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Holly's Greenhouse HFGH 2 Heating

Dover, PA(Zone 6b)

How are you trying to retain heat?
I've incorporated a modifications in an attempt to retain heat. First off I'm using a 20k BTU Heatstar LPG heater as my primary. I have covered the northernmost side and roof with used 6 mil uv resistant heat retaining poly. I got the poly from a friend who's recovering his hoop house. I covered the interior of those walls with 3/4" foil backed foam panels, and insulated the base and lower wall with covered straw. The factory supplied polycarbonate is a double wall 6mm and rather inefficient. Any future replacement will be with heavier triple wall to defray the increased material cost. Ric

I forgot to mention I have old cast iron radiators painted black under the sunward bench to collect solar. I plan to fill these with antifreeze and possibly attach a collector.

This message was edited Dec 19, 2012 12:32 PM

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Mooresville, NC(Zone 7b)

Just saw this post, love the idea of the reflective panels.

Dover, PA(Zone 6b)

They really seem to be working, were not expensive, and I probably can # them and store them in the barn. Ric

Provo, UT(Zone 5a)

what size is the greenhouse? what temps can u keep in there?
great pics.. good luck !!!!

Dover, PA(Zone 6b)

It's a 10x12 and we keep it in the mid 50s. You can see the whole story on this link Ric

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Dover, PA(Zone 6b)

Heat requirements have been a bit higher than predicted by the gas co. Today I covered the northeast end of the GH with left over 6 mil poly. It seemed to make a real difference and I will soon see just how much pretty quickly with the weather headed our way. Ric

Las Cruces, NM(Zone 8a)

Looks good Ric; your posts help me be grateful that we live in a warmer climate. Still we've had yet another winter with temps below average (third in a row for us.) So retaining heat is retaining money spent on my electric heaters.

I used foil faced insulation on the inside north wall of my GH and I do think it helps. I am able to leave mine up year round since the north side of my GH is close to our house, and wouldn't get much sun anyway. If I had to, I think I could also cover the lower half of the north side of my roof, too. I don't really think my plants would lose that much light, and I have read that most greenhouse heat is actually lost through the roof.

I have considered adding bubblewrap to the inside of the greenhouse roof for winter, but my bills have not been high enough to force me to do that extra work. ;-)

You may have read this elsewhere, but if you replace any poly panels in the future with thicker panels than the Harbor Freight supplied 4mm, watch out for the roof. The small channel at the peak of the roof will only accept 4mm thickness, so you'll have to be a little creative to figure out how to use thicker poly on the roof, or perhaps crimp or modify the top edge to slip into that channel. (From your posts, I'm sure you will have no problem finding a way to defeat this challenge.) Same with the panels in the roof windows and doors...I think those may have to stay 4mm to fit into the grooves.

The wall panels could be ordered in any lovely thickness with no problem, since they just sit in the outside of the frame.

Your beautiful photo above just makes me crazy. You have no idea how luscious that looks to a person trying to garden in the Chihuahuan desert. Good job!

Dover, PA(Zone 6b)

Sheri, The upper edge of 4mm roof channel could be cut off and replaced with a piece of flashing riveted or screwed in place and calked. Working both sides at once you could just clamp both flashings in place at once and rivet or screw them after the new panels are in place. I've already thought about it a bit. LOL Ric

Las Cruces, NM(Zone 8a)

See, I knew that wouldn't slow you down one bit. :-) Seems like there is a solution to everything, if you're willing to put a bit of time and work into it.

Part of my concern about that particular problem is working on it up high; I do better work with my feet on the ground. My husband would probably be game, but I'm a little more wobbly working on a ladder. If I lived in a colder climate like you do, though, I might be motivated to try it. I'm guessing you'd see a nice difference in heat retention with thicker poly on the roof.

When you cross that bridge I hope you'll do a thread about it, no doubt it would help others facing the same challenge with the HFGH.

Dover, PA(Zone 6b)

I got a like new Anderson sliding glass door with screen and plan to replace the awful leaky Harbor Freight door with it. It will reduce my opening from 6' to just under 3', but should save a whole lot of heat and expense.

Dover, PA(Zone 6b)

I'm not too happy with his plan as I like the wider opening, but I must agree it will conserve some heat.

Provo, UT(Zone 5a)

no greenhouse here..yet..:) but..where the 1st one is going up..probably june/july 2014..
it will be on north side of back of house..gets good sun though..but using the insulated reflective
panel on north side..i like.. reflects back light..good..but also..added insulation to that side of
greenhouse..which i know im gonna need winter 2014.. at least so heat costs dont bust the bank..
much thanks to u all for your ideas and postings of experiences !!!!

Dover, PA(Zone 6b)

777, Your welcome, I too like the reflective insulation, and will post more pics when the door is done.

Fabens, TX(Zone 8a)

Hope to be able to see your improvements soon, look forward to it.

