DIY Ground Source Heat Pump – Part 4: Selecting in Ground Tubing

Post image for DIY Ground Source Heat Pump – Part 4: Selecting in Ground Tubing

by Tim Fulton on September 8, 2009

With a capable drilling rig, AC Hacker turned to selecting parts for the rest of the system. Specifically, we’ll be looking at selecting the tubing that must be laid in the ground.

PVC and CPVC are not a good choice. They both get brittle eventually and will crack under pressure. Pex would be a good material. However, with the way it is made, it is not possible to weld it together. Copper would also work well, but it is very expensive.

So, that left AC Hacker with what he had read about many small residential systems using, HDPE (high density polyethylene). Its that black water tubing you’ve probably seen at the home improvement store. AC Hacker found that HDPE comes in two schedule ratings, 40 and 60. The 40 was too thin to think about using as he feared it might be crushed by the weight of the soil on it. But, the schedule 60 looked like it would be up to the job.


The next hurdle is that HDPE needs to be welded together. AC Hacker looked into what kind of tools would be needed for this. He found McElroy makes a tool called the MiniMc that is made specifically for welding plastic pipe. The bad thing is it costs $2000. He also found that even renting it was very expensive.


Since that would blow the budget for this project out of the water, AC Hacker decided to look into how hard it is to weld the tube without this tool. He picked up a teflon skillet from the local junk store and heated it up on his stove at home. He placed a couple short pieces of HDPE on the skillet and monitored the skillet’s temperature with an IR thermometer. At about 300°F (149°C) he noticed a bead forming around the tube. He picked two pieces up and pushed them together. The above was his first result. So, plastic welding is indeed possible without the very expensive tool.

For more details about the tools or project check out AC Hacker’s forum thread that tracks all of his progress.


1 SR December 5, 2009 at 6:42 pm

Sorry to say but pipe fusing that looks like this is substandard and should ALWAYS be rejected!

SR (Certified Geothermal Pipe Fuser)

2 AC_Hacker December 8, 2009 at 3:54 pm

Hugh Jim Bissell, also a Certified Geothermal Pipe Fuser, and ‘frequent flyer’ on the Homemade Heat Pump Manifesto, has over 3000 welds to his credit. He has been very helpful in advising this blog.
If you would like to put together a tutorial that would teach people how to weld plastic pipe to your standards, with detailed procedures and photos, I’d happily edit them in to the appropriate place in the blog.
Just email the text and photoa to me at my operamail address:
…I’ll take care of the rest.

Best Regards,


3 SR December 10, 2009 at 1:24 am

This is NOT something that can be taught over the Internet, it’s hands-on physical learning with the proper instructor, training, tools, and guidance. There’s an exam and certification process for a reason. Perhaps Hugh needs to be re-certified; you should consider taking the course with him… unless you’re happy being a ‘Hacker’.



4 AW December 29, 2009 at 1:43 am

Why is it that nearly without fail every forum or blog has somebody who posts rude and condescending remarks? I just don’t get that at all.

5 A D January 27, 2010 at 4:03 pm

“Professionals” often get upset when they realise that the skill they possess is something other people possess of without the “exam and certification process”. Unemployment is a scary prospect for some This website has been brilliant for planning my proposed thermal storage system. Why seek perfection when what we need is adequacy in these instances, the real ltest of this system is its functionality and reduced cost.

Thanks AC Hacker

6 Billbobagns June 20, 2010 at 4:15 pm

Installing a system for a customer requires a level of professionalism to withstand the liability that something might break years from not.

Installing as system for one’s self, (hacker) may be much more tollerant of system break-downs when one is doing the complete system for 2k instead of 15k.

I expect to do a 5 Ton DIY system for myself, but would NOT trust my own plastic welds underground. I will buy long pieces to make my loops or hire someone to weld them for me.

7 Billbobagns March 6, 2011 at 8:24 pm

I must “back up” a little and update my post. Since I posted that I would not trust my pipe welds underground, I have purchased a $2500 pipe welding system for up to 2″ HDPE. I’ve made a few “tests” with it and now feel I can weld this pipe as well as anyone!

I bought my McEnroe in three separate buys on Ebay for a total of $600. I have everything for 2″ and 1/2″ butt welds and fittings for 3/4 and 1″ socket welds!

8 Certified Fusion Welder January 13, 2011 at 11:05 am

SR is right. The weld is horrible. For pipe this small, I would recommend socket fusion couplings, not butt fusing. Scary stuff.

AC Hacker: I honestly could not think of a better name for you. You are a true hack. Your right, true “professionals” do get upset when they see a skill they have been school on and certified in gets balked at as unnecessary. You are the Billy Mays of HVAC. Slick to the last. Good luck to you sir.

9 Mike November 28, 2011 at 4:44 pm

I think the two professionals have little to worry about here. The people who are really interested in sites like this are very unlikely to purchase a professionally installed system like this – we either like the idea of doing it ourselves, don’t have the money to pay professional rates for an off-the-shelf fitted system, or both. The people who are most likely to buy professionally fitted systems either won’t look at the site in the first place (because the very idea terrifies them or hold no interest whatsoever) or will look at the site and have their fear confirmed – fitting these systems as a DIY job takes a lot of time, effort and skill. So, as all of this seems obvious, why are the two professionals so negative? Either they are really worried that the site is so good it will lead to a huge rise in the numbers of people fitting these systems themselves; or they are harbouring the peculier assumed elitism that some guys just can’t seem to avoid falling into. For my part I’d like to thank Mr Hacker for producing this interesting and helpful website. What the planet needs is more energy efficient systems in operation, not narrow minded, protectionst attitudes toward the technology. For those of us who want to do our bit for the future but don’t have the spare cash to invest in a bespoke professional system, or just like the challenge of creating something functional with our own hands, this site is great – thanks!!

10 chris April 13, 2016 at 1:39 pm

I do heating take offs for a living and most of the so called
geo thermal professionals with tickets or not have about a 50 / 50
chance of their systems working I have see alot of so called pros turn there
backs on customers because the proper research wasnt done and the system
was doomed to failure from the start , I actually like the idea of ” hacking it out ”
yourself before throwing a bunch of money you will never see the return on

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