Lines in trench concern - clay

[Wood-row Wilson]

Long story short, I'm expecting my Garn Jr. delivered and with the help of heaterman installed yet this year, but really I'm just getting started. I can hear my propane furnace firing as I'm typing this, so you can say I'm getting a little excited for my new system!

I'm sold on the foam in trench method, so in preparation to lay and insulate the lines, I started to dig to locate my propane line as I will need to cross it at some point. Needless the say, I didn't find it (someone is scheduled for Tuesday to mark it out) but ended with a nice size hole. Now, I knew that I had clay and what I see since digging early this week, along with some good rain, is not a huge surprise...standing water! Especially in the spring and fall, I can dig a hole and have a pond.

The trench I will be digging is by a full-size back-hoe, probably 24". I have foam board I will using to make a path to contain only the necessary amount of foam, instead of filling the entire trench. Of course, I'll be using closed cell foam and also plan to line with plastic.

My question is, will I be okay still having so much water retention in the ground during certain times of the year? If what I'm doing won't work, I can't imagine what will! Thanks!

 

[1kzwoman]

www.garn.com recommendation are to not place piping in Continuously wet soil.

 

[airlina]

I have the same issue with clay on my land. I went back and forth over what method to use and ended up putting in Logstor pipe for the run to my new boiler shed. The pipe has a nice thick waterproof jacket, then a waterproof membrane , then a rigid foam insulation around two 32mm (1") pex lines. Diameter is 5 " . I used a backhoe to trench 48 " deep from the boiler shed to the house, then pipe in trench and just to be safe covered the pipe with sand before backfilling with the trenched clay/dirt. All this was done during a recent dryspell, so no water in the trench during the installation. The only downside is of course the price. Luckily my run was short, 70'-cost was $1238 . Bruce from upstate NY

 

[Wood-row Wilson]

Thanks for the replies, guys. I have roughly 120' run to the furnace and another 50' I'd like to run to the water heater. I'm afraid of going with the Logstor type pipe, my installation costs would skyrocket. I'm hoping to get additional opinions...if the foam is closed cell anyways, there won't be any water intrusion and I'll wrap in plastic as extra security. What if I dig the trench, continue with my plans to make the trough with foam boards, then only put sand back in the trench? The problem would be that it's still surrounded by clay, but that would at least help the water pass through quickly by the pipes.

Thanks for your input! My biggest fear is having to do this again, so I want to do it right...while still satisfying my budget. Hopefully there's a way?

 

[easternbob]

do you have enough grade on your property that you could continue the trench and install some drain tile to daylight?

 

[stee6043]

24" in Michigan? Frost line is 42" where I'm at. I assume it's the same in much of the lower peninsula. Did you consult with Heaterman on your planned trench?

I'd suggest you need to plan for a deeper trench...twice as deep.

 

[Highroad281]

I've been agonizing about this same problem for months now too - commercial product vs foam in trench. Similar situation, high water table and frequently wet soil.

I was initially sold on foam in trench, but research eventually led me to sites and details that changed my mind. Read this FAQ about closed cell foam being "water resistant" very carefully: link. http://www.uscomposites.com/faq_foam.html#14

From what I've found even the recommended 4 lb foam is at best still only 80% closed cell. Without a way to effectively skin it 100% water tight with epdm or similar it's going to become a heat sink eventually. You may never notice the heat loss if it's buried deep enough, or if your pump flows enough gpm you may see only a few degrees additional drop but without the water tight casing around the foam it's only a matter of time. By the time you have gone through all the extra cost and labor to do this correctly are you really saving $10/foot?

Seems there are a lot of guys here who have used this method and are happy, not disputing that. Maybe they have ideal conditions, but not me. The fact that the better commercial products have been in service for decades is something that gave me some peace of mind as well.

Just saying. Like many things, it costs a lot because it is worth it. I only wish I was more informed about what this stuff was going to cost me when I decided to supply heat from a detached building.

 

[BoilerBob]

Thanks for the replies, guys. I have roughly 120' run to the furnace and another 50' I'd like to run to the water heater. I'm afraid of going with the Logstor type pipe, my installation costs would skyrocket. I'm hoping to get additional opinions...if the foam is closed cell anyways, there won't be any water intrusion and I'll wrap in plastic as extra security. What if I dig the trench, continue with my plans to make the trough with foam boards, then only put sand back in the trench? The problem would be that it's still surrounded by clay, but that would at least help the water pass through quickly by the pipes.

Thanks for your input! My biggest fear is having to do this again, so I want to do it right...while still satisfying my budget. Hopefully there's a way?

Whatever you do, do not fill a clay trench with sand. It will never dry out and be a direct path for the water to get to the foam.
I have never install heating lines under ground but have trenched lots of domestic water pipes, some in clay.
If you are in clay, the best material for backfill is "dry" clay compacted. The water will not penetrate through dry clay. We have build ponds with clay only, no liner.

Do it right the first time.
Good luck.

 

[Wood-row Wilson]

24" in Michigan? Frost line is 42" where I'm at. I assume it's the same in much of the lower peninsula. Did you consult with Heaterman on your planned trench?

I'd suggest you need to plan for a deeper trench...twice as deep.

My mistake the 24" is in reference to the width of the bucket. The depth needed to go is still an open discussion at this point, and I feel I can go whatever depth I want with unlimited access to a backhoe.

