""I am in limbo right now with questions....."" ask them here.

Most of us in zone 5 and above have nothing else to do until march. Well we have the rake leaves thing, and the put the plastic over the windows stuff and remember to buy 5 gallons of gas and stick the winterize gloop in it, and take the cutting bed off the mower and fit the snowblade and snow chains to it.

But after we have done all that we have plenty of time to discuss things!

Oh I forgot! We have to take the battery off the mower/snowplough and bring it inside 'cause the instruction book says so.....

This is by no means a complete list of considerations. They are just the ones I came across building mine. I look forward to seeing what others add. A coldframe/greenhouse can be simple or complex depending on what you are trying to accomplish.

Some considerations when building a coldframe/greenhouse.

The technical difference between a Coldframe and a Greenhouse is a Greenhouse is heated, a Coldframe is not. Other than that they can be identical structures. The basic structural considerations are Foundation, Framing and Glazing and Utilities. How permanent or temporary your structure will be will help you determine the type of materials and how they are constructed.

A Foundation serves several purposes. It anchors the structure to the ground and it provides some frost protection. It also provides the base upon which you will attach the framing. The colder it gets and the deeper you dig the foundation the more protection you will get. The material you choose to build your foundation can be based on answering a few questions. Is this a permanent or temporary structure? Will it be heated? How much frost protection do I need to provide. The material can range from Cement to 2x4s. Cement is for a very permanent structure. If your building a Coldframe that will need to be moved in the next few years you wonÂt want to choose cement. But even for a permanent coldframe Cement is not necessarily the best answer. I live in the PNW. It freezes a few weeks of the year. For my permanent greenhouse I used treated 2x12Âs buried 8 inches into the ground for my foundation. If I were building a temporary coldframe I would go with either 4x4Âs or 4x6Âs as the foundation.

Anchoring the foundation. Once you have decided whether your building a temporary or permanent structure and have chosen your foundation material you need to decide how to anchor it to the ground. The size and weight of the structure will tell you how strong your anchors need to be. If you have a 20x 12 structure and it is framed with PVC it will be very light and provide a great deal of wind surface. It will be like putting a sail out in your yard. You need to keep it where you want it to be. If your foundation is cement it will act as the anchor. Otherwise you need to provide an anchoring system. Metal spikes pounded into the ground and then secured to the frame. Or you could sink your corner posts into the ground, 2 to 3 feet depending on the size of the structure, and either tamp the dirt solidly around the posts or pour cement. Again itÂs one of those permanent versus temporary considerations. I personally have not had to answer this anchoring question. I am sure there are many methods that others have used and can suggest.

Water, Electric and Heat. Utilities can be as simple as a garden hose, an extension cord and an electric forced air heater. Or as complex as running underground water, electric or gas lines. Again that permanent/temporary question will help answer this question. Budget and your experience will also play a role. DonÂt try to do Gas or Electric if you arenÂt experienced. Contact a professional and get a quote. If this is a permanent structure you will want to plan to have utilities run underground and into the structure.

How much electricity/amps will you need? Count the number of items youÂll run, fans, motors to open louvered vents, heater, mist system. You can find the amp requirements for each piece either on the box or from the mfg. Add them up and youÂll know how much electricity youÂll need to have.

What should the Frame be made from? You can use many materials for the frame. Metal, wood, PVC. Each has advantages and drawbacks. PVC is cheap, light and easy to work with, but it is not the strongest, can react poorly with some glazing (causing them to deteriorate more quickly) and it limits the type of glazing you can use to polyethylene film. Wood is heavier, still pretty easy to work with, very strong and flexible, but it is more expensive and requires a bit more technical skill to work with. Metal is the strongest framing. It is more expensive than PVC but not as expensive as wood. Most likely youÂll have these pre-fabricated and delivered so design wise they are not as flexible as wood or PVC . Which one is best? Depends on what you are building, how youÂll use it and what you want aesthetically.

To me PVC greenhouses often look sloppy. If I were building a permanent commercial greenhouse IÂd choose a metal frame. I ended up building a wood framed greenhouse because I think they are the most aesthetically pleasing and for my purposes, a retail nursery, aesthetics were/are important to me.

Glazing. What to use to cover your coldframe/greenhouse. Polycarbonate panels, corrugated fiberglass, polyethylene film. There is always a trade off. Some offer better insulation while others are expensive. Polycarbonate panels are generally rated to last ten years, though everyone says they will last a good deal longer than that, but they are expensive. They will insulate better then even double walled polyethylene film, but of course you have much greater up front cost. Most commercial greenhouses are covered with a double layer of polyethylene film. An air blower is attached and blows a layer of air between the two sheets. This is what provides the insulation.

