Rob,
I am so glad you asked this..... For up north folks. Beware... My 30,000 unvented gas heater could not keep the gh warm during a cold snap with high winds. Brrrr We went to menards yesterday and purchased a torpedo heater kerosene with a thermostat for 180 dollars. We have it plug in as a backup peace of mind.... It will only kick on during cold snaps -0 zero weather with high winds. Granted I dont have bubble wrap up yet. I do have sheets of plastic overlapped hanging down the doors which helps alot. I should take a picture. I have not seen anyone who has done this also. I should also say. The natural gas heater does not have a fan on it to shoot the heat, where the torpedo heater does. I placed the fan by the natural gas heater to shoot the heat across the gh. Barb

How did I fare? Only so-so. I insulated the door with an extra layer of plastic, that helped lot. I did manage to get my north wall insulation up, but I tweaked my rotator cuff (or labrum or something) hanging up the cover for my exhaust fan. Put a real damper on the morning workouts for several weeks. All of the overhead work got put on hold for a while. I had most, but not all, of my solar pool cover panels up on the glazing.

Still managing min temp of 57 or 58F, but I suspect using more propane than last year.

Ouch, Stressbaby, hope you're feeling better.

For the first year I'm satisfied. I've kept a min temp of 46°F on the coldest nights we've had...high teens. I have not been horrified by the jump in the electric bill for the two 1500w heaters, but it's hard to separate that out from the house electric. I guess I should get one of those Kill-a-Watt devices to measure usage (hope it doesn't turn out to be a Kill-a-Spouse with ensuing arguments.)

I'll probably going to add bubblewrap to the roof for next year, and I may extend the north wall insulation onto the lowest part of the north roof. I now know I don't need a solar pool cover for winter in this climate...even without a pool cover, my problem has been too much heat during sunny winter days (my exhaust fan is kicking on at 90F most days, even in early Feb, with shadecloth still in place.)

I had a two month propane bill come to 900 dollars and my 1400 cubic foot house with the heater set to 65 at day and from 9pm to 6 am set to 60 I'd say it's been all too expensive. Now I'm shifing from grafting to growing seedlings only in the future. Next year my heating bills will be cheaper because I can buy fuel cheaper (new construction), I heavily doubt that will cut fuel costs enough, for me. Anyway, I'm having a ball like always.

Dax

6x8 HFGH here... Heated w/an electric 1500W "Umbrella Stand" heater. I bought a KKONTROLS thermostat unit to turn it on when temps dipped I did the calculations and it appears that the GH is consuming roughly 200 KWH/mo or $50-55 worth of electricity. Not cheap, but in the scheme of things, I think it'd cost a heckuva lot more to replace the plants I've got stored in the GH (which are all lookin' pretty fat 'n happy, BTW).

I did add plain ol' packing-type of bubble-wrap to the ceiling to minimize heat loss.

Outside nighttime temps have been averaging in the low 30's thru winter (dipping, a couple of nights, into the high 20's).

No complaints from me (and DH's complaints were quickly squelched when I replaced all of our "normal" incandescent X-Mas Lights w/LED's @ appx $200!!! FWI: LED's definitely *did* make a difference in the Dec PG&E bill!)

-Nancy

Hi
Had a typical winter but the low was only 35 so didn't get a complete test of the heating system. I have 1500 gallons of heated water but still had to make a choice between keeping the water warm or the air.lol The system worked fine in the 40's but could not keep up in the 30's
A very unusal front this year as it was windy and overcast at the coldest time. Of course ,had that not been true would have been much colder for longer duration.
Did make some progress as at no time did it overheat and the humidity stayed above 50 percent but air dropped into the 40's water dropped into the low 60's.
Again had to move more sensitive plants into the house and had to add insulation to the water system.
Now if I could just arrive at how many watts are necessary for next year. gary

It's been typical Ohio weather here. Periods of below zero temps followed by a few days in the upper 60's, then back down to 20's and 30's. Because of the plants I'm growing and experiments I'm attempting, I've been keeping the temps around 68 or so. One long stretch of cold wacked the gas bill but still not so bad. We had the temps in the house way up as well for a pup out of surgery. Normally the greenhouse is set higher than the inside of the house!! No kidding.

