Heating a Small Worm Bin in the Winter

Worm Bin Heater

As all my loyal readers will know, I’m very interested in the topic of winter vermicomposting (and winter composting in general) – and it’s something I’ve been doing myself for the last few years. That being said, I’ve always advocated the use of large-scale systems during the winter, since they will generate and hold warmth a LOT more easily than a typical worm bin ever could. Of course, I’ve always been thinking in terms of natural heating – the warmth generated via microbial (aerobic) respiration during the decomposition of organic wastes.

In all honesty, it would be next to impossible to keep a normal-sized worm bin active (or the worms alive, for that matter) if kept outside in temperatures that are consistently below the freezing mark – when relying on natural heating that is!

But who says you have to heat the system naturally??!

Not Mark Glatting – someone who has recently jumped into the wonderful world of vermicomposting. You see, Mark likes to think outside the box – or the bin, I should say!

He’s come up with a really nifty way to keep his worm bin cozy during the long winter months. Mark decided he was going to keep his new worm bin out in his garage this winter – where temperatures have regularly dropped below the freezing mark – and decided to create a simple system to ensure that his bin stayed relatively warm.

MacGyver would have been proud!

Bin warmth is maintained thanks to the circulation of warm water through the system. All that’s needed is a bucket full of water, an aquarium heater, a fountain pump, a thermometer, and some tubing.

Here is Mark’s brief summary of his concept:

My goal here was maintain a sustainable habitat under the harshest conditions that I could not control…the weather. I felt that if I could do that I would be a success. The purpose of this experiment was to see if I could keep the bin from freezing. The bin is in my unheated garage. My materials consisted of a five gallon bucket,an aquarium heater, a fountain pump, 13 feet of 3/8 tubing (not PVC) and a thermometer. The tubing I coiled around the inside of the bin so the cool water would always circulate back into the bucket. I also put a brick in the bucket to displace some of the water so I do not have to cycle 5 gallons of water but four. It is easier to heat 4 gallons than 5. My project worked! The bin did not freeze nor sour after 3 weeks.

…and some additional information:

The heating system itself is very simple. As you said some insulation would help a great deal. I did not take temperature readings inside the bin. I was looking for frost and to see if it would turn sour. The aquarium heater came from Wal-Mart, it is rated at 200 watts and has a thermostat.The fountain pump came from Wal-Mart as well, but I don’t know how many watts it is. One thing I considered was to have the bucket higher than the bin using gravity as a tool to make the pump not work so hard (water flows down hill).
I have a two car garage that has no insulation at all, is not heated and it did get below freezing in the garage a number of times.I probably spent $50.00 US for the whole thing. I am not sure how much electric I used, the system itself can be used in case of an emergency. If we were expecting bitter cold I would fire it up.Remember the heater has a thermostat

Worm Bin Heater

I think Mark’s idea is fantastic, and I was really pleased when he enthusiastically granted me permission to share it with everyone here. A lot of people have asked me whether or not it was possible to keep a small bin active during cold weather, and up until now I’ve just assumed it would be more trouble than it’s worth.

In my mind, Mark’s system changes that. This is something that would be very inexpensive to set up, and – given the low wattage of the heater – almost certainly pretty cheap to maintain. I suggested that one could increase the effectiveness of the system even more if the worm bin sat in a larger box filled with straw, or some other type of insulation material (even scrunched newpaper would probably work well).

Did I mention that Mark is planning to come up with a system to keep his system cool in the summer?
Stay tuned!

[UPDATE]: I received an email from Mark, letting me know that credit for the worm bin warming system should actually go to his wife Letty. My apologies, Letty!

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    • Eve
    • February 14, 2009

    What a great idea. I have been planning on building a blue barrel flow through and putting it in my unheated garage next winter. Now I know how to heat it. And I wont wait for next winter to start.

    • John H. from Orlando
    • February 14, 2009

    I guess this is a good idea, but I rather see folks not use extra electricity (however minimal) to recycle their green waste. I always have thought of vermicomposting as a way to be more environmentality sensitive. Using extra energy to help decompose your food waste seems counterproductive.