There are several other elements that turn your basic covered structure into a living, breathing coldframe/greenhouse, shade cloth, misting systems, heating and ventilation systems. I have yet to deal with the specifics of these so I have little to offer. But you should know if youÂre going to add them as they will influence what you build it out of and how you construct it.

To build or to buy. Building is almost always cheaper unless you can get one second hand. Though you usually have to deal with deconstruction, moving and reconstruction. With one that is 20x12 you will most likely need a second pair of hands. The construction techniques are not very difficult, but some of the pieces are both heavy and awkward. DonÂt be afraid to try to build it yourself. You will make mistakes, but rarely are they the kind that will be either costly or dangerous. Most of the materials can either be cut or resized to fit most eventualities. And after youÂre done you will feel a great sense of pride at what you have accomplished. Good luck.

jb, what a great post!

I am still trying to limit my number of questions that I ask at one time.

My question I have for the day, I cant seem to find any suggestions for in my books. It is about heating and using gas for heat. We use natural gas for heating our home, yet, the gas tank is a long way away from my future greenhouse site, and this area is also separated by our driveway. Since my greenhouse will function as a backyard nursery, shouldnt I have another, separate gas tank installed? Surely, it wouldnt have to be a large tank. Or, is there somehow a gas tank that is connected to the heating unit? I need to read more into how much gas is used on average to heat a gh, but I first wanted to question this tank issue. And I would definately have a professional do all this work, no doubt about that. I have a flower bed that sits right on top of our gas line and have turned this into a raised bed, yet, I am still paranoid about hitting that gas line. I do not dig more than 6 inches, but still........ I have been told that it is probably 2 foot underground, yet, where this flower bed is located is right where it comes up out of the ground and attaches to the house. I am paranoid that it is higher under the ground at that point than along the rest of the line.

I definately want the expenses for heating to be separated from our home expense. So, this will require a separate tank? Installation expenses?? Will this significantly raise the cost over having another gas line run from the same tank we use for our home? Or, perhaps,I wont need a tank at all?

I appreciate you all, and will have more, very basic, questions.

Before you can answer the question about what kind of heater you need and what enrgy source to use you need to answer the question of what exactly you are building. The type of heat you use will be determined by the insulating factor of the glazing you use, the minimum temp you want to maintain and the minimum temp outside the greenhouse. There are calculators on the net that you can plug in all those factors and it will tell you how many BTU's will be required to maintian that temp. Then you can selelct a heater that will do the job and from there determine whether gas or electric or some other alternative, such as circulated hot water, will be most appropriate.

If you have a tank for your house it is probably sized to heat that house and not more. A seperate tank is probably a good idea. Deffinitely ask your supplier. We use propane and our tank is not big enough to do both the house greenhouse without having more frequent fill ups.

I too use propane to heat our house and Gh. I just finished having the 250 gallon tank removed and had a 500 gallon tank buried so it won't be such and eyesore. I may have to fill it again in February...

If you have natural gas you do not have a tank in your yard.
By law if you have a business you must be able to seperate the business from personel use. So you will diffently need a seperate tank if you have propane or a seperate line if you have natural gas. Usually the only added expense for propane is the line and hookup. Most companies set the tank free or for a very small fee. You can buy the tank or rent it. Depends on your company. With natural gas you will need a seperate line and meter. Some companies charge others don't.
"Surely, it wouldnt have to be a large tank. Or, is there somehow a gas tank that is connected to the heating unit? I need to read more into how much gas is used on average to heat a gh, but I first wanted to question this tank issue."
If the LP gas company doesn't charge by tank size get the biggest you can. Less fill ups and less chance of running out.
All gas tanks are connected to the heater. But if you mean like a small tank right next to the heater as in a gas BBQ grill, or one of the stand alone heaters and 20lb tank. No. The tank would not be big enough and you also do not want your tank in the greenhouse. It must be outside and so many feet away depending on your building codes or the gas company codes.
Mylu just posted that for her 30x60 she used 3,000 gallons last year. At $1.50 a gallon(depends on area and cost) that would be $4,500. It also depends on what temperature you have outside and what temperature you want inside.
Before you can figure that you need to know your structure size, the material it's made of, the insulating factor and the outside low and inside high, and the cost of fuel in your area. Then you have to take into account how effecient your heater is. Even though two heaters have the same BTU's a power vented will use more engery than a non-powered vented one. The heaters are rated as to effecientcy
so read the specs and compare. You may have to pay a little more upfront to get a better heater but will save in the long run in fuel cost.

By law if you have a business you must be able to seperate the business from personel use.

State or federal? If federal, so you mean for tax purposes?

