How to remove moisture from your home: Part 2 of 2 - Extractor fan

Ventilation hole and probe finish
The automatic ventilation system finished and working

As we indicated in the previous post, in this one we will talk about the positioning of the extractor and details to be taken into account for the system to work properly.

It is possible to extract moisture directly by placing an opening to the outside in the lowest part and placing the fan directly (the coldest and most humid air tends to be in the lower part of the room), but in my case, being a ground floor in contact with the mountainside, I had to bring the humid air from below to the top, so I used 90 mm diameter PVC pipe, with a fan connected to it in the lower part.

Another advantage of using a tube is that, by extracting the air away from the outlet, we can leave the gap between the hole and the tube open and the outside air will enter through it, without the need to open another hole. It should be borne in mind that the gap should not be too narrow, or the flow rate will be reduced as the air will have a lot of resistance in its movement.

If we do not have a ventilation holeas was my case, we will have to do it. We have two options; either call a professional who will make the hole with a glass crown in a moment, or with a cheap electric hammer, after delimiting where we wanted it to appear on the inside, we measure with reference to something visible on the outside (a column, wall, etc.), we mark the area and drill. It is very important not to perforate any of the main columns of the house..

Materials for pipe laying

Depending on your needs, this can vary a lot; for example, we can replace the PVC pipe with any other durable material that is somewhat resistant to the passage of air. In my case I have needed:

  • An exhaust fan/exhaust fan or fume extractorWe can use one recycled from an old kitchen extractor fan, or one from a large computer. Keep in mind that the greater the distance and the larger the room, the more power and size must be in accordance. In this case we are dealing with a room of 30 m3 so a 10W is sufficient. Noise is also very important; the less dB it emits when operating, the better. Ideally, it should be placed outside, out of the rain.
  • 3 m of PVC pipe, 90 mm diameter. Available in construction warehouses.
  • 2 elbows or bends PVC 87º diameter 90 mm. for the breaks.
  • An eccentric reduction from 110 to 90 mm. to position the fan connected to the pipe.
  • Galvanised perforated Apollo tape to fix the tube.
  • Screw anchors and plugs of the size required for the size of the holes in the Arduino grid and box.
  • And the necessary tools; electric hammer; cable, adhesive tape, crosshead screwdriver, etc.

Let's get to work

The first thing to do is to open up the passage for the pipe at the bottom of the wall, but where we have no water problems that it can enter (by placing it a few centimetres higher), or with the humid air when leaving, and that it cannot be blocked in the future.

It is important to check that there are no electrical, water, gas or any other type of conduits in the area. to drill the hole. Metal detectors are available to check this, but it is best to examine adjacent areas to see if anything could pass through the site. And if in doubt... probe very carefully.

Marking the area to be drilled

After a couple of hours of effort (it was 50 cm of concrete), drilling inside and outside, we chopped the area until we had a hole free enough to place the pipe. A tip: These hammers are not very strong; to advance more quickly it is convenient to use the flat pointer and not to sink it, but to go removing small pieces; it will help us to begin with the widest to be able to work loosely.

View of the street from the hole
The street can be seen through the interior

The next step is to lay the tube. I have used recycled pieces I had in the warehouse to assemble it; in total 3 mts. of pipe. The one we put towards the outlet is important that it protrudes a little to cut it just flush with the lid or grille, so that it is connected directly to the outside.

Normally the parts are so tight that no need to use glue to fix them to each other (a small gap of a few tenths of a millimetre will not affect performance), making it easier to fit it and to release it in the future if necessary.

The tube placed on presentation still unmoored

Perforated galvanised tape is usually used to fix it, it is well fixed and allows flexibility of placement. You can also use a wire, or whatever you can think of.

Once the pipe is in place, which will extract the humid air from the lower part of the "storeroom", We proceed to attach the box with the Arduino controller to the wall. where it is visible so that its status can be verified:

The fan has a power cord with a plug, and to activate it with the relay, I had to connect another wire to one of the poles, so that when I connected it (closing the circuit) the fan would start up.. We can connect it by accessing its junction box, as I did, or we can do it directly by cutting the power cable.

