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SHCS for a Pre-Fab (Harbor Freight) Greenhouse?

Posted by waterstar 7b SC (My Page) on
Wed, Jan 8, 14 at 10:14

Can I use the SHCS system for my Harbor Freight Greenhouse?

I have tried to read the articles, but it is a bit confusing for a newbie. I need SHCS for dummies. ( :

I will only be growing plants in pots, not in the soil. (Using this for starting plants and holding over sensitive ones) Greenhouse is 10x12 with peaked roof of 10 ft. and four roof vents. Air cubic Volume is only 1080 and I only need to move a small amount of air. I think I only need about I need 159.6 feet of 4" tubing. I have very heavy red clay soil.

Specific Questions:

1) Do I have to build a concrete foundation? I was just going to put the greenhouse frame on brick (over sand) and put in a brick walkway inside.
2) Can I bury my tubing in the clay or will it clog with I need to use rock instead? And if I do that, how will it get any heat exchange with the soil? DUH.

Thank you in advance for helping me. So far I have read some of sunny john's info and will be looking into L. David Roper's site (I just read about it on this site).

Follow-Up Postings:

RE: SHCS for a Pre-Fab (Harbor Freight) Greenhouse?

Dear Waterstar,

Yes, I agree it is confusing! It took me many readings of Sunny John's site to understand how it works.

I am not sure about the foundation. I think it is possible to excavate, install the tubing and then backfill the ground flat enough to put the greenhouse on brick but you probably need to mechanically compact the soil. You should insulate the heat sink around the perimeter to protect your heat from being siphoned away by the frost layer.

About clay soils Sunny John says, "Our experience shows that heavier subsoils continue to act as good heat sinks if the tubing has 6" of subsoil above it (8" OC from the surface) You should go deeper if your soil mass is lower."

Whether on not it makes sense for your greenhouse, I don't know. It seems to me that your greenhouse is a little small for this system but I have heard of people using SHCS in a small greenhouse and being happy with it. Sunny John did say that having the tubes at least 30 feet in length is optimal. For the greenhouse I am building it will only be 20 feet and I am using stone for the storage medium.

I would not worry too much about soil/clay getting into the tubes unless you are in an area with a high water table. If you are, I would use stone because then the water can come in and out without bringing in any mud.

Contact David Roper. He is wonderfully helpful!

RE: SHCS for a Pre-Fab (Harbor Freight) Greenhouse?

THANK YOU! Really appreciate your advise. Am reading David Roper this AM and will contact him. ( :

RE: SHCS for a Pre-Fab (Harbor Freight) Greenhouse?

Shcs works fine for small greenhouses, 200ft of 3" ADS would be a good place to start. Dont scrimp on the fan cfm, heat transfer when cooling the greenhouse in summer is much more efficient at higher flowrates, typically 20-30 gh airchanges per hour, diminishing returns begin to appear at around 50 gh airchanges per hour.
The original thinking was to keep the air velocity in the tube low to allow more dwell time, experience of using the shcs for some years shows its the amount of time the entire volume of greenhouse air spends underground versus above ground.

Getting the full potential from the installed tubing length is not achieved at low velocities (aka long dwell times).simply because the air cools to the soil mass temperature well before it exits the tubing, essentially it just coasts through the remaining tube length without getting any cooler.

Large scale shcs installs are largely unaware of this as they dont have the fan capacity to test 30 - 50 gh air changes per hour..

RE: SHCS for a Pre-Fab (Harbor Freight) Greenhouse?

Hex2006, are there advantages to using the 3" ADS in smaller greenhouses compared to 4" ADS? If so, would it be due to the ability to have more tubes with a slightly closer spacing than is recommended with the larger tubing? Cost per foot? Other reasons?
Thanks, Anna

RE: SHCS for a Pre-Fab (Harbor Freight) Greenhouse?

Hi Anna,
I used the 3" (80mm) as its the most commonly available size over here. I wish i could give you a better reason but thats it :)

RE: SHCS for a Pre-Fab (Harbor Freight) Greenhouse?

Hi Hex2006,
Thanks, that is a great reason. :-) I have just been reading some of your SHCS related posts but could not see the images. What distances did you use between the ADS horizontally and vertically in your 15 armed "monster"? Or is the horizontal distance irrelevant due to the circular floor space?

Hi Waterstar, I hope you don't mind me asking questions in your thread. When I was reading posts by hex2006, the suggestions made about "wing insulation" seemed relevant to your greenhouse plan.

RE: SHCS for a Pre-Fab (Harbor Freight) Greenhouse?

Most of the photo`s hosted on the web based photo sites have long since lapsed but most are still there on John`s old shcs forum. Andy`s (Andrew Collins) shcs is also on the same forum.

RE: SHCS for a Pre-Fab (Harbor Freight) Greenhouse?

Thanks, Hex2006, I saw the photos and diagrams in the thread on your installation on WOW!

RE: SHCS for a Pre-Fab (Harbor Freight) Greenhouse?

Hi Anna
The horizontal tube spacing is around 4" at the plenum and fans out radially to around 2ft or so. I have 60m of 80mm tubing forming the 15 equal length loops which attach to the central plenum. The looped tubing arrangement coupled with the greenhouse air being fed directly into the lower tubes provides a higher average efficiency over the season than the usual method of feeding all the tubes on all levels at the same time.

ps: Its a good idea to download a copy of the shcs calculator from the numsum website as its closing down on 15th april 2014,

This post was edited by hex2006 on Sat, Mar 22, 14 at 0:59

RE: SHCS for a Pre-Fab (Harbor Freight) Greenhouse?

I did an adobe floor in a house with radiant floor heat. We put down one inch foam with the reflection side facing upward. In my view, worth the cost. Adobe is basically clay soil excavated from the site and about 10 percent concrete added for strength, so I would think the same principle. You top with linseed oil to seal. I would think the problem of clay soil in a greenhouse would be the moisture factor and having continuously muddy feet. The problem we ran into with the adobe floor is where things sat on it a long time, mold would form. We ended up resurfacing with concrete and laying tile. So my druthers would be sand with pavers or tiles. I find walking on gravel to be tiresome.

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