Both. I once had a sewing business and a room I only used for sewing. When we did the taxes I was told if I so much as ironed a shirt with the same iron that I used for my business the whole thing was void and illegal. I am not sure about this year but it has become very difficult to operate a business from inside your home. I know my neighbor has to keep his business confined to one level of their 3 level home. And nothing else can be in the room that does not pretain to his business.
With a greenhouse you diffinetly have a seperate space but it would be very difficult to seperate the utility bill as as to what is home use and what is business use without a seperate meter. Etc etc.
Since I do not have a business I haven't kept up with the current rules.

So it's just for tax purposes, not necesarily a 'law'... In other words, you can mix and mingle all you want, but don't expect to write any of it off your taxes...

Okay, once again I have one of those basic "I should know this already" questions..........natural gas is not refilled into tanks, only propane? Something I did not know........I thought we had natural gas, it is all I am familiar with, and hubby makes references to it all the time. It might just be "habit" for him,since it is all he is used to either, when he actually means propane. We have access to both here, but are currently using propane.

Yes, it is definitly time for me to really delve into all of this, I dont mean just serious researching, I mean actually doing it---building and maintaining my gh/coldframe with utilities and such, if I ever intend to reach my goals in the next few years.

I have so many things to get lined out..........considering before today I thought our gas service is actually something else! My husband takes care of the bills, so I dont pay too close attention.

My "slow pace" of reaching my goals has gone on too long. It is time I jumped in there and "did something" with my savings. Though, just like all of you, finances will certainly bump you back into the snails pace, or, on a real bad year, no pace.

Okay, so, sticking with a question. I was informed by the nursery owner who will supply me with the building materials for my coldframe that the double poly with squirrel cage blower will protect me from frost. My cold frame will be 20 x 12. Let's say that this year I decide not to have any heating unit whatsoever. If you were me, living in zone 6, it was late March and you are hardening off. You are forcasted for lows in the mid to late 20's. Do you trust your plants to remain in an unheated cold frame at those temps?? I mean, lets assume that I have done a spectacular job of insulating my unheated cold frame. Is this a situation where I need to adjust my thinking on what is safe, what is not? I have been told that it will be safe for me, which makes me question why it is that I couldnt use it also as a greenhouse, considering that those low temps are pretty average all winter long, with occasional cold spells. This is where I am confused.

Really, the only heating at this point that I need for 2006 is to keep them from frosting. In the past, my method for hardening off has been to, simply, bring flats back in the house, and move them back out in the morning. Sounds simple! Until you are moving 200 of them!

I need to look into the link yet for the heater calculator, perhaps this will help me learn how many space heaters it may be necessary for me to have on hand. We have about 10 of them already, not sure where they all come from, but I can read the info on the back of the heaters. I once tried to familiarize myself with BTU's and such, but I admit to just letting the info flow out and I would think "I have plenty of time to learn all this stuff". I have the best of books that explain it all, it is just time for me to learn it seriously.

Thanks you all, for rediscussing basic issues that you have probably explained again and again.

You could also buy garbage cans with flat lids, fill them with water and use them as 'table legs'. Maybe a pallet or something for the table tops. They could be heat sinks in the spring and used to store alfalfa meal and such when not in use as heat sinks. Double duty is always good.

You would need about 4 gals of water for every square foot of greenhouse space.

now mind you I am not recommending this for a permanent fix, just to help you along for one year. If you wnat to become a professional grower, you will need much more professional habits than what I have just suggested.

First step is to get the Gh up, then worry about how and when to fill it.

Ellen,

"You are forcasted for lows in the mid to late 20's. Do you trust your plants to remain in an unheated cold frame at those temps??"

No way!!! If your coldframe has nothing in it but benches and flats by 7am with an outside temp of say 25F then inside it will be...... 26F.

However, if you had a few hundred gallons of water in there or several tons of rocks that got warmed up during the day then you may be able to stay above 32F inside if the temp got to 25F outside.

Otherwise in an unheated structure, with no thermal mass added, by dawn inside temperature is a couple of degrees above outside temperature. (the dirt on the floor of the structure has some thermal mass)

Do you ride a bicycle?

Using an unheated structure is like riding a bike.

Chris, I was with you until, "Using an unheated structure is like riding a bike."

Huh? SB

I don't care what the person told you. You may not get actual frost in the chemical term. But if it stays 25*F for a week with no sun in the day to warm it up everything in there will freeze. And if it's wet in there you will have ICE. Even with water barrels and other stored thermal mass. If the temperatures stay low enough constantly with no sun for several days you are in trouble without heat.
I have seen 20 days of 20 degrees here in Georgia. No sun for days. Ice inside on the windows of my greenhouse with minimum heat. If I had NO HEAT I would have NO PLANTS.
And I am on average 15* warmer than you are.
I've got pretty good protection, alarms, heaters, etc. But do you think I leave my $150 banana plant out there in the greenhouse?. Not the first year. Not til I knew everything worked right and would stay above freezing with minimum heat.
The best insulated house(home) will have busted pipes when that once in 50 years you get wind chill of -50 degrees. I know. I've been there.
I think in ANY zone that gets below 32* you stand a chance of a very hard freeze that can last for a week.
One day, two days, you may be OK. If the sun comes out each day you may be OK.
But you must be prepared. A back-up for the back-up as Monk would say. It' a jungle out there. Or in some cases a blizzard.

