Building a Walk-in Cooler

First comes the framing, of course.  Good building practice calls for pressure treated lumber on the bottom against the concrete, and I think untreated lumber should be OK for the rest of it.

The end studs are screwed to the walls and the bottom 2 x 6s are screwed to the floor with Tapcon screws.

Finished framing


Since there is drywall on the basement walls, I covered it with plastic to protect it from any condensation that might seep through from the cooler.

Insulation recommendations from the Cool-Bot folks say to use 4 inches of foam.  Since there were already 2 inches of foam on the basement walls, I added a 2 inch foam piece to each one.  The foam could be glued on, but I used long screws and fender washers to hold them.

In the wood-framed walls, I cut the foam slightly oversize and pushed it into place.  The snug fit was all it needed to stay put.  Where there were gaps, I used spray foam and that really locked the rigid foam into place.

Walls and ceiling are foam covered.


Next went on an exterior door and some cheap 5 mm plywood.  An exterior door is important because it is insulated and it has good seals.  It’s pretty tough (at least for me) to try to build something that will be as well sealed as the factory-made door.  When I’m inside with the door closed,  I can see only a tiny sliver of light at one corner of the door.   Two foam panels are on the floor covered by plywood, and I put a few trim boards here and there and to help hold on the flimsy plywood.

It’s done.


I picked up a used 12,000 BTU/h LG brand air conditioner, which is probably overkill for the size of the cooler, but the price was right.  Inside, the cooler measures about 4 feet x 5 feet x 8 feet tall.  In hindsight, making it 8 feet tall was probably not the best idea.  Seven feet would have been plenty.

The business end.

The small black box you see below the AC unit is a device called a Cool-Bot controller.  It controls the AC so that the temperature inside the cooler can get much colder than the AC could normally get it, and also keeps ice from building up on the AC unit.  You can check out the Cool-Bot at Cool-Bot.


Comments on: "Building a Walk-in Cooler" (70)

  1. What is that little control box you have mounted below the AC unit? It looks like you tapped in to the AC wiring with it. Can you provide more details please. Thanks, -Dale

  2. thinmac said:

    Hi Dale, sorry about the delay in getting back to you. The control box that you see is a Cool-Bot controller and I can see that I should have added some details about it to my post. I’m going to do that right now, so check it out and see if it answers your questions.

    • Did you use a standard exterior door and hang it backwards, hinges out? Would this cause a problem with adding more insulation to the door on the inside? How do you sanitize the interior walls? Looks like a great design. We are just getting started on this project.

      • ET, that is exactly what I did. I don’t see that it would interfere much with adding insulation to the inside. I think you could just set the insulation back from the door edge a half-inch or so to get clearance for the door jamb. I haven’t given any thought to sanitizing the walls.

        Good luck with yours. Having a cooler definitely adds a lot of flexibility to your picking and marketing schedules.

  3. What did you use on the floor. In the build picture it doesn’t look like anything but in the final picture with the door it almost looks like you have plywood down with foam. I hope to use your design for my beer cooler 🙂

  4. You have it right, David. I put 2 inches of foam on the floor with some half-inch plywood to walk on.

  5. Have you had any issues with condensation drip from the back end of the AC unit? Also, once it was cooled to temp have you taken note of energy consumption? Is it very efficient? This is a great idea. I just googled for home-made walk in cooler and found it. You’ve inspired me 🙂

  6. Hi Drew. I’ve added a drain tube to a fitting that is already on the back of the unit, so any condensation goes into a bucket on the floor. There really hasn’t been much. Efficiency-wise, I can’t really say, but users and the manufacturer of the Cool-Bot claim that it is not expensive to run. Good luck with yours if you decide to go for it.

  7. What can I do if I want to train or know how to build a commercial cooler or freezer.

  8. Timothy – sorry, that’s way beyond anything I know.

  9. Hey, great idea, I’m wondering how low can you realistically get this room with a window unit and the Cool-Bot? Can you get it down to near freezing, say 35-38 degrees?

  10. Scott – All I can tell you for sure is that I set it at 40 degrees and it had no trouble getting to and holding that temp.

  11. What is the cost for the cool bot device. Has your it been effective for you. Thanks Rick.

  12. Elizabeth said:

    Scott, Since you use this for flowers I’m curious as to how the humidity level is. Have you had any issues with not having enough humidity? Are you flowers ‘drying’ out?


    • thinmac said:

      Liz – I’m not sure if you actually meant to ask Scott this question, but being as how it’s my blog, I’m going to assume it was for me. You brought up a good point about the lack of humidity in this kind of cooler compared to a standard floral cooler, and I have read that other users have tried adding moisture to the air with extra buckets of water or hanging wet towels. It seems clear that the longer you try to store flowers in the cooler, the worse the effect of low humidity will be. In my case, I haven’t tried to store flowers for more than about three days, and they didn’t seem to suffer. I haven’t tried to measure the humidity level so I can’t help you with anything factual. Thanks for the interesting question.

  13. Reg Bouchard said:

    Reg here
    Thinmac,could you elaborate a bit on the insulated door? What R rating?