I've had a hell of a time with my blue flame ventless heaters the last couple of years. I spent the first season getting the air exchange figured out to keep the flame nice and blue...and too keep one of the heaters from shutting down. At the start of this season, the remote receiver stopped receiving commands from the remote unit. Not a convenient time to discover this. DESA acknowledged that they had "issues" with these units and sent me two replacement sets. These receivers operate by radio frequency instead of line of sight like the old ones. This was a nice feature. After a couple of weeks, one of the units stopped working. WTH? After long talks with the tech folks and my own Sherlock Holmes investigation, it seems that these new units chew thru batteries at a much faster rate...especially when they cycle as often as they would in a greenhouse in Ohio. I opted to go with rechargeable batteries and switch them out each week to be safe. So far so good. Now...I'm a little chilly here, I think I'll go out to the greenhouse to warm up!

That was funny Jay...you might take the bed out there and sleep at night. Sounds like you have had lots of fun this winter.

Its nice to see how everyone is working with what they have in their climates. Spring is on the way so things should be looking better in a few weeks, gas bill wise anyway.

Hope nobody hates me for this, but my 12 X 16 X 12ft. high freestanding Cross Country held (and continues to) at 72 deg. 24/7 all through the blizzards, sub-0's, ice, freezing rain and averaged about $20 - 25.00 per month extra on our nat. gas bill.

It was all that ground insulation, bubble wrap and solar pool cover coupled with the high efficiency, dual combustion direct vent heater.

From what Dax wrote, it would seem that the payback in fuel savings our H/AC guy predicted if spent a few hundred up-front and went with that heater, came even faster than expected.

This is the 1st winter for our Cape Cod 10 x 16. (It's 15.5' tall at the peak) Since we were just overwintering ferns this year we were able to keep temps in the mid 40s to upper 30s overnight. It's been really cold here this winter. Many terrible windy nights in the teens & averaging in the mid to low 20s in January. We did not insulate the north wall or use bubble wrap this winter - just no time & wanted to see how the house would perform. Still need to work on covering a drafty door a little. Just got our Jan bill & it was up around $55 to $60 higher than last year, mostly from the greenhouse, but some also because it was a colder Jan. I was really afraid it would have been much higher. All in all I'm happy.

Kim

Birdwidow, can you describe your heating setup in a little more detail please? Where it is setup, venting, and so on? I thought very seriously of having a new furnace put in our basement and then venting the heat into the greenhouse. I opted not to do this for a variety of reasons but chiefly because I didn't want hot air blowing directly onto any plants. I'd like to hear your story anyway. Thanks, J

Yes Birdwidow, I would also be extremely interested in hearing more about your set up. Your fuel costs are amazing for your climate zone.

We've had a fairly mild winter here, with 15 nights in the 20's but only 7 nights in the teens, with 14* being our coldest night this year. My records aren't perfect though, because I forgot to record the temps on five nights. The average low I have recorded for this year is 32.8*.

My heating costs have been $50-$60 a month for my greenhouse, a 12' X 35' X 12' tall, double poly walls with a solar pool cover inside covering the top and half way down the sides of the greenhouse. The ends are 8mm polycarb. My plants are mostly tropicals and my low temp in the greenhouse this winter has been 40*. I have used two 1500 watt electric heaters this winter because I've found them to be less expensive to run than using my propane heaters, with propane running $2.35 a gallon here. I don't heat the greenhouse during the day because it's generally over 70* by mid morning. My exhaust fan runs half the time during the daylight hours.

My greenhouse is not well insulated at all this winter. We moved last year and I barely got it up before the first freeze, and ran out of time to get it insulated well. There are large air gaps all around the bottom and it has four vents open for the propane heaters, which should have been closed up since I've rarely used the propane heaters this winter. I also don't have my ceiling fans up yet. I feel the solar cover has been my key to lower heating costs this winter, and feel my costs will be substantially lower next winter when I get a chance to seal up all my air leaks. The greenhouse is too packed full of plants right now for me to be able to reach all my air leaks. The plants will all be going outside in about a month, and I can't wait. :)

So far our winter has been pretty mild. (knock on wood). I used my electric heater two nights so far. It kept it about 50 in there. The day temp has been in the 90's in the greenhouse, so I've been more worried about that. My orchids are starting to get mold. So I guess I'll have to do something about a ventilation set up. I have been procrastinating. There are so many choices, I am confused.