    • Dustin
    • February 17, 2009

    I agree with John, but at the same time I cant imagine the heater uses a great deal of electricity. Can you deposit more food inside the bin or earlier than normal to increase bacteria activity and increase temperatures that way? I am curious what the general temperature is inside the bin. I currently have a plastic bin inside of my uninsulated garage with the lid off and night temps around freezing give or take a few degrees and my bin temp is about 75 degrees F. Does anyone have any input on my temp? What is the general range?

    • Bentley
    • February 24, 2009

    John – while I agree in principle, I also feel it’s important to look at the ‘big picture’ here – if this means the difference between worm composting in the winter and throwing all your wastes in the garbage all winter long, I personally think this is a much better option to use a bit more power. It all comes down to the question of what offers the most ‘good’.
    Here is an analogy which is a little ‘out there’ but hopefully it will help to illustrate what I’m getting at. Consider Al Gore, and his global warming lectures and subsequent movie. Regardless of how you feel about him as a former politician, or even whether or not you believe in Global Warming – the fact IS, he has played an important role in getting a LOT more people focused on environmental issues in general – so overall a lot of ‘GOOD’. He has however flown all over the country and around the world to promote his message. Air travel is a major cause of pollution and greenhouse gases. Some might say Gore doesn’t practice what he preaches. So, should he have just stayed at home and kept his mouth shut? (some would say ‘yes’ – haha)
    Absolutely NOT – overall, I think there has been a lot more good than bad that’s come from it.
    Sustainability in general is only going to come about on a large-scale by relying on modern technology. We are well past the point where we can all give everything up and go live in caves.

    Ok that was a REALLY long-winded reply. Sorry John – I don’t want you to think I’m picking on you here. I definitely agree with the essence of what you are saying. I could definitely see how this might be a bit ridiculous if this system used the same power as a major appliance etc., but in my humble opinion, this is pretty minor in the grand scheme of things.

    • Bentley
    • February 24, 2009

    Microbial heating is an awesome thing – there is no doubt about it. I am totally in awe of the fact that my outdoor worm bed is sitting at ideal worm composting temps, yet outdoor temps are very winter-like.
    Volume is critical for sustained heating however. Adding more food waste to a smaller system will help add some more heat in the short term, but the law of diminishing returns will come into play eventually. Your waste will pile up and eventually you won’t have any more room in your system to add more. The bin should stay warm for a period of time, but eventually (and inevitably) it will drop in temp – especially if the location of the system drops below freezing on a regular basis

  1. When it came to heating my bin, I had several goals. I was trying to sustain a worm habitat under the harshest conditions. Bentley is correct when he said there would be a surplus of feed stock. Then what?
    I precompost my feed stock for two reasons; first, to try to destroy weed seeds and second, to destroy as many pathogens as possible. So, there is no decomposing energy left. My opinion is, that if the habitat could not sustain, what is the point of paying $25.00 for a pond of worms, only to have them die? I also wanted high quality castings that have a lowered value of pathogens.
    By the way 99% of my reasearch came from this web site.
    Thank You Bentley .

    • steve
    • March 3, 2009

    ok, I wont touch on what I think of Al Gore, but he has done good, and assuming he flew commercial flights that were going where he went anyways…………………………..
    Ive been tossing around the idea that a big warm compost pile, leaves grass clippings and manure as well as whatever else you compost, should be a reasonably warm temp in the middle,(run piping thru center of pile then into worm bed,)60-70 degrees even in the toughest of winter, as long as it has some mass, and maybe has a vapor barrier over it during extreme winter chills, any thoughts?

  2. Steve,
    That’s a great idea! Go for it! May I suggest that you try your project without any worms in the bin? If your project fails or needs tweeking you won’t lose any worms.

    • Bentley
    • March 9, 2009

    Hey Steve,
    That’s exactly what I did this year – check out my posts in the “winter composting” category on the blog. I have straw bale walls, and a layer of straw over the top – along with a thick tarp. It has worked very very well, maintaining temps in the 70’s during some extremely cold winter weather.

    EDIT: Just realized what you meant, Steve! That’s a great idea too.

