Earth Tubes: How To Build A Low Cost System To Passively Heat and Cool Your Home For Free

Earth Tubes

When we build our pole barn house we know we want to put in Radiant floor heating to heat our home but haven’t decided on how we want to cool the house. So I have been researching the best option for keeping our house cool in the hot humid summers of Iowa and I came upon a an interesting concept that we might consider incorporating into our building design, Earth Tubes. In this post I will explain what they are, how they work, some of the draw backs, and how I would build a low-cost design.

What Are Earth Tubes

Earth Tubes are a passive heating and cooling technique that uses tubes that are buried at least 6′ feet  in the ground that has air passing through them and uses the constant temperature of 50 degrees of the earth to cool and dehumidify air in the summer and warm air in the winter before entering the building envelope. They are often used as a supplement to conventional central heating or air conditioning systems. They work best in extreme climates that have high heat in the summers and very cold temperatures in the winters like Iowa.

Earth tubes are sometimes not installed correctly because they are poorly misunderstood and are somewhat experimental but are nothing new. They were was first used by the Romans a couple of thousand years ago. They also gained popularity again in the 70’s and 80’s but many failed because of improper installation that caused water  (from condensation)to collect in the tubes and after a few years developed mold or bacteria and the air coming from the tube was then unhealthy to breath.

How They Work

In the summer hot humid air enters the tube from the outside and as it goes through the tube, the earth surrounding the tube cools the air and causes condensation to build on the inside wall of the tube. This cools and dehumidifies the air before it  enters the house.

In the winter cold air will enter the tube and the earth at 50 degrees will warm the incoming air before entering the house. This will especially work well with a wood stove or fireplace because they consume lots of air when used and usually cold air is pulled from under your doors and around your windows as well as other places that leak air in the building envelope.

The Drawback of Earth Tubes

There are criticisms of earth tubes and the biggest are the high cost to install a system for something that just supplements your heating and cooling needs and the condensation that forms in the tubes in the summer. The systems that are most cost-effective I have researched calls for a wide trench at least 8′ feet deep with several inches of gravel at the bottom and then several tubes at least 6″ to 8″ diameter and around 80′ long with a continuous slit on the bottom so condensation can drain out and then they must have some type of land scape fabric or sock put over the tube so no bugs can enter the slits in the tube. You can see where this would cost thousands to do. But with this system there is still a concern with Radon entering the tubes from the ground and getting into the house.

a continus slit in tube to allow condensation to escape.

a continuous slit in tube to allow condensation to escape.

How I Would Do It For Less

I think I have come up with a less costlier solution for doing earth tubes and we hope to  incorporate them into our home design if I can get it done at a low-cost. Sometimes the best plan is the most simplest one and mine is very simple.

Our Hillside and Pole barn house

Our Hillside and Pole barn house

As you can see from my wife’s drawing above of our hillside how I would do our earth tube design. My earth tubes will follow the natural curve of our hillside 6′ 1/2 feet under ground and will not have a slit until at the bottom of the hill where the last few feet will have a slit and a fabric sock to allow the water to drain from condensation and to keep insects out of the tubes. Only the last few feet of the earth tube will have gravel under it with another 3″ pvc perforated pipe imbedded in the gravel that goes to daylight to drain. This cuts cost and also stops all worry about Radon Gas getting into the system. I plan to use two 100′ rolls of 6″ non-perforated plastic drain pipe that you can buy at McCorkels in Columbia Iowa for 99 cents a foot and it will be in a straight line, not serpentine like the photo at the top of the page.

100 ft rolls of 6" nn-perforated plastic drain pipe at MCCorkels in Columbia Iowa for 99 cents a foot.

100 ft rolls of 6″ non-perforated plastic drain pipe at MCCorkles in Columbia Iowa for 99 cents a foot.

The reason I chose 6’1/2 feet for the depth of my tubes instead of the recommended 8′ is lots of people do field tile in the state of Iowa and most of their trenchers can go down to almost 7 feet, so I think I can get it done for a reasonable rate. I think it will still work at that depth, any less depth will not have a stable enough temperature during extreme heat or cold to work properly. The whole key to this design is to have the earth tube slopped like on a hillside to a place where this condensation can drain out to alleviate the mold problem. At the bottom of the hill where the earth tubes come out on the hillside will look something like the photo below.

