Earth Air Tubes


Upper Pond – Pig Drinking Resevoir

I got the following letter in email this morning asking about our house’s earth air tubes. I’ve gotten quite a few other letters and comments asking about this. To the uninitiated, the basic idea is to draw air into the house via tubes in the ground to either warm or cool the house. A fan can be used to drive the air or it can be completely non-electrical using a solar chimney or simply the natural drafts of the house. I’ve mentioned this a few [1][2] times before in regards to our old farm house and cottage. I share my response to D.P. below so others will benefit from the questions and experiences.

Good afternoon,
Hi, my name is D. P. and I work for a tribally owned health consortium in Anchorage, Alaska in the Department of Environmental Health and Engineering. Soon I will be assisting villages with various air quality projects they see are needed (control of open burning, woodstove-replacement etc.). While researching ways to improve air quality both in and outside of the home, I often run across renewable/clean energy projects that not only cut down on cost and resources but would also have a significant positive impact on air quality, such as the earth tubes (improved ventilation without great heat loss). I am very interested in learning more and was hoping you could provide more information on how you installed them, did you have plans to build from?

I didn’t have any plans – this is the sort of thing that is a bit unique. Seven years ago I designed and built our earth air tubes to fit our situation based on experiments I had done and reading (see below). For the old farm house, basically we dug a 70′ long by about 2′ deep by 4′ wide trench (I’m doing these numbers from memory, the 70′ is right, the depth is approximate). The trench went from the basement of our house down hill and exited the earth at a point lower than the house penetration. This allows for drainage of cold air down and water down as well as rising warm air inflow. Realize I’m designing for a cold environment to warm incoming winter air. If I was designing for a southern climate where I wanted cooling I would change the configuration to drain cool air downward into the house.

In the trench we placed stone for drainage (2″ washed crushed stone). On the bed of stone we placed four parallel 70′ long (10′ interlocking smooth walled sections) 4″ diameter drain pipes giving a total of 280′ of pipe length. The pipes were spaced a few inches apart from each other and wrapped in filter fabric. Most of the pipes were solid walled, the last 10′ of each tube, furthest from the house, was perforated with the holes on the bottom for drainage. This was probably overkill in retrospect but I was worried about water in the pipes, especially condensation during the warm summer months when the system would act more like an air conditioner / dehumidifier.

Drainage is very important. Figure out how to make sure the pipes are not going to fill with water, have mold build up, etc. You don’t want to get Legionnaire’s disease, black mold, etc. The incoming winter cold air is wonderful at drying the pipes. In southern parts of the world the incoming high humidity could cause problems due to condensation. In wet areas water could pool in the pipe. Being on a slope helps a lot. Hard in some areas… We’re in Vermont and everything is sloped.

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We covered the pipes with some dirt, perhaps 4″, and then two layers of 2″ closed cell insulation. The first layer was two sheets side by side and the next layer was one sheet that overlapped the seam of the previous two sheets of insulation. The reason for the insulation is the pipes are not very deep – we generally have shallow soils on our land and in much of Vermont for that matter. In Alaska you’ll want the insulation too I would expect due to the deep frost penetration. We then covered the insulation with dirt to bring the trenches back to level. Each layer should be well packed to prevent settling.

It is advisable to put hardware cloth 1/4″ screening over the ends of the pipes inside and outside to keep vermin out. Window screening inside of that helps keep insects out. A dust settling chamber can be setup if dust is an issue from local roads, pollen, etc. I would use a ~2’x2’x2′ chamber with a deep stack of furnace filters. Slow moving air through filters is very effective for dust removal. Clean the filters periodically. Put the filter system on the incoming end, that is to say away from the house, to keep the pipes cleaner.

Our winters get down to about -45°F and we have months below -20°F many years although this past winter was quite mild. We have high winds. It’s not to dissimilar from Alaska – I lived in Fairbanks, Anchorage and Kenai long ago. The earth air tubes have made a huge difference for our old farm house here in Vermont. I would think they would help folks in Alaska too for exactly the same reasons. The winter air in our house went from being stale to fresh. Our sinuses were much clearer afterwards and the air is no longer so dry during the winter – an effect I had not predicted. The outdoors can be -45°F and the air coming into the house at the pipe exit in the basement is 35°F. That gives us a 80°F heat gain from the earth on the fresh air. We heat with wood and now we have no back drafting so the wood furnace works much better.

