This is a sticky inspired by Tenman, who suggested it as a topic to address one of the most critical components in a boiler system, namely the underground line set for those installations where the boiler and / or storage is in a different building from where the heat load is.

Not all installs use underground lines, and it is this moderators opinion that if it is practical, one is better off designing a system to avoid them, however this is often not possible.

However, it is worth noting that if an underground lineset is used, it will probably be one of the most expensive parts of the entire installation, sometimes costing even more than the boiler itself.  It certainly is the most difficult and expensive part to have to redo if one doesn’t get it “right” the first time around.

It can also be a critical part to determining the performance of an entire system, with bad design choices causing poor system performance, high operating costs, and excessive wood consumption….

If one goes through the threads here in the boiler room, I would say that after the standard causes for performance issues such as bad weather sealing, and less than ideally seasoned wood, bad line set design is one of our more common issues, and one of the harder issues to fix.

This is NOT the place to try and save money by going cheap on the design!!!!

So how does one do it right?

1. Make it big enough - there is an often linked to Taco paper on sizing pumps and other system components, including the lines.  [url=http://www.taco-hvac.com/uploads/FileLibrary/SelectingCirculators.pdf]http://www.taco-hvac.com/uploads/FileLibrary/SelectingCirculators.pdf[/url] Before doing any other planning, figure out the heat loads, and determine the size of the piping needed, per the formulas in this paper.  In case of doubt, go bigger. 

Lines that are to small will cause problems of not delivering enough heat on cold days, or doing so only by using excessively large and power-hungry pumps (which can have their own problems, particularly on open systems)

OTOH, there are relatively few problems caused by oversized lines.

Note that large sizes of PEX can be hard to find, and even worse to get fittings for, not to mention the high costs of the tooling needed for the very few connections one will need to make - it can sometimes be advantageous to do multiple parallel runs of a smaller size PEX, something that works especially well if using the “Foam in Place” insulation method described below.

2. KEEP IT DRY - one of the common failure modes for lines is to have ground water infiltrate the insulation system.  A system that may work perfectly when dry can become nearly worthless if it becomes compromised by moisture, as damp insulation becomes a good thermal conductor, and once wet drying an underground line is nearly impossible.  Pay attention to drainage in the trenches, with plenty of gravel and so forth to keep the water away from the lines.  Even more important, choose insulation materials that are in themselves waterproof - we see lots of horror stories about lines that are wrapped in bubble wrap and stuffed into a drain pipe, especially after they have been in service for a few years.  OTOH, there are several very successful installs with closed cell spray in place foam installed in a properly prepared trench.

3. Keep the runs short - saves money, and the less time underground, the lower the temperature drop that even the best lines will experience….

4. Insulate it adequately - Even a one or two degree no-load temperature drop going through the lineset can add up to a suprisingly large amount of heat loss over the course of a heating season, possibly as much as several added cords of wood worth….

5. Include some “support” lines - I always urge that unless you have already included other provisions for it, that you include a few runs of 3/4"conduit for electrical power and / or computer data lines (remember you can’t put low voltage stuff like data lines, and AC power in the same conduit)  Those extra runs cost almost nothing to add when the trench is open, but can be a problem to add later…

Gooserider

This project was done by Larry (aka Tennman ) from this site. I just added the pictures. Any questions please ask Tennman.

First I want to thank Rob (Taxidermist) for posting these pics up for me…again. Aside from a few minor additions to the process I incorporated, this is the method discussed and presented here by Heaterman and others in the Boiler Room. If you search on Heaterman’s recorded data from a system install in the Fall of ’08 the heat loss for this method is remarkable. So I want to acknowledge those who were the inspiration for what follows.

This post documents our second approach to what I believe can become the most critical component of the boiler system if you have a long run like ours. If done poorly it can be the greatest loss of efficiency in the whole system, trust me I know.

What follows is the objectives and method for our second method of insulating our 1 ¼” hePEX. My first underground approach was hastily done because November ‘09 was near at hand and I wanted to move on to the IMPORTANT stuff, install the boiler, and try to save money (bad set of priorities). If I say this once I’ll say it a thousand times, the potential energy loss from this component of the system poorly done will dwarf all the gee whiz stuff we do with controllers, the latest boiler technology, etc. AND this is compounded by a relatively long run. Our home is a historic dwelling so I was committed to having the boiler barn appear at home with our other outbuildings in vicinity of the house which resulted in a 170 foot underground run.

Goals:
1) Use CLOSED cell polyurethane foam to prevent water contact with the Pex.
2) Provide at minimum 3” all around each line with 2”-3” insulated spacing between the lines.
3) Protect the foam as best possible from being contaminated as a result of the foam blowing gun. Even if the foam is closed cell, voids with dirt clods and trash will hurt the insulation properties.
4) Completely enclose the lines, void free to prevent water contact with the Pex and water migration down the lines into our root cellar.