I think just adding a pool cover and bubble indoor insulation could help me big time. Good job birdwidow. I'd like to also hear more about how and what steps you took to insulate the type of floor you have. I'm now being told that my concrete slab is causing a ton of heat loss. I'm trying to learn how as suggested, I might be able to insulate a six foot wide x 24 foot long slab. Anyways, it's a good / bad deal right now some say. I wouldn't want to trade it for anything right now but evidently it's costing me an arm and a leg.

Dax

For those who asked: The cheap heat in my GH started with ground insulation that covers the entire base under the floor, then runs 2 ft. down the outer edge of the foundation and 2 ft. out, all the way around it.

We started by digging out about 2 ft. below the level of the eventual floor and installed a floor drain that leads to a sump pit under the sink in the GH that in turn, connects out below frost line to a 100 ft. gray water drain.

We first laid in about 6" of med. sized river stone, to assure good drainage, then fine limestone siftings, screed and packed to a slight slope from the front and back walls, to a gutter drain in the center that spans the width of the floor.

Over that, we laid a moisture barrier: heavy, nylon reinforced plastic sheeting. Over that, 2-1/2" thick type 250 insulating foam.

Over that, 3/4" OSD and over that, 3/4" cement board, as a solid base for the glazed quarry tile floor that is as warm to bare feet in winter as the basement floor of the house.

On the outside of the foundation, we dug a deep narrow trench and lined it vertically with 2" type 150 foam, down 2 ft. then laid more, from the base out 2 ft., sloped a bit away from the the foundation. We lined the outer edge of that foam "flange" with garden timbers, then filled in the space between the timbers and the base with decorative stone. It hides the foam and the 1/2" mesh hardware cloth over it (critter proofing) and gives the foundation a nice, finished look.

The heater is a direct vent, dual combustion 45,000 btu Sterling, which is highly energy efficient and due to the dual combustion and direct venting, burns only fresh air, so it allowed me to seal the GH like a tomb.

Another great help is a pair of 52" ceiling fans that run continually in opposite directions, keeping the air continually circulating front to back, floor to ceiling.

The interior of the GH is lined entirely with heavy 1" bubble wrap and excepting only for the door, which is an insulated, standard storm door, is wrapped in a heavy solar blanket. It's called "Diamond Clear" and as much of a chore as it is to get it on, then off twice a year, it laughs at any wind that comes at us.

We calculated that between the insulation, vapor barrier, flooring materials and the upgrade on the heater, we spent about $600.00 more than if we had just set the GH on some timbers and poured in some gravel. But it's not that much when you think of how little it's costing to keep it warm this bitter winter, and the many more to come, that I hope to live to enjoy using it.

Sorry for the long post, but I couldn't describe it all in just a few sentences.

birdwidow...your welcome to write all you want. Its great that we can share our knowledge.

I'm never shy for words so no problem at all with your explanation. The more the better. I didn't realize you went to such lengths to insulate. Amazing amount of work involved I bet. I think I'll put up with a little higher gas bill instead! Wears me out thinking about it. Got any pics? I'd sure be interested in seeing your setup.

Those guys are of course kidding. Great detail. That information is worth it's weight in gold.

Thanks,

Dax

I'm gratified that my long, detailed description didn't offend, because I truly am glad to share what I learned in the process of designing my GH foundation. But most of the credit has to go to Nathan Hurst, (nathanhurst) who no longs posts here, which is a pity, because he really does understand the dymanics of heat. It was Nathan who blew holes in my original plan and in private e-mails, patiently explained why I needed to insulate against cold to affect my desire for GH that would hold a steady, quite warm (for a GH) temp, regardless of the weather and- most importantly- Nathan explained HOW to do it.

Those who have read my previous posts over the past already know that my need was really driven by the fact that my GH is as much a tropical fish room as a plant growing space.

However, the ceiling fans really do make a difference, particularly in summer, because one of the truths I've learned is that given the right insulation, installed in the right places, using it as a passive method to keep a GH warm in winter is child's play compared to the opposite in summer.

But it all starts UNDER the foundation, and why I keep urging those who haven't yet started, to first- look to their soils, then start digging to suit it. The river stone under my GH was necessary to accomodate our severly hydric soils. (But it's also among the richest, most productive cropland on the planet) Those on dry, highly permeable soils would have no such need.

