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oldmudhouse Las Cruces, NM(Zone 8a) Aug 13, 2007
Well, weve finally started building our Harbor Freight 10 by 12 greenhouse. The frame is up! So far were happy with the quality of the parts, but the manual (as many have posted) is awful. A really patient spouse is very helpful, and so is a sense of humor (which I lost around page 5.)
Ive done lots of reading about this greenhouse, especially in the Garden Web greenhouse forum, and were making modifications to increase the strength. Im using the Garden Diary feature to document confusing steps in the assembly, and to show our modifications as we go. Im hoping some of the photos will be helpful to other folks here at Dave's who are building the Harbor Freight 10x12.
Click here to see my work-in-progress diary about our greenhouse:
http://davesgarden.com/journal/d/m/oldmudhouse/
Our greenhouse is sheltered on the north by our house. It will get full south and east sun, sheltered a bit on the west end by bushes. Were planning to place all four roof vent windows on the south side. Weve added some additional bracing since this photo, but it basically still looks like this:
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oldmudhouse Las Cruces, NM(Zone 8a) Aug 13, 2007
Ill use this year round for my cacti and succulents. They need protection from the cold about 5 months of the year (figure 45° minimum.) The rest of the year they need protection from scorching sun and the wicked-beaked Thrasher birds that poke holes in my plants.
This greenhouse sits in full desert sun! To help, I thought wed build some screen panels to replace some of the polycarbonate panels during the summer. (I dont know how many, or which ones, so any suggestions are welcome.) The poly panels will be affixed with clips and screws, so I should be able to remove them at will. Also, were planning to build some simple screen doors that will slide on a track inside the greenhouse, so I can keep the poly doors open, the screen doors closed, and the dratted birds out.
It will get hot inside when the panels go on, so first we want to work on the electrical, water, and floor. Time to face the thing that scares me the most about having my first greenhouse heating and cooling.
Id love to keep things simple, but because of our summer heat, Im thinking Ill need screens for ventilation, shade cloth, AND an exhaust fan (16). This greenhouse has four roof vent windows as well. My plants will take temps up to 100°, but thats the max. Our normal summer temps can sometimes reach 100°, so I can only imagine what it would be inside a poorly ventilated greenhouse in full sun.
If you can read my scribbles, Ive made a drawing with my plan for bench location. Im thinking 12 concrete pavers for the walk areas, and gravel under the benches. Id really appreciate ANY comments, since this is all new to me. Specifically, though, I need to figure out the following so we can size and locate the electrical:
1. Using online heating calculators, it looks like well need about 10,000 BTU. I guess thats two 1500 watt heaters, or one larger heater. Do I just sit the electric heater(s) on the ground? Does location matter?
2. Wheres the best location for the exhaust fan? If I put an exhaust fan high in the back (east) wall, would it work to just use my screen doors as a vent on the west side?
3. I understand I also need a simple fan to keep the air circulating 24-7. How big should it be for a 10x12, and wheres the best place to mount this fan?
Thanks so much for any help!
Sheri
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begoniacrazii Northern California, CA(Zone 9a) Aug 13, 2007
Thank you for this thread and the link to your blog. We're buying this greenhouse and I've also done the research that you have. But this will be a nice bonus to getting started and not having to reinvent the wheel.
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oldmudhouse Las Cruces, NM(Zone 8a) Aug 13, 2007
Oh, good! That's what I was hoping. There's no point in all of us having to reinvent the wheel, and you'll probably be able to build on what we did and end up with something even better. I sure did benefit from everyone else's ideas.
I really do think this is a good deal for the price; even after the extra work of doing the modifications to make it more secure. I'm excited! :-)
If you get stuck at any point feel free to d-mail me anytime, I seem to have the part numbers tattooed in my brain right now. And, if you find any parts in your kit are different from mine, I can add notes to my blog to help keep it more current for other folks.
If you haven't already purchased, you might keep an eye out for a discount coupon from Harbor Freight. Sometimes they'll put them in flyers...I had a 10% off coupon I used for mine, and they applied it on top of the sale price without blinking.
Sheri
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jimrader Rancho Cordova, CA(Zone 9a) Aug 14, 2007
I recomend an evaporative cooler, You could have one sitting on the south side where ir would get the most sun. Take a look at mine on the thread "Harbor Freight 10x12 Greenhouse installed Evaporative Cooler" It is lowering the temp by 20 degrees and adding some needed humidity the plants love
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oldmudhouse Las Cruces, NM(Zone 8a) Aug 14, 2007
Thanks Jim, I did look at your thread and website, and you are moving right along!
