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

About these ads

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.
This entry was posted in Building Projects, Pole Barn House. Bookmark the permalink.

23 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.

  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.

  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”.

  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.

  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.

  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.

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s