# Insulated underground pex options...



## kuribo (Apr 12, 2012)

I am looking at insulated underground pex for a 40' or so run from my boiler building to the house, and have come across two types of insulation that are used in the better quality products (not even considering the bubble wrapped products). Logstor and Thermopex (Central Boiler?) use polyurethane foam which has an r value of about 6 from what I can find out. The others, Micro-flex, Wirsbo (R-flex) and Heat Seal, use polyethylene foam, which seems to have an r value of only 3 or so....I need 1 1/2" ID which rules out the Thermopex. Logstor makes it but does not have the dual pipe available anywhere and I would have to $pecial order it....While my run is quite short, maybe the lower r value of the polyethylene insulation products won't matter much....I have considered foaming the lines in the trench but have high ground water and am not sold on that method yet....What say others?


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## rowerwet (Apr 12, 2012)

85 feet of thermopex in my back yard, 4 years and no complaints, the snow didn't melt over it, the septic tank always melted off first, and the ground stayed frozen. Never noticed any real loss from the run, thermopex is the best for the money in my book.


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## woodsmaster (Apr 13, 2012)

How about two 1 " runs of thermopex. That would = around $26.00/ '


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## katman (Apr 13, 2012)

woodsmaster said:


> How about two 1 " runs of thermopex. That would = around $26.00/ '


 I used 1 1/4 inch thermopex for 100 foot run at $18/ft and am very satisfied.  Uponor has a similar product and maybe in larger diameter but for my size was about $6 more per foot.


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## woodsmaster (Apr 13, 2012)

If you did dual thermopex 1" you wouldn't have to find the large tool and fittings that can be expensive. I used 1 1/4 and ended up using barbed fittings so I wouldn't have to buy the tool.


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## kuribo (Apr 13, 2012)

woodsmaster said:


> If you did dual thermopex 1" you wouldn't have to find the large tool and fittings that can be expensive. I used 1 1/4 and ended up using barbed fittings so I wouldn't have to buy the tool.


 
I can't use two 2 pipe assemblies as the hole through the foundation is not large enough and I really don't want to cut another...

Anyone have any input on the polyurethane versus polyethylene insulation?

Anyone have any issues with the sprayed in place foam in a trench method?


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## StihlHead (Apr 14, 2012)

I went a cheaper route and it works fine. To keep out the water (the biggest heat loss factor in buried pex lines) I used 4 inch corrigated drain pipe. I used foam sleeve insulation over the one inch PEX lines and stuffed them into the drain pipe and buried it all. Both ends of the pipe are well above ground and I used foam spray to seal the ends. I also used one red and one blue PEX line to ID them. The foam is not that great as far as insulation goes, but it keeps the PEX from coming into contact with the sides of the corrigated pipe, and away from any water outside the pipe that would rob heat. One outer shell pipe is a better than two, as the dual heated lines inside will retain the heat better.


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## ALASKAPF185 (Apr 14, 2012)

Both Logstor and Uponor pipes have nearly identical heatloss data. Logstor I believe is easy to find on their site, but you have to request it for Uponor I believe.  These 2 brands are the top of the line, tested and approved. Can't go wrong with either. From memory and on jobsite info the Uponor is 1.5*/100-150' of pipe at 180* supply temp on a 10 degree day burried 36" @ 4.1gpm for 1 1/4" I.D. pipe. Thermopex is also good, other than the size you need. Is the btu load that large that you need 1 1/2" pipe or are you just trying to keep velocity down and use smaller pumps?


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## kuribo (Apr 14, 2012)

The Uponor product uses foamed polyethylene insulation as mentioned above. The r value for that material is about 3.5 versus the 6 or so for the polyurethane foam. Given that, it is hard to understand how the Logstor with nearly twice the r value could have nearly the same heat loss as the Uponor....

There are three or four companies now making this insulated pex with the polyethylene foam insulation. It has a much lower r value but is a lot easier to work with....It seems though that it is every bit as expensive as the polyurethane product at what should be much poorer performance...

I will need to move a fair amount of water at 180F to get my storage up to temperature when the supply- return delta t is small. 1.5" is the way to go.....


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## woodsmaster (Apr 15, 2012)

Kurbio, how many KW boiler are you putting in.


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## kuribo (Apr 15, 2012)

200000BTU/hr, 60Kw....


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## Tennman (Apr 15, 2012)

Oh boy.... R value is a function primarily of two parameters. Coefficient of thermal conductivity of the insulator and then thickness of the insulator. I can't at the moment look up polyethylene but the space shuttle External Fuel tank uses polyurethane. What's that tell you. On my 60Kw BioMass I go almost 400' round trip with 2 - 1 1/4" lines. Flow velocity a little high with 0013 pump but works fine. I would have liked to use 1 1/2" to cut down pumping losses but 1 1/2" pex was dramatically higher. READ the Sticky about foam sleeves and corregated hose. I'm biting my tongue. Can post more later but bottom line most here are successful with 1 1/4" for longer distances at that capacity boiler. If you want to pay for it tho 1 1/2" better because of lower water velocity to carry that much energy.


