years or so, mind you, so keep that in mind.  But you never have to worry about, say, hail shattering your roof, and don't have all that weight on the frame.  And as for the frame, again note my experience... be *very* wary of rust.  I would *never* use painted steel, ever again.  If you already have painted steel, if you can be bothered to tear it down, find a local place that does galvanizing and send it off (note: galvanizing will add a little thickness to the metal, so make sure it'll fit back together!).  There's also zinc-bearing paints, and while they're better than regular paint, they're not as good as proper galvanization.  A galvanized steel greenhouse would be fine, although I'd still prefer alumium. But be careful with alumium - you should use plastic spacers wherever it contacts any other metal, and not anchor it directly in the ground or into concrete. Aluminum resists corrosion superbly in the air and in fresh water, but is very susceptible to galvanic and chemical corrosion.  If you're designing the greenhouse yourself - or if the one you're importing is kinda cheapo - don't underestimate how bad snow and wind loads can get.  And of course insulate the north side, but that goes without saying.
« Last Edit: January 02, 2018, 04:21:56 AM by KarenRei »
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Triloba Tracker

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Re: Heating a greenhouse on a budget??? Ideas?
« Reply #4 on: January 02, 2018, 11:43:34 AM »
And this is why i have no desire to have a greenhouse :)

Couple people I know are wanting to get into greenhouses, and I'm saying to them "WHY?!?!"  :o

Jus crazy bout dem pawpaws!

Walt

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Re: Heating a greenhouse on a budget??? Ideas?
« Reply #5 on: January 02, 2018, 01:27:48 PM »
OK, your greenhouse is already built, so this is for people who haven't built yet, or you if you ever want to rebuild.
I started building my greenhouse by digging a hole in the ground 20 feet square and 5 feet deep.  That about 6 1/2 meters square and 1 1/2 meters deep.  I put top of recycled glass on for a roof because it was free.  I couldn't have bought it on my budget.  A few years later when a meter of snow crushed it, I used plastic and it worked too.
The greenhouse was made mostly for starting spring vegetables, but I did try to overwinter some tropical plants.
WITHOUT suplimental heating, tomatoes survived winters inside.  So did a fig tree and a few tropical house plants.  I am in central Kansas, USA, zone 6, almost zone 5.  And while the tomatoes didn't grow between December and March, they did survive.  That means it didn't freeze.
Given the price of heating, I thought the in-ground greenhouse, AKA grow hole, was a bargin, even though I hand dug it.  Those with more money would want to hire a backhoe.

KarenRei

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Re: Heating a greenhouse on a budget??? Ideas?
« Reply #6 on: January 02, 2018, 03:44:44 PM »
You dug a 6,5m square / 1,5m deep deep hole by hand?  Wow, you're seriously hardcore  ;)
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D-Grower

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Re: Heating a greenhouse on a budget??? Ideas?
« Reply #7 on: January 02, 2018, 07:00:23 PM »
Yes very hardcore Walt! Have heard of such methods but have yet to try anything of the sort.

I would have considered never building greenhouses if I hadn't already owned tropicals I fell in love with before moving here though I had one of the greenhouses from down southward. Lots of rare special tropicals I seed grew and such too so I'm attached to them for personal reasons.

All in all lots of good info to consider here...thanks y'all but certainly keep it coming as it isn't an easy issue to decide the future for either way.

DG
Trying to grow it all!

D-Grower

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Re: Heating a greenhouse on a budget??? Ideas?
« Reply #8 on: January 02, 2018, 07:16:11 PM »
Oh should have mentioned that the bed sheet and incandescent Christmas lights worked or so it seems this past night. No major damage that I could see yet on anything near the lights or covered! However in the greenhouse but away from lights and covers did get burnt. Good thing that was only canna edulis plants and the rhizomes will live on anyway.

Chose incandescent purposefully too might I add. I'm sure that LED let's off some heat but not nearly as much due to less energy use. The "waste" heat is what I was going for and it so far worked or so it seems. Thursday is our coldest day though before warmth thinks about returning Sunday. However not much colder so wish me good growing vibes of success!
Trying to grow it all!

KarenRei

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Re: Heating a greenhouse on a budget??? Ideas?
« Reply #9 on: January 03, 2018, 03:09:48 AM »
Quote
Chose incandescent purposefully too might I add. I'm sure that LED let's off some heat but not nearly as much due to less energy use.

I'll repeat that it's not nearly as much of a difference as you may be thinking.  If you put in 1000W of incandescent bulbs in your greenhouse, you're getting about 970W of heat, and then assuming that 2/3rds of the light is absorbed in the greenhouse, an addition al 2% bringing your total up to 990W.  For a 40% efficient LED fixture, you get 600W of heat, and then of the 2/3rds of the light emitted converted to heat in the greenhouse, that raises it to 867W. So for a given power consumption, the incandescents only put out 14% more heat, but the LEDs put out 13 times more light! 

But wait, it doesn't stop there. Most of what incandescents put out isn't heat directly, persay, but near-IR, which is radiated out and becomes heat when is absorbed by objects.  You'll notice this yourself if you hold a hand near an incandescent and feel the warmth from the light - that's radiant heat.  If you're losing 1/3rd of visible light out through your glazing, odds are good that you're losing a similar amount of near-IR through it as well (depends on how the glazing responds to NIR).  LEDs, by contrast, emit their heat directly via convection from the forced air through their radiators.  If we look up the ratio for incandescents, I come up with that for a 3% efficient incandescent, about 84% of the heat is emitted as IR, while only 13% is via convection off the glass.  If we apply the same "2/3rds absorbed" ratio to the IR, we get only 700W of heat to the greenhouse. Even if we boost the absorption ratio for the IR to 80%, we only get 820W.  LED fixtures, however, are only lukewarm to the touch and radiative losses are proportional to the temperature to the *fourth* power.   So that 867W of heat from the LED should be effectively what you're actually getting.