Cactus, I was referring to using it as a Cold frame in the spring, when she brings her plants out to harden them off. Sorry I didn't explain myself better...

stressbaby,

Riding a bike, you put energy into it then you can coast for a while.

Coldframe, you get energy in there during the day and enough is stored you can "coast" through the night. If you don't get that energy back in there the next day then you may not coast through the night without additional heat.

The numbers I worked with last year were, if the water in the top of the barrels was 55F or more I could just get through a night with a low of 25F. If the next day was cloudy and the water did not go back up to 55F then I knew I had to do extra work to get through the night. (blankets over flats etc)

Cactusfreak just posted a good description of this "Thermal Flywheel" effect.

Webuss, I was referring to Ellen's post. Please read it and give your opinion. Esp. about why not just go ahead and use it as a greenhouse. I think she means without heat.
From what I've read zone 6 has -20 wind chill very often.
Ellen's post:
"Okay, so, sticking with a question. I was informed by the nursery owner who will supply me with the building materials for my coldframe that the double poly with squirrel cage blower will protect me from frost. My cold frame will be 20 x 12. Let's say that this year I decide not to have any heating unit whatsoever. If you were me, living in zone 6, it was late March and you are hardening off. You are forcasted for lows in the mid to late 20's. Do you trust your plants to remain in an unheated cold frame at those temps?? I mean, lets assume that I have done a spectacular job of insulating my unheated cold frame. Is this a situation where I need to adjust my thinking on what is safe, what is not? I have been told that it will be safe for me, which makes me question why it is that I couldnt use it also as a greenhouse, considering that those low temps are pretty average all winter long, with occasional cold spells. This is where I am confused."

Her post once stated using all the utilities. Then she states no heat, asking why can't she just make it a greenhouse if it will work as a coldframe (and I'm assuming she means as is) and having an average of 20 degrees or an occasional cold spell 'during the winter'.
She ask what we would do.
I would answer her question with a big NO NO NO and NO WAY.

I doubt the cold spells are occasional. Going by my zone and experience 20* maybe an AVERAGE but it does and will hit ZERO at least once and stay there long enough to lose what heat you have stored. It only takes once.
And Mylu has already posted the importance of also having exhaust fans and circulation fans. For the days when the sun does come out. But 2 days later it will drop below average.
You need to base your plans on the COLDEST it will get NOT the average.
I don't care if it only get's ZERO once in 5 years.
What if you have your entire years worth of plants in that coldfram, you're away from home, you have no heat, no alarm just a few hundred gallons of water stored in barrels. It's 40 degrees when you leave. All of a sudden you have recording breaking low temperatures that last 2 or 3 days.
'What do you think will happen?'

You guys are ALL giving wonderful, insightful information.......I am pleased with every single one of you guys!

Gotta go finish the dishes and let some of this absorb.......

CACTUS - There is no way I would risk that much work. I mean that isn't even a risk. Might as well just compost them and go prop your feet up to read seed catalogs. hmm...Great idea actually. Anyway, it is the equivalent of risking yourfinancial investments by setting your money on fire. It's not a risk, it's a forgon conclusion of what would happen. I live in zone 8b. I would not do it here. In fact I spent all day reinstalling my propane heater.

ELLEN - For the record, I cannot see any way for you to raise a crop, overwinter, in an unheated greenhouse in zone 6. If you want to go back to plan A, which is what I would do for this year, and then concentrate on giving yourself the year to finish a GH,

Start your seedlings indoors just as you have always done, and when you think it is time to harden them off, put them in the GH to protect them from frost and wind. That way you won't have to move them back and forth. Buy the cool frame you were looking at, take the winter to erect it (on a level area), and work on getting the floor put in, the frame double poly'd, research what type of heat you want to use for winter of 06-07, and do not try to do it all in the next couple of months. Take time to do it the way you want to do it...The suggestions I gave earlier were for after you bring them out and want to harden them off.

Okay, I have been doing some homework tonight and would love to hear how my progress is coming along. Please, everyone, remember that my math skills are rusty, so bear with me.

First, I want to summarize what my plans are, I know it gets confusing when I get ahead of myself and ask questions about regular greenhouse functioning. Also, I want to summarize what I have learned, just so that you all can monitor whether I am on the right page with you.