Dover, PA(Zone 6b)

I had back surgery on Veterans Day and didn't get my new door in. With the current temp of 3*F and gusty I wish I'd have made it a priority.As I watched the temp drop to 40 and just below I realized I had to take action. My heater is rated 20k BTU and just could not keep up. According to the charts I only needed 14K, I ASSumed a 40% overkill was enough. Last night I added 2 5k electric heaters and it was enough to reach a stable 55-56*F temp. I will undoubtedly will be adding some more insulation to the north wall and possible some bubble wrap to the roof.
I also need to add an alarm,last month, for some unknown reason the heater did not come on one night and we lost some tropicals, coleus cuttings, and a few of my begonias.:-{

Dover, PA(Zone 6b)

A Sliding Door on the Harbor Freight Greenhouse
By Ric Sanders (@Eric4home) on October 27, 2014
After the brutal winter of 2013 I realized that I needed to improve my HFGH if I was going to use it year-round. I believed the doors were one of the major problems. I was able to get a very good Andersen 6' sliding patio door and wanted to incorporate it into the existing structure.

The first step was to disassemble the door end of the GH, retaining all parts for potential reuse. I constructed a frame of pressure-treated 2x6s, with a 6x 5/4 base. I cut out the base frame of the GH and inserted the PT frame. The frame is set off-center by about 3' because only one side of the patio door opens. I used the cross support I had added (1 aluminum angle) to square the frame into the front of the existing gable.

After fabricating an aluminum flashing for the top outer side of the 2x6 frame, it was inserted with the upright bars outside the flashing, which were shortened and bolted in place. The original cross pieces were shortened and bolted in place, without the door track.

To serve as upright bars for the wood frame, the doors were disassembled and the uprights were screwed into the wood with stainless steel screws.

One was placed back to back to the reused door jamb. All parts were assembled, using sil foam to seal them to each other.

The rest of the job was cutting the glazing to fit and inserting it using clips, screws, and caulk.
Exposed wood surfaces were painted with an enamel, and the windows were cleaned.

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Dover, PA(Zone 6b)

he north facing wall of our greenhouse is bordered by a mixed evergreen planting so it contributes very little light. It also is the predominantly windward side, the impact in the winter is significant. I decided to replace it with a more efficient wall.

The first step was to replace the poly panels with painted concrete panels. This material is often called Hardie Board. Ours were cut from 4x8' sheets and painted with enamel. The panels were caulked and secured with stainless steel self tapping screws.
4" bolts were fitted into the stud tracks and 3" foam panels were put in place using adhesive to secure them together. The foam is a non-absorbent type used in basements. We were very fortunate and got ours from Freecycle.
PVC shower panels were fitted over the foam and secured using the bolts and stainless steel washers and nuts were used to prevent rust stains. I still need a small piece to complete the entire wall but most of this material was salvaged from construction sites.
The result is a attractive water proof wall as a backdrop for our plants that is probably R20+. The panels I removed were saved and will be cleaned and added to the other side doubling the glazing and thermal integrity of that side as well.

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Las Cruces, NM(Zone 8a)

Ric, good to hear from you again. Those changes look wonderful. A lot of work, to be sure, but those changes will surely make a difference for you. An added bonus is the new wall and sliding glass doors look great, too. Such a nice, clean job on all of it, including that north wall, with the waterproof surface (great idea to use those PVC shower panels.)

We enjoy re-purposing and scrounging materials whenever we can. Freecycle can be a great source. We haunt our local ReStore frequently too. Good for you for being able to salvage these materials. Love it.

I take it your original Harbor Freight panels are still holding up okay? If so, this must be evidence that folks in colder climates, perhaps with less brutal sun, get many more years out of their HF panels. (At least more years than we do, down here in the hot sunny southwest.) It's great you will be able to reuse the panels you removed, by moving them to the other side.

Have you added any extra poly panels to your roof? Just wondered if you had resolved the challenge of adding extra thickness to that (skinny) little groove built into the roof ridge framework. Or did you decide to add bubble wrap to the roof, instead, as mentioned above?

Here's hoping your winter will not be as brutal this year. I am still loading plants into my HF greenhouse; almost done with the annual Great Plant Stuff-In. Each year it's a challenge since I tend to keep most of the same plants, and they are always bigger than last year! I still have screen panels on the south side, but in the next week or so our night temps will fall low enough so the summer screen days are over. My two electric heaters are in place and ready.

Once again, your posts help me to be thankful that our winters here are not as tough as yours. You've done a great job!

(Terri ) South Bosto, VA(Zone 7a)


I have read these posts with much interest and need to ask your help with something. I have the smaller hf greenhouse and my panels need replacing, as almost all the panels especially the roof have holes in them. Could someone please suggest a supplier for replacements?