A big issue in our area is radon which is a radioactive gas put out by the granite below us. I had a concern that the earth air tubes might collect radon but the opposite is the case. They are reducing the radon concentration in the house by diluting the air through fresh air exchanges. “The solution to pollution (radon) is dillution.”

I’m very pleased with the results and have come up with some improvements for our new system. We have been building a new house further up the hill and I’m incorporating improved designs of the earth air pipes there.

  1. Extending the insulation wider to create more of a thermal shadow.
  2. Longer pipes to get more effect.
  3. Out-flowing air pipes parallel and below in-flowing pipes to act as a heat exchanger.
  4. Pollen/dust filter – put it out at the input end of the system so the pipes stay clean.
  5. Solar stack to drive system or electric fan or chimney stack around wood stove – I went with the latter on the tiny cottage and that works quite well in addition to being a non-electric, passive system. For our old farm house I simply used the draft of our wood furnace to drive the system and that worked well. Also the farm house ceilings/attic leaks some so that drives the system some too.
  6. Clean-outs on pipes at ends and any bends.
  7. Build a little housing of stone to protect the ends of the pipes at the downhill side.

I would love to incorporate probes for humidity and temperature logging in the soil around the tubes and in the tubes themselves to gather more data but it costs too much. I’ve been doing it with simple digital min/max thermometers I stick in and monitor daily.

For details of our new Tiny Cottage. Our family built the new house all by ourselves for under $7,000 and it requires only about 3/4 cord of wood for heating. This is a design that would work very well in Alaska and can easily be scaled up. The cottage is on a floating slab which works well with permafrost from what I’ve read. Cost was kept down by some salvage such as the windows which are from an office building. In our case we anchored the slab to the ledge of the mountain but in Alaska one could float it on the p
ermafrost. In that case I would pour the slab a little wider to get even more floatation – engineer it. The cottage uses ferro-cement for the barrel vault roof which minimizes the cement volume while maximizing the strength, easily done by people with some simple form work. This makes it strong enough to take any snow load – no need to shovel the roof. We are living in it although like with most owner built things we still have some things to finish. We were able to build most of it in about two months – two adults, a 14 year old and a 10 year old plus the help of a three year old. If it were built on a slight mound on the permafrost then earth air pipes might be able to be put under and around it.

What resources did you find helpful in your research before installation?

Mostly I spend years thinking about it and doing experiments. I built progressively larger models and took measurements with temperature probes. Build one and run it for a year to see how things go. The articles I found on the net all talked about burying the pipes far deeper than is possible where we are (10′ minimum depth) and about using far larger pipes than possible (18″ minimum pipe diameter). It is rare to be able to dig down deeper than 18″ before hitting ledge. While those might be ideals the reality is one has to adapt to the situation and the 4″ pipes worked at a shallow depth with insulation.

Putting the insulation above the pipes was my way of achieving much greater depth. Soil has an R factor of about 0.1 per inch. Insulation is about R5 per inch. Thus with 4″ of insulation I effectively gained 5×4/0.1 = 200″ = 16′ of depth. Not really because the heat curves around the edges of the 4′ board but still it was a vast improvement over simply burying the pipes.

I just did some Googling and here is a search pattern that will bring up some links about earth air tubes for further reading. Another good source on this general topic comes from earth sheltered housing. John Haite has written some excellent stuff on this under the heading of PAHS which stands for Passive Annual Heat Storage which uses similar ideas. There are two good overviews on Wiki [1][2].

Do you think its possible to run a series of earth tubes to an entire village?

Sure. Although personally I like doing things on a per home basis. That way if there is a failure it only knocks out one set, not the entire village. Think if an animal gets into a pipe and dies… or a skunk sprays… or some practical joker throws a dead fish in… If the pipe serves the entire village it’s a nightmare. If the pipe serves just one house it’s an inconvenience. Small scale is beautiful.

I am finding mostly earth tubes are used for cooling,

Yes, that was what I saw too in the few articles I found. For us the tubes are for heating fresh air. Our climate is more akin to yours so warmth is more of an issue than cooling. Our summers rarely get above the 70’s here on the mountain. Interestingly, 1,000 to 1,500 feet below in the valley the climate is very different. Down there cooling is an issue. It always amazes me when I go down off the mountain just how hot it is a mere few miles away.

and most do not address the problem of permafrost.

