Geothermal Pipe – What to Use and What to Stay Away From

All geothermal pipe is not considered equal, not even close. Even though most pipe looks the same, there are several key things that you need to consider when deciding what pipe to buy for your geothermal installation. Most geothermal contractors aren’t familiar with the different types of geothermal piping, and typically only carry one type in stock. Remember, in a typical geothermal installation there will be thousands of feet purchased and installed. Most of this pipe will be buried underground, never to be seen again. The good news is most of this pipe carries a 50 year warrantee (twice the expected life of a heat pump). The bad news is if you put bad pipe in the ground, or it starts to leak, it will be VERY expensive to remove it. The goal of this article is to show you the options, and (of course) the pros and cons of each type of geothermal pipe.

Geothermal Pipe Types

The most common types of pipe are: Polyethylene, High Density Polyethylene (HDPE), PVC, and CPVC. The last two might even be common to you, as they have been used for over 20 years in housing construction. It is very common to use PVC for the drain pipes on sinks and bath tubs, as it is fairly robust and relatively easy to manufacture in larger sizes (from 4″ – 12″ diameters are common). CPVC pipe is commonly used for potable water piping. CPVC piping replaced copper piping as the cost of copper exploded in the past few years. Although there are several types of commonly used piping in construction, they are certainly not created equal. Remember, this piping will go in the ground for years and must be able to have enough rigidity to circulate water.

Polyethylene Pipe

The most commonly carried piping by geothermal contractors is probably Polyethylene (PE). This is a good thing, right? Right, but it isn’t without drawbacks. PE pipe can be manufactured to be straight or curved, giving versatility to be used as not only traditional wells but also in a “Slinky” configuration. Polyethylene pipe has good physical characteristics, but not great. Polyethylene pipe cannot be glued and connected like other types of pipe, but must be “heat fused”. This process is not difficult, but contractors must be trained on it and have equipment for it. Polyethylene pipe has above average pressure ratings, but not quite enough to be used in the deeper vertical wells.

Polyethylene Pros:

Good Chemical Resistance, Slow Degradation.
Heat Fusion provides great sealed loop.
Can be used as horizontal wells or slinky configuration.

Polyethylene Cons:

Not enough pressure rating for vertical bores.
More expensive than PVC & CPVC.

High Density Polyethylene (HDPE) Pipe

HDPE Pipe is considered top of the line geothermal piping. It is essentially a higher grade version of polyethylene pipe, with better rigidity, thermal properties, and chemical resistance. HDPE pipe manufacturers warrant their pipe for 50, 75, even 100 years. It truly is that good. HDPE pipe comes in different grades, but most are very rigid and are ideal for vertical well fields. HDPE has great pressure rating, and provides the same quality seal as polyethylene pipe, as it also must be joined in a heat fusion process. HDPE pipe is among the most expensive pipe you can buy, but as any manufacturers website proclaims, the lifetime cost of HDPE is worth it.

HDPE Pros:

Best chemical resistance, will not corrode or degrade.
Excellent for vertical wells, large pressure rating.
Heat Fusion provides great sealed loop.
Excellent for horizontal well fields.

HDPE Cons:

Doesn’t have great bending radius, not ideal for horizontal slinky configuration.
More up front cost.

PVC Pipe

PVC pipe is some of the most commonly used pipe in residential construction. It is used for piping not under pressure, although it does have reputable pressure ratings. It is typically used to carry sanitary waste and general drain waste. PVC pipe has good resistance to many chemicals, and will not degrade easily. PVC pipe is easy to assemble, as plumbers have been gluing and assembling complicated pipe configurations for decades.

PVC Pros:

Perhaps the most widely used pipe, readily available, easy to assemble.
Great chemical resistance.
Cheap.

PVC Cons:

Doesn’t have great bending radius, not ideal for horizontal slinky configuration.
Not a great sealed loop.

CPVC Pipe

CPVC Pipe has been used to carry pressurized potable water for years. CPVC is a low cost piping option that is sufficient but has weak chemical resistance. It will degrade if it comes in to contact with most oils and cleaning agents. It has good pressure ratings, and comes in many configurations. Similar to PVC pipe, it uses adhesives to create a sealed piping system, so it is not ideal for a continuous loop.

CPVC Pros:

Cheap and readily available.
Good pressure ratings.

CPVC Cons:

Poor chemical resistance.
Not a great sealed loop.

We’ve mentioned pros and cons, but we want to take the opportunity to be more blunt… STAY AWAY FROM CPVC PIPE FOR GEOTHERMAL PIPING APPLICATIONS. There are documented cases of CPVC geothermal loops leaking, and manufacturers will not give warrantees on it. Glued joints don’t last over time, and the pipe is not very resistive to cleaning agents. In fact, if there was a leak of almost anything (compressor oil being the main concern) CPVC will begin to degrade with even the most minute amounts (in the parts per million). We cannot and do not recommend CPVC for anything related to geothermal applications. Not indoors, not in the ground. Stay away from CPVC.

Our Geothermal Pipe Recommendation

When deciding what type of pipe to use keep the aforementioned in mind. Our recommendation is as follows:

For Vertical Geothermal Wells: Use HDPE Pipe.
For Horizontal and “Slinky” Ground loops: Use Polyethylene or HDPE pipe.

The benefits of HDPE and PE pipes are such that make them ideal for geothermal piping applications. They provide great sealed loops, with more and more contractors being trained each day to provide heat fused joints. Since the pipe is going in the ground (hopefully) to never be seen again, HDPE and PE pipes provide the chemical resistance necessary to prevent degradation (both by cleaning agents and by ground chemicals). Also, for vertical bores, we recommend you use HDPE because in addition to these benefits, HDPE is the only pipe that provides the exceptional pressure ratings needed for vertical geothermal wells. We recommend these piping types for geothermal applications to make sure you get a quality installation. You will also get a generous warranty, and the peace of mind of piping that will last.

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