Air Intake of Earth Tubes

It will come out of our slab in the pole barn house like in the photo below.

I would also have a door on ours so I can turn it off if not needed. We would probably only use the earth tubes in extreme weather.

There is some argument whether you need a fan to move air through the tubes. I think in the winter no fan will be needed as the cold outside air enters the tube and it starts to warm from the earth, it will rise naturally like in a chimney, especially with the fireplace going will help pull the air into the tube. The summer is when I think you will need a low velocity fan to pull the heavy colder air up the tube and it maybe something as simple as below.

thCADM39IZ

If we do earth tubes we will have them installed and in place before our pole barn house is built. I think the best place is on either side of a wood stove or fire place, or by your cold air return if you have a conventional heating and cooling ducted system. Another advantage of this design is you could flush these out once a year to get rid of any dust or dirt by sticking a garden hose in the earth tubes from inside the house.

As you can see my earth tube design is a simple design with a simple concept and will not cost much to do. I will let you know more when I find out what it will cost to have the two trenches dug. I think with all the hills in Iowa this design will work for a lot of homes there. I am interested to hear what many of you think of earth tubes and if you think my design will work?

Update

I have talked to one person that does field tile in Iowa and he said he can do it with tube and trench for 2.00 a foot. So if I do 200 feet of earth tube it will only cost 400.00. Now he did say that since it was such a small job they may charge an additional 300.00 just to come out and set up. So I think I can get it done for 700 bucks. Now this has got me thinking, if I do 4 earth tubes which will bring my total to 400 feet, will that still be considered a small job and would they still charge me 300 for setup? If I could get 4 tubes done for 800.00 it would be even better.

Earth tubes

The two pictures above and below are from a house in Missouri. The owner of this house said the earth tubes did not work. The tube is 2ft by 80 feet long. This system failed in my opinion because the tube was only buried a few feet under ground and the fan he used to pull the air from the tube was a high volume fan. This system would have worked if the tubes were buried at least 6 ft and it would have been better to use four 6 inch  pipe instead of one 2ft pipe.

earth tubes 2

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About Gordon Milligan

I am a conductor for a commuter railroad in Chicago IL, I have bought a 40 acre farm in South Central Iowa that I plan to retire to in 3 yrs. I want to raise and grow most of my own food using sustainible and organic methods. I have a blog that journals my journey to becoming a farmer.
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42 Responses to Earth Tubes: How To Build A Low Cost System To Passively Heat and Cool Your Home For Free

  1. Very interesting concept! You are putting so much thought and research into everything, you are going to have an amazing farm and home! Would earth tubes be a reasonable addition to a barn (without additional heat/air)? Maybe keep it a bit warmer in winter and a bit cooler in summer?

  2. Thanks Susan for your reply, I don’t think a barn would be a good candidate for earth tubes unless it was going to be insulated and then it might be worth the cost.

  3. John Copsy says:

    Hey Gordon,
    Why not use flexible water line to bury in the ground instead? you can use a low voltage circulation pump and run the lines in your floor, or use those copper radiator lines with the fins on them that run around the edges of the room along the floors like they use with the package boiler systems. They use those systems up in Alaska everywhere because they are so effective and much cheaper to use. I have even seen people up there run the line through their wood burning stoves to heat the house. You can also use 12v DC pumps and don’t have to worry about the power going out, just hook it to a car battery for emergency use. A lot of people had solar battery chargers to run DC powered systems, and had solar panel chargers for them for emergency use. You can use glycol in the lines and don’t have to worry about corrosion too.

    • Thanks Johnny for your advise, I didn’t know those radiator lines with the fins that run around the room were so energy efficient. I see those in a lot of homes I look at but don’t like the look. Your idea about using flexible water lines in the ground is something I might look into. Thanks for your input.

      • steve says:

        It never ceases to amaze me. So much information on earth tubes.. use multiple small pipes to get the needed air flow air change per hour.. People wanting to discount drainage YES water does flow down hill. Think adding a terminal end with gravel bed is the way to go. Common sense.
        Reality.. one only needs to follow 1/4 inch per foot as is done with standard plumbing greater fall is fine but also see people draining towards the house .. that is DUMB. Never drain water towards the house unless you want mold and mildew.