Attention: It is important to take safety precautions when working with voltages above 50V.Make sure that the cables are unplugged from the mains when carrying out any manipulation.

Detail of the cable to be connected to the relay
I have held the fan in place with grey duct tape.

If several devices are to be connected, we will need a power strip with several socketsI screwed one to the wall for the occasion.

To conclude, it is important to place a filter or mosquito net. to prevent small insects from entering the room through the ventilation hole (being at a low height, they can enter too easily); I have stuck a piece of mosquito netting with silicone.

Required material: Mosquito net and metal grill

Mosquito net glued to the grille with silicone

On the outside we cut the tube flush with the hole. In the photo you can see where I originally placed the external sensor, which I changed to another position later as it was partially in contact with the indoor environment and the values were not quite correct.

To give you an idea of the effectiveness of the extractor fan, on the first day it was running for several hours at a time, and the stones on the floor that were hit by the air became damp:

To get the most accurate values possible from the external sensor, I made a small opening in the wall.I placed the sensor base glued with the hot-melt glue, and it will be covered, as we have seen in the picture at the beginning, by a smaller grid.

I hope you found some of these ideas useful, I look forward to your next visit my dear readers!

16 thoughts on “Cómo eliminar la humedad de tu casa: Parte 2 de 2 – Extractor”

  1. Hi David... I have a question about your system, by how much have you managed to reduce the humidity? Is the long term change noticeable?

    1. David Losada Gacio

      Of course, although it all depends on the speed at which the air is renewed (fan flow rate), just look at how humid the floor got in the first few hours; the humidity went from a 95€ to a 70%, which is still high; I am considering putting another fan in another area.

  2. Hi, your mechanism is very interesting. I'm about to do something similar but with an extractor fan without a humidity timer. I'm going to program it directly with a timer to turn it on for x amount of time each day. I have a part of the case with a floor as an air chamber, old house with wooden floor, about 30m2. I have a grille at the back of the house and one at the front, but I can see that it doesn't get enough air and when I open a small door (it's not a cellar, just an air chamber), I can smell damp and I have a couple of walls with damp that I caught from there.
    My questions are the following, I don't know much about the subject.
    1. Do you think that the extractor fan that I place to let the air out to the street should be placed flush with the floor or ground, since that is where there is more humidity? or is it preferable to assemble something so that it is halfway between the ground and the floor above?
    2. Somewhere I read that this problem is mainly because these spaces are not sufficiently well ventilated, that the ideal is that the outside and inside temperature, humidity permitting, should be the same outside as inside. I think that in my case, the ventilation through the pre-existing grilles is not sufficient for this. In this case, would you advise me to put an extractor fan facing the back so that air comes in from outside and one at the front that takes it out?
    It seems to me that this, by helping the air flow, would solve the humidity problem.
    What do you say?
    Thanks for the post and the answers!

    1. David Losada Gacio

      Hi María, normally the lower part has a lower temperature and a higher relative humidity, but it doesn't matter too much either.
      What we do with ventilation is to keep it at bay, but it does not solve the problem, we usually have to go to the root, and it usually comes from masses of soil or damp elements with which the wall or material is in contact. I talked about it in my blog:

      1. Hello David, yes I read that post before. I tell you, my house is a bit old, it has, what is called an air chamber between, there is the ground and about 50 cm above, a wooden floor supported on braces. It is not possible to walk in there, you can only crawl in through a small opening in the floor by means of a lid. The house has foundation dampness in some parts, if I look at the ground (the lower part of the air chamber) I see that it is damp in some parts, that is, there is no solution, I can improve it so that this dampness does not go up to the wood and in the future it can rot the floors and lower the dampness so that it does not affect the foundation of the walls so much.

        So, what I wanted to know is your recommendation for:
        1. Install an extractor fan in a grille with an exit to the street, which the house has already had from its origins, to take the air outside.