Patience helps too. My GH sat in boxes for 6 months as we prepared the foundation, then another growing season, as we finished the details before I could actually "move in." The wait was worth it, but had we been 20 years younger, it would have taken far less time and used up far fewer jars of liniment.

birdwidow...do you think maybe your foundation is working because of your zone where in my zone 7b or 8, where the ground only freezes a little, I might not see the same benefits? You might have found something that many northerns need to think about before putting up a GH in that climate. I am just wondering if it would be worth is in my climate where we see a few 20 degree nights a few times a year.

The type of application your greenhouse is serving comes into play as well. Birdwidow is using her greenhouse to raise fish as well. So a good, solid foundation is a must. I plant trees directly into the ground and use the hose vigorously. Her methods would not work for me. I did, however, insulate around the foundation. I can't see where insulation in any case would be a bad thing. Still waiting for some pics! I want to see how your furnace and venting is set up. Thanks

orchiddude: Anyone who constructs ANY type of building they wish to heat in a cold climate, from GH to garage to home, MUST address foundation insulation, unless they want to burn $ on heating bills.

But if your ground never freezes, or does so just at the surface AND you only need to heat no more than about 30 deg. above outside temps, you might be as well off putting your money into wall/base insulation. As the coldest air is always at the bottom, sealing the bottom sill is always a good idea and for that, when it's a retrofit- gap filler foam works as well in a GH as it does around doors and windows in homes.

ohiojay: No digital camera, but the set-up for my furnace & vent is pretty clearly shown on:

http://www.littlegreenhouse.com/accessory/heater-sf.shtml

I mounted my furnace close to the floor on the premise that heat rises, but I use the ceiling fans to create total air circulation. The furnace is set at the back (SW) wall, oppposite the NE facing door, so the ceiling fan at the back end turns to pull air up and the one by the door, down.

The result is continual air movement, top to bottom, front to back, so they also produce the same effect as HAF fans. Better, because every cu. inch of the interior space has air movement. They are just wet location rated Hunter outdoor ceiling fans, available at most any home center. Fairly innexpensive to buy, silent running and very cheap to operate. Mine run 24/365. Lower speed in winter, high in summer. But in summer, as they are mounted directly under the roof vents, they both turn to pull the cooler air from the floor up, and out.

BWs anecdotal experience seems to me to be contrary to the research findings which suggest that only 2-3% of your GH heat is lost through the perimeter...FWIW. This according to studies sent to me by cuestaroble, and I must admit that I do not know where those studies were performed or in what type of GH.

I haven't a clue as to what percentage of heat may be lost through the floor. All I do know is that if I stand on the uninsulated floor in our otherwise very well insulated and heated detached garage in the deep cold of winter wearing socks and tennies- my feet get really cold.

But I can go barefoot on the glazed quarry tile in the GH in the same freezing weather and be comfortable, which is good because I often trudge out there in the early hours wearing only sheepskin slippers, then take them off to prevent soaking them as I splash around, topping off tanks.

It could be that the quarry tile is acting as a heat sink, absorbing warmth from the air, then sending it back up? Again, I have no idea. All I do know is that my GH has stayed warm all though one of our worst winters in many years, holding a steady 72 deg. 24/7, on the cheap for fuel.

It could also be all of the insulation combined, but we just received a $185.00 gas bill for the entire month of January that in addition to the GH, heated a 2300 sq. ft house, a detatched 4 car garage and fueled a gas WH, dryer, and stovetop burners, and this is is the slow cooked soup season.

I can live with that.

It's been awfully cold here. And worse yet, really windy all winter, so my LP man is happy.
I wonder how happy he'll be when I charge him $250 apiece for his tomato plants...LOL
I think I need more insulation, if I walked barefoot in my greenhouse, I think I'd get frostbite! Well if something else didn't bite me first. I've been feeding those mice and voles a lot of mouse poison this winter, so far with good results. I don't think it helps any to have all your greenhouses backed up to a cornfield.

I'm going to insulate my slab, I've decided that much. I did find a 1.5" gap where I thought the greenhouse was attached to the floor however, it's easier not to explain, but this gap ran for seven feet. It was filled with can foam immediately. I already feel a big difference, believe me.