  14. thinmac said:

    Hi Reg. I don’t really know the R rating of the door. There was probably a sticker on the door when I bought it, but that’s gone now. It’s just a standard lumber yard insulated steel door – nothing special. If I had to guess, and I guess I do, I’d say that it was maybe an R-5.

  15. Reg Bouchard said:

    Thanks a million. It was exactly the info I needed. Take Care

  16. Curious about the amount of heat the AC generates in the garage. Also, how often does the unit cycle to maintain your 40 degrees? Have you attempted to get lower?

    • Tom – I didn’t notice any rise in temperature in the basement when I was operating the cooler. Most of the heat that the AC ejects into the room is heat that seeped into the cooler from the room, so basically most of the heat is just flowing into the cooler and back into the room, leaving little net change in the heat content of the room. The exceptions to that would be the heat that flows into the cooler through the basement walls, which are fairly cool to start with, and the heat generated by the operation of the AC itself. These would add some heat to the basement, but that seems to be a fairly small amount, judging by the lack of temperature rise there.

      I don’t have a good answer for you regarding cycling times. It wasn’t anything I tried to monitor. I also never tried to get it colder than 40, though I seem to remember reading somewhere that it was possible.

  17. How much did everything cost you?

    • Good question, Lina. The approximate values of the major expenses were –
      Foam insulation $200
      CoolBot controller $300
      Used AC unit $100
      Door $100
      Add some for lumber and assorted doo-dads and the total is pushing $800.

  18. Great project. Has there been a noticeable increase in your electricity bill?

    • Hi, Tim. As I remember, there was a small uptick in the bill during the growing season, but I can’t remember the amount. Not remembering is probably a sign that it wasn’t too much.

  19. Hi, nice job on your cooler. I’m just getting started with my project. I haven’t even poured the concrete yet for the floor and was wondering if I could put 4 inches of insulation under the concrete instead of on top? Also, I was originally going to put the AC unit on the outside of the building, but after seeing your design it may be better on the inside especially since winters here get below zero. I have 10 foot ceilings I can work with. Could I put it on top? What do you think?

    • Hi, David. I’m not any kind of expert on these things, but I know that foam is sometimes used under basement floors in cold climates like yours and mine. If I were starting from scratch, that’s exactly what I would do, just so I would have a nice easily cleanable surface to work on. Also, having the concrete’s mass inside the insulation envelope will help to even out temperature swings in the cooler. Those are my thoughts anyway. Good luck with your cooler.

  20. Jojo Lee said:

    Will a design like this pass health inspections? Would like to show this to my boss at the bar I work at and see if she wants to make one for our beer storage.

    • Short answer: I haven’t a clue.

    • Fred Torreano said:

      We are doing one for our bar. The local HD wants a sealed floor and fiberglass panels on the walls and ceilings. Also the condensate drain is a major item. Panels are about $30 for a 4×8 sheet. They have been very helpful if you keep them in the loop from the get go.

  21. John Jung said:

    I noticed a copper pipe near floor level. Is that anything to do with this project? Thanks for all the detail. I’m thinking of a beer cooler for a man cave.

    • thinmac said:

      Good eye there, John, but no, that’s just part of the baseboard heat in my basement. You must be expecting a lot of company if you want a walk-in cooler for your beer.

  22. Nice work!!!! Wanting to do the same thing to hang/cool moose quarters in my basement. Was wondering about having a window unit air conditioner in my basement. Are there any concerns with “exhausting” an air conditioner indoors? Thanks in advance.

    • Hi Al — The exhaust is just warm air, so all it will do is warm up the basement a little. The only downside I noticed was the noise from the AC unit. It was right under my bedroom so it was a little annoying at night.

  23. I see all electrical items are inside the cooler. In case of emergency you will have to access the inside and if it is blocked it means trouble. I do not know how the controller works but been inside it means opening and closing of cooler to see if it is working/adjusted properly. Making the AC unit work harder and whatever you are protecting/cooling/etc. will be expose to varying temperatures and humidity levels. A good idea will be a camera and a light switch to see the interior from outside/some distance without affecting or changing temp./humidity constantly. I know, it may add cost to the project that can be recovered with the saved energy. You mention it was too high, try adding some bags filled with foam peanuts to reduce the unused space and add insulation at the same time. A project that can be adjust by using a more powerful AC unit. Thank for the Ideas, great project.

    • Thank you, Juan, for your thoughts. I’m not convinced that it would pay to put a camera inside. During the season, I’m going in and out of the cooler several times a day with flowers — plenty of opportunities to check on the workings of the AC unit.
      I appreciate your taking the time to give me helpful suggestions.

  24. hi thinmac,thanks for your idea,i want do same like this in my garage,What I worry about is The heat emitted by A/C work.In the garage temperature may be more than 30 ℃ in summer,when the A/C wrok,how many temperature will increase? more than 10℃?