        As to the fan. personally think a low velocity axial fan is best.. This for a couple of reasons. inline is more efficient . One should run the fan continuously as it displaces the air and the chance of toxic chemical off gassing and radon drop to near zero. So running it 24/365 makes a lot of sense Additionally the earth does not give up or absorb heat readily so with runs of 100 ft you will only see 11cfm in the pipes.

        Using multiple small pipes Makes more sense than one large pipe. Because of the fact that the ground will only absorb a finite amount of heat per foot, using multiples makes more sense for having enough surface area to move heat.

        Since you are looking at trenching to 6’/6in would suggest you cap the top of your tubes with as wide a piece of rigid foam as you can install in the trench as this will give your system more time to move the heat out and around the foam.. likely equivalent to going down to the 8 foot level.

        I find it odd that people do not seem to understand that you have to go down deep enough to get to a place where the ground temp is stable on an annualized basis.. which seems to be between 8 -10 feet for most applications.. Ground where you are is at 50 degrees.. but here in Tn it is closer to 57- 60 degrees … one really does need to know what the annualized air temperature is for their specific location. This is part of why the earth tubes might not be to effective in S Florida. But effective in south Tx where the air tends to be drier

  4. thistledog says:

    Great post; great idea! Thanks for bringing it to my attention. We’ve got hot humid summers here too, and our projected house site is on a hill that would work well for earth tubes. I’m trying hard to figure out every design element to use that will make it possible to not have to use (too much) air conditioning, and this might be the clincher. Had never heard of it until your post, but there’s a lot of info out there about it now that I know to look.

    One thing I’d like to mention is in reading how the air exchange works in the tubes, the serpentine layout is really important, as it mixes the air and keeps it from moving in layers, thus aiding in transferring cold from the earth, and preventing the moisture problem. Don’t sell yourself short on an important design element for a few bucks, if you can help it. It may not be that important but it jumped out at me.

    I’ll probably rent or borrow a backhoe and dig my own trenches. Seems like the ultimate diy job for someone like me. Thanks again for posting about this.

    • Hi Kay, glad you liked this post and it may be some help to you building your own home. There is some argument in having your tubes layed out in a serpentine or in a straight line. When I first started researching earth tubes I thought the same thing like you, that they needed to be in a serpentine layout, but If you look at most commercial designs for earth tubes they all use straight pipe design only with much bigger pipe. The link I put in the first paragraph will take you to a site were the guy has a good argument against serpentine layout look here. He says that the serpentine layout will cause too much turbulence and the air flow will not be able to move through the pipe. Serpentine layout you would have to have a fan all the time to work. With straight line pipe you will have better natural air flow with out a fan. He explains it much better then I do with all the scientific facts to go will it. He has really done his research. I think if you have 80 to a 100 feet of straight pipe that is more than enough tube to cool or warm the incoming air. Plus the biggest criticisms of earth tubes are the cost to put these in. Even doing it yourself renting a backhoe you could do it for a lot less then other folks but it would still be more than having a company that does field tile that can do it for 2.00 a foot. Look at that guys site Kay and let me know what you think.

      • steve says:

        consider this for a moment.. 100 feet of tubing.. NOT NEARLY ENOUGH if you look at the heat exchange delta t of the earth tube you will discover that in short order.

        Think more along the lines of one set of tubes every 6 feet. why 6 feet? because you do not want one pipe leaching off the other pipe when it comes to letting the ground recharge its capacity to exchange the ground to air temp.

  5. Here is a quote from his site “Many Earth tube designers incorrectly assume that their flow will be laminar. They tell you that you can “add turbulence” and increase heat transfer by choosing tubes with rough or corrugated surfaces, laying the tubes in serpentine patterns, etc. These “enhancements” increase pressure drop dramatically. A few quick Re calculations show that they are not necessary for most earth tubes”.

    • steve says:

      totally agree with your assessment the actual flow thru the pipes cfm is very very slow. so sepentine makes for more resistance. one thing I have seen is filling part of the trench with gravel, to cover tube.. think that is also incorrect as solid mass of earth is a better conductor of heat than gravel with lots of air spaces that act as insulation. Remember Fiberglass insulation works by providing lots of air as the actual insulator.

      • David Hafner says:

        I thought exact same thing as I read. Full earth contact with pipe is much better than gravel surrounding it with tiny air gaps which hinders heat transfer. If not back filling with earth, at the very least sand would be the next best alternative. Smaller tubes rather than large ones would work better simply because you need the heat to transfer and that only happens on the outside of the tube. While large tubes may be used in large commercial buildings one should consider the size and air requirements of those buildings in comparison to your home. Large commercial sized tubes used in a residential setting would have lots of warm air in the center that likely would never get the chance to transfer the heat properly.