1. For this upcoming season, I only need a coldframe. I will not be doing any growing from seed on out inside any kind of outdoor structure, it will all be done inside my home. (I think the confusion set in when I questioned why I couldnt use an unheated greenhouse in the winter months, since I had been told that my doubly poly house would tolerate temps in mid 20's). I have no intention of trying this for my precious plants!!! They will be safe and warm inside the house in what will someday be bedrooms for my toddler twins (the are currently occupying a downstairs nursery).

2. Though a cold frame is, by easiest terms to understand, an "unheated greenhouse", this is actually a bit misleading, because (depending on zoneage), the cold frame operater is still going to have to heat from low temps during the hardening off weeks. That is, the weather during late March could be identical to what it was like in late February. The distinction is made then that the difference between the two is that heat is used ONLY to protect from freezing.

Therefore, my cold frame IS going to require heating.

3. I have attempted to do my homework concerning area of my cold frame, cubic feet, Btu requirements and that sort of thing. I would love for someone to doublecheck me. My husband is of no help tonight!

Coldframe: 20w x 12 L x 9.6 H
Arches: 1 1/2 inch galvanized 18 guage square tubing
Purlin: 1 inch 18 guage sq. tube

Area: In order for me to figure this, I had to determine bow length. This information was not given, so I had to attempt to figure it myself, by first finding the circumference. Using 2(3.14)r, my measurements are 2 x 3.14 x 9.6 with equals 60.28. Divided in half gives me 30.14 feet for a bow measurement. PLEASE, can anyone confirm this for me? I plugged this measurement into the heater calculator that JuniorBalloon posted and got 746 feet as the area for my greenhouse.

Minimum BTU output: for an outdoor temp of zero degrees and an indoor temp of 65 degrees: 36,554

I played around with this for a while, entering different temps and such. Even though it is just a cold frame, shouldnt I plan for severe low temps just as if it were a greenhouse? Therefore, I should enter in the lowest temp possible.........correct?

4. I also found a formula in one of my greenhouse books for determining heating requirements. The formula is: H = Ka(t1 - t2). For a plastic covered house, it gives the figure of .80 for the heat transfer coefficient, which is represented by the K. a is the exposed surface area, in square feet. t1 is the desired indoor temp, and t2 is the outdoor temp.

Does anyone use this formula?

Where I get confused is determining "exposed surface area". Can someone explain to me what this is and how I figure it for myself? I dont think that simply L x W is going to give me the answer!

5. I have some confusion about the BTU Input and Output issue. Can someone explain further? In my notes it seems the only explanation is that the output is the effeciency rating. I can see that different heating units have both of these numbers listed. I would like to understand this further.

6. Weebus, you are still completely on the same page as me, I didnt mean to confuse you. I throughly intend to grow all my plants indoors and use my coldframe for hardenening exclusively.

I also should add that I do not intend to ever use my future greenhouse for the summer or fall months. I only want to grow bedding plants exclusively. Maybe, someday, waaaaaayyy in the future I will expand to other things, but for now, my plan is to have my future greenhouse(s) out of commission between the months of June through December.

Weebus, you read me like a book when you mentioned not deciding something in the next few months! I could easily do that.......and live and learn with whatever I chose as my purchase. But, I will not make a hasty decision. However, I know I cant waste too much time because, in reality, I only have a few months to make decisions for my ventilation and such, and now it is evident that I will need heating also. Though I still have a few months, as we all know, those months can just fly by if I put it on the back burner. In just a month, it will be time to start begonias already!!! And mine are still blooming outside from this season!!

The plan for now is to purchase the frame and end wall frame, and spend the winter excavating for the floor. Which leads to next question........

7. I read that anchoring the frames requires using 36 inches ground stakes. Can someone enlighten me on what kind of tool is used ot pound those stakes into the ground? And, will this be an easy task if the ground is frozen?

8. Is there a difference between "quonset" and "hoophouse"? The reason I ask is, it seems that I see quonset, it is next to a picture of a hoophouse that has sidewalls, where as a regular hoophouse may or may not have these sidewalls. I am just curious if this was a distinction or not. Would it not be better to purchase a coldframe with those sidewalls? For the sake of salvaging all available space in the coldframe? It seems that these shape coldframes are a bit more expensive as well, though would be worth it if it saves space.

I have so many questions that I have forgotten most of them. I need to rest my brain for the day........it is late anyway.

My brain is really hurting..... Currently 75mph gusts here and I refuse to look outside!!! Just got the F$@*&%ing greencoldsunspacethingy covered and now it gets exposed to this wind 5 months before I need it?

Hey the wind ain't so much a problem as the sharp pointy cornstalks breaking the speed limit and hitting it!.

I am just going to do #5 as my concentration is not here but outside at the moment.

