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Greenhouse Radiant Heat at Fox Creek Farm

Raymond Luhrman owns Fox Creek Farm CSA with his wife, Sara. The 350 member CSA has pick-up sites throughout the Capital District. For more information about the farm, visit their website, www.foxcreekfarmcsa.com. He recently was having problems installing his greenhouse heating system and shared the feedback he received as well as pictures and diagrams.

From Raymond:

Two weeks ago I posted a question regarding the suitable materials for greenhouse radiant heat. I experienced lots of little leaks at couplers with 200PSI black poly. PEX would not work well because of the lack of UV resistance. Thank you for everyone sympathizing with hunting for leaks – and thanks for all the suggestions. I put quite some more time in the house, but right now it is not leaking, and it’s germinating the first plants.

 

In this post:

 

1. The replies I received (in general, folks like Trueleaf products form California for bench heat, and don’t use PVC adapters when using black poly).

2. What I ended up doing to resolve the problem

3. Sketches of the plumbing plan, plumbing wiring plan, and the other climate control (overhead heat, venting) for your reference.

 

 

1.      Replies:

 

I feel your pain.  We used pex for a heated table, keep the pex covered as much as possible and no issues after 3 years.  Anyway, that is not your situation.

 

At the risk of being simplistic, I wonder if you have seated the poly hose well enough onto the pvc fittings.  Try to get as many barbs into the hose as possible.  It is extra stiff this time of year, and a heat gun (like for stripping paint) can warm up the tube to a more flexible state, then cram the sombitch home.  Use a couple of radiator clamps on each junction.

 

Perhaps you have done this already, just my idea for a first step.

 

Next thing, perhaps the pvc barbs have cracked?  Are they tensioned or stressed?

 

Is your antifreeze mix right?  It is bloody cold.

 

I hate chasing leaks.

Raymond  the 200PSI 3/4 could be your problem.  While heating the pipe to install barbed fittings, the torch heat weakens the sidewalls of the pipe and channels are created when you install the barbed fitting.  Because it is 200 psi pipe the wall thickness is so great that regular worm clamps do not apply enough force to close the now grooved pipe fully around the fitting.  There are 2 solutions.  One  change to regular ASTM 3408 or 3608 pipe being in the 100 to 125 psi range.  This pipe with thinner side walls will close better with clamps.  Or the second use the pipe you have, cut or take out all the fittings you put in and reinstall them using LIQUID TEFLON. This product is the same as teflon tape but goes on as a paste and will fill the grooves you created inserting barbed fittings into the thicker walled pipe.   I sell this product in pint containers for $24, however if you need to find it locally the hardware store might have it, or home depot.  This stuff is like never seize, one can lasts a long time and it is good to use on all barbed and threaded fittings.    Hope this helps.

I’d avoid using poly barbs – the brass ones allow you to heat the fitting and and crimp the water line much more securely

 

Raymond, The problem with black poly is that it expands and contracts with temperature changes. The same with poly fittings. The best way to get a seal using poly pipe is to use brass fittings.  There is UV protected PEX that works but you must use the proper fittings. As long as you have an expansion tank with pressure safety valve(so you don’t get too high water pressure and blow everything apart) and water supply(either live water or a storage tank) a few drips are not a big issue.  I personally use all sweated copper for my germination house boiler system, with valves to drain it at the end of the season. ed.

We use Truleaf  products for bench heating,  They are in california.  Their bench heating kits work great.  We have had them for over 10 years.

 

The one thing that jumps out at me is the use of pvc barbs. If you use stainless barbs you can really clamp down on the black poly. Also, heat the poly as little as possible to start with a tighter fit. Good Luck.

Is that black poly good for hot water?  Maybe things are expanding with the heat.  I’ve usually used CPVC, which is a heat-rated version of PVC, or Pex, which I think you can get in a UV-rated version.  The Pex is so much easier to deal with than anything rigid.

 

its all sometimes very frustrating! try double hose clamping, using a good nut driver to really tighten.  many of those fittings are ever so slightly not the right dimension.  brass fittings sometimes the same. sometimes better.  best advice is to slightly warm the pipe end with a little butane/propane hand torch(don’t over do, just a quick couple of seconds, always moving). immediately put the fitting in and tighten.  the softened plastic allows you to really tighten more around the barbs. also, the lower psi piping is easier to work with….  ie 100psi, less black plastic that you are trying to compress.

 

 

Raymond, for the past five years we have used an excellent product from True Leaf Technologies in California. They sell their UV-protected tubes in 1000’ spools from which you can cut your own lengths. They  make an L-shaped barbed start that you insert into holes drilled into CPC or standard PVC pipe. Use the smallest drill bit and it will be leak-free. Very easy to order online.

 

2.    What I ended up doing:

 

I replumbed the house using the WIRSBO system PEX. ½ inch PEX fits nicely in ¾ inch 200 PSI black poly (it would also have fitted in lower grade black poly), taking care of the UV issue. Using a limited amount of black electrical tape to shield PEX that is not covered by black poly or insulation materials. Using plastic T-s, elbows and ¾ to ½ inch reducers. 30% glycol in the system for freeze protection. I considered getting the better metal adapters for the black poly, but those things are expensive! As I was initially planning on using PEX (but the guys at the plumbing supply place advised against it for reasons of UV exposure), I already mailordered quite some PEX fittings anyways, so that was sitting in a box while I was setting myself up for that black poly disaster.

The PEX does not leak, the 90 degree bent supports make for a very nice flow through the pipes, and everything is working fabulously.

 

3. Technical plans – someone asked to share the plans – they are attached greenhouse plumbing and wiring. They work for us – you may want to consult with a plumber and/or electrician if you are not confident with these kind of projects”

Raymond was also kind enough to share some pictures

Greenhouse bench layout

Greenhouse bench layout

The Radiant heat setup- Note on-demand flash water heater.

The Radiant heat setup- Note on-demand flash water heater.

The Germination chamber

The Germination chamber

Next week I’ll write about the advantages of radiant heat in benches for transplant houses.