    • David
    • April 18, 2009

    I’ve read about a particular farmer stacking up an enormous compost heap in early winter, he has a system of copper tubing going through it to heat water for his home. I think it might also heat his house…

  3. Actually as Mark mentions about the siphon idea, the pump should be lowered as to have water siphon push water into the pump. This will put less stress on the pump as long as not set too much lower. Set the pump level to where the siphon begins to work. This will prolong the life of the pump.


    • Rom.Calgary
    • July 29, 2009

    You could use this setup to cool the bin as well. I used to keep a marine aquarium and had to get a chiller for the few months of summer that we get. It is controlled the same way an aquarium heater works and if you combine the two (depending on the power of the heating and cooling systems, the amount of water being cooled, max and min temperatures, etc.) in your setup you may be able to maintain a very small temperature range.

    • Bentley
    • July 30, 2009

    ROM – thanks for sharing that – sounds interesting. I’d be curious to know how much these ‘chillers’ might cost. I certainly wouldn’t need to use one in my location, but those living in extremely hot regions might want to use something like that.

    • rom
    • July 30, 2009

    I hear you, where I live my basement does a pretty good job of keeping my worm bin from overheating.

    It’s cost prohibitive to buy one for a worm bin (in the $500 and up range, mine was borrowed for a couple years), unless you can find a used one at a good price. Cheaper than buying new fish and coral every fall though. Probably more cost effective to get a cheap air conditioner unit and jerry-rig it to cool the area around your worm bin which still would be more than I would want to spend for a worm bin. I just saw the aquarium heater setup and thought to myself, “hey, that works the other way too”. I like tinkering but not if I have to spend a lot of money.

    Here’s a thought. Same setup minus the heater and use a larger container of water (long rubbermaid bin?). Have the water returning to the bin fall onto a pile of stuff, (rocks,small rubber balls) whatever you can pile up above the water line to give lots of surface area to get as much of the water to evaporate as possible. The evaporation should cool the water. Not like a chiller or air conditioner but cooler than the water returning from the worm bin.

    The creel I use for fly fishing works in the same way. You just dunk it in the water every now and then and the evaporating water keeps the fish from smelling without the use of a cooler full of ice.

    Not really necessary where I live but i like tinkering with stuff.

    • Greg
    • July 19, 2010


    You could always use a solar panel and battery to produce the electricity for the system. That would add cost to the system, but would be green.

    • Ryan Green
    • December 26, 2010

    Hey i have had my worms in freezing tempatures and they can stay alive but im not sure if they feed or eat quiet as readily. It would be a great experiment for someone to try whether or not the cold weather will slow the eating cycle down of a worm or not? If someone trys it let me know what your results are.



    • Dale Seavey
    • November 1, 2011

    Have you heard of anyone using an electric blanket to keep worms in the above freezing zone in the winter for a bin?

    • Louise
    • November 4, 2011

    Hej Dale
    I plan to use heating cables as the ones I use to keep the waterpipes from freezing in the barn, they come in different lengths and are controlled by a termostat – and they are suited for outdoor use.

    • Dale Seavey
    • November 8, 2011

    I have been using a heating pad along side of the bin, which is covered in towels to keep light out and heat in, and have placed it on a timer so it will go on for a couple of hours a night and be enough to keep those wriggling worms happy. They seem to be thriving!
    Thanks for the feed back and the ideas!

  4. I use some heating cables for reptile tanks. I have a 50 watt and a 25 watt both controlled by a HydroFarm Thermostat. So that I can use the heater on different bins of desired I mounted the cable on some expandabe screens from Walmart. Without the thermostat the 25 watt works better as it only get to about 85 degrees in my 65 degree basement. The 50 watt will go to around 108 degrees. When sung the thermostat the 50 watt seems to work better. Without the heat cab;es the temp is about 65 degrees and with it’s 78 degrees.

    • Nancy Lichty
    • April 1, 2012

    Your system in intriguing. We also keep our worms in bins in our garage during the winter. If we don’t leave our doors open when plowing snow, it doesn’t freeze. However, when it is cold, they don’t do much composting. So we wrapped the bins in an old Velux (velveteen foam) blanket and left a light on them. They seemed happier this winter. I do check to see if the bins are TOO moist and leave the top uncovered and the drain open for a litter air circulation.