""I can see that different heating units have both of these numbers listed. I would like to understand this further."" A propane or kerosine or oil or wood heater loses some heat up the flue. Also they do not burn 100% efficient. The BTU rating is based on the theoretical BTU of the fuel they use. The actual BTU is what heat they produce after all the losses. An electric heater is 100% efficient. All the energy in comes out as heat. (yeah an electric heater if it has a fan is 99.99% as some of the energy is converted to noise and the rest is wasted moving air around....)

I'll take number 7.
You need a sledge hammer or a wood axe that has a hammer type end on one side. You need something with weight so a regular hammer is not a good choice but will do if you have the strenght to pound it many many times.
Since you will be aiming at a very small spot you could put a block of wood on top of the anchor to give you something to aim for.
If the ground is frozen it will be harder. Also if the ground is bone dry. You can soak it first to soften it up. It will harden and compact once it freezes or dries up.
Number 8. Go back to the area surface calculator page.
Look at the quonset/hoophouse. The same general idea. Both are interchangable terms. Yes, get the sidewalls.
Number 4
Part 1. Same formula just a higher heat loss factor. The higher the number the greater the heat loss.
Part 2. Go back and read the formula. It tells you it is not simply LxW and you did the formula using the numbers it said to use. What was the other factor? The height. And in your case the lenght of the bows. In my case it's the side walls. Because I have a gable style greenhouse.

I'll take #3 and part of #4.

The formula is a little more complicated than that, involving sin and cos, but you are close since your height almost equals your radius. Here is another calculator, and it includes segment area which is your end walls.
Arc length (bow) = 30.625
Segment area = 149.17
Total area = (30.625*12')+(149.17*2) = 665.84

Without knowing how JBs formula calculates total area, I can't explain the difference. To be conservative on heat calculations, I'd use the larger figure.

K is just 1/R value. It is the same formula as Q = A*deltaT/R. Most versions I've seen use Q instead of the H to represent BTUs.

'Where I get confused is determining "exposed surface area". Can someone explain to me what this is and how I figure it for myself?' You already did that in #3. JBs calculator gives 746, mine gives 666. It is the total area of the GH through which you may lose heat. It doesn't count the floor.

'I played around with this for a while, entering different temps and such. Even though it is just a cold frame, shouldnt I plan for severe low temps just as if it were a greenhouse? Therefore, I should enter in the lowest temp possible.........correct?' Correct. The formula Q (or H) represents hourly BTU requirements. For calculating the heater capacity you need, you want to plan for the coldest single hour of need. For planning on fuel consumption, you can use the AVERAGE temperature, but you must remember to multiply by 24 hours/day, 30 days a month, and so forth.

SB

Robert, please we don't need complicated.
Using Ellen's first figures I get an area of 833 which equals 37,902 BTU's. That means she should get a 40,000 BTU heater.
Do you agree or should she get two 20,000's. That way if one goes out she want be completely without heat. And she could have them set a different temperatures. But them you must consider the 'Throw'. But that's another question.

Sorry. I got up early. :-)

By any method, it seems to me we end up with 35-40K BTU. I agree, Louise, I'd go with two 20K BTU heaters.

SB

Okay, has everyone doublechecked my measurements? I am concerned that I may have calculated wrong.

I know I need to do this again and again and again until I can do this in my sleep before I finally "get it".

At this point, I am looking at 40,000 BTU and am comparing prices in my FarmTek catalog (the only catalog I have at this time). It is pretty obvious that a heating unit is going to cost me every bit of $500 to $1000. And that is just for the unit, it is not counting the other pieces that I am sure will need to be purchased to go along with it.

I guess this is astonishing for me because, one minute I am thinking that I wont need any heat, the next.........

Or, am I just getting ahead of myself? I mean, I know other people use space heaters and other simplified means......I mean, I want to do this the right way, so I know in the end I will just end up purchasing the right size heater, but right now the price tag is hurting a bit!

Or, I could always choose to carry the flats back in and out of the house again..........

NOT!!!!!!!!!

Everyone, your information is invaluable for me. I have been doing a lot of reading in my books, and checking the posts, and it is really nice to feel like I have someone to "talk" to as I am absorbing information.

Ellen, what type heater are you considering?
Check QCsupply.com.

Take a look at one of these. Quite a few people that used to hang out here use them, I have never had a problem with mine...

Click on the heater link on the left side of the page and up in the left corner should be a picture of it, click on the pic.

when i put up the greenhouse 2 years ago,many folks here recommended the vent free propane heaters.and i liked the idea of when the power is out-the greenhouse is still warm.last year when power was out,we almost went to greenhouse to keep warm!anyhow,back to the subject,i bought a used vent free propane heater.works great.i was really surprised how little propane it used.i used 150 gallons all last season.the greenhouse is 14' x 20',and i maintained 50 degrees.this year i'm gonna bump it up to 55.propane seems to be the best option as far as i can see.