I was also thinking of perhaps trying to put some sort of poly over them, like in a hoop house, has anyone tried that?
I havent really been able to use it much, its so small and only has 1 roof vent, that it gets too hot during the day and does not retain heat well at night. If i could figure out something that might help at least keep it water tight and not allow such extreme temp fluctuations, i might be able to actually make use of it for winter sowing

Fort Worth, TX

I do not have a HF greenhouse, but one thread down is a discussion on a solar pool blanket and I have ordered one to cover the roof, a bit of the south side, and the upper 4 ft of east and west side over my home made greenhouse. My bottom portion is plywood so I used Owens corning pink between framing and contractor's trashbag moisture barrier.

The windows and gaps around them , and storm damage to one edge of my clear fiberglass waffle roof have served as vents in our Texas heat, so rather than replacing and attempting a perfect seal I'm putting a 14 mil solar blanket from roof edge down with tucks and folds. The south side windows get little winter wind so I'm not worried about a tight cover over them, as they are what I would open for venting.

Climate is interesting around here. Last Saturday it was 90, it may freeze here tonight...

Las Cruces, NM(Zone 8a)

Dragonfly53, I had to replace the roof panels on my HFGH 3 years ago (holes, yellowing, brittle.) I researched prices on materials, and finally cheaped out, ordering more panels from Harbor Freight. However, I know I'll have to replace them again, in time. Right now I need to replace the side panels, but I've been buying time by simply patching the small holes with clear duct tape. The tiny holes are only in the exterior layer, and so far my walls aren't as badly deteriorated as my roof panels were.

In October of 2011, my price research for roof panels turned up the following:
The Harbor Freight price for 12 roof panels with shipping was $135. No crating fee; shipped by Fedex Ground in a cardboard box for $12.99. They arrived in about a week in good condition, and of course were already the right size to install quickly, no work to cut the material to fit.

I found a distributor for Solexx (a white translucent material, not quite as rigid as polycarbonate; it ships in rolls.) The price for enough Solexx to cut twelve roof panels would have been about $300 (including shipping to my location.) I've read Solexx is a good material, but I wasn't sure I'd like the white color, and I was worried I might lose too much light, when I used my 60% roof shadecloth on top (I didn't want to buy new shadecloth, too.)

The best price I found on high quality (10 year warranty) 4mm twinwall polycarbonate was from FarmTek. My price was $435, including the crating and shipping fees, at that time. This would have been the best solution, since it would last a long time, but the cost was so much higher than HF...I cheaped out.

When you talk to companies, be sure to inquire about the additional crating and shipping fees, as those can be quite high with sheets of polycarbonate (except those from Harbor Freight.)

I haven't covered a frame with poly plastic, but this heat calculator might be helpful. You can input the size of your greenhouse, and your average winter temps, to see what kind of heat is required to keep your desired temperature. You can play with different kinds of covering materials (4mm polycarbonate, thicker polycarbonate, fiberglass, 4mm and 6mm polyethylene plastic, etc.)

As you can see, the sheets of polyethylene plastic are not as efficient at retaining heat as the other materials (even the cheapo Harbor Freight 4mm polycarbonate panels do a better job, on that front.) So, you may find you still need to add heat, somehow, depending on your plant needs.

I hope you find a solution, I know the panel problem is annoying with these greenhouses! Other than that, I'm very happy with mine. Too bad their panels don't hold up in some climates, though.

Las Cruces, NM(Zone 8a)

Gypsi, I have read good things about using solar pool covers. Others have told me most heat is lost through the roof, so it sounds like a good solution. My two little electric heaters seem to handle our fairly mild winters here, but adding a solar pool cover would be my next step to try. I hope it works well for you. Glad it's not freezing here...yet!

Fort Worth, TX

well even without the pool cover didn't do too badly last night. See my post on the pool cover thread. I designed it to hopefully NOT add to my electric bill.

(Terri ) South Bosto, VA(Zone 7a)

Thanks for the information everyone; I think that is going to be a project for next year, as it does make sense to just replace the panels, rather than trying to fit plastic over the frame and then have to heat it. Getting my finances in line right now for Christmas and next years taxes so no extra spending money right now, at least not in that large an amount, LOL!

Dover, PA(Zone 6b)

Terri, if your panels are not too badly deteriorated you could just attach GH plastic over them. I got a used piece last year from a local grower and put it over the north side and roof and it worked fine.

Fort Worth, TX

I am thrilled with my pool cover so far. Need to hook up the clothes dryer to its vent into the greenhouse but the tube seems to be suffering from dog or cat damage, then I can actually dry my clothes and heat the greenhouse too. (I disconnected in summer for a reason, still had plants in it.)

Dover, PA(Zone 6b)

Last winter I tried adding a pool solar cover (clear) and saved nearly 1/3 the heating cost.

I've come up with a vent system for a small GH that works with covering the top and sides with poly of a solar cover. As soon as I build and install it, I will share it with you.

Fort Worth, TX

Looking forward to it

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