        Any plastic tube can be a bit of an insulator too (though poorer one) which also hinders the transfer of heat. Concrete tubes can’t be cleaned properly and likely are fairly expensive. While common drainage tile is cheap it would face a similar cleaning problem in addition to possible holding water in the many grooves which can allow mold to form in the tube.

        Though initially more expensive, I’d personally consider one or more runs of 4″ – 6″ rustproof metal pipes (copper, aluminum, etc) with a nice smooth bore that eliminates collecting water in grooves, can be easily cleaned and quickly allows for the much needed heat transfer. Tube diameter should be based on run length and air requirement calculations to ensure air resistance in the tube is kept at reasonable levels while maximizing heat transfer. Keeping each line of tubes spaced many feet apart would make the system work better as well. While I understand cost is a factor to consider one must remember the whole purpose of these systems is for it to work properly in the end.

  6. Woody says:

    Just a thought; If you’re going to contract the trenches and pipe and he wants to up charge, see what your cost would be from installation of your drain field for your septic and the additional trench for your air system.

  7. wannabuildapolebarnhome says:

    I have a friend that did this type of system. I HIGHLY recommend putting a serpentine to your tubing, otherwise there is not enough turbulence to heat or cool the incoming air. My friend’s is a straight line and it just sucks in COLD or HOT air…..

    • Thanks for stopping by, I would like to hear more about your friends system, like how big and how many tubes did he use and how long his tubes are. What type of pipe and things like that. Please email me back and let me know. gordonmilligan56@gmail.com

      • Update, I have talked to the friend of the person who responded above and I have added two pictures of his earth tubes. I don’t believe if his tubes would have been laid in a serpentine layout it would have made a difference. His tubes did not work because they were buried way to shallow and the fan he used was a high volume fan to draw the air in. I believe his design would have worked if the tube was buried at least 6 feet under ground and he used four tubes instead of one 2 ft tube and had a fan the pulled the air slowly through the tube. This house is a off the grid house and is a very beautiful home with a lot of good features and you can see more of this house http://www.brunerridge.com

  8. Simon says:

    Hey Gordon,

    Nice site, I am encouraged to see all the interest in your comments section.

    As I said on my page, there seems to be a wide tolerance in working designs, and I think yours will work. For 2$ a ft, I think you are getting a great deal and you made the right compromises. Once it is up and running, I hope you will take some good temperature data and share it. I would go for more tubes (as you suggest) and use up the setup cost more efficiently (lower price per ft).

    Mostly I like your plan although I have a small beef with the phrase “constant temperature of 50 degrees”. At 20 ft, it may be constant, but once you put in the earth tubes, constant is out the window. ;^)

    Here are the possible weak points (as I see them);

    If you do need a fan (most do), that computer fan probably won’t cut it. It can’t handle the pressure and will simply recirculate air near the exit. You could block the spaces between the square fan and surrounding pipe to improve your situation somewhat, but if the drag in the pipe is high enough, it will just circulate thru the blade tip gap. It will feel like air is blowing at the fan end, but no (or little) air will be drawn in the other end. Perhaps try a squirrel fan (like an automotive blower) instead. But you can fiddle with that sort of thing later (fine tuning).

    I like the economical idea of only slotting and covering near the end of the pipe, but suggest an additional concept. A slope change… If you only slot the first 10 ft, make sure that it has a steeper slope (perhaps ending in a dry well if your water table can handle that depth, or perhaps leveling out again and running deeper for a while). The deeper earth will be a bit cooler and hopefully pull more water out of the air in the slotted portion. Once the air is further up the pipe, the corrugations will prevent most of the drainage from running down to the slotted end portion anyway.

    Also, you mentioned the screen at the top end, don’t forget the bottom end. You don’t want critters moving in. Use two layers of screen, one fine one to keep the bugs out and a strong coarse one to keep the larger critters out.

    I would be concerned about cleaning things with a water hose… It may work perfectly because you are using a solid pipe, but I have heard of it causing erosion and other problems with perforated pipe. In either case, you will be filling every corrugation in the tube with water that could hang around for a while. I am thinking that a 6 inch ball, soaked in bleach, and pushed with an air cannon or pulled thru with a rope (fished with a wire puller) may be a safer way to clean out the tube on rare occasion.

