How to Buy PEX Pipe Systems for Remote Building or Outdoor Boiler Installation


What is PEX Pipe?

PEX is an acronym for Cross Linked Polyethylene.  It is a relatively hard plastic, which is somewhat flexible in longer lengths.  PEX pipe is very strong, smooth-walled, and can generally withstand fluid temperatures up to 180 degrees Fahrenheit without significant loss of strength.  Most PEX pipe made for heating applications includes a barrier that is extremely resistant to oxygen infiltration.  PEX is ideal for connecting heating plants and outdoor boilers to remote or detached buildings, as it will not corrode and is made in long lengths.  Long, uncut lengths mean buried PEX can avoid fittings that could leak underground.  For an underground burial, PEX is often packaged in a waterproof, flexible, and rugged plastic sleeve that is filled with insulation. These underground pipe systems lose very little heat and will last many decades if installed correctly.

The advent of outdoor wood boilers has increased the popularity of buried PEX systems for remote boiler installations.  PEX pipe systems for this application are generally pre-insulated and contained in a watertight, plastic casing.  The pipe system is ideally buried below the frost line, but above the water table for best thermal results.  Anecdotally, one inch diameter PEX has become a commodity item while larger sizes are often very expensive and/or hard to obtain.  Cost and availability are driving purchase decisions that often result in the wrong size pipe being buried underground for decades.  This article addresses underground PEX pipe systems, especially the fallacy of one-size-fits-all PEX pipe systems. 

While using PEX tubing for remote, underground applications has become commonplace, finding reliable information about properly sizing the tubing to adequately meet heating demands is difficult.  Buried PEX tubing can be seen as the backbone of a remote heating system.  PEX and its installation should be viewed as an investment in the heating system.  

Reviewing Underground PEX insulation

One of the best ways to ensure long-term success with buried PEX is to only use brands with high-quality insulation.  It is essential that valuable heat from the boiler is not lost to the ground.  Some manufacturers specify R values (insulation values) for their pipe systems.  

Other manufacturers specify the amount of heat lost per hundred feet. 

There are several insulation systems that are best for buried PEX systems.  Some manufacturers wrap PEX in layers of foam like a cinnamon roll.  Some of the wrapped foam includes multiple layers of reflective foil.  

Other manufacturers use various types of solid foam filling around the PEX.  Manufacturers are striving to keep R Values (insulating values) high while retaining system flexibility while keeping costs low.  Regardless of the insulation system, it is essential to keep water from entering the outer, waterproof barrier from the ends or from damage to the casing.  Water can quickly destroy insulation value.  Good brands will have strong outer barriers and professional quality methods for sealing the ends of the pipe system.

Buyer beware: Some claims of high R values are based on tests conducted on insulation in different applications, such as wooden wall structures, not pipes.  Keep in mind that the highest R value for commonly available foams is R6.8 per inch for Polyisocyanurate.  Most PEX systems have no more than 1” of insulation between the PEX pipe and the outer casing.  Any ratings with R values beyond 7 bear close scrutiny.  Ratings of heat loss per 100’ do not use universally accepted test methods.  Some manufacturers test heat loss of systems lying on the snow.  Others test at relatively low flow rates.  It is important to know how each pipe system is rated in order to make a fair comparison between each system.

Why Properly Sizing PEX Pipes Is Important


No one would ever want to breathe through a drinking straw.  Using pipes that are too small creates similar flow restrictions for boilers.  The bigger the boiler, the bigger the pipe that is needed to move heat.  Also, because pipes create friction to flow, the longer the pipes, the more flow restriction there is.  For those reasons, pipe size must account for both the size of the boiler and the length of the run.  

Right-sizing PEX can be the difference between a cold or comfortable house.  An undersized pipe can also damage boilers or require oversized, energy-hungry circulators.  Different boiler outputs and heating loads require different pipe sizes to ensure enough heat is transferred from the boiler to the building.

It is possible to compensate for undersized tubing with extra-large circulators, but this solution can lead to noise in the pipes, high electric bills and premature erosion of fittings.  In some cases, power bills could be thousands of dollars higher over the life of the boiler, more than making up for the initial cost of right sized, high-quality pipe systems.  Conserve electric power by using smaller circulators, saving money and decreasing the carbon footprint of the heating system.  

Choosing the right size PEX for each job requires specific heating knowledge and a little math.  For best results, ask an expert at a reputable supply house. 

Tarm Biomass recommends installing residential, solid fuel boilers in basements or in existing and conditioned utility areas. This positioning reduces heat losses, as heat escaping the boilers can diffuse into the home rather than outdoors.  However, locating boilers in separate outbuildings can sometimes make more sense.  Outbuildings can simplify installation, given space and chimney requirements.  When it comes to firewood handling, a boiler located at ground level is always easier to heat with. 

If you need help finding the correct PEX piping for your applications, we're here to help. We specialize in a variety of wood burner and fuel boiler solutions for all kinds of buildings. Contact us today for more information about our products and services!





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5 thoughts on “How to Buy PEX Pipe Systems for Remote Building or Outdoor Boiler Installation

  1. Could someone explain the ten “head loss”?
    Does the size of a secondary building change the pipe size used for burial?

    1. Hello Jeff, Yes, it can. The pipe size needs to be large enough to carry the BTU’s required for heating the building. Also, the longer the pipe run, the more resistance. With every 100′, you lose 6′ of head lose and you need at least 5′ of head loss so your circulators do not “cavitate”. For example, if your boiler is 80,000 Btu/hr and your total loop distance is 100′, you would need at least 1″ ID pipe and a pump that can move 8 GPM at 11′ of head.

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