Method:
1) I used a trencher for the first attempt which made about a 6” wide trench. To prevent damage to the expensive 1 1/4” Pex we used a mini-backhoe to dig up/recover the Pex and make the trench you see here. This resulted in a trench about 12” wide which I really didn’t want (extra foam, more cost) but actually worked well allowing us to work in the trench as you can see.
2) After extracting the homebrew insulated approach, we leveled the bottom of trench and laid the plastic. 4 mil worked well, thinner would have blown around too much and thicker would have been too stiff. This is very cheap protection to prevent contamination from trash getting in the foam.
3) Hooked up the Pex lines at BOTH ends. My Pex fittings were already on so if we had foamed the lines with them shifted even several inches I’d been screwed and would have needed to add another joint. Once foamed obviously the Pex will no longer move.
4) Neither the foam contractor or I had ever done this before so after the foam equipment was out and ready we had a team meeting to discuss what we were going to do and how. This team meeting is very important to get everyone on the same page from the beginning.
5) We decided on a 3-man team: 1- the foam gun guy, 2- the guy managing the Pex spacing close to the foaming process, and 3- the guy keeping the Pex suspended so the foam guy can spray onto the plastic under the Pex lines and then lower the Pex at the right time into the expanding foam underneath.
6) We started by filling the access conduit where the Pex lines go thru the slab into the boiler barn. We started at the barn and worked towards the house. Guess I figured that if we were going to screw up while learning I wanted that to be out at the barn.
7) The Pex lifter (me) held up the Pex so the foamer sprayed foam on the plastic under the Pex. As the foam expanded to about 3” underneath I lowered the Pex line while the spacing guy held them apart then the foamer just sprayed on top making sure there were no voids as the foam expanded around the Pex.
8) Repeated this process in roughly 2’ sections working continuously and literally within 10’-20’ we were cooking as a team. It took us about 30 minutes to do 170’. We were walking on the foam immediately when done. The heavy mini-backhoe drove over the stuff repeatedly leveling and replacing the dirt back within an hour of spraying.

As a result of all this our Wirsbo-Uponor oxygen barrier hePEX is encased in a solid block of foam about 10” wide x 7”-8” deep. It was easy and cost competitive with the commercial pre-insulated stuff. Lord willin’ I never see this part of my system the rest of my life. Come December ‘10 I’ll be able to give the delta T’s from four sensors (two at the boiler and two at the HX).

Costs:

Uponor Wirsbo 1 ¼” hePEX = about $2.80/ft (not including shipping)

My cost to foam = $4.70/ft (this will vary based on contractor)

Total $/ft = $7.50 (does not include dirtwork, etc.)

Had I done this initially we would have saved between $1,500-$2,000 because of the re-do expenses and would have been able to focus on other “first season” issues. Hope this is helpful to those that come after me.

IVE DECIDED TO REPLACE THE LINE SETS FROM THE BOILER BUILDING TO THE HOUSE.  THE EXISTING LINES ARE 1 1/4” BLACK IRON PIPE SANDWICHED IN 2” BLUE BOARD.  IVE KNOWN FOR A LONG TIME THAT I HAD TOO MUCH LOSS AND SINCE I RETIRED THE AQUA THERM AND REPLACED IT WITH AN ECONOBURN & STORAGE,  ITS TIME.  I HAVE READ SOME COMMENTS HERE—ALL GOOD.  THERE IS NO FOAMING CONTRACTORS NEAR BY.  I WOULD LIKE TO RE USE THE BLK IRON IF NOT PITTED.  IT MAY BE POSSIBLE TO DIG UNDER THE LINES WITH OUT UN HOOKING.  I HAVE ALSO THOUGHT ABOUT CUTTING THE LINES AND INSERTING THEM IN A CASING,  BUYING CANNED FOAM, BUT WONDER IF THIS WOULD BE ENOUGH INSULATION.  THANKS

Wood Thing, You can find a sprayfoam contractor on http://www.sprayfoam.com .  I put my pipes in a 6 inch drain pipe then filled pipe with foam, then foamed the whole pipe outside with a couple inches around pipe. You have to use 2 or 3 pound foam, as that is the only foam that will not take on water. Most can foam does not meet this spec. You can get some DIY foam that works. You have to line trench with foam to keep dirty out. I loose no degrees off my water temp in 100 ft of pipe. Spray foam keeps the warmth at home. Foamit Up

taxidermist what was the cost per ft. Im glad to see that you wrapped your lines with plastic. I have dug up a number of lines that were sprayed with a foam that were “water proof” Gooserider said it all.So many out there are in for a rude awaking.