We have two evaporative coolers on our house, so I'm familiar with them, but I'm hoping to do something less elaborate for my greenhouse...and less expensive. Since I'm growing mainly cactus plants, I'm thinking the increased humidity would not be as big a plus as it is for most greenhouses. (Although, it would feel good while I was working in there!) Looks like you and your plants will be very comfortable in the hot months. :-)
Sheri
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oldmudhouse Las Cruces, NM(Zone 8a) Aug 15, 2007
OK, after more research, I can't find any reason not to use my screen doors as a vent for my exhaust fan, so the plan is to put the exhaust fan high on the back wall.
Maybe it doesn't matter where the HAF fan goes in a small greenhouse, so I'll probably put it in the middle of a side wall, up high. I'm still deciding on what to buy for the HAF fan.
Apparently some people do hang heaters up high, but others sit them on the floor. Since heat rises, and I don't plan on having a tangle of plants sitting on the floor, I guess I'll sit the heater(s) on the floor, probably on concrete blocks. I haven't settled on a heater yet (one larger or two 1500 watt heaters.) If my greenhouse was longer than 12', I'd think it would be good to put a heater on both ends, but this is so small I'm guessing it doesn't matter much.
Apparently some heaters have built-in thermostats and some don't. The exhaust fan will have to be connected to a thermostat, and it seems to matter where you mount the thermostats (to get correct temp readings). I'm thinking they'll go on a panel on the center back wall, and perhaps sheltered from direct sun by some kind of shallow box.
I'm still reading...if anyone reads this and thinks I'm heading in a wrong direction, feel free to give me a heads up! Thanks,
Sheri
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jimrader Rancho Cordova, CA(Zone 9a) Aug 16, 2007
I think we are supposed to keep the air circulating
and keep it warm in the winter
and keep it fresh
If I insulate it and make it air tight
I can heat it cheaper
but
once I bring in fresh air I have to heat it
does this sound correct to those of you who have sucessfull winter growing ?
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oldmudhouse Las Cruces, NM(Zone 8a) Aug 17, 2007
Jim, this is a bit like the blind leading the blind, LOL.
Ive also read that air circulation is important it distributes the (warm or cool) air more evenly in the greenhouse, and it keeps the plants healthier and seems to lessen insect problems.
Im not sure Im right, but I think fresh air in winter is more important if youre using gas heat. Natural gas would be expensive for us to run to the greenhouse, and propane and kerosene make me nervous. I like the convenience of electric, but that will be expensive if I cant keep it pretty airtight on cold nights. Im working on that.
Back to air circulation A friend of mine suggested using two HAF fans, one in each end of the greenhouse, mounted high, pointing downward. Thats my plan now for HAF fan location.
Well have wiring in place to add an exhaust fan later. For heating, this heating calculator (http://www.littlegreenhouse.com/heat-calc.shtml) says we need around 10,000 btus. Thats two 1500 watt heaters (5100 btu each) or one larger heater. Were looking at this 240v Dayton heater from Graingers; it has a high setting of 13,650 btuh and a low setting of 10,238 btuh. http://www.grainger.com/Grainger/items/3VU34
For the heater thermostat, were looking at the ACF Single Stage Thermostat for $33.95 on this page, since it says it can be wired for a 240v heater:
http://www.littlegreenhouse.com/accessory/controls.shtml#prewired
Jim, I know you were asking about this 1500w heater on Graingers: http://www.grainger.com/Grainger/items/3VU33
and Eggs_Zachtly replied that he successfully used two similar heaters, each with a thermostat. This type of heater seems to sell for a wide range of prices ($20 on Farmtek, $70 on Charleys) and I cant figure out why
they all have nearly identical specs
? Anyway, if I use the Grainger price of $46, that would be two $46 heaters, and two thermostats ($34 each) so the total would be about $150. My total for the larger 240v heater ($115) and one thermostat would be about the same, and seems a bit simpler (?) so thats where Im leaning
unless some really helpful person with experience wants to jump in here with comments (hello, welcome, anyone!) :-)
Anyway Jim, I know your greenhouse shares two walls with your house, and Im not sure how to adjust the above heat calculator to reflect that. I dont know if this helps, but thats where we are today. Staggering onward
Sheri
Edited on 8/20 for correction...figured out the thermostat mentioned above doesn't have an amp rating to handle the heater mentioned above. So, back to square one...maybe two 1500w heaters and two thermostats is where I'm headed. I'm starting to hate this electrical stuff. Anyway, onward...
This message was edited Aug 20, 2007 10:13 AM
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