    • Jeanne Sandstrom
    • July 18, 2012

    What do your outdoor bins look like? Is there any danger the redworms would escape and cause a problem?

    • Nate
    • July 28, 2012

    What about using a solar hot water heater panel to heat water and store under the worm bin?

    • Bentley
    • August 2, 2012

    Wow – I’m way behind in commenting on this one. Sorry folks.
    Lots of great ideas being shared – thanks!

    JEANNE – my outdoor “bins” are actually windrow beds. Composting worms stay in environments that are favorable to them so it’s not so much that they would “escape” as it would be moving to a more favorable environment. Red Worms (Eisenia fetida/andrei) have not been found to cause any “problems” whatsoever (assuming you are talking the concerns relating to forest ecosystem disruption) – largely since they don’t thrive when not living in very rich organic matter (such as that found in compost heaps and manure piles).
    NATE – sounds like a great idea! Makes me wish I was more of a DIY-tech kinda guy!

    • jen
    • August 6, 2012

    I just started vermicomposting this year and feel it has been a great success. I’m going to bring them in for the winter but one whiff of rotting anything and they’ll be banished to the garage. I’m gathering that as long as the bin is in good shape they’ll just hibernate til spring?

    • Gusty
    • October 15, 2012

    And how about if in the middle of compost bin you put a coil to heat water. Rather than conveys in a tank it circulates near the wall of the bin.
    Are at the beginning and I don’t mean much.
    What do you think?

    • ron
    • October 25, 2012

    I have a worm inn that i keep outside during the spring and summer months, but going to try the garage this yr during the winter instead of the basement. My plan was if the temp got to low, i was going to dig a hole in the middle of the bedding and place a plastic container in the hole. Maybe something as simple as a milk gallon, fill it with water, and put a small aquarium heater in it rated for a 1-5 gal tank. The ratio of width vs height may be a factor, but I would figure that even on the lowest setting of the heater, the heat will radiate and allow the worms to either migrate up/down as needed for food.

    • ralph
    • October 27, 2012

    it seems like the simplest heating system would be a heat mat for seedlings(40 watts, about 9 by 18 inches) attached to a timer. It would be placed under the bin and the timer used to regulate the temperature. I suppose insulation could surround the bin for colder climates. What is the lowest recommended temp for worm activity?

    • Dale Seavey
    • October 29, 2012

    I have to say, the heating pad wrapped on the side of the bin with towels over the bin worked like a charm in an unheated shed in Oregon.

    • Dale Seavey
    • October 29, 2012

    I did use a timer on the heating pad.

    • nate
    • November 19, 2012

    i made a similar system integrated into by blue barrel system using 3/4 metal pipe i could use 1/2 in. tubing running threw the pipe in the bottom of the flow threw bin and one in the middle of the barrel heating the pipe and in turn the barrel. in the summer i put frozen 2 liter bottles in the water and it cools it quite nicely

    • Corey
    • November 16, 2013

    I had supplemented heat to my “1-2-3” ft. worm bin with a 25 watt aquarium heater submerged in water in a 1 gal. pickle jar. It’s only November and we had a cold week. Today I built an exterior box for the worm bin and lined it with 2 inch insulation panels with a fitted, insulated top. The worm bin fits perfectly snug. Unfortunately after poking around in the bin (after I built the insulating box of course) I see the frost last week killed all my worms. The aquarium heater couldn’t hack it. Logic tells me that instead of US desperately trying to provide heat to the WORMS, a system large enough should provide an overabundance of heat, enough that could not only keep the worms’ habitat comfortable, but also add supplemental heat to OUR homes/green houses without the odor! If this can’t be accomplished on an individual/single household level, then maybe all organic wastes from residential neighborhoods could be allocated to an enormous centralized worm bin with piping somehow delivering the heat to the homes. My garbage plus your garbage definitely won’t produce much heat. But if the entire neighborhood’s food-waste/yard-clippings etc. went to one gigantic worm bin, the heat being generated would be enormous. In large cities especially this concept could be revolutionary, where the restaurants alone output considerable amounts of food waste. Combine this with schools/cafeterias/apartments/hospitals and homes… we’re talking some serious heat! As long as the worms can safely keep their distance from the core of all that heat. Just some thoughts. If anybody has anything for me to read or look into on this matter I’d be very ambitious to read it. As for me, I’d be grateful to just not have to pay an extra utility bill to keep my worms from dying in the winter, even if this meant building a deeper bin and building an additional, well insulated box around my bin, that I could easily disassemble for the summer months. I rent and can’t create an enormous compost heap to pipe the heat to my bin as some people suggested. Thanks a lot everyone, Corey.