    • Hi, Zeger. I think the answer is that your garage will heat up very little. Here is my reasoning: 1) Heat seeps from the garage into the cooler. 2) The AC unit pumps the heat back out into the garage. The heat that is pumped back into the garage is the very same amount of heat that seeped into the cooler in the first place, so there is no net gain of heat by the garage.
      But, 3) The electric motor in the AC unit does produce some heat and that will heat up the garage a bit. If it is a 1/2 horsepower motor, it will produce heat at a rate of 380 watts, the same amount of heat you would get from about four 100 watt incandescent light bulbs. I can’t see that heating your garage by very much.

  25. Hi, I was wondering if you have any update pictures? Did you make any improvements since you first built your cooler? Or is there anything you wished you didn’t different?


    • Hi, Jay. That’s a good question, but I don’t really have a very good answer for you. I got out of the flower farming business a few years ago and the cooler is now history. I sold the AC unit, the door, the Cool-Bot, and the insulation panels and I now have that corner of my basement back. In the time I was using it, my only wish was to have made it seven feet high rather than eight feet, but you probably already read that in the post.

  26. Kristin said:

    I hope that I didn’t miss this question. I didn’t notice anything substantial in the ceiling frame for hanging deer or whatever animal from. I am about to start building one in my garage and I was concerned about making sure I have reinforced studs to hold the weight of hanging meat. I would like to eventually buy a calf to process. Any thoughts on this? Thanks for your post. It is really awesome. Really helping me get over the anxiousness I have about build this.

    • thinmac said:

      Hi, Kristin.
      You’re right about nothing structural being in the ceiling of the cooler, and I suppose that would be pretty important if you have a need to hang carcasses in there. Not personally knowing the length of a hanging deer or calf, I imagine height might be an issue too. Mine was about 8 ft tall. The other thing I wonder about is temperature. Is 40 F going to be cold enough for meat?

      Things to think about.

      Good luck with yours.

  27. I thank you so mush ,I am definitely going to try it, it might be a bit challenging for my as a female ,because I am that Handy, butl it will be done .it looks great i think you did a great job. My ? ,Is it a freezer type or a refrigerator just to keep things cool ?

    • thinmac said:

      I’m glad you like the cooler. As the name suggests, it will only cool things down like a refrigerator, not freeze them. Good luck, if you decide to build one.

  28. Awesome cooler I have been wanting to build one for a long time but was not sure where to start I plan to hang deer in it during the early season it sounds like this unit will only go down to 40 ?? I like to hang my deer for 10 days at about 38 will this unit take temp down to 38 or is 40 as far as it will go

    Great job

  29. Thanks for info have one more question? I see you used 2×6 floor plate for walls and 2×4 walls any reason for the 2×6 plates??


    • No good reason really. I knew the four inches of foam was going to extend out a half inch beyond the 2×4 studs, and for some reason that escapes me now, I thought I’d like to have the floor plate extend beyond that.

  30. Hey Thinmac,

    Did you run into any issues with condensation on the drywall behind the insulation? I see that you used plastic sheeting, was that helpful? I’m building a cooler inside my garage which already has drywall.


    • When I was done with my cooler and took it apart, there was no sign of moisture on the drywall, so I think it’s safe to say that the plastic did its job.

  31. I currently have a small room off the main house. I live in eastern NC… Summers can get hot…I have a AC in that room, going thru the wall to the outside… Do you think that would work, or should I have the AC exhaust inside….? And my other question, tho it sounds a bit extreme is, do you think bricking up the wall is a good idea, to help maintain the coldness…? I have always wanted a cold storage room, this looks doable… As a kid we had a cold cellar in the inground basement of an old Victorian home in NY…. Fruits and veggies would last all winter…. Trying to replicate that in NC

    • You definitely want the AC to exhaust outside the room you’re trying to cool. Judging from your questions, I think it would help you a lot to read the information on the CoolBot website.

      I’m not sure you would want to spend the money to turn your room into a cooler just to store fruits and veggies all winter. If you do decide to go ahead, the best of luck to you.

      About the bricks – they don’t make very good insulation and probably wouldn’t help you much.

  32. Do u have issues with the ac freezing ???? If it continues to run wouldn’t it freeze? I have that issue just trying to keep an account running in my window

    • Hey, Rob. I didn’t have a problem with the CoolBot icing up. There is a temperature sensor that fits in the cooling fins, and if it detects freezing temperature it temporarily shuts off the cooling cycle. As far as I can tell, that does the trick.

  33. The only flaw I see or maybe i missed it,but you should really have a vapour barrier on the exterior of the cooler. Warm moist air will condense on cold surfaces right. So, it’s like your house but in reverse. Cool bot explains it on there website.

    • You probably saw the plastic I put against the drywall, so I’m guessing you’re talking about the two walls facing the interior of the basement. I can’t really see the need for a vapor barrier there in my case. True, water vapor could make its way through small voids in the wall, but, there’s no interior surface to condense on. There’s a two inch slab of foam and that’s it — no interior lining at all. It’s like a house wall where the sheathing, house wrap, and siding was left off.
      Make sense? Thanks for your thoughts, Shane.

  34. This is so awesome. You have inspired me. I have done one weddings flowers and they were beautiful but I was a wreck making sure they survