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My Attempt/Guide at Radiant Heating with an Immersion Heater and Pump

WARNING there are lots of pictures to follow. I used the general idea found from the github page on immersion heaters and ran with it. The steps below are for a drawer style set up. I believe this could easily be modified using rigid airline tubing bent into a coil and placed in the mesh bags for the open bug mealworm farm kit.

Started with a sterilite drawer system from walmart IMG_7978

Reflectix insulation from lowes which is basically like reflective bubble wrap. IMG_8037

Cut to fit the drawers and used hot glue to adhere the sidewalls to bottom. The ideal of the sidewalls is to direct the heat upward. Also the insulation is not glued directly to the drawers so this can be modified later if necessary. IMG_7979

Using standard airline tubing used for aquariums I made a coil pattern in the bottom of the drawer. I used clear scotch tape to keep the tubing in place and directed the tubing out the back of the drawer through two holes I made using a 1/4 drill bit. Be sure to leave about a foot extra tubing going in and out of the drawers to allow for the drawers to be opened completely without snagging issues. IMG_8033 IMG_7984 IMG_7981 IMG_7983 IMG_7986

Insulated a 5gal bucket and used and old bathroom trashcan as the actual reservoir for the water. I used duct tape to make a seal between the trashcan and bucket for when the water evaporates and drips back down from the lid. IMG_8008 IMG_8009 IMG_8022

I used a 200watt submersible heater and a 120gph submersible pump. IMG_8039 IMG_7988

Now to connect it all. The pump comes with a 1/4" connector so a small section of 1/4" inner diameter tubing is required. Also needed is a reducing coupler. I used a 1/4" to 1/8" barbed coupler and secured the airline tubing side with a zip tie because of the pressure coming behind it. IMG_7990 IMG_7994

To split off to each drawer I made a ring of sorts with 1/4" t-connectors. The idea of the ring was so that one drawer was not necessarily getting more flow than the others and so the heat would be fairly consistent throughout. I did the same configuration for the return tubing back into the bucket. IMG_8026 IMG_8016 IMG_8017

I used a small section of tubing and and on/off valve to go to each drawer from the T and a coupler and another small section of tubing for the return lines. The on/off valve gives me the ability to adjust flow to specific drawers and even turn a drawer completely off if not using it. IMG_8013 IMG_8030 IMG_8027

Ok finally everything is connected and water is flowing through all the lines. IMG_7995

Now to prevent heat loss to and from the drawers I used left over reflectix and some foam to wrap the exposed tubing. IMG_8020

Finished product IMG_8021 IMG_8042

Now for some temperature measurements. Placed directly on the coils I was getting temps around 82-83. About 1 inch off the coils temps were around 80 and place about two inches off the coils the temps were around 77. This was consistent in all 3 drawers and this is with the heater set on its highest temperature setting. IMG_8038 IMG_8023 IMG_8043

The entire project took me about 4 hours to complete and everything used was purchased from Amazon, Walmart and Lowes.

My cost were as follows: Airline tubing 50ft - Walmart ~$6.00 Reflectix insulation - Lowes $16.25 1/4" ID tubing 20ft - Lowes $5.47 1/4" Coupler 15ct - Lowes $4.36 1/4" T connector 10ct - Lowes $4.65 1/4" On/off valve 3 ct - Lowes $3.86 Submersible Pump 120gph - Amazon $13.99 200w Submersible Heater - Amazon $13.24 1/4" - 1/8" Barbed Coupler 25 ct - Amazon $3.75

Everything else mentioned I already had around the house so that brings my total cost to $71.57 This price could be reduced if I had a re-do. I just went with was convenient at the time.


  • beautifully documented @megology. Thank you. :)

  • @megology - this is an awesome implementation of the concept! I particularly like how you used the Reflectix to line the drawers and the loop + shut-off valves is brilliant.

    Would you mind if we ported some of this over to the wiki page to improve those instructions for future experimenters? (with attribution of course!)

  • @andrew - of course! I will continue to update this thread with any issues I find or improvements that could be made as time goes on. I've ordered a mesh bag from here that I'm trying along side this and plan on incorporating it into this system as well.

  • Just wanted to post a small update. I plumbed in a second drawer to this system identical to the first. Initially there were temperature variations between the top and bottom drawers just due to the size of the pump and gravity. Fortunately restricting the flow to the bottom drawers with the on/off valves actually did the trick and now with the same heater and pump I'm getting very consistent 80 degree temps in all 6 drawers now. IMG_8129

    I know this is off topic for the thread but I've toyed with the idea of trying the mesh bag out and suspending it in the drawers. Would the small space of the drawer restrict the airflow too much for this idea?

  • @megology If you hang the bag in the drawer, you'll probably want to open it periodically to make sure you have enough air in for the higher density of mealworms in the bag vs the single layer bedding. You'l also have to be careful with the temperature as the worms themselves generate quite a bit of local heat while moving around in their meal, particularly as they approach harvest size.

  • edited April 2014

    The answer to the air problem could be to drill a line of small holes in the plastic just under the handle -but only on the drawer holding the mesh bag(s). If not needed the line could be taped to reseal.

  • I just saw this (I was out of the country for a few weeks) but seriously good work, @megology! How is it all going several weeks later?

  • This is long overdue but just wanted to give a quick update. The set up has been working fantastically. I have only had to make a couple changes from the original design.

    I found the airline tubing, when warmed from the heater, would become very pliable and kink in areas where it had to bend or turn. Fixed this by changing out the airline tubing to and from the reservoir with thicker polyethylene tubing, used for irrigation, and adding 90 degree connectors. Because of the thickness of the polyethylene tubing I didn't have the need to re-wrap with insulation. IMG_1299 IMG_1300

    I left the airline tubing in the drawers because it allows for maximum heat transfer. I also made my own custom trays using acrylic sheets and super glue to take advantage of drawer space. IMG_1301 IMG_1302 IMG_1303

    Temperature has stayed consistent in all 6 drawers as previously reported.

  • This is a really great idea! Maybe this could also be suitable for bigger operations if you can solar heat groundwater en make it go through a rearing chamber. But this might be too expensive ; don't know about that.

    How much mealworms do you produce weekly/monthly? And do they really not climb against the insulation?

  • The 'Reflectix' tray at the bottom of @megology's wonderful invention is the same as I made to go under my Tiny Farm's frame as a catcher for the frass. It is great. sturdy enough and 'heat keeping'. I am now thinking that I will construct a tent cover in a similar way. It will open at the top (and front?) for access straight down into the bags. I plan to overlap the material instead of working out a sealing method. It is stiff enough to hold itself in place - if sealing was necessary for some (bugs entering) then sticking "Velcro" on would possibly work. Give me a little time, but I will share once complete.

  • edited December 2014

    Yes the Refectix is awesome. My initial thought was to use foam board insulation but when I saw that at the store it seemed easier to use and proved to be way more versatile.

    @entojesse I bought my first mealworms back in spring and Ive just kept them cycling to get numbers up. So not sure on my numbers but I'd say I have in the tens of thousands now....definitely ready for harvest lol. Also the mealworms are not in direct contact with the insulation. They are in trays that sit in the drawer. See the third to last photo on my last post.

  • Good to hear it's doing fine. I see the tray now, smart idea to make it so tight fitting :) I'm curious how much this would yield per month, could you post that once you're starting to regularly harvest?

  • I kept my silver base tray a just a little bit loose as i regularly lift the frame out of it to scoop up any escapee meal worms. It is so easy to make with just cutting the silver material and taping up with duct tape or similar. It has lasted well over time as well.

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