Thanks,

Dax

P.s. I'll bet your greeenhouse is-stunning, Birdwidow. I can only think of a botanical center while reading about "tropical fish" and plants, and a rock surface. Sounds cool. Later.

sandy: My GH backs up to horse pastures and is as close to a barn as it is to our house, but there are no mice in it, because we critter proofed it. The only way to permanently address the problem of mice in a GH is to kill those in it and concurrently; install what will keep their relatives them out in future, which is incredibly easy to do when constructing and still pretty simple to retrofit.

Dax: Thanks to BC Greenhouses designers, my GH is a handsome structure, but hardly stunning. The interior is as best, utilitarian. My planted show tanks are in the house. All of the tanks in the GH are breeders, which means for the most part, bare bottoms with the only live plants in pots. The quarry tile was simply the easiest way to get a floor that was both waterproof and a snap to clean.

Contrary to what some may think, it wasn't so much difficult as tedious. It took time and patience.

(Alas, one of the worst aspects of advanced age is that by the time we finally acquire patience, we have so little time remaining to enjoy it's benefits.)

I haven't a clue as to what percentage of heat may be lost through the floor.

The answer, for the average GH, is zero. BW, you are keeping your GH warmer than average at 72, so you may lose some heat straight down. The temp differential between your 72F interior and the 55F soil straight down is 17F. However, most of us are keeping min winter temps in the 40-60 range and so the differential there is negligible and no heat is lost.

The perimeter heat loss is what you prevent by insulating vertically around the foundation. I've often wondered if that study showing 2-3% perimeter loss was done in a warmer climate. There is a way to calculate perimeter loss. This paper and this paper indicate that an uninsulated perimeter loses 0.8 BTU/linear ft-degree F-hr whereas an insulated perimeter loses cuts that in half to 0.4 BTU/linear ft-degree F-hr. I haven't taken a really close look at the numbers, but some quick calculations show that for a smallish, 6x8 GH, at 55F, avg outside/ground temp of 30F, the heat lost out the perimeter amounts to about 13% of the total heat lost. That's way more than the 2-3% in the studies discussed here previously.

I think right now, my north wall needs looking into if I plan to drop my $250 winter gas bill down to less than that. I have seen one thing this year that I didnt see last. THis year I had 25 times more plants in the greenhouse than last year. I have it packed full. My heat loss was less and so was my gas bill. That told me something right there, a full greenhouse is a warm greenhouse. I wonder if I insulate the north wall with 2 inches of something if I could knock off about $100 next winter. It would probably cost me $200 to insulate unless I found something cheap.

I've used almost $150 in K1 kerosene this winter, 42 gals. Many nights I haven't had to use the heat at all. Tonight the low will be 42 and 39 tomorrow night so I don't need to heat. My floor is brick and it picks up heat from the ground. At these temps the greenhouse stays about 7-10 degrees higher than outside. Now when it gets below freezing I need the heater. When outside temps are in the teens I can easily stay near 60 using both heaters. I have 2 small fans which keep the air moving. One is a recycled kitchen stove vent fan and the other is a small 2 speed fan I bought at the thrift store for $4. 15 winter ago when I first started heating, I could go through a winter for $50.

Stress: We did insulate around the perimiter, with 2" thick Type 150 dense foam around the outside edge to 2 ft. down and more of the same as a sort of flange, 2 ft. out. The two parts are ovelapping and sealed with expanding foam. We used at least 3 large cans of Great Stuff, making sure the entire perimeter was literally airtight. The extra dense, 2" thick Type 250 foam is under the floor.

I haven't the knowledge of thermodynamics to debate the scientific merits of what we did. All I do know is that it worked, just as Nathan said it would. -0 deg. outside, comfortably bare (if not toasty) tootsies inside. Wet ones no less- and a very low heating bill.

While there has also been about 400 gallons of heated (76 deg. avg.) water in the GH, all of the tanks are up on stands, so even if the water helped warm the air; what explains the warm floor, if not at least in part- all that insulation under and around it?

I pulled the plug on my mid way through winter. I have a 8 X 8 glass GH that I insulated with bubble wrap but I was still unable to keep it warm enough in there with an electric space heater. I'll open back up the middle of March and give it another go.

Haven't opened the G'house yet - it's too cold. -28 c tonight (-18 F). It takes 300 # of propane for a week when it's this cold. Gotta open up soon, though. The sun room is full and all of the light shelves in the basement are full. As soon as night time temps are hanging in at -10 or warmer it'll be open. (or sometime next week 'cause I need the space).