Wednesday, July 2, 2014

DIY incubator

How I built a $6 incubator that achieved a 71% hatch rate.

Important Note! Please use your own common sense. You'll be working with electricity, water, sharp tools and heat. If something doesn't make sense, or seems unsafe, stop and consult an expert before proceeding. Please don't hurt yourself.

A few months ago, I was standing in my local farm supply store, looking at the tanks of chicks, pondering what I wanted to do to expand my flock of laying hens. This is a pretty common place for me to find myself in April, to be honest. I stand there, thinking about how ridiculous it is to spend $2.69 on a chick that someone else hatched. Am I going to keep buying a few chicks every year like this? I go to great lengths to avoid buying a $15 sack of feed, but I spend the same on a few chicks every spring? Not to mention the risk associated with introducing outside birds to the flock year after year. Compound the risk over several years, and the odds that a disease outbreak could wipe out my back yard flock go up dramatically.

After some thought, this seemed like a simple enough decision. Yep, I was going to get an incubator and hatch my own eggs. Amazon, here we come! Aaaand hold on a minute. Cheap incubators have terrible reviews. They just don't work that well. Good incubators are EXPENSIVE. Well, $150 might not seem expensive, but to me that's a fortune to spend on something that is supposed to save or make me money. I could buy a whole lot of eggs from someone else for $150.

At this point my mind shuts down. This is a dilemma. I sit at the table and explain the situation to my wife and she looks me square in the eye and says "Why don't you just make one?"

Uh. Hm. I dunno. I mean, I hadn't thought of that. Here I spend every weekend tinkering with stuff, building things out of salvaged and scrounged materials and it never occurred to me to just build one. My wife's brilliant, really.

So, I did a lot of research on incubators. I read a TON of inexpensive DIY incubator plans, most of which had never been tested, and those that had been were used to hatch only a couple eggs just to prove that they could hatch an egg. I researched good commercial incubators. I read up on hatch success rates and the science of hatching chicken eggs as told by universities and commercial hatcheries. I talked endlessly to the two people I know well who have lots of experience hatching chicken eggs. And this design, though simple, is what I came up with after all that. A low cost homemade incubator that has been tested with documented results.

chicks hatched in DIY incubator
These are the chicks hatched in this incubator, at 3 weeks old.

Things you need:
Please note: Links are to show you what we're talking about. In true homesteader tradition, I recommend and even expect that you will scrounge this stuff from junk piles, clearance racks, and beg/borrow the whatever else you need. If you buy all this stuff you aren't saving money.

Styrofoam cooler  - something like an Omaha Steaks cooler is perfect for 15 eggs or so. It should have thick walls. It should look like this
Bottle lamp kit - Something like this or you can salvage an old lamp.
25w light bulb - Like this
Computer fan - One of these will work
Thermostat - This is what I used
12v DC adapter - Here's one that works with the fan I linked
Digital thermometer with probe - One like this works and this has a hygrometer too.
Piece of glass out of old 8x10 picture frame, or similar sized plexiglass, plastic, etc. As long as you can see through it and it's reasonably rigid.
small plastic bowl
1/4 inch galvanized steel mesh. You only need about 3 square feet of it, so if you have or can locate some scrap, that might work.


flat and phillips screwdrivers
wire stripper (or whatever tool you're comfortable doing this with. I use a small sidecutter)
Duct tape
Electrical tape
A couple feet of tie wire or string
Something to cut styrofoam with. I use an old steak knife.
Heavy duty scissors, tin snips, or something to cut wire mesh.

First, I'm going to talk about each of the components, as some background on what their purpose is, and how to help yourself select the right parts.

