Let’s build a humidifier!

(see update at bottom!)

If you have a fruiting chamber, you probably have a humidification system. Or you need one. Maybe you’re looking to upgrade your system and not waste your life filling tanks every day. Either way, it’s time for a change, and you’re starting to get a little bit wary of running 110V appliances in 95% relative humidity.

NOTE: This is for a very basic 4-tier mini greenhouse setup. You’ll want something significantly more beefy for anything larger than two of those.

There’s a lot of options, some of which scale up to units that will keep an entire massive outdoor greenhouse at the desired humidity, but let’s assume you have one of the 4-tier mini greenhouses that are popular with mushroom growers. I have one in my living room where I test-fruit kits (I do want to make sure I’m giving people the correct instructions.) For this, I went with a system using a pond fogger and a 5 gallon bucket.

A pond fogger is exactly what it sounds like. It’s meant to create a little bit of fog in your outdoor pond or fancy water feature. It’s basically a ceramic disc that vibrates extremely fast and creates a jet of mist up through the water. I recommend these units (they come with a float) from House of Hydro. If you’re in (obscure place) I guess it’s Amazon time, but at least get the metal-bodied units without LEDs. If you’re ordering off Amazon, I’d recommend this one.

NOTE: A single-head fogger is probably enough for a single fruiting chamber. For two 4-tier greenhouses you’re probably gonna want a three-head. Or two single-heads, if there’s room in your bucket for two floats.

The trick is that you can’t just stick these things on the bottom of the “pond”, they don’t have enough power to push that much water to make mist, they need to sit around 3/4″-1.5″ below the surface of the water. Since the water drains as the humidifier runs, the fogger head needs to be on a float that keeps it a constant distance below the surface. If you ordered your fogger from House of Hydro you already have a float, if you ordered from Amazon, either grab a float from HoH (they’re cheap) or read on for the extremely DIY method.

Bear in mind that schedule 40 PVC pipe was used for this. 1″ is the INSIDE diameter. If you do decide to make the couplings permanent please research the procedure and consider that you need both primer and cement.

You will need:

  • one 5 gallon bucket with tight fitting lid, clean
  • one 3-4′ piece of 1″ PVC pipe (the white kind)
  • one 12-16″ piece of 1″ PVC pipe
  • a few scraps of PVC pipe (just buy 8 feet and have leftovers)
  • silicone (if you’re just press-fitting the pipes)
  • tape
  • a blower fan of some kind (axial or squirrel cage)
  • two 90 degree PVC fittings
  • a pond fogger, either from Amazon or House of Hydro or wherever
  • a 1 1/4″ drill bit, I used a spade bit made for wood
  • a 1/2″ drill bit (or whatever you need for your fogger’s power cord)
  • coarse sandpaper
  • PVC primer and cement if you intend to make joints permanent

Okay, so here’s the design basics. The pond fogger produces mist but doesn’t pump it anywhere. A fan that can survive that kind of humidity is… expensive. We also don’t want to be putting giant buckets of water on greenhouse shelves. So, what we’ll be doing is putting the pond fogger in a 3/4-full 5 gallon bucket with a tight fitting lid. It will sit there producing fog. Then we’ll pipe in some air from our PC fan through a hole in the top. This will force the air (and fog) out another hole in the top through a pipe to our fruiting chamber.

Take your bucket lid and drill two 1 1/4″ holes, each about 6″ from the center of the lid. Clean them up with the sandpaper. Drill another hole (wherever’s convenient) to run your pond fogger’s power cable through – how big this hole is depends on the model you have. Thread this cable through first thing before you forget. You’ll need to tape over this hole later so fog doesn’t spew out it. Fill the bucket half full of water. Don’t forget to get as much of the cable in the bucket as possible without it tangling – it’ll need some slack as the water level drops.

Take your long section of 1″ PVC and press-fit it through one of the holes in the lid. You’ll need to sand around the edges a bit to make this happen. Ideally it will stick a couple inches into the bucket but not to the maximum water level. Put a 90 degree fitting on the other end, and attach the short 12-18″ section of pipe. This goes from the bucket to your fruiting chamber. I’ve found the only coupling that needs silicone is the bottom of the 90 degree where it comes up from the bucket; since this isn’t carrying water under pressure there was no need for primer and cement for any joins.


Mount your fan to a box (as flush as you can get it), and cut a hole in another part of the box for a short section of pipe. Tape everything up. Ensure the air is blowing out the pipe without much blowback and with decent force.


Get a 4″ scrap of pipe and press-fit it into the second hole on the lid. Attach a 90 degree fitting and fit your fan box to that. Adjust the height of the pipe down into the lid so your fan box rests on the lid without strain. Tape everything up. You can use cardboard for this, no moisture should be going through it unless you mounted the fan backwards.

If you have a float for your pond fogger, just put it in and skip to the next step. If not, you’ll have to make one. Styrofoam and a flowerpot works, there any many other methods. You just need it to float freely and keep the fogger head about 3/4″ below the surface of the water (or whatever you find gives you the best results.) Personally I ziptied two pontoons made from empty 30mL squeeze bottles to it. Test it in your kitchen or bathroom sink to dial in your ideal depth. If it’s a jet of water with no mist, you’re too deep, if it sputters and cuts out, you’re too shallow. It’s got an auto-shutoff (in theory) so you can play with it a bit while it’s on (although wisdom would say not to have it out of the water for very long.) Shortly after building this, I discovered that I actually CAN buy one from Canada, and pretty cheaply at that, so I’d honestly recommend you do that.


Ain’t pretty but it works.

Now, assemble. Put the lid on the bucket, fire up the pond fogger, and fire up the fan. In a few seconds you should start to see mist pouring out of the end of your pipe.


After that, just attach it to your humidity controller or try to find a setting that gives you good results. With a cheap Amazon pond fogger and USB powered fan, even the lowest fan speed setting pumped almost too much moisture for one fruiting chamber.

Do remember that since the fan is taking in room air, your misting now also counts as air intake. After installing this I only used an exhaust fan in that chamber.

Tip: have your pipe to the FC tilted slightly down towards the coupling so any condensed moisture drips back into the bucket and doesn’t leak everywhere. Now all you have to do is keep it full, which is a lot easier when there’s 5 gallons of water. I don’t like having to disturb the joints every time I fill it, so I drilled a third hole for filling and keep it capped.

Best of luck, happy growing!


Better lid design. Turns out ducting it straight down through a hole in the lid with an actual legit blower fan works way better.


All “sealed” up (yeah I filled a void with silicone, what of it.)

IMG_6209 2.jpg

If you’re wondering how it’s still getting any intake air mounted like that, there’s a recess in the bucket lid and the blower fan also has 1/2″ standoffs.

Finished product, for two small starter-type FCs!


2 thoughts on “Let’s build a humidifier!

  1. Awesome info man, I found your blog site through facebook. I have a similar set up with the 4 tier but I’m only doing 4 blocks at a time right now until I get more confortable growing them. Got a couple questions I am hoping you can answer for me: What’s the maximum number of blocks could you grow in one of these at a time? Also, do you have lighting inside as well or just the clamp on lamps outside? My plastic has that same square mesh pattern and I’m wondering how well the light penetrates through it. Thanks!


    1. Light penetrates OKAY but I use LED strip lights (waterproof) run along the edges of the shelves now (although that 4-tier doesn’t get much use these days.) They’re about $17 on Amazon, a 16ft strip is enough to do an entire 4-tier, plus power supply (unless you have a 12V/5A supply lying around, which I did.) As for maximum number of blocks… if you were really packin’ em in, potentially upwards of 25.


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