Whatever you do, do not fill a clay trench with sand. It will never dry out and be a direct path for the water to get to the foam.
I have never install heating lines under ground but have trenched lots of domestic water pipes, some in clay.
If you are in clay, the best material for backfill is "dry" clay compacted. The water will not penetrate through dry clay. We have build ponds with clay only, no liner.

Good luck.

Thanks for the input, and that makes sense. Not sure I have dry clay, though...it is what it is.

From what I've found even the recommended 4 lb foam is at best still only 80% closed cell. Without a way to effectively skin it 100% water tight with epdm or similar it's going to become a heat sink eventually. You may never notice the heat loss if it's buried deep enough, or if your pump flows enough gpm you may see only a few degrees additional drop but without the water tight casing around the foam it's only a matter of time. By the time you have gone through all the extra cost and labor to do this correctly are you really saving $10/foot?.

Well, it is all about heat loss so I have to do the math. Forget for a second about anything getting wet, and you have to say a higher amount of closed cell foam (lets say double) will experience less heat loss in a 120 ft (one way) run than what you buy ready-to-be-buried pipe, right? But introduce the possibility that it gets wet and you have a completely different story..

do you have enough grade on your property that you could continue the trench and install some drain tile to daylight?

This is a possibility...I don't have a ton of grade along the path that I'm going, but I could dig it slightly deeper at one end then it does drop off eventually...


Thanks everyone for your help in making the right decision

 

[mstoelton]

Do NOT put sand in a trench that is surrounded by clay and expect that it will stay anything close to dry. In fact, your trench will gather water like a swimming pool. The water will seek the path of least resistance - the sand and pond there. You will need to provide a gradient (slope ) to drain the trench area if possible or create a french drain/well to drain the water from trench.

I am a Certified professional Geologist - I have seen this pooling effect in clay soils happen many times.

 

[Highroad281]

Well, it is all about heat loss so I have to do the math. Forget for a second about anything getting wet, and you have to say a higher amount of closed cell foam (lets say double) will experience less heat loss in a 120 ft (one way) run than what you buy ready-to-be-buried pipe, right? But introduce the possibility that it gets wet and you have a completely different story.

I also assumed this was correct but it turns out that with under ground lines there needs to be a careful balance between R value of insulation and surface area exposed to soil. If you read the Uponor Ecoflex design guide there is a reference to this.

Just going by the specs it seemed to me that their single 1.5" line in the 6.9" casing was the way to go at R8 compared with the twin tube 1.5" in a single 6.9" case at R4.

But looking at the heat loss specs the two single cased lines actually perform worse than the twin even at double the R value. The data presented to support this claim makes sense, and I respect the fact that they publish it freely even though selling the single lines at 2x the footage required would be more profitable. The Logstor guide backs these facts up as well.

Above ground in a dry chase sure, lay on 2x the foam. Under ground where the lines are going to be in moist soil be careful not to discount all the lessons and engineering that has gone into these products regardless of which one you chose.

 

[Wood-row Wilson]

Thanks again for the input, and I will certainly not put sand back in a clay trench...it would be more work anyways.

Since I initially posted, the water is no longer in the hole that I dug. Just to clarify, my water table is not high but I think what I do experience is a slow drain through the clay. I'm paying close attention to all the details, but I'll be honest to say that I'd still like to be convinced that I'll be okay with the foam in trench method, outside lined with plastic. I'd be looking at a savings or nearly $2,000 by my estimates, but also know this is an investment and want to make the best decision

I uploaded a picture to give you all a better context of my situation. The idea is to put the Garn Jr. in my detached pole barn as pictured at the top of the screen then run lines to my water heater as well as my furnace.

On additional thought is to enter the lines in the crawl space and run the remainder through the port hole window and into the furnace. Would it be okay to lay either solution (Thermopex/Logstor or foam in "trough") on the floor of the crawl space, not buried? This would mean I wouldn't have to dig the remaining distance (which I want to put a concrete slab or deck on), wouldn't have to drill a separate hole in my foundation, and it would be accessible if I ever needed to access it. Minimally, I could do the foam in trench under the house and in the crawl space, right?

 

[Fred61]

This is not a good time of the year to evaluate how water ponds in clay. Although I do not have clay native to my land, I was the recipient of several thousand yards that were hauled out of a school construction site. When I erected a vinyl picket fence on the stuff, I figured that if I dug the holes very large in diameter and backfilled with 1/2 inch crushed stone, the clay would not expand and grab on to the post when it froze. It took three winters to jack the posts 2.5 feet up and actually reach the surface. All winter long and well into mid summer, I could remove the decorative finial and see water down in the bottom of the hole. After re-setting one post I decided to trench the fence line and allow it to drain to lower ground. Haven't done it yet; no incentive.

Here in Vermont the "side hill state" where the cows have two legs on one side shorter than on the other and the pitchforks have the tines angled from long to short so they'll match the land, there is always a path to drain to lower ground. If you cannot drain your trench, I fear that you will see/feel the effects of the surrounding water. Not having lived or dug dirt in the flatlands, I am not able to recommend a solution to your predicament. Perhaps a remote drywell.

 

[sjfrench]

All clay and rock here in Missouri as well. For my Garn trench install, we dug down 48". I put foam board at the bottom of the trench. Then ran a glued and sealed PVC pipe suspended through the trench that ran from inside the Garn barn to the house (moisture can't get into the ends of the pipe). Then ran all 8 supply/return lines of pex through the PVC pipe (it's only a 15' run, but I wish I'd separated the lines for efficiency) - then filled the entire trench with closed cell foam (into the barn and under the house).

Dang - that foam is expensive!