Styrofoam Cooler

This is the incubator, really. The size is only important as far as it allows you to fit all the components into it, and that it will hold enough eggs for your purposes. I used an Omaha Steaks cooler that I had laying around, but you could easily use a foam shipping container or even a larger plastic cooler if you want. I'm not saying you should go buy this, but something like this is what I'm talking about. Just make sure that it's not smaller than 10x10x10 inches inside. Any smaller than that and you won't be able to fit the components. That size would probably be appropriate for 8-10 eggs or so. Ideally, you'd have 12x12x12 inches inside, or larger. You don't want the entire space filled with eggs, the chicks need a place to stand and dry off after hatching where they won't be standing on eggs or in broken eggshells. The sides of the cooler should be thick enough to insulate well and be strong enough to handle being worked with. Anything thinner than an inch is probably going to be too weak to be durable.

Bottle Lamp Kit

This is your heat source. Honestly, you shouldn't buy a bottle lamp kit. You should find an old junk lamp that's ugly as all heck and take it apart. Hit up a yard sale or auction and you can probably get one for $1 or maybe even free, if you don't already have one laying around.

25w Light Bulb

Find the chandelier style 25 watt bulb with the normal large end. I found a pack of 4 of these at walmart for $2.50 just recently. It's a good idea to have a spare bulb. If you use a particularly large cooler or box, you may need to go to a 40w bulb, but in my tests 25w worked fine as long as the temp outside the incubator was above 60F.

Computer Fan

This is any old 12v fan you can find. Take apart an old computer, stop by a computer shop and they might sell you an old used one for $2. Just make sure it's 12v and 1 amp (1000 milliamps or ma) or less. The simplest fan is the best, you don't want thermostatic controls, speed switches, or anything else to complicate the wiring. Just a plain old 12v fan.


This is probably the most important piece of the project. The basic idea is that the thermostat turns the light on and off to create heat, withing a pre-set temp range. The thermostat we use is normally used in a water heater, and isn't designed for fine tuning the way we need to for this project. Ideally, I would use a wafer-type thermostat, but this is what I could get easily so I used it and it really did work quite well. Commercial forced air incubators in the $150-$200 range typically hold about a 2-3 degree temp range, and mine with the water heater thermostat did that or better.

12v DC Adapter

This is to power the fan for circulating air. I'm betting you can scrounge up an old one for an ancient blackberry (sorry bb fans) or some other obsolete phone or electronic device. I say 12v, but most computer fans will run on lower voltage as long as there is sufficient amperage to start the fan. You can play around and see what works for you with your fan, but it's best if you just find a 12v 1 amp adapter and use that.


This is to make a window in the top of the cooler. You can use whatever you want for this. I used an old piece of plate glass, which is probably not the safest. Clear plastic would be best. You could probably even grind the edges off an old CD jewel case to make it flat, and use that. You just need to be able to see inside so you can monitor progress without removing the lid.

Small plastic bowl

About a 2 inch high tupperware or similar bowl that will hold about a cup of water. This goes under the screen shelf to ensure proper humidity during incubation.

1/4 inch mesh

We are going to make the egg shelf with this. We can't just lay the eggs in the bottom of the cooler, so we'll be making a shelf elevated about 3-5 inches off the bottom of the cooler that the eggs will sit on and the chicks will stand on after hatching. Nothing larger than 1/4 inch mesh, or the chicks will have a hard time walking on it. I use this mesh because I can cut it and shape it to whatever I need.

So how does this all go together?

1. Prep the cooler and test fit the light socket

Well, first of all we need to prep the cooler. You're going to make 3 holes in it, two of them near the bottom. and a third next to the fan. The first is for the lamp and the second is for the thermostat wires to come out. Please see the picture below to get an idea of the component layout. I strongly recommend following that layout. We'll be putting the lamp near a corner, but not so close to the corner that the heat from the bulb might melt the styrofoam and to allow better heat circulation. It should be positioned so that the light bulb is at least 1 inch away from the adjacent side. Position the hole for the lamp so that the bulb is about 1 inch above the bottom of the cooler. Not the center of the bulb, the edge of the bulb. If the cooler bottom is 1 inch thick, you'll need to go up about 2.5 inches to get this clearance. Once you know where the lamp and bulb go and you've double and triple checked your clearances, make your hole. I did this with a steak knife, slowly carving away the foam until I had a snug fit. Once you have a hole, insert the lamp socket and make sure it goes far enough in that the bulb won't be touching the foam. If so, you may need to insert the light socket further, or possibly countersink the whole arrangement so it goes in far enough.