Okay, now I need to ask some pretty basic heating questions, perhaps are some that I should know, but never really paid attention to. For starters, I am reading suggested models that are labeled as "vent free". Yet, I read in my books that vented models are recommended, and in some cases it has stated that vent free models are not effecient for "commercial greenhouses". So I need to understand what is meant by "venting". Is this an internal component of the heater? Or an external? I am just speculating here, but I assume that heaters have an output speed or pressure or some measurement that I dont know, that forces the air out. OR, does the heat just blow out on its own? I question this I guess, to understand how quickly the heat will fill up the room. In our ductwork at home, obviously, there is some force that blows the heat through the tiny vent, which can be felt quickly into the whole room once the heat kicks on. Is this force that blows the heat through considered to be an important component in a heater for a greenhouse? Or do all heaters basically work the same way?

Another question, I have read into using poly vent tubes,and I do recall that we used them in the greenhoues I worked at. However, that was a very large greenhouse, it must have been 80 plus feet long. Is it necessary to use these in smaller houses too?

Question #2 How are heaters erected in the greenhouse? I am seeing pictures in my books of heaters actually hanging from chains from the sructure of the gh itself. Are the arches that I am going to use going to be sturdy enough for this? Or does the heater need to be more of a free standing unit? Can they be built into the end wall?

Thank you for the heater links, I am relieved that there are some more affordable units available! I guess I was thinking that the options for greenhouse units was limited.

Blowers blow the heated air out into the GH. The heater I posted
has a blower built into it.

Vented means the waste product (CO2) is being vented to the outside. Non vented means it isn't.

The age of your manual will depend on their point of view on vented vs. vent free heaters. The heater nowadays are so efficient that there is little to vent. There are people who will say, probably even on this board, that you must vent your heaters. It simply isn't true. I have used mine for about 5 years, a guy named orchid dude, who used to post here, grew and sold amazing orchids. He used a vent free.

One thing you want to do though is if your GH is sealed pretty tight, you want to run an intake to the heater so it can get a suppply of oxygen.

If you had a 30 x 150' GH, obviously you would use what I have shown you. You will have a 12 x 20. I have a 14 x 20 and mine does well. I am a couple of zones warmer, but mine is more than I need. I never have it turned up on high.

No you dont need a blower tunnel.

Yes, your structure, if erected properly would hold a hanging heater. Or at least any heater you would use in your GH. I just build a shelf for mine.

Ellen,

I think your internal temp is a bit high for hardening off plants. Others please correct me if I'm wrong, but I think you just need to keep the plants from freezing or slightly above what ever temp they can normally sustain when they are outside in the ground. Perhaps for the plants you are growing that is 65 degrees. Lowering that number will change the BTU required and will save you money on the heater as well as lower the calculation for gas consumption to maintain that temp.

Another question I have for you is about hardening off. If you have a heated greenhouse protecting your plants will that allow them to harden off? I am thinking it won't and that in my own operation-to-be I plan to start and overwinter plants in my greenhouse. To harden them off I plan to use hoop house structures with removable coverings of either polyethylene film and or shade cloth. In my case I will be doing the hardening off at a time when frost is a rare occurrence so that is a factor I don't have to deal with. But the goal of hardening off is to slowly expose your plants to normal outside existence.

jb

JB,
That is a great discussion that we really haven't touch on enough. Do you care if I start a new thread on hardening off where we can all discuss it, and it not get lost in this one?

Good idea weebus.

jb

Okay, but I want to mention something about it on here also in conjunction with the heating discussion.

jb, you are right, I keep finding myself getting ahead of myself, and planning for futuristic purposes also of heating a fully functioning greenhouse. I think that is where I got myself backwards. I was thinking that I had calculated incorrectly, in the sense that I only need heat of any kind in my cold frame for protecting from frost. I do not need to maintain any daytime temps (as long as it is above freezing!) with a heat source (but definitly with ventilation). So then, would I need to only calculate my indoor temp at, say, 35 degrees, and see what my BTU rating would be?

I will do that, and see what happens.

I once posted the same inside temp, of 35 degrees, and Deep Roots suggested 40. His rationale was that would give you more time to fix a heater problem. It is deffinitley a good idea to have a backup. I plan on having a portable kerosene heater just in case.

jb

Okay, I changed my indoor temp to 35 degrees and this time it was 18,277. Definitly a huge difference!

jb, thank you for pointing out this error! I feel very much relieved.

Okay, so help me with a visual of how my heat gets erected. Lets say I build some kind of shelf to put my heater on. Can Ijust use wood? How far from the end wall should it be? How high do you all put your heater up? I have read several different methods of doing this in my books, I have even read that some will use vent tunnels UNDER their benches. Do you keep your heaters close to the plants, or direct the air upwards? I would like to hear how everyone does this differently.