Permafrost will have some interesting issues. A little bit like our ledge. It may be that you need to make a much wider insulating cover which will produce a vertical shaft of heat. Consider placing pipes directly under the homes so the thermal shadows of the homes themselves help the system. It is definitely an interesting variation problem…

I am not an engineer and I’m sure there are places in Alaska this would/wouldn’t work but just wanted get more information and advice from someone who’s seen/constructed these first hand.

Speaking as an engineer, don’t let them get their hands too tight on the project and make it too big. There is a serious distraction among engineers to over build projects, to make them bigger than necessary. It’s an ego thing: “Who has the biggest pipes? er, tubes…” You know what I mean. :)

Outdoors: 75°F/56°F Sunny
Farm House: 78°F/68°F Flipped compost pile
Tiny Cottage: 68°F/62°F

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About Walter Jeffries

Tinker, Tailor…

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29 Responses to Earth Air Tubes

  1. karl says:

    i did some research regarding earth tubes. i would have used them for cooling. the issue here is in missouri is the high humidity. the condensate in the tubes can become a health hazard–black mold and such. proper drainage and moisture disposal without allowing critters in is very difficult.

    i’d think that heating from a permafrost environ would be nominal. the best temperature that you could hope for is just below freezing. given that information a good snow cover would have the same effect. so why disturb the permafrost? lay your tubing on the ground in summer and let the snow cover it.

    annualized passive solar might be a better option. heat a huge soil bed during the summer and tap off the heat sink in the winter. that’d probably never pay off though. interesting problem…

  2. Edward says:

    Walter your tubes are an open system? Why is that? Would a closed system be more efficient since it would not have to raise the air temperature as much?

    • KIRBY says:

      Edward, a closed system would not provide the fresh air, and would need energy to return the air to the underground pipes.

      With the open system and a solar chimney, air is drawn through the pipes and up the chimney by solar heating alone.

  3. Anni says:

    What was the cost of yor system?
    How much money do you think is saved?

  4. Mellifera says:

    Walter,

    You rock. I was trying to tell somebody the other day that you don’t have to have a career (nay, not even at a fabulous non-profit) to do good things for other people. Ie… withdrawing from the rat race does not necessarily equal withdrawing from humanity. I don’t think they believed me, but now at least I have a good example to cite. ; ) How else would you have the time (or inclination) to experiment with things like that?

    PS: I have a pig question that might be original, I’ll email you.

  5. Edward,

    We went with a open system (one that draws in air) rather than a closed system (one that recirculates the air) because getting fresh air is important for a number of reasons:

    1. for the wood fire which burns a lot of oxygen;

    2. for us to breath;

    3. humidity control;

    4. radon gas control.

    A closed system could have actually exasperated the radon issue because with each cycle it could pickup more radon cycling it back to us.

    Additionally, the soil temperature is lower than the house goal temperature so a closed loop wouldn’t have done us much good since we’re trying to warm the air. When the incoming air is below the soil temperature then it gets warmed as it passes through the earth air tubes. The wood furnace plenum in the old farm house further warmed the air.

    Anni,

    The cost of the system is pretty trivial because I have backhoe to do the work and I engineered it myself. In addition to that I was already digging the trench in order to put in a horizontal ground wire for our fencing system – I simply made the trench a little wider.

    Costs: (2001) Total = $500
    1 load of washed crushed stone ~$150
    28 sections of sewer pipe at = $80
    26 sheets foam insulation = $260
    1 roll soil fabric ~$10

    Hiring a backhoe would probably cost $500 to $1,500.

    Having someone else do the system would cost something more but it really isn’t that hard and the failure mode isn’t too bad. it is worth anyone who’s a little bit handy considering doing themselves. Heck, you could even do the ditch digging with a shovel.

    I don’t have a good number for how much money the earth air tubes saves us because I haven’t measured the air flow – we don’t use a fan and cash savings wasn’t why I did it. Playing with a calculator I come up with a cost savings of about $700 to $1,500 per year compared with heating oil. This gives a one year payback on the system if you do it yourself.

    That means that over the past seven years the system has saved over $5,000. Except we heat with wood instead of oil and we cut our own wood. Still, it has meant we spend less time cutting and splitting wood, less time feeding the fire, the house has been more comfortable, the wood furnace hasn’t back drafted and we had much fresher and thus healthier air.

    Realize that the air coming out of the tube into the house is not fully up to what most people consider to be a comfortable home temperature so you would want something to raise it up to ‘room temperature’. This could be a wood stove, solar, propane, oil, electric, etc. What the system does do is make it so the home heating system doesn’t have to work as hard and that is where the savings comes from. Additionally you get fresh air in the house.