    • Hi Simon, thanks for stopping by and letting me know you think my design might work. I appreciate your opinion and I promise to take good temperature readings and share my findings and I also promise to tell the truth if it really works or not so others will know if they want to do earth tubes. I will take your advise on the fan and screens for the earth tubes, they sound like good ideas.
      I look forward to following your project on your earth sheltered home and would do one of those too if my hillside was facing south. You will be seeing me more on your site.

  9. Simon says:

    You mention the earth tubes entering the house near the wood stove… If your wood stove allows it, you should run one of the pipes right into it for combustion… The earth tube air will never be as well conditioned as the air already in your home, better to have it sucked up the chimney rather than the air inside. Better yet, have a shorter pipe to bring in less conditioned air for combustion and hook up your earth tube to the blower fan instead. The blower fan can assist with drawing it up the pipe, but you may need a booster if it is not powerful enough. Leave room for fans, etc. so it won’t look ugly later, maybe a recess in the floor?

  10. Steve says:

    Hi Gordon

    Im in the UK and earth tubes are hardly ever spoken about. Im in the process of having a house with a basement made. My thought was to wrap the earth tubes around the basement slab before the walls are built up. This would save any additional excavation being necessary. My other idea was to have the earth tube go direct to the heat recovery unit which would then distribute the air more evenly around the house.

    Regards Steve

    • Hi Steve, thanks for stopping by. That is a good idea having your earth tube go directly to a Heat Recovery Unit, I was also maybe thinking along those lines with an ERV Energy Recovery Ventilator. Keep in touch and let me know what you end up doing.

    • steve says:

      the biggest problem is you eventually will end up leaching the soil temp from around your basement. Really need to rethink about close to the house. Better to move the heat from the ground that has capacity to recharge heat rather than siphoning heat from your house.. Remember heat moves to lower entropy.. eg heat moves toward cold.

  11. Brian of Creaqtive Building Solutions Atlanta, Ga. says:

    With regards to passive cooling and heating:

    I love your enthusiasm but there are dozens of problems with your approach. Here are a few.

    Problem #1. Six inch Corrugated DWV is a no-no for health (Respitory) reasons.
    If you are in love with your “Open System” with weep holes near the end, use straight smooth plastic piping. Your cost will increase due to the joints, but then you MAY have fewer pesky medical bills if it drains properly.

    Problem #2. Moving cold air “uphill” from a 100′ tube with a fan on the inside of the house simply cannot be done. Cold air sinks! Forced air from the outside would be necessary and even that, for the same reasons stated by Simon in an earlier post, is very inefficeint. The cooler heavier air will push back unless you get some sort of dynomo blower to run constantly. This may consume a good bit of energy above what you are trying to conserve.

    Problem #3. “AIR” is a very poor medium for transfering heat. Your best bet is to consider much smaller piping and a 10% anti-freeze to water ratio in a “Closed System”. Run this to a heat exchanger to capture Mother Earth’s ambient terperature.

    Your plan sounds cool, as it did back in the ’70’s but the plain truth is it is not cost effective when properly installed. At the risk of sounding rude, it might be a better idea to set aside the Mother Earth magazine for now and invest in a few science books. While passive systems do work, unfortunately, not as inexpensively or as simply as you may think.

    • Thanks Brian for pointing out my problems with this approach and appreciate your input. First I am not a hundred percent sure the corrugated pipe will be as much as a health problem with my system as you state and the reason I say this is because with this plan I plan to flush it out from inside the house with some type of solution that will kill any bacteria that may be present but still won’t be harmful to breath. I would do this several times a year.

      Problem #2 will be harder to overcome and I know this will be hard to push heaver colder air through the tubes. I was thinking of using a solar fan much like what they use in attics at the air intake box at the bottom at the hill or maybe at the opening in the house or maybe even both. I am sure I can figure it out some how where it will not cost much to operate.

      Problem # 3 is the harder problem to overcome. I agree with you air is a poor medium and I probably would be better off doing what you say with the water pipe into a heat exchanger.