Okay, I know I have mentioned that I have several electric space heaters. We use them for heating our garage in the winter if it is necessary for a particular project going on and we spend a lot of time in the garage. Could I not use these same heaters in my greenhouse? I mean, since I have them already? Dont get me wrong, I will buy an expensive heater if need be, but if these heaters will suffice for this season. Is there anyone who relies on these heaters in their greehouses?

I just checked the heaters for a BTU rating, and it is not given.............sigh.........

What are you going to do if the electricity goes out?

Also, remember, you will be heating your GH to 50*+ in the coming future, so the heater you want to buy will need to be larger than 18000 BTUs. I would stick to the origianl figure. The only difference will be gas consumption for this year.

Weebus,

What do you grow in your greenhouse that you maintain 50 degrees?

jb

I grow a lot of perennials, but that's not where the fifty degree target comes from.

Plants photosynthesis between 50* and 86* If you want to GROW plants, you need to keep them in that range. If you are simply wintering over your plants, then use the lowest temp of your least hardy plant.

Obviously, there are exceptions. This is just the universally accepted range.

How excellent to learn this. I do, at least at this time, plan to just over winter, but a day may come when I will want to push plants or try to grow tomatoes early or something else that I yet do not know.

Thanks,
jb

JB,
Not to jump in on Weebus. But we maintain about 52 degrees in the dead of winter an 55 before and after. Our temp alarms are set to 45 so we have time to react.
We grow about 130 veriaties of 1st year flowering perennials and start them to the week on a week to flower schedule. Target day May 1st.

Mylu,

Are you trying to get perenials to grow and flower earlier than they might normally do so?

Thanks,
jb

That's good Mylu, the range is 50*-86*. If you tried that with bananas, I would guess your success wouldn't be as great. With lettuce, you could go lower even yet.

You aren't jumping on me, I am just stating a temperatue range that has enormous scientific backing. I could say a few things about germination rates and plant growth in the temperature range you state, but it wouldn't do us much good.

JB, to germinate, you want to keep your temps at 60-80*, with obviously 70 being just right.

Weebus is giving some good points. I even try to keep tomatoes over 60F to avoid catfacing of the fruit caused by lower temps once the plants start blooming. I'm not always able to maintain that temp but I find that the plants can handle a little colder temps if the circulation fans are moving the air inside the GH. Circulation fans help in a multitude of ways: 1.When temps are low they elliminate "Dead air spaces" which can be quite colder than the area near a heat source; 2. When inside temps are high they help with plant cooling by evaporation; 3. When you get a few rainy days and condensation gets out of hand on your plants the fans will dry them off and prevent a fungal outbreak that will ruin the crop; and 4. Circulation fans are a great pollinator for many greenhouse crops in a season where bees aren't available.

Everyone should install a few of these $39 Walmart fans as a "Security blanket" for nights where the heat source just can't keep up. I know some are thinking that the fans will just increase heat loss but they do work. If you check your GH thermometer at 2 AM some March morning and it reads 32F, then the circulation fan switch will be the very first thing you reach for, even before you run for a lighter to fire-up the portable propane heater.

Many of us will put plants in a GH in March and then wonder why we aren't harvesting one full month before the neighbor who planted his out in April.If we could keep the temperature up inside the GH as Weebus suggested, we still wouldn't be harvesting a full month before our neighbor, but we would be much better situated than if we just kept the plants alive most nights. I'm just wondering how many of us are going to react this coming year with fuel prices so high. Are many of you planning to heat as usual, drop back on heat and try to just keep plants alive thru cold nights or are many of you just going to wait a few more weeks before starting plants in the GH? There has been alot of points tossed around in this thread about heat sources and I suspect that only a dozen of us have the money to burn (me excluded). If you spend $1000 on fossil fuel for this winter/spring are you going to be able to get it back?

Your post points up some of the differences between a hobbyist and a professional grower. The pros will do what they have to get the plants to market. I am in no way implying one is better than the other, but many on this thread are not hobbyists and the considerations are different.

We all have to take into consideration, when it comes to heating and min temp choices, exactly what it is we are trying to accomplish.

jb

At home, I am a hobbyist, but, I don't smoke, drink, or gamble and I can't take it with me, SO...

If I remember correctly you do like to gamble.:))

jb

I do? Oh, you're talking about hte thread on GP. If the gaming industry relied on my once every 3 or 4 years of gambling, they would have those big fancy casinos. More like a card room in the back of someone's garage. But for me to make a point of going to a casino to gamble, it doesn't happen

would NOT have the big fancy casinos. Big difference eh?