The 2nd hole is for the wires that go from the light socket to the thermostat and back. You can make this hole just by pushing a screwdriver through the foam. The thermostat will turn the light on and off as the temperature fluctuates. The thermostat and its wires will be positioned along the same side of the cooler as the bulb is, in the other corner. We want the thermostat far enough from the bulb that it's sensing air temperature and not radiant heat from the bulb, and raised off the bottom of the cooler. So, the hole for these wires should be about 2 inches off the bottom of the cooler and should be about 1/8 to 1/4 inch in size. Just enough to push the wires through.

The hole for the fan wires should can go pretty much anywhere close to the fan, you can see where the fan is positioned in the picture below, as well as the location of the thermostat and the light bulb. The thermostat is lifted off the bottom of the incubator using a chunk of the leftover foam cut out when the window was installed in the lid. These are small wires, so you can probably make them by pushing a screwdriver through the foam.

Note, since this is a salvaged cooler, it's got some staining and looks pretty dirty. It would also look pretty similar after hatching a batch of chicks, so make sure before starting a batch of eggs that you wash everything thoroughly. I use a cup of water with just a splash of bleach to decontaminate. This rig isn't pretty since it's all scrounged and salvaged materials, but I'm too cheap to pay for pretty. Your exact installation may vary, depending on what materials you are using, but this is the basic idea.

It should be mentioned that the placement of the fan, light, and thermostat are what they are for a specific reason. The thermostat under the fan because it ensures a steady stream of airflow so that it can react quickly to changes in temperature inside the incubator. The light across from the fan so that it has continual airflow over it to keep temperatures near it cool and to circulate warm air quickly. The thermostat is as close to the level of the eggs as possible while still being under the mesh shelf, but raised to keep it away from water in the bottom of the incubator, with the adjustment screw facing up so that if you do need to adjust the temperature after starting incubation, you can reach through the mesh shelf with a small flatblade screwdriver to do so. With the lid on, this makes a nice clean circulation with pretty much no areas of low or no air flow.

Once you have a hole for the light socket cut, test fit the light. It should fit snugly enough that it won't fall out. Remove the light socket and set it aside.

2. Wire the thermostat to the light and install the light and thermostat

Please do all wiring with the light unplugged. Don't kill or injure yourself by electrocution over an incubator. Seek advice from someone who knows electricity if you don't understand how to do this part.

The light socket's power cord will have 2 wires. A plain colored one and a striped one. Split the two wires apart, and trim about 12 inches of wire off the striped wire and set aside. Strip the end off the non-striped wire and connect it to the #1 terminal on the thermostat. Strip the ends off the 12 inch cut off wire and connect one end to the #2 terminal on the thermostat. Connect the other end to the brass colored screw terminal on the light socket. Connect the remaining end of the striped wire (still attached to the plug) to the silver screw on the light socket. Wrap all exposed connections in electrical tape for safety. The terminals aren't covered in tape in my picture so that you can see it, but before testing or operation, I cover all connections in electrical tape.

At this point, we need to test the light. Make sure you aren't touching any of the wiring, and that it's not touching any conductive surfaces. If you plug it in and you did everything correctly, the light should come on. If you did something wrong, the breaker will either trip, or the light will simply fail to come on. If it trips the breaker, your wires are probably backwards somewhere. If the light doesn't come on, check the switch on the light socket. If after this it still isn't working correctly, seek the advice of someone qualified to work with electricity. Please don't hurt yourself over this!