        2. In another room, but in an almost straight line to where the extractor fan would be, install an extractor fan that brings outside air into the air chamber. Keep in mind that all the floors are connected, it is a whole air chamber and the floor is supported on braces.

        My reasoning is that if the idea is to make the outside and inside humidity equal if I put air in the bottom grille, and take it out through the front grille of the house, this would lower the humidity and help it equalise with the outside humidity.

        3. The other option I have is to just put an extractor fan in the front and not to put anything in the back. There really is a musty smell when you go near the grille, and you can also see it when you look at the ground. I bought a dehumidifier, one of those bathroom and kitchen dehumidifiers, 300m3. I have about 30m2 of chamber.

        It is not easy to access that part and I am going to do it myself, both because of costs and because people don't seem to know much about it.

        What do you recommend me to do about this?

        Thank you very much.

    2. David Losada Gacio

      Hello again Maria. It's a good idea, because you circulate the air from the street, but just one extractor fan in one of them is enough; the air would automatically enter through the other one. One of these cheap low speed kitchen fans will be enough, it will use very little and will last a long time. Another option to avoid problems and consumption is to open some more ventilation holes in other areas; the wind would do the same job; the fan and relay usually give problems after 10 years. greetings!

  3. Hi David! I have bought everything, display, sensors etc. When I compile it gives me error, I wanted to try the version without diaplay and it doesn't compile either. Also in the schematic the dht11 sensors are wrongly connected (positive and negative upside down) so I burned 2 sensors and an arduino one 🙁
    Did it work for you as published?
    Thank you very much

    1. David Losada Gacio

      Hi Cristian, in the diagram as you can see there are 4 poles in each DHT, and it is NOT INDICATED which one corresponds to each one, it is your responsibility to verify which is the positive, negative and data, as EVERY MANUFACTURER puts the contacts in different pins. If you look at the pictures, you will see that I had it connected in a different way; the scheme is indicative in terms of the sensors.
      As for the compilation error, I need more information, indicate the error you are getting, the line you are getting...

      1. Hello again David! thank you very much for answering me and for being interested in my problem. I tell you, last night I started again with new parts 😉 I re-downloaded everything except the adafruit gfx library, I installed another one that contained a "fonts" folder and it worked!!!!
        Now the display and the sensors are working!!! only the fan relay and the error relay are on, is that so? if the answer is yes, then I should switch the fan to normal closed?
        Sorry David that in my first comment I was not so kind, I thought it was another of those projects that never work and only make you waste time and money on components.
        Again, thank you very much for your interest and if I can help you in any way, count on me.

        1. David Losada Gacio

          Thanks for your confidence Cristian, yes, unfortunately there are many "inventions" that promise a lot and are useless, just as a curiosity (I can think of the homemade solar cell, the mobile phone battery charger with two candles, etc) and if you understand the subject, you can see that they are useless curiosities.
          This one, on the other hand, has been working for me without modification since I published it two years ago, and it shows.
          You mean that it stays ON (flashing) and the fan relay is on (if the humidity and temperature conditions are met). If it is from the error, it means that there is a humidity and temperature sensor incorrectly connected.

          1. Sorry David, I expressed myself badly. What happens to me is that in equal conditions (having one sensor next to the other), the fan relay is energised with its LED on. Is this how it works? I should clarify that the relay module I bought has the 5Vdc but they are only activated when you put a 0 (or negative) in the signal.

          2. David Losada Gacio

            In that condition it should turn off, your relay works in reverse then; you have to change in the lines where the relay is handled, change the HIGH to LOW and vice versa; for example "digitalWrite(onRele, LOW);" would change to "digitalWrite(onRele, HIGH);", I think there are three lines you have to change.

          3. Thanks GENIUS! I'm going to try that tonight and let you know how it goes.
            Do you have any other good inventions I can make? I'm just getting started with arduino and I'm testing them out.
            Best regards!

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