    Mellifera,

    Why thank you, that was very nice of you to say. As to having the time, well, a little mania goes a long ways… and a lot of mania goes a whole lot further. The old “It’s not a bug, it’s a feature” ploy. :)

    Cheers,

    -Walter

  6. Hello Walter
    How about that…. mania?

    You put yours to such good uses.
    And you do such a methodical documentation

    My mania usually occurs in the early AM which concludes to a crash around 2:00 to 6:00 pm

    Last night I fell asleep at around 8:00 with the kids.
    Around 4:00 A.M. My head was spinning with Ideas.
    What to do? What to do? Create a you-tube video of my wife make herding goats look nearly impossible?

    The wanna BEE farmer tends to race from project to project without careful documentation and introspect. Off to the next project, hobby or WRECKreation.

    I settled on organizing the aftermath of several projects in the barn.
    This gave me tremendous feeling of accomplishment. I can now see 2/3rds of my work bench.

    One minor problem. When I went up to our bedroom to get ready for work I noticed my alarm clock had the batteries ripped out. Ooops I forgot to turn off the alarm for 5:30…. Again.

    Wow I had not thought about heat tubes for our house!
    Sounds like another cool project too add to the list of the next back hoe rental.

    I was thinking of methods of makeup air for the oil burner.
    To quote Tigger
    “TTFN”
    WBF

  7. Maggieliz says:

    I’ve been following your blog for years; your family and your farm is simply amazing.

    Have you considered writing an article for Mother Earth News or Back Home magazine? This is exactly the sort of thing that they’d publish, and they pay a reasonable amount for articles.

    Plus, this kind of information is terrific.

  8. Sandra says:

    Walter,
    I saw your posting about the Primavera LX-400 printer and was wondering if after using the printer for a while if you would still recommend it. I also have additional questions:
    – Do the labels stay attached firmly on product when it is placed in the freezer?
    – Does the ink fade or run over time when placed in the freezer and product is later thawed (condensate)?
    – Have you found the printer to be as cost effective as you had originally thought?

    Thanks,
    Sandra

  9. Anonymous says:

    Hi Walter,
    i have been trying to research EATs for a school project and then apply that for a system at my own home. i live in melbourne australia in a temperate climate and will be using them for cooling.
    my house is on a 150′ x 30′ block and my soil bed is 30′ x5′. i will wet the soil with grey water from an upstairs shower to use evaporation to aid in the cooling. ther is conflicting information on pipe types. i was thinking of using a corrugated poly pipe in order to enhance turbulence and heat exchange. a 40 watt fan will drive an intake from in a fernery. as my air will be piped up to the second story i will install a drain at the bottom of the riser with a p trap. clearly my use is significantly differnt to sugar mountain or alaska but the principles are the same. i would appreciate your thoughts.
    davd

  10. Aye, your climate and goals are definitely different than our situation. Still, earth air tubes could work well. My understanding is your climate is quite dry and that should help prevent mold buildup.

    I would strongly caution against the corrugated tubes. In my tests I found they filled up with garbage and are impossible to clean should that ever become necessary. I have read that corrugated tubes also breed mold better – a bad thing – due to water collecting in the tubes.

    I have some qualms on using the grey water to cool the system. Make sure you’re not going to produce a breeding ground for bacteria and molds.

    Build a small model version and test it for a year or so to work out the kinks.

  11. Sandra, you have inspired me to write an update on the Primera label printer. See this post.

  12. Andrea says:

    I love following your journey to your own home and how your family has actually truly built it yourseves. I do have a question. You had mentioned you will be earth sheltering your home and you have mentioned the work of Haite. But you have insulation under and all around your house that would isolate the house from the earth. Why? Dont you want the warmth of the earth in the winter and the coolth in the summer?

  13. Andrea, good question. My response got long enough that I turned it into a post. See it tomorrow.

  14. Randy Duams says:

    Walter,
    I am a engineering student in QVCC in Danielson, CT. I was just wondering how much money, you have saved in the time you have ran this system. coming into this project I really had no idea what I was looking for. My final presentation for class is on the air to air heat exchanger with earth tubes, and it sounds like you would be the best resourse to ask on the turn over on this style system.

    • I don’t have any other data aside from what is in the article above and those linked by it. I have seen some studies on the web. They all recommended much larger diameter pipes than I use and a much deeper burial which is not possible on our mountain due to the ledge and bedrock. Here is a search pattern.

