hi this is Tony from fresh cat mushrooms calm and I wanted to show you the process for building and designing a laminar flow hood for growing mushrooms I'm actually building a new one for myself right now so I thought I'd make a video to show you the process for specking of the components and actually building the box because it can be a little bit confusing at first what is a laminar flow hood and why would you need one for growing mushrooms well technically what we are building isn't actually a laminar flow hood it's more like a laminar flow cabinet or flow blocks but most people use the term laminar flow hood anyway so that's what we're gonna use in this video a laminar flow hood is basically a big wooden box with a high efficiency particulate air filter or HEPA filter in the front and a squirrel cage blower fan on the top the purpose is to blow the air through the filter and provide a clean stream of air with no contaminants that you can work in front of a new mycological work most people start off doing lab work using just a still air box which is essentially just a tote with two holes in it that you can put your arms through and do clean work on the inside and although it does work it's a little bit cumbersome and having a laminar flow hood and a big open space to work from will really be a game changer for your lab work and for growing mushrooms now the process of building a laminar flow hood can be broken down into three basic steps number one you need to choose an adequate filter and you need to find a filter that's big enough to do the stuff you want to do number two you need to find a blower fan that's strong enough to push the air through that filter at a specified rate and number three you got to build a box and wire it up now for that I'm going to be hooking up with my good friend Jeff over the home stud who's going to be helping me to construct it and to put it all together so when choosing a filter the very first consideration is size you can find filters as small as 12 inches by 12 inches or you can go all the way up to 24 inches by 48 inches now keep in mind the bigger your filter they're gonna be much more expensive also you're going to need a larger and more expensive blower fan to push the proper amount of air through a bigger filter now a 12 inch by 12 inch flow hood might be good enough before you're doing as Eggar transfers your work with petri dishes but if you plan on doing inoculations especially with mushroom grow bags you may want to consider getting at least a 24 inch by 24 inch filter or even a 24 inch by 48 inch filter to give you lots of room to do your work you also want to make sure that you get the right type of HEPA filter the HEPA filters you find at Home Depot or any other retail store probably aren't good enough they're just not thick enough to provide that laminar flow and they're not efficient enough to remove all the particles that you want to remove from your air you need to find the much thicker HEPA filters that are specially designed for laminar flow these filters will have a rating for efficiency and for pressure drop at a certain flow you want to find a HEPA filter that has an efficiency of at least 99.99% at 0.3 micron this means that it's going to remove 99.99% of all particles that are bigger than 0.3 micron in size this is perfectly sufficient for any kind of mycological work you also want to keep in mind the pressure drop of the filter as the blower pushes air across the filter media the friction between the air and the filter will cause a pressure drop meaning that the blower needs to work harder and harder to push the right amount of air through the filter most HEPA filters will have a pressure drop rating of about 1.0 inches of water gauge which is actually quite a bit you're also going to want to add on to that rating about 0.1 to 0.3 inches of water gauge for the pre-filter a pre-filter is essentially just another filter that you're going to put on the outside of the blower fan so that your main HEPA filter doesn't get clogged up with big dust particles dog hair or whatever else might be floating around in the air so this is a filter I ended up getting it's a 24 by 48 inch filter and you can see it's covered in particle board or wood some of them are just metal but the particleboard ones are kind of easier to build into a box its efficiency rating is 99.99% it doesn't say 0.3 micron on this label but it does say in their literature and it has a resistance of 1.0 inches of water now when you get your filter keep in mind that the fins on the front of the filter are really delicate and if you batch them they will Bend and break and all sorts of stuff and actually if you can see on this filter even though it's brand-new it's already got some of the fins that are kind of bashed up that's not a huge deal we can go ahead and straighten those out and even if you end up with tiny little rips in your filter that's not a huge deal either because you can usually just cover them over with silicon so now I have my filter I know the size of it to be about eight square feet and I also know that the resistance of the filter alone is going to be about 1.0 inches of water adding to that the pre-filter that we're gonna get will have a total resistance of about 1.3 inches of water gage now with all that information I can go ahead and try and find a fan that'll be sufficient enough for this laminar flow hood now for a laminar flow hood you want the air speed coming out of your filter to be able 100 feet per minute but keep in mind that's a velocity and most fans are actually Specht out in a volumetric flow rate or cubic feet per minute so you need to convert that velocity into a volumetric flow rate and you do this by simply multiplying 100 feet per minute by the area of your filter so in this example my filter is 24 inches by 48 inches which is about 8 square feet if I multiply that by 100 feet per minute it gives me 800 cubic feet per minute or 800 CFM now I wish it was as simple as just going out and finding a fan that puts out 800 CFM but it's a little more complicated than that because the fan will put out a different flow rate depending on how much pressure it's pushing against so this is where the pressure drop of your filter comes into play you know that your filter is going to have a pressure drop of about one point zero to one point three inches of water and you know that you need to provide 800 cubic feet per minute of air at that pressure so this is where you got to go to the manufacturer of the fan and find what's called the fan curve so this is what a typical fan curve will look like and it basically just plots out the flow rate of the fan versus the static pressure of the system that your fan is in and they'll typically be a curve that goes down like this so what you want to do to spec out your fan is to find the point on the y-axis where your static pressure of your filter is and draw a line straight across until it intersects with the curve and from that point you draw a line straight down and that will tell you what the flow rate of the fan will be at this specific pressure and then you can determine whether or not that fan is adequate so it's simply a process of looking at a bunch of different bankers and finding one that fits your needs and here's the fan itself it is a Dayton one TD you tube and let's open this thing up and see what it's like so there it is and as you can see it sits pretty large but it has to be that big I think it weighs about 26 pounds but in order to push a sufficient amount of air through that big of a filter you do need quite a large fan so keep in mind when you order a blower fan like this it's typically not gonna come wired so that you can just plug it into a wall and it's not gonna have a switch so you'll need to do a little bit of electrical work to wire it up put a switch in and put a plug in it so you can just plug it in and use it also every blower is gonna have a different shape of outlet and some of them have a nice flange where they're easy to mount onto the top of your cabinet but some of them won't have any mounting hardware whatsoever so you'll need to come up with a way to properly mount it on top of your flow cabinet okay so now I've done a lot of the hard I have my filter i SPECT out a fan and now all I need to do is assemble it into a flow hood so in the next video I'm going to show you what materials I got and how we actually constructed that into a working laminar flow hood that's it for this video thanks for watching I'm Tony from fresh cat mushrooms comm and we'll see you next time