Assuming that everything works correctly, it's time to unplug the light, disassemble whatever wiring is necessary and install the light and thermostat into the incubator. You should only have to remove the wires from the thermostat to do this. Remove both and install the light socket into the hole you cut, and install the bulb. Next, insert the thermostat wires through their hole, place the thermostat inside the incubator in its corner, and reattach the thermostat wires. Re-tape any exposed connections and then test the light again.

3. Install the fan

The fan should be placed as close to the top of the incubator as possible without hitting the lid. This makes the air circulate top to bottom. Figure out where the fan goes, and if necessary use a strip of folded cardboard to space it 1/4 inch from the side of the cooler, so that it can draw air from the back side. Make sure that the fan is blowing away from the wall of the cooler, into the middle. Once you identify the location, make 2 holes on each side of the fan and attach it to the cooler by running a loop of wire through the holes, and around the face of the fan. Twist the wire (or tie the string) on the outside of the cooler, securing the fan in place. Quick and dirty. You can spend more

Strip off the ends of the fan wires, and strip off the ends of your 12v adapter. connect the wires of the adapter to the wires of the fan. Temporarily wrap in electrical tape and test the fan by plugging the adapter in to an outlet. Make sure the fan works and is turning the proper direction. There's only two options here, so if the fan doesn't work, unplug the adapter, and switch the wires, re-tape and try again. If it still doesn't work, it's possible that your adapter is the wrong voltage or amperage for the fan, or either the fan or adapter doesn't work at all. Ask for experienced help at this point if it's still not working. Assuming everything works, unplug and disconnect the wires, insert the wires through the hole you made for them. Re-connect the wires and wrap in electrical tape. Test the fan once more just to be sure.

4. Install the window in the lid

Lay the window piece, either glass or clear plastic on top of the lid. Make a mark around the outside of the window piece. Set the window aside and make a new line 1/4 to 1/2 inch inside the existing line. This is the line we will cut along to remove the foam. Cut out the foam with a knife, set the window over the hole. Secure the window with electrical tape or duct tape. I used electrical tape on mine, but would use duct tape if I did it again.

This is what mine looks like. Again, not pretty, but functional.

5. Test run #1

We're ready for the first test run. Set up your thermometer and hang the probe into the incubator. Using a small flatblade screwdriver, turn the temp setting on the thermostat all the way down. Put the lid on and plug the light and fan in. The light should come on and the fan should be moving air. Note the temperature in the incubator and make sure it starts heating up. Monitor it until the light goes off. It will probably turn off at about 96 degrees, depending on your thermostat. Keep watching until it comes back on. Let it cycle a couple times to make sure it works. There's no need to adjust the temperature at this time, we're just trying to make sure that all the components work. We'll do tuning in the 2nd test run. What you are looking for  is a narrow temp range. If the temp swing from low to high is less than 4 degrees, you should be ok.

Temperature discussion

At this point, we should probably talk a little about temperature control in the incubator. Once we're running, we want to hold a temperature as close to 100.0 F as possible. This doesn't mean that there can't be some temp swing as the thermostat goes on and off, the important thing is that the average temp inside the egg stays there. An egg is mostly liquid, at first, and therefore it holds heat to some extent and doesn't fluctuate temperature as fast as the air does. What this means for you is that if your thermostat turns the light on at 98 F and off at 102 F, that gives us an average temp of exactly 100 F, which is perfect. The temp inside the egg may swing between 99 and 101, but that's still ok. What we really want to avoid are large temperature swings, or extended temp swings. Just saying that the low is 98 and the high is 102 isn't necessarily good enough, if the incubator spends most of the time at 102 and only drops to 98 briefly before the light comes on. The best way to test the temperature would be to put the temp probe inside something that has the same mass and heat retention properties as an egg. One way you can do this is to put some water in 2 ziplock bags and sandwich the temp probe between them. Another would be to wrap the temp probe in plastic and submerge it in a small cup of water, about the same amount as an egg, inside the incubator. This will give you a good idea of what the actual temp inside the egg will be as the incubator goes through its cycle.