  15. Kim says:

    Hi Walter
    What would you say is the rate at which air passes through your earth tubes? How many air exchanges do you figure you get each day?
    I’ve been doing some calculations to see if they could work for a passive solar building we are thinking of, but when i look at the flow rate that would be necessary to get at least 3 or 4 air exchanges a day, it doesn’t seem like the air could heat up fast enough to come out close to a comfortable temperature at the outlets. They would be about 73 ft long (22m), but i can only get in three 4″ tubes due to cost, because we’d have to run them through the foundation to get the length, and there are some awkward things about that. This post has really been a help. Much thanks if you can tack on those numbers.

    • I’m not sure. We ran four tubes, each 4″ in diameter, in parallel. This gives more surface area and a more gentle airflow as well as lower cost. The air going in at the outside end is our fridge winter air which can drop to -45°F. By the time it gets to the house end it is well above freezing. This is the worst case scenario. Most of the time it is warmer.

  16. Jess says:

    Love the airtube idea. If we all did things like this it would save having to pump so much oil and buld more nuclear plants.

  17. Shane says:

    I love the idea of the earth tubes. Have you thought of running water lines through your compost? I read an article about that.

  18. Bob says:

    I found this web page while reading up on solar energy solutions on Wikipedia. I became totally engrossed reading all about your tiny house. I am glad that you have spend so much time documenting your efforts. Thanks!
    As I currently live in an apartment I am frustrated that I can not try out any of your ideas, but a techie can still dream. Perhaps someday I’ll get to try myself.

    • The amazing thing is that we built our cottage for about the cost of one year’s rent for most apartments. That doesn’t include the cost of the land, which we already had, or the septic and water, which we already had. But even adding those things to the bill it still means that one could buy land, put in a septic, a water well and build a tiny house for two to three year’s rent cost. There will be real estate taxes each year but maintenance is nominal and heating costs are nominal. After that it’s all savings.

      • Dorothy says:

        It is amazing to do be able to do so, I mean build a whole cottage for the cost of a years worth or rent. Living in the city like me, most people do not realize how valuable our time is. We mostly follow every day life mechanically doing things we dont really like. I do not really understand the value of time and what we can really do with it if we put our minds to it. Reading your blog makes me want to re-think things.

  19. Larry says:

    In the title of the photo at the topi is says pig drinking pond. But it looks like you swim there too. Arent you afraid of the pigs pooping in your swimming water and making it yucky?

    • No, the pigs don’t have physical access to the Upper Pond. That area is outside of their fence pastures. The purpose of the Upper Pond is to act as a reservoir. We have several springs that feed that pond. All the springs drop to a fairly low flow in the heat of summer. The Upper Pond acts as a reservoir to get us through dry spells like August.

      One inch black plastic pipes lead from the output of the Upper Pond to a series of watering troughs[1, 2] throughout the pastures. The pigs drink from those watering troughs and stay out of the reservoir.

      We also have several pig ponds[1, 2] for them to swim in, but we don’t swim there, although the ducks and geese do.

  20. Dan says:

    Hi,Thanks for sharing your experiences, i have a question and i dont know if it ever crossed your mind, if mold or radon”may” be a problem for earth tubes(although i have read the blowing of fresh air into the homes actually lowers the radon risk.) i wonder why not just put metal pipes and ran and close loop water system to draw out the cold or heat and put a radiator to blow out the coolness from underground,water is a better conductor or temp than air, so i think shorter pipe with smaller dia may just do the trick. a low wattage wilo pump will be needed to circulate the water.

    • Radon in the air pipes isn’t a problem if the air pipes are sealed and bringing in fresh atmospheric air. If the air pipes were perforated and drawing in air that might be an issue but the air coming through is being exchanged so much that it is better than a house which is closed up and having radon issues so even then the earth air tubes can reduce the radon.

      If I understand what you’re suggesting then you’re describing a closed loop system which also works for just getting heat or coolth. This is variously called a geosystem, heat exchanger, heat pump, etc. In our case we want to also get the fresh air both for breathing and for our wood stove so the open system is better here. I did consider running a closed loop system into the pond but have never tried that.

  21. VB says:

    I read your blog like every week. Your story-telling style is witty. Love it. Keep doing what you are doing!

  22. Farmerbob1 says:

    “was perforated with the wholes”

    I think you meant ‘were perforated with holes’, since you were using were before. The rest looks like a partial edit that never got cleaned up :)

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