(To be fair, the light captured by photosynthesis doesn't get converted to heat - at least not immediately. But only a couple percent of what hits plants gets captured as chemical energy - and honestly, you want them getting that couple percent!)

It may be weird to think that you might get actually *more* heat from LEDs than incandescents (since we're so used to incandescents feeling hot and LEDs only lukewarm), but it's the details that matter.  We're not talking about heat per unit light; we're talking heat per unit input power.  1000W (and a true 1000W, not 1000 "LED watts" - they're often marketed at much higher powers than they actually are) is a large, heavy, extremely powerful light, far brighter than a 1000W of incandescent.  The sort of thing that you just glance at and then the whole world seems off-color for the next couple minutes***.  You shouldn't be picturing two equally bright bulbs in the comparison, you should be picturing an incandescent vs. a far larger and brighter LED.  The LED won't feel as hot, only because it's emitting its heat convectively from a large fan-cooled heat exchanger, and its light over a much larger area without the NIR component.  There's no super-hot glass to touch or concentrated IR flux to feel, just a spread-out radiating array of visible light.

To put it another way: if you're putting 1000W in, regardless of the method.... it's going "somewhere".  The only question is how much is getting radiated out through your glazing.  Believe you me, when you get to kilowatt scale LEDs, they actually *do* put out lots of heat.  You should see how hot my grow room gets when I shut the door.  I had several inexplicable waves of plant deaths at one point, and I eventually tracked it down to me accidentally shutting the grow room door. It gets to be like a sauna at the upper levels if that heat can't get out.

But of course, people are always averse to capital costs, and would rather take a long-term loss (higher overwintering death rate, slower growth rates due to overwintering sugar depletion, etc) than invest properly upfront.


*** - "Blinding" is what your plants want!  The sun is a blinding object, and the goal of light supplementation is to try to replicate it to some extent!  :)  Yeah, the UV is the most blinding component of the sun's radiation, but not the only one; even with a UV filter, the sun can still blind you just from its visible and IR flux alone (your eye's lens concentrates all that light into a pinpoint on your cornea, after all!)
« Last Edit: January 03, 2018, 10:30:09 AM by KarenRei »
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D-Grower

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Re: Heating a greenhouse on a budget??? Ideas?
« Reply #10 on: January 03, 2018, 09:56:55 AM »
Very interesting stuff! A lot to take in but I understand what your saying. I'll have to do some of my own research on the subject. Thank you sir I like learning new things!

DG
Trying to grow it all!

TriangleJohn

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Re: Heating a greenhouse on a budget??? Ideas?
« Reply #11 on: January 05, 2018, 07:57:19 PM »
My greenhouse (actually a hoophouse that I seal up as tight as possible in the winter) is 20 by 30 with a 15 foot center ridge. I used to heat it with an old wood burning stove but going out there every hour or so to toss more logs on the fire got old after a couple of years so I broke down and bought a poultry barn electric heater (slightly cheaper than an electric greenhouse heater). It did require an electrician to install a 220 line to it but I already had one because the lot used to have an above ground swimming pool. On a normal winter it only costs me $35 - $50 per month for four months of hard winter. During really cold snaps (like right now) it costs me about a $100 per month. I'm in zone 7b so winters are generally mild. The hoophouse sits on the asphalt pad of an old basketball court which extends out beyond the structure, so when the sun shines it heats up and transfers a lot of heat to the floor of the hoophouse. I also allow it to heat up in the middle of the winter, the peak of the day heat will warm up the potting media in the pots and that will keep everything warm long into the evening.

lornem

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Re: Heating a greenhouse on a budget??? Ideas?
« Reply #12 on: January 07, 2018, 05:34:37 PM »
Another inexpensive solution is installing a water heater. Remove the insulation as best you can and set it up in a loop of your choice of waterline a few inches from the edge buried a few inches powered by a small circulation pump available online for about $25. If needed you can add a car radiator with fan or use a barrel for more volume but at zone 8 most likely not needed. Your choice of electric or gas.
 I am zone 5 and also have 2 layers of bubble-wrap between 2 poly layers. You can get a 4' x 250' roll for about $50.

D-Grower

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Re: Heating a greenhouse on a budget??? Ideas?
« Reply #13 on: January 08, 2018, 09:14:02 AM »
Very cool ideas dudes! My plants did take a bit more damage but all should survive still at this point. Praying not to get anymore cold below 35F! Otherwise the setup I made worked enough to not sustain anymore massive damage. Thank the Lord for that!
Trying to grow it all!

Walt

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Re: Heating a greenhouse on a budget??? Ideas?
« Reply #14 on: January 09, 2018, 01:33:01 PM »
You dug a 6,5m square / 1,5m deep deep hole by hand?  Wow, you're seriously hardcore  ;)

Yes, I really wanted an earth-sheltered greenhouse and I had a break from my summer job, so I spent the winter keeping warm by scouping dirt.  But I only removed about 1 m. of dirt from the whole area,  Then I dug trenches leaving benches of dirt.
Winter was over by the time it was done.  Then I lived in it with my plants all summer.  Watching the night sky at night was great.  I wish I was still living there.

SoCal2warm

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Re: Heating a greenhouse on a budget??? Ideas?
« Reply #15 on: January 09, 2018, 10:04:16 PM »
See these videos, using the ground deep down as a thermal battery:

https://www.youtube.com/watch?v=o2NtBCS2_WQ

https://www.youtube.com/watch?v=IZghkt5m1uY

 

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