We know that chickens, and birds in general don't hold perfect temp with their eggs when setting on them. We don't expect to have a perfectly stable temp throughout the incubation. What we want to avoid are long periods of low temperature or any periods where the internal egg temp rises above 103 F.  According to my research, the IDEAL temperature for incubation is 99.5 for the first 17 days, and then approximately 100.2 for the last 4 days. Without an expensive digital thermostat this would be pretty tough to accomplish, so we aren't even going to try. We'll shoot for an average temp of between 99.5 and 100.0 F, and the only adjustments we make will be to stay within that range. This is where the memory settings on your thermometer come in handy.

5. Final Assembly

Now we need to get things buttoned up and ready for a longer test run. First, cut a chunk out of that foam you removed when making the window, and make a stand for the thermostat. You can glue it in if you want, but you want the thermostat raised off the bottom of the incubator for two reasons. First, so it doesn't get wet, and 2nd so that it is closer to the level that the eggs are in the incubator, so that it reacts to the same air the eggs are exposed to. Once you've got the thermostat situated, it's time to make a shelf out of the 1/4 inch mesh. This is simple, so I'm just going to show you a picture of one.

Excuse the dirty table, I took the pictures at our soap making station since it has the best light.

To make this, you measure the inside of your incubator. Say it's 12x12 inches. You cut a piece of screen that is 13 inches by 18 inches. You fold a half inch of mesh down on 2 sides, so there are no sharp edges, and you fold the other 2 sides down 3 inches each, to make a shelf that's 2 inches high and fits snugly inside the cooler. Now, this isn't necessarily easy. I recommend wearing leather gloves while working with this stuff, as the wire is sharp and will cut you. Also, the mesh won't make a nice perfect shape for you. If it fits snugly, though, you can make it hold its shape once it's inside the incubator. There are some considerations with this. Before you put it in place, set your bowl in the bottom of the incubator. No sense in having to take the shelf out later to put the bowl in. The shelf should fit under the fan and over the lightbulb with some clearance between it and the lightbulb. Preferably about an inch between the bulb and the screen. It sucks getting it in there, trim and re-bend until you get a snug fit all the way around. You don't want a chick getting its foot stuck in a gap. Once you've got it fitting properly, it's staying there until after you hatch your first eggs and need to disassemble for cleaning. Note: I bend the mesh over the edge of a table or workbench, with a chunk of 2x4 to act as a break of sorts.

Next, we're going to cut one more small piece of mesh to make a screen that goes over the fan. Cut a piece of screen 1 inch larger than the fan in both directions. Fold the edges over all the way around to make a box, slide this over the fan, and wrap with duct tape to cover any sharp wire edges. This guard is not installed in any of my pictures, so I apologize. The point of this is to make sure that chicks don't stick their body parts into the fan. The fan is blowing out, so it wouldn't suck them in and severely mutilate them, however they could still get injured without a screen over the fan.

6. 2nd Test Run

For our 2nd test run, we're going to focus on monitoring temperature, humidity, airflow and function over a longer period. Assemble your incubator, plug everything in, add water to the bowl under the screen (you can pour the water through the screen or use a small tube and funnel to fill. Either way works), set the temp probe on the screen at the egg level and close it up. Let it run for a half hour and check the temp. Adjust up or down using the screw on the thermostat. You need to make VERY TINY adjustments. It may not even seem like the screw moved. Remember, we're making fine adjustments with a device that wasn't designed for such fine adjustments. Tinker with this until it will run at a specific temp for a half hour without fluctuating below 98 F or above 102 F.

If your temp probe also does humidity, you can measure it there. If not, no big deal. Our target is 50% relative humidity for now, and the bowl of water and the moving air should make sure we achieve this without issues. If you want to test it, that much the better. I don't measure humidity in mine. I just try to make sure that it's humid for the first 18 days, and then REALLY humid until hatching is complete. If you're measuring humidity, you'll need to run it for a couple hours or even overnight to really know what the humidity is. If you've got the temp right, leave the lid closed for a few hours and then check the humidity.