      Thanks for your input, the problems you have pointed out are all very valid and I am sure it will steer some people away from this idea. I think I will still try my idea because it will not cost much to try and if it don’t work it wont be hard to shut it down and close it off. By the way I don’t read Mother Earth News, too many ads.

      • just a bit of thought.. yes pulling up air thru the pipe.. heavier colder air.. true.. but you are also pushing air out of the other pipe.. so it is a column of air maintaining balance.. makes it easier to move the air and does not require as much power as one might think

  12. Brian says:

    It sounds as though you have a positive attitude and are quite ready for the challenge. That’s important. I do, despite the numerous ads, read Mother Earth type magazines. I was merely looking for a polar opposite as a comparison to a more scholastic approach.

    What drew me to your site is that I too am about to embark on the same journey. I am (actually, I retired last week) a general contractor of residential and commercial construction. My wife was diagnosed with advanced COPD when she was just 48 years of age so Black mold is something I have researched and will add safe guards to prevent.

    I work(ed) with engineers, Architects and professional HVAC personnel for more than 25 years and have seen, heard or read about passive systems throughout my career. Our goal is to get off the grid as much as feasibly possible.

    I have your e-mail. If you have no objections I will be happy to send you my e-mail so we can compare notes. Brenda and I are currently closing on a 6+ acre tract in North East Georgia. Passive systems were key in choosing our location. We intend on starting our construction in less than six months. I will be happy to keep you informed regarding our success and failures as we proceed.

    Brian.

    • William says:

      Hi, i am a Civil Engineer and am working on the idea of earth tubes for urban house,Please can you share temperature difference the earth tubes crated?

  13. William says:

    Hi,Milligan , i share the same dream as you have of becoming a farmer, interesting that we live continents apart, i live in India, may be some day i may be rich enough to live my dream.I am a civil engineer by profession and an architect by nature, regards

    • Hi William, hope you can live your dream someday of becoming a farmer. I have not yet started living my dream yet of becoming a farmer and won’t for about another year and a half. To answer your previous question I have not built my house yet so I have no data to give you on the earth tubes. I will start to build sometime next year around Sept. 1 2015. Make sure you sign up to follow so you will know more when it happens. Good luck on your own dream of becoming a farmer, if you want it bad enough you will make it happen some how.

  14. derek says:

    I find it disturbing that a link to a web page that will make a point about a post is no longer there, barely a year after the post! I tried to go to http://www.brunerridge.com/ and get redirected to http://copperheadmill.com/

    It suggests to me that the technology is so new it is not reliable.

  15. Irshad says:

    Hi I want to use this geothermal heating and cooling system in my Poly-house. Am confused with the Fan to be used. Can I Use 10″ HyperFan which is 1050 CFM ? or lesser to circulate the Air inside.
    Example My Poly House Volume is 50000 Cu Ft.

  16. Rod Shelton says:

    I would to know if you have done this yet?

  17. NJ LONG says:

    Dear Gordon, I am 80 year old woman who has lived on a farm many years past. My husband and I have 10 acres in Tenn. on a fairly steep hillside. We are in the process of building a Pit Greenhouse facing due south . My plan was to put the passive cool/heat system behind the north wall at about seven feet down into the soil. I have been concerned about how far I should take the pipe away from the greenhouse and if we should use a six inch or two or three small pipes. I viewed a house in Arkansas about 40 years ago and they had about a six inch pipe and it circled deep and then returned to another part of the house. No fan. If we install this system in our greenhouse where we will have no supplemental heat due to the south exposure to sun and insulation at night. No glass in insulated north roof, north wall is lined with concrete blocks
    (painted black) to hold soil of hill side that has some small rocks included in the soil. Probably can sift most out. We were very happy to read your blog and all the responses.
    How many times did Edison fail with the light bulb before we can now go to the moon?
    Cordially, N. J. Long

    • Hi Mrs Long, thanks for looking at my blog and commenting. I am amazed that you are so active at your age and hope to still be like you when I am 80.
      I think you will be better with two or more pipes and 6″ or 4″ pipe will work. I didn’t do this on our current house we are building but would like to see pictures of your project if you would like to share them. Good like on your project and thanks for stopping by.

  18. Would love to know how the project is coming along….I have one question. Corrugated drain pipe is well, corrugated. Even with a sloping elevation water could sit in the ridges and develop mold and insect breeding ground. Am I wrong about that? Thanks. I am interested in doing something similar just want to learn any pitfalls!

