The plastic will work pretty well the same as any uninsulated greenhouse. I built one last year and only switched to a prefab one because my structure was a little too hillbilly - I am not a carpenter!
I used two kerosene lanterns to keep my 6 x 8 structure approximately 5F higher than outside. That worked well until things dropped below freezing and I had to switch to a gas heater.
If your lows are not down at freezing you might be okay with this just some lanterns - and don't believe the stories about a couple of light bulbs being good enough - tried it and discarded that one. Just watch it during the day- it can heat up pretty fast in the sun and you need to vent sometimes.

I have never had greenhouse (heated or not). But I have used COLD FRAME. Which is basically a trimmed down unheated greenhouse. I found it practical and useful early in the season, to germinate seeds, to shelter plants over cold nights. It works best in sonny cold early spring days. BUT then it does not have the convenience of a walk-in greenhouse.

And the neighbours can't hear you talking to your plants :)

One way to cope with cold nights in green house is to have objects, structure in there that absorb solar heat and stores it. Like stones, rocks, metals, containers filled with water , at direct sun. Then at night, when is cooling , those objects will release heat.
It also depend on the design and location of a greenhouse. You wouldn't want to have glass All around it. Maybe 60% is enough Insulate the remaining 40%. Actually one long side with glass facing SOUTT_ SOUTHWEST should be enough. That is about 35% glassed exposure.

The next way is to have a thermostatically controlled back up heater, say to kick in @ 45F and shut off @ 50F. In zone 10 this should not be very costly. Say, in average 20 night in a year temps drop below 45 to 40. and it cost $5, to heat it. So you the cost is just $100.

This post was edited by seysonn on Thu, Oct 31, 13 at 8:55

Thanks you guys for the input. I like the idea of rocks/bricks to help absorb the heat.. I'm a little disappointed to hear that the plastic doesn't really do it. but I might have to try it this year for the sake of cost constraints, and use some mats to try to keep the base of the plants warm at least.

One of my other issues is going to be that it will be between the house, and an east facing fence(~4ft wide). It gets plenty of light during the day, but won't be ideal.

I'll draft some plans and followup here on how it goes.

Regards, -E

I'm thinking my gas heater is only going to cost maybe $50 a month - when the bill comes and I either confirm this, or get a nasty surprise, then I'll make the decision when to shut down.
Whatever your plans - have fun - we're doing this to have a good time and enjoy the bounty so whatever gets our jollies is super!

I built a similar greenhouse this year as well. I am at 10x20x8 w/ 45 plants. Am currently using soil heating coils to keep soil temp at night ~ 50 degrees (min). I don't have room for any of the typical man-made heating elements (i.e., rocks, water barrels, etc.). Due to the roof (8ft) in the GH I am having to consider heaters as well to help supplement heat.

I bought the Cedar Ridge Blue Flame heater from Lowes. It will use either propane or natural gas. It's a dandy little unit. Has a slight break-in period where you need to fuss with the controls but after a couple of days, it just hums along. I've got the heater on minimum to try to keep costs down. This is my first month running it so I don't know how much the bill will be. Right now (5 in the morning) the GH is 49F- and this is the thermometer reading near the floor. The outside temp is 30F.

Forgot to mention that a cheap fan makes all the difference - it helps keep the hot air from accumulating at the ceiling.

It's kinda funny. We have had winters here that it snowed off and on for days along with weeks of highs in the teens. I have an 8' x 26' polycarb greenhouse (solid polycarb - except for the studs, no wood walls), I would have 4-5 heaters going 24/7, average winter I would run 2-3 heaters at night. Well, so far this season we have had several nights already where they temps dropped to around 35, I have about 12 plants in the greenhouse, I haven't even shut the doors. The plants are doing great. I'm starting to rethink the need to keep it warm at night.
Pam

CanadianLori - Appreciate the info a/ weblink. I will check it out later today. I'll look into the "Double GH" idea for the cold nights.
Living borderline 7B/8A, history notes that avg temps for winter (Nov-Mar) are:
Nov - 68/46
Dec - 59/39
Jan - 57/37
Feb - 62/39
Mar - 69/46

Lows aren't too bad; however, I need to keep the soil temp at min 50 for sure.

Kuvzszlr - nice size on the GH. Let me know how the polycarbonate performs. Being that this is the first year I have decided to use a GH, I wasn't going to spend >$500 total (GH, Irrigation, Heating, etc.).

I am thinking that I do need some sort of low level heating to keep the low-level airspace heated. My hope is that I can erect heating elements slightly above plant level a/ couple this w/ the soil heaters can keep the ambient temp at a/or near 50-60 during all winter months.

I love the polycarb. I've had a greenhouse for over a decade now... it started out 8'x10' and fiberglass. Hated the fiberglass cos it darkened over time. But looking back, I think that might be a good thing, the polycarb stays clearer and thus hotter. I don't have the expensive double or triple walled stuff, considered it, but went ahead and went with the corrugated single wall stuff at Lowes. It works well. I'm sure the double paned stuff would be better, but I don't think the price is worth it, and installation is more difficult and requires more hardware. I love my greenhouse. ;-)
Pam

I put a slightly larger fan in the gh - a 10" one. Now the temp is 61F steady, 24/7.
Should it be higher?