Let the whole thing run for at least one day. Don't remove the lid during this time. If after this time the temp is still stable, you're ready to hatch eggs.

Operation Instructions and Concepts

Our incubator does not have an egg turner, so when you load your eggs, mark the top with a pencil so you have a point of reference for turning. You'll be opening the lid at least once per day, preferably twice, to turn the eggs. You don't need to turn them much, I just roll them slightly over, maybe 15 degrees each time. Back and forth until you get to day 18 and lockdown until hatch is complete. Try to keep the time the lid is off to a minimum, and after closing you should monitor for a few minutes to make sure the temp comes back up to where it should be. When you go to turn eggs, always check the max and min temperatures in the memory of your thermometer. If necessary, this is the time to adjust the thermostat. You should not have to, but just in case, this is when you do it. Make sure that if you do, you monitor the incubator for at least 30 minutes to make sure the temp is stable and correct. Remember, it's better to be 0.4 degrees off target than to keep opening and closing the incubator over and over again, constantly messing with the thermostat.

If you know anything about incubators, at this point, you're probably wondering how we increase humidity at the end of the incubation cycle. Understanding that humidity is critical while chicks are hatching, we know we need to get above 70% humidity. If we don't, the membrane inside the shell will dry out, shrink, and effectively shrink wrap the chicks inside the egg, killing them. So how do we do that? I thought about that a lot, and decided that the best way to increase humidity is to increase the surface area of the water so more evaporates. For the first 18 days, the water in the bowl has enough surface area. On day 18, I open the lid and pour about 1/4 inch of water in the bottom of the incubator. This increases the surface area of the water dramatically, and makes sure there's enough humidity. Also top off the water in the bowl at this point if we need to. After day 18, you're in lockdown mode and the lid of the incubator should not be opened. You should have enough water in the bowl and in the bottom of the incubator at this point to last until hatch is complete. Expect to see condensation on the window after day 18 with the increase in humidity.


I built this incubator hoping that it would hatch something, anything. I didn't expect it to be perfect, I only expected it to be functional. Honestly, I'm very happy with the results.

I started with 21 eggs from my brother's mixed flock. He hatches eggs for his own flock in a $200+ incubator that isn't much different from this one, except it has an egg turner. His results with his eggs after 3 hatchings this spring were about 65-70% hatch rate, after subtracting infertile eggs. He has 1 rooster and over 30 hens, so some eggs will be infertile, and many of the hens are older, meaning the eggs aren't as likely to hatch. In my batch of 21, there were 4 that showed no development when candled at 5-6 days. I left those eggs in the incubator, just to see if I was right, however none of those 4 ever developed. Of the remaining 17, 13 of them hatched. 12 of those chicks survived past 3 days, and all are still running around the coop, now 4 weeks old. The one chick that hatched but did not survive did not absorb the yolk sac correctly, and when it hatched it was covered in yolk and blood. It was unable to stand and could barely move even after 8 hours. It passed shortly after that. Among the 12 that survived, there were no deformities in feet or beaks, all the chicks are healthy and growing. My success rate is 12 out of 17, for a rounded 71%.

The gross part

I decided to analyze the 4 eggs that showed development at candling but did not hatch. Of those 4, 1 looked to have quit at around day 10. There was nothing significant about day 10, I couldn't find a cause for it other than that it was a weak egg. The 2nd quitter looked like it made it to around day 15-17. Again, there was no directly attributable cause for this. The remaining 2 held fully developed but dead chicks. I shut off the incubator on the morning of day 23. It's possible that these chicks might have still hatched. I don't know. I do know that a chick hatching on day 23 has a low chance of survival. I made a note to let the incubator run to day 24 next time, just to see.


Overall, this was a successful experiment for me. I feel that this incubator can achieve the same hatching success that most of the small incubators that those of us with backyard flocks would purchase, and certainly better than the cheap incubators would do. My next plan is to build a scaled up version of this using the same principles in an insulated cabinet.