    • Gary wildeveld
    • January 28, 2014

    My bin is outside on a stand using cinder blocks for the walls. I attached a heating pad under the floor keeping the compost temp over 50 deg.

    • angusmacduff
    • May 24, 2014

    I built my VB24 this past winter. I didn’t have to buy anything to build it – everything was down cellar or in the sheds. I used a piece of 1/4 inch plexiglass for the front and it is covered by a sheet of Naugahyde to keep it dark. I had planned on keeping the bin in the cellar but decided to move it to the garage so that I can use horse manure. I’ve added another sheet of lighter plexiglass to the front with some washer spacers. Now I can slide the seed starter heating pad down between the two sheets of plexiglass. I have some two inch solid foam insulation that I will add next fall – along with a couple of furniture pads to go over the top. I think that I or “we” will be fine.

    • Bobb241
    • July 2, 2014

    I have been keeping outside compost bins for a fair amount of years, and up until completing Bentley course last, had never really thought of intentionally working with worms. That has all changed now, and I think the heated bin is outstanding. When you live in North Dakota, you need to temper the need to use some amount of energy to help keep the worms alive, and solar doesn’t help much when the sun is gone for days at a time. I plan to keep my “gonna-be-built-soon” bin in our unheated garage, which last winter spent many consecutive day well below -1F. I understand that folks in Florida can get away with no heat, but just like keeping engines idling and the car plugged into electricity (and not to keep charged) some ideas come from the environment we live in, and some should be mindful of that point.

    • Ralph
    • July 7, 2014

    I got lazy and didn’t heat my worm bin in the unheated garage last winter and they survived quite a bit of cold, down to upper teens outside. They were on the floor and I didn’t check to see if they were starting to freeze or not.

    • Mark Krisburg
    • November 6, 2015

    The secret to keeping worms warm in the winter and cool in the summer is INSULATION! Water heaters often have insulation that is wrapped around them called a water heater jacket to keep the warm water warm. Do the same with the same material to any barrel. Then, use a few inches of water in the bottom with the worm bin elevated so it is not in the water (unless it is waterproof). Use your pond heater in the water with its thermostat. A small thermostat will keep everything at the perfect temperature provided you have used a nice layer of insulation. For box worm containers, consider using Styrofoam sheeting attached all around the sides. For odd shapes, use expanding foam that hardens to a rigid insulation between the worm bin and anything that might serve as a “container” into which the worm bin can be placed for this “foaming” procedure. Even a larger cardbox would work fine.

  5. In post #34 I wrote about my plans for last winter using a seed starter heating pad. It worked great and the worms were happy. I had to bring the bin into the cellar in an unheated area. I’m glad I put six inch wheels on it.

    • Darryl
    • November 9, 2015

    Hi there, I’m looking for some advice. I started a worm bin this summer and want to keep it going during the winter. I live in NY so the temperature will get into single digits for days at a time and if we get another polar vortex we’re talking below zero.
    To combat the cold I plan to move the bin to the shed in the backyard and buy soil warming cables. My question is where I should put the cables. Should I bury them 4-6 inches or should I put them at the bottom of the bin so the worms have access to the topsoil level? I was thinking I would cover half the bin with cables so they can go to the other side if it got too warm (the bin is 2’x4′ and 16″ deep). I’m going to set the thermostat at 70 degrees.
    Has anyone else used the cables?