Following up on the greenhouse construction, I'm happy to report that its up! Alas, its become more of a late winter greenhouse. Its made out of 0.75" PVC conduit, modified PVC fittings, and a giant sheet of non-condensing film, 2nd sheet will be cut out for the ends.

Now I just need to figure out how to attach everything and include ventilation... then power for fans, and shelves for the plants. Will update on that progress, and how well its keeping temps up.

Happy New Year everybody!

Looks like a good build. Ess. what I have just a smaller scale. Heating wise I would get a 1500watt ceramic heater (110v). That should work fine. Also, get an old oscilating fan a/ have it blow the hot air around.

My setup is a 10x20x8 green house. I have ~80ft of soil heating cables (4in deep). Two 1500watt ceramic heaters a/ the fan. I can keep it @ 45 degrees minimum at night.

That is awesome!

Where did you find the green pvc? I am planning on purchasing a bunch to make cold frames and would much rather have green than white.

I winter over Ghosts with just a simple EMT hoop house covered with plastic. Got one in a large pot in the green house.
My main green-house is 12'X24' with an 8' deck running the length and an 8'X12' work area in the back. The covering is polycarb on the roof, and 6-mil GH plastic on the sides and ends. These roll up in the summer so we can use it as a deck/dance hall. I put a 36K Hot Dawg propane heater in it and keep the temp at 50 degrees. Two ceiling fans on low keep the air circulating down from the 12' peak.
You don't have to be a carp to build a GH, just get a few tools. Lots of good advice and materials are floating around the web.

Thanks you guys! Forgot to include the dimentions: its 20+ft long, by 7+ft high, and tapers from 46" to 40" wide. I think I understand now why the gents who installed our wood flooring went back and forth so often between measurements and wood cuts.

@CanadianLori: I was looking for green pvc too, but could only find it online, and I couldn't justify the shipping costs. I found the grey pvc at the local hardware store (Lowes), its meant for electrical conduits, but has the same pressure/strength 40psi rating as the white pvc. I was just told by the staff that I shouldn't use it for water lines. To sweeten the deal, it was half the price of the std white one. The fittings were more difficult though. It was hard to find a store or website that even sold 4way and 5way fittings, so I had to go with the white ones from a greenhouse supply company.

Not sure if I'm going to put a heater in there.. honestly, i'm a little nervous of leaving an active heater in a tight space next to the house. I figure I'll keep an eye on the temp fluctuations as soon as the entries and ventilation are up.

do they get any sun in there?

chiemilo:
Had an 8'X20' temporary GH we used to put up on our deck, and we kept it warm with a "Milk Barn" heater that you can still get at Home Depot for $25. It's got a fan and two settings and a thermostat. Just elevate it off the floor and it should be fine. I've still got two that I use in the shop along with a propane bottle infrared heater.

Update:

So far kindof good. I cut the plastic sheet and have it tightly fitted around the long sides and top, secured under the entire structure. But I learned that the strongest 3m double sided tape is no good for the non-condensing material. It makes a nice covered tent, but I'm having trouble figuring out the ends (want to put doors on both ends). I'm trying to stay away from staples or screws to hold the plastic down. We get a lot of wind here, and I don't want any holes to get stretched over time, nor do i want it to look too home-improvised. Does anyone have any recommendations on securing greenhouse plastic? The best solution i've found so far are pvc snap-on clamps.

@judo
it gets sun, but its east facing, in a narrow corridor. Once I get it fully wrapped, I'm going to build some benches ~3ft high to place the plants so they get as much light as possible.Definitely getting my dollars worth out of that mitre saw.

In other news, I'm starting seeding this weekend in the garage chile chamber. Sprouting 72, with around 25 new varieties. Looking forward to 2014!

Good luck to everyone's sprouts this year!

-E

A Winter greenhouse, depending on the latitude and winter chills, should have a specific design. For example, building and placing it in the middle of yard, with 100% exposure with glass or plastic, is not going to be efficient. A winter greenhouse should be different from spring/summer greenhouse. The ones attached to the south wall of a house are the most practical ones with the least energy emergency heat requirement.

JMO

Agreed seysonn. I'm fortunate that the cold hasn't been severe enough to hurt the chiles i have outside right now, not sure if it will anymore. South would be ideal, but the main reason it is on the east side of the house was to take advantage of dead space not being used for anything between us and the neighbors driveway, and because I didn't want to mess with the yard setup.

I'll be honest with you, I'm no expert, I'm just an engineer that plays with hot peppers and visio. I think the part I like the most of this project is that its evolving as I work on it, the more I realize I have to account for hot summers, high winds, ventilation under the house, etc.. I don't think I'll know what the final product is going to look like until I make it through a whole year at the new house.

take care you guys, E

Visio??!! You'd sure be handy to have around! I'm less comfortable with Visio than probably any other program out there. Ugh!