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## kuribo (Apr 15, 2012)

I have read the sticky, several times....Especially took to heart this advice:

*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.  http://www.taco-hvac.com/uploads/FileLibrary/SelectingCirculators.pdf 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.

######################################################################

The math, as well as the manufacturers such as Taco, say I should be using 1.5" pex. I plan to do this right.

Seems there are only two manufacturers making the polyurethane insulated pex: Thermopex and Logstor. As I said, Thermopex doen't make a 1.5" product, so they are out. Logstor doesn't stock it and would have to special order from Europe and charge me crazy money. I could go with two 1" lines for each supply and return, but am worried about how to get those through the foundation without cutting more holes or having some sort of leaky splice outside the foundation underground. How have people dealt with using two lines for each supply and return when it comes to getting them through the foundation?

The other option is foam in place, as I said, but I am not sold on the long term viability of that method....I can get a local contractor to spray my trench for about $6 a foot....

UPDATE: Just found 2 or 3 other polyurethane insulated pex manufacturers...Will check these out- maybe someone will have dual 1.5" available....


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## Tennman (Apr 16, 2012)

Chris, The only compromise in my system is the flow velocity. Sounds like you did some math from the data in the Taco Datasheet. I built spreadsheet of that datasheet. I assumed that most of the time my 205kbtu/hr boiler could output 180kbtu/hr. An 80% output from boiler rating seems to be pretty common. Assuming a 30 degF deltaT drop at the HX calculates out to 12gpm necessary to pump that energy output rate to your house. Recommended water velocity is 2-4 feet/sec. My 1 1/4" lines are running at 4.4 feet/sec which drove me to the Taco 0013 pump to provide the horsepower to get the flow at my computed head losses. Since I was totally green and designing the system myself based on research, reading here, and asking questions just like you.... I saw essentially all 60 systems worked fine with 1 1/4" Pex. BUT If I had the chance to turn back time I'd have spent the money for the 1 1/2" which over the 30-40 years remaining in my life I'd have more than made it up in electricity costs. And of course insulating in place cost is the same for either size pex. But as you read in the Sticky..... I thot with my first underground attempt I'd SAVE MONEY and use sleeves in corregated black lines (only cost me about $2000 to fix that bad decision). In hindsight the extra $300-500 in purchasing 1 1/2" and then foaming in place probably would have been a good investment for me but the return on investment in electricity savings probably would have been many years. So, bottomline, yes 1 1/2" is marginally better but only if you intend to foam in place. Otherwise the cost of 1 1/2" Thermopex or any of those types of products are so incredibly expensive I'd say it's not worth it. There you go... given your run is only 40' there are many successful 60 class boilers here using 1 1/4". If you know you'll be in this house for the rest of your life, like me.... well.... you could go bigger... maybe... But to answer your "what's best" question..... foamed in place 1 1/2" using polyurethane closed cell foam flowing the water slower letting you maybe use a smaller pump. But again, the savings/year will probably be quite small.


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## kuribo (Apr 16, 2012)

Thanks for your thoughts....

Yes, at a 30F delta, the 1 1/4 is marginal. Have you done the calculation at a 5F delta T? I want to be able to get my storage up to full temp.....The price I am finding for 1 1/2 is about $20 a foot. If I foam in place, with the cost of the pex and the foam, it comes to about $18. 1 1/4 would be about $14 a foot, or $250 or so less.....Would rather spend the extra $250 and not something that is marginal....


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## Tennman (Apr 16, 2012)

I agree. If the cost difference in the tubing is only $250 then it is a no brainer and you possibly use a smaller pump. At a 5 F delta thru the HX the gpm goes way up to extract the same 180,000 btus/hr. Maybe others will chime in but a 5F drop with reasonable gpm just isn't leaving much energy in the house. BTW, my system is water to air. I know the radiant guys are more efficient since they can use much lower temps. So at this point others are more experienced than me on the radiant stuff. Nice to be able to choose between Good or Really Good! But in the overall scheme of your project, $250 is less than 2% if you're doing the work yourself. So now just flip a coin.


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## Armaton (Apr 16, 2012)

Chris,

Is your storage in the house, or in the boiler building? From the thread it seems that your boiler is in the building and storage is in the house. If this is the case then 1.5 inch is the way to go. But, if storage is in the boiler building, maybe you could use a buffer in the house and not need such a small delta T. Eliot worked me up a plan that utilizes a buffer in the house, water from the buffer will go round and round to my DHW and WTA HX until expended then back to storage, thus buffer may mix, but storage stays stratified. Just a thought


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