    • Barb
    • November 25, 2015

    Hey, I just had an idea, as a novice vermacomposter, (curently have my lil worm bin in my guest room),,,,,,,, so far so good,,,,,,,but I got guests coming,,,,,,,so,,,,,,,here is my idea,,,,,,,I have an outdoor, stone circle above ground fire pit at my stone patio. why couldn’t I centre my worm bin in the middle of this fire pit for insulation. They have access to the ground and go deep for the winter?

    Will they come back as I add food?

    And will they survive Canada’s 25-30 below Celcius temps for a few months until spring? I could put straw bales around it inside,,,,,,, but with possible deep snow (fall), I may not have access from Jan. thru until April. Thoughts?

    • Bentley
    • January 7, 2016

    Darryl (sorry for delay) – if I was using the cables I would likely start by testing them OUTSIDE of the bin. As Mark mentions above, insulation is really important. Place the bin in some sort of insulated box (maybe surround it with straw bales etc), and try simply putting the cables underneath the bin. If that doesn’t seem to warm it up enough, then try putting them right in the worm habitat (maybe buried midway?)


    Barb – Based on the temperatures you mentioned, unfortunately a typical home worm bin simply won’t have enough volume to handle the cold. Digging an actual compost pit (setting it up like a typical worm bin) MIGHT work, but you’d need to make it pretty deep and add lots of insulation material at the top (again, to handle -25 to -30 C for extended periods).


    By the way -if you are interested in the topic of cold weather vermicomposting (or vermicomposting in other climate extremes) you might want to check out the “Extreme Vermicomposting” package:

    • Darryl
    • January 11, 2016

    Thanks for the advice. What I ended up doing was going to Home Depot and buying a roll of insulation ($8). It was perfect because it is 16″ by 25 feet and the 54 gallon Rubbermaid bin I use is just under 4′ long and 20″ tall. I simply taped it on, wrapped it round once then taped it again. Then I took a piece of the remaining insulation and laid it down in the bottom of the bin. I covered it with burlap ($3 yd), a layer of dirt and pebbles and another piece of burlap..

    When I got the cable (24ft), I took an old metal refrigerator rack (36″ by 18″) and tied the cable down to the rack. I put that in the bin and put the vermicompost back. The weather has been mild so far but when the temperature has dropped I’ve had no problem. I have a thermometer in the bin and the vermicompost at the bottom of the bin is at about 80 degrees. I have tons of worms and I constantly see new ones maybe a quarter inch long so they are enjoying the food and the surroundings. I’ll let you know what happens when it snows and when the cold wind comes in.

    • Yuri
    • July 4, 2020

    I’ve recently learned about vermicomposting and I’m very excited about starting my own worm bin. My biggest concern at this time is winter. We recently moved from Phoenix to Flagstaff and right now the weather is perfect, but come winter I’m worried about keeping my future worms warm and healthy. I’ve been doing some research and many resources offer information on very cold weathers, often below zero temps. Looking at some averages winter for Flagstaff at its coldest I would be looking at around 43 degrees f (high) 11 degrees f (low). We live in a studio apartment with an uncovered patio and my husband is not onboard to keeping the bin indoors during the winter (crossing my fingers this will change!) and we don’t have access to a garage. What would be your recommendation to keeping my future noodles warm? Darryl’s comment seemed very doable with a roll of insulation and I am planning on getting a thermometer for sure.

    Thanks in advance for your help!

    • Bentley
    • July 8, 2020

    Hi Yuri – anything below the freezing mark with a small worm aboveground worm bin is going to be a challenge unfortunately. If your husband isn’t on board with a fully active indoor system, maybe he would at least be OK with a passive “insurance bin” so you can at least keep a culture of worms going indoor just in case. As far as the outdoor set up goes, I suspect you might need to rely on insulation + some sort of artificial heating rig. If you get good sunlight during the winter you could likely get some solar heating as well using a little makeshift greenhouse over top of the system etc. Good luck!

    • Diane
    • December 17, 2020

    Use an ice chest as a worm bin instead of insulating your containers. Put a thin block of wood or stick under the lid to keep a gap open for a little air flow. Use a brick or cinder block on top of the lid to weight it down and keep it secure.

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