Sorry guys. I haven’t been checking this sticky. Taxi posted my process above but it’s up to be to provide the details. First off I need to talk to Goose or someone to figger out how to edit the above post to correct an error. The cost/ft of the pex needs to double for two lines. I was just in a hurry to type it up and didn’ think. I want to reemphasize that there are TWO types of foam CLOSED CELL and OPEN CELL. Both have a purpose in life. There are applications where you want to foam to breathe and “leak”. For example, sprayed on the inside of a metal roof you want OPEN CELL so if you get a leak you’ll know and fix it. We want CLOSED CELL for our application which is water impervious. The spraying contractor must be told what you want.

I was thinking to do the same thing with my future Waste Oil Boiler. It would run under a large driveway and truck turnaround, so it’ll be placed in 8 or 10” corrugated sewer pipe. I wonder if plastic would still be needed?

I presume you intend to insert non-insulated pex into the corregated pipe then blow foam around the corregated pipe. Better than nothing but less than ideal. The pex will radiate into the cavity and the return line will inevitiably absorb energy from the supply line. Making the sewer pipe cavity nice and cozy will cost you energy you want to dump into your home. This is assuming I understand what you intend to do. I’d still do the plastic since it doesn’t cost but maybe $20 and makes whole process cleaner. But if the trucks will be driving on the foam, why the use of the corregated pipe? Unless the foam was quite deep I might worry about crushing the foam long term. If it was a high traffic area with heavy trucks, I’d be concerned of eventually of damage to the foam, not the pex. Others here like Heaterman may have experience with long term durability of the foam in a high vehicle traffic environment. I’d PM Heaterman and ask how deep you need to be for the traffic loads to pass into the trench and not into the foam. Basically anything you warm between the boiler and the HX is a waste of hard earned wood BTUs.

I thought my idea was good, the corrugated to hold the ground up, it’s a driveway, not a road. The one supplier I looked at was just an inch or so of foam, and I would use 3-4”, so wouldn’t that be better??? My foam would be INSIDE the 8” or 10” corrugated, and I would hold the pipes up with wood blocks with holes for the PEX to keep it centered. The pix are 4” blue corrugated, $15 a foot!!!

Ahhhh….. Foam INSIDE the 8”-10”, yes that will be excellent provided you are successful at achieving one key and difficult operation. My First Failed Attempt (futhermore referred to here as the FFA) used 6” dia x 8’ ft long corregated pipe sections and I covered my 1 1/4” pex with the standard split foam insulation sleeves. Unbelieveably tedious to install sleeves on both pex lines, duct tape together, slide a section of corregated pipe, snap together, repeat many times for ~170’ THEN come back and drill lots of holes in the corregated pipe and inject closed cell polyurethane Tiger Foam. All together probably cost me $7-$8/ft (BIG savings huh…..totally wasted). For all the world to see here, this is why it failed. Because the two lines with sleeves fit so tightly inside the 6” when I injected the foam it could not expand completely around the sleeve and pex bundle. I had filled most of the cavity with the sleeves AND I saw the foam coming out all the millions of pin holes in the sewer pipe (should have been my first warning). My helpers were already tired of the whole job and the foam was not encapsuating everything as envisioned so I soon saw injecting the foam as a waste of time. Turns out those sleeves acted just like sponges when water seeped thru the corregated pipe. The tiny good news was that some of the water surely drained thru the pin holes in the bottom, but the sleeves stayed water soaked. When I dug up this disaster last spring all of the INSIDE of the corregated pipe was covered with MUD! I type this not just for you but the thousands who will read this sticky after us. IT IS VERY DIFFICULT FOR US DIY’s to INJECT AND GUARANTEE COMPLETE 360 deg ENCAPSULATION OF THE PEX LINES WHILE MAINTAINING PEX SEPARATION. For this reason and based on my experience, if you really want to use the corregated pipe, I would do the foam injection out of the trench up on sawhorses so I could inject into TWO holes AT LEAST 180 deg apart. The large dia will give the foam more time to expand and having a hole on the other side you will see if it is expanding. But I’d inject on both sides just to be sure. I can’t emphasize this enough, IF YOU GET WATER CONTACT ON THE PEX…. YOU’RE SCREWED!

