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insulated underground pex

Post in 'The Boiler Room - Wood Boilers and Furnaces' started by woodsmaster, Mar 7, 2010.

  1. Tennman

    Tennman Minister of Fire

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    599
    Loc:
    Southern Tenn
    Thanks for the reply HM. The big old farmhouse you mentioned pretty much describes our 4800 sf old place. When/if I add storage it will be in the boiler barn where all the piping is 1 1/2" black iron. So I can easily run 1 1/2" to storage for those short runs if needed. I started another post specifically asking about the flow velocity in my PEX with the 0013 and EWD assured me I'm ok at a little over 6 fps. Appreciate the inputs from you guys who are installers helping those of us DIYs. Bottom line I now feel good about foaming my existing PEX and restoring my lawn for the last time.

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  2. greenheater

    greenheater New Member

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    Dec 1, 2008
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    Central Michigan
    I'm happy with my 140 feet of logstor 1 1/4 inch... but I purchased it 3 1/2 years ago and understand its tougher to find.
  3. heaterman

    heaterman Minister of Fire

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    Flow velocity in pex is probably less critical than copper because of the fact that there are usually far fewer fittings in a given loop. When you are in the 6fps range with copper you will hear a little flow noise but usually no objectionable. The real issue to me is that when you get much above that 6 range you can start to introduce some noticeable deterioration in the fittings, especially short sweep plumbing elbows. I've seen pinholes in copper ells that were only 5-6 years old and the whole fitting could literally be squeezed and deformed with only finger pressure due to how much material had eroded away. As to fittings for your 1-1/4" pex, or any pex for that matter, the more I read and learn about brass fittings, the more I tend to avoid them if possible and go to bronze. Observing what has happened to a few systems using brass fittings with fresh water has me questioning whether they are a good choice if bronze is available. There are chemical interactions that can cause the brass to "de-zincify" and fail structurally. Do a google for dezincification and enjoy the reading.
  4. ewdudley

    ewdudley Minister of Fire

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    Here's one google result:

    http://www.hghouston.com/coppers/brass75.htm



    Central heating systems

    Water in these closed-circuit systems is de-aerated during heating. This suppresses dezincification, even if the water used to fill the system initially is one known to cause dezincification in aerated plumbing systems. Consequently radiator valves, pipe fittings etc. for central heating systems do not have to be of dezincification-resistant brass.
  5. heaterman

    heaterman Minister of Fire

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    Ahhhhh yes. But many of the readers here are using brass fittings in open or semi open systems where O2 can easily enter the system.
  6. ewdudley

    ewdudley Minister of Fire

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    Good point! I've been kind of locked-in to a all-the-world-is-a-pressurized-system frame of mind.
  7. HeatGeek

    HeatGeek New Member

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    Sep 27, 2010
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    Loc:
    Central NH

    Hi Guys, I'm new to the forum and am in the process of installing a sizable system. Large non-presureized wood boiler is about 450 feet from the house which is further than any installation I have heard of. I've already got an underground line (PEX-FLEX/LOGSTOR dual 1" ID) from the boiler into my shop in the barn at about 130 feet. (Of course the shop is heated first!).

    For the house (about 4500 sq ft) I am planning the same 1" ID line because at 450 ft and around $12/ft, the cost is ginormous just for the line. Boiler and house are very close to the same elevation, except I am going under a (drainable) pond that lies between the two. I plan a large circulation pump at the boiler and one at the house. Heat transfer in the house will be via water heat exchangers one for DHW, one for forced hot water heat.

    I've read Heaterman's posts on the heat transfer numbers for various size lines, but have not seen much on getting water 450 feet each direction and how that might play into the water line size to use and the overall design. I think 1.25" or 1/5 " line is around $25/ft. Makes me have $ nightmares.

    Any comments are welcome.
  8. Tennman

    Tennman Minister of Fire

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    Southern Tenn
    I built a spreadsheet to do the flow rates and flow velocities required to get the btus from my boiler barn to our house. Built from the Taco Datasheet. Our home is slightly larger than yours. Unless your home is very energy efficient, which ours is certainly not, 1" will be pretty small to pump the required btus/hr to your home. AND we're pretty far south. If you are spreadsheet handy I'd be glad to send so you can see for yourself how the long runs affect the pressure drop and literally how a 1" line limits you when you MUST push water that's heated to no more than 175-180F. You are creating a pipeline of energy. To get the same quantity of energy thru a smaller pipe means the water has to flow faster, which means more drag, electricity... on and on. People here, myself included, with much shorter runs with houses your size run at least 1 1/4. For my house I was concerned 1 1/4 was too small, the reason for my question to heaterman. BTW read the Sticky about my underground adventure. Any way you do it 450 round trip will be priceyu.
  9. HeatGeek

    HeatGeek New Member

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    Sep 27, 2010
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    Loc:
    Central NH
    Thanks much Tennman,

    I appreciate the comments and would like a copy of the spreadsheet. Thanks also for the pointer to your stickey which I've now read. House is pretty well insulated, but I agree that length water line scares me. Think my e-mail is available from my profile. Thanks much
  10. woodsmaster

    woodsmaster Minister of Fire

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    $25.00 is a little high, more like $16 - $17 for 1 1/4 logstor or thermopex. Still a lot of money!
  11. heaterman

    heaterman Minister of Fire

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    Loc:
    Falmouth, Michigan
    You can buy 32mm MicroFlex for about $18/ft and that stuff is about the best I've found. Multiple layers of closed cell encased in a 5" flexible shell rather than the usual 4. Very flexible and easy to work with. Not like wrestling with an anaconda.

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