    • Thanks for commenting Jonathan, I never did this, I was just thinking about doing it. It was too unproven for me to take that chance. I just built my home and didn’t do it. Sorry, your concerns may prove to be right but I just can’t tell you.

  19. Robert says:

    Gordon I have been planning my earth air heat exchanger for the past year following purchasing our forever house in South Carolina. I came accross your sight and earth tube plan and it is very similar to mine. After looking over all the post I felt I need to share some of the data I have collected. A quick bit about me, I have been in nuclear power for close to 30 years and practice and teach all those heat transfer and fluid flow equations that we have all came accross in our research. Earth Tubes have been used all over the world and there is an amazing amount of data backing the calculations and actual real world performance. trust the equations. The math works! But you have to know the data from your land. In my area the deep ground temp is 66 F with a 14 F swing that lags the air temp by 3 months. I can not dig that deep but I can go down 6 feet with my soon to have backhoe. I dug a 6 foot deep test hole in the middle of my planned site. It’s a 2 foot deep fox hole with a 4 foot deep 8 inch wide hole. Moist sandy compacted clay. I leave the hole open to the air and test it every day. Air temp is in the low 90 s, @ 3 ft it is 74.4 F, 4 ft is 73.5 F, 5 ft is 72.5, and 6 ft it is 71.6 F day or night even if it’s 80 outside or 90. Before people put money in to a project I recommend taking a few hours and digging test holes and lowering a thermometer down an getting data. A full years profile would be best. Use smooth wall pipe with a continues slope open at the end for condensation to run out. Thin wall PVC (4″ sewer pipe) is best, put the coupling end up the hill side to prevent moisture from holding in that small seem every ten feet. For 4″ PVC you need at least 50 feet at 6 feet deep for a proper leg. Transition from the 6 foot deep leg to the structure using 45 degree elbow, avoid a 90 if at all possible. Install a tee with a cap or similar access so it can be cleaned and data collected if desired. Slow air flow is not better. You need a rate that will give you adequate transfer units (mixing), you want 5. For 50 feet of 4″ PVC that is 332 cubic feet per minute. Because of my yard, trees, slope… My legs will be 175 feet with a 16 foot drop in elevation. I can’t change the earth that much so I need more pipe. The longer the leg results in more head loss ( friction) and does not improve heat transfer. Longer is not better! You need to install the correct number of legs. For me my target is turning 92 F air in to 72 degree air and cool my 3000 square foot house. Use this equation BTU Output= (change in temp)X(flow rate)X1.08. If I use a Home Depot 4″ induct 30 watt buster at 190 cfm I get an output of: (20F)x(190)X1.08 = 4,104 BTU/Hr. If I use a 6″ 390 cfm fan I get 8,424 BTU/Hr. Twice the cooling. As stated in an earlier post you have to pump cold air up so more power is better. Thermal driving force between 90-70 F is low at 0.0018 psi for a 22 foot rise but don’t be fooled fans move volumes they don’t make much head (pressure). For heating it is on your side, to go from 40 F to 70 F it will generate 0.0033 psi of lift. Sounds insignificant but if it were a 20 ft by 20 ft ballon it would lift 200 pounds so in this case even a very small fan could be the best option. My area and square footage I should have a 5 ton AC unit or 60,000 BTU/Hr but for a earth tube going 24/7/365 I should be able to maintain with 2 tons, half the capacity with twice the operating time. The calculations for my plan and current ground data that I have collected indicates that I need 4 legs with at least 250 cfm and I can expect 23,000 BTU/Hr or 1.9 Ton AC capacity. Hope this helps someone, plan to start digging this winter once it’s not so hot outside.

  20. Robert says:

    Just a side note: the cost for 800 feet of pipe, fittings,fans… Is $1,200. A 50% reduction in my electrical cooling cost will pay for the materials in 9 months. After that the savings will cover my tractor payments for other projects. My electric bill shows each day’s high and low temp and with my log book temp data from my test hole I should be able to determine if my land with a air earth heat exchanger will be a cost benefit before spend a dime on materials. I started all this research a year ago to find a project that would generate enough money to justify the high cost of a tractor backhoe. My wife checks my home work so if the math doesn’t support then I don’t get a new toy. Every piece of land is different so I encourage anyone thinking of doing a earth tube to gather all the data you can and double check your math a mistake could be costly!

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