Now if I were you and I had just gone thru the what I had, I’d forget the corregated pipe, dig the trench maybe a foot deeper and foam in trench just like I did. Making the trench deeper allows more surface on the side of the trench for the vehicle loads to “shear” into the ground (distribute the loads into the surrounding ground). Just going a little deeper will protect the foam and assure you get that critical pex encapsulation for far less work. Or if you’re still nervous lay something on top of your foam in trench before you refill with dirt. There will be some voids but soon, in time, those voids will fill with dirt. My 2 cents. Getting good encapsulation in that corregated pipe while keeping the tubes separated and centered is far more difficult to achieve than digging deeper or placing a load bearing surface on top of the foam. We can only hope someone will reply here with a trench depth over a high vehicle traffic area that worked. Mine was a little over 2’ and the backhoe ran over it repeatedly. I can also report that this season’s performance is unbelievable compare to last with our new insulated line. I’ll post later with hard data.

Ok… I typed this for posterity Corvairwild. I was excited because I first read your handle as Corsairwild. But got it, you’re a car, not airplane guy. Best Wishes to you and all who come after. So here’s my warning, “Those who ignore the lessons of history are doomed to repeat them.”

Hi TENNMAN… I read your post to my wife, and so much fer the corrugated idea…

I just had a 1” water line installed in a 5’ deep trench last month, so it’s fresh in my mind, and I WAS thinking that sometimes what seems like a brilliant idea, until you try actually do it!

The area between the whse and house is a turnaround for the driveway, so the traffic will be minimal, and I’m not anxious to spend the extra on corrugated sewer pipe. Unlike the rolls of 4 or 6”, the larger size is far thicker, and two layered, or double walled. I bought some damaged sewer pipe last year, but forget the price.

Maybe I should use the factory installed insulated underground pipe I pictured above, but find either as thicker insulated version, and line the trench with low quality 2x wood, and foam it, all wrapped in thick plastic…

My concern was the exorbitant price of the above piping, and the seemingly small amount of insulation. I just can’t believe that 1” or so of white foam is really an effective amount of insulation. We’re talking 180f water in 50f earth.

There must be some heat loss specs fer the piping???

If I was to purchase a pre-insulated pex product it would be one of the polyurethane injected/molded products. I can confidently say there is no way to get better energy transfer at a lower cost than the foaming in the trench process. There just is no way to practically manufacture a two-line insulated pex product that is about 14” of solid closed cell polyurethane in cross section like can be done in the trench. We used a minibackhoe with a bucket that dug a trench about 12”-14” wide. So our pex has 3” spacing AND about 4” all around which was the result of filling the trench width with foam. If you are just talking personal vehicles, not heavy commercial trucks driving on the buried lines, then I wouldn’t be concerned about driving over it routinely if it was 2’-3’ down. Whatever you do… DO NOT worry about saving $500 on this part of the system. The underground done poorly will translate into you spending hundreds of more hours in the woods cutting, moving, splitting, and stacking because of lost efficiency. I’m reluctant to present our temperature loss data yet. It’s so good I don’t believe it yet. Great pics by the way.

The bottom line on all this either foam it in trench with sprayed closed cell insulation or use the Thermopex product.  If you think you can make something yourself a little cheaper be prepared to dig it up and redo it the next year.  A little bit of failure makes the whole thing useless.  Like the headline says “NOT THE PLACE TO SKIMP”!!

Ok, OK!!! I won’t skimp. I just didn’t like the only product I looked at locally. Their blue stuff above, and $15 a foot. they’re nukin futz!!!

I was thinking to use a better product, and THEN foam the trench, which around here should be 5’ deep, due to the extreme cold. I would def use anti-freeze in the lines, but still feel I should go below the frost line, 4 feet.

BTW, the pix, (from TL, CW) are a solid wood horse I bought my wife as a wedding present 18 years ago for $125, with our then stray kitten on the back.

My wife, our Lab/Beagle we just put to sleep this summer, 14 years old, and our found Pekingese Freekazoid Mugs, on Lake Champlain, near Burlington Vt

Mugs and me at a Marina on Shelburne Bay Vt a few minutes before they asked us to SCAT! Here’s the vid I made of that moment… (Couldn’t find that moment, but here’s the recreation path immed adjacent to the marina…

http://www.youtube.com/watch?v=1YQqG346gss

http://www.youtube.com/watch?v=OhRe0TQCl7Q

And Mugs and his (late) best buddy, Lady Bug…

Here’s an idea:

Dig a 2’ wide trench 4’ deep or so.  Lay down sheet plastic on the bottom of the trench.  Put one level of cinder block along both sides of the trench the entire length of it with the open sides facing up/down.  Spray foam plain old OB PEX in between the cinder blocks.  A 24” wide trench with 8” block on either side will leave you a 8x8” empty space between the block to run the lines and spray the foam.  That’ll provide you extremely great insulation and the block will provide you support for vehicles driving over it.  Backfill and compact the dirt and you’re done.  Never worry about it again.  Maybe drop a couple electrical conduits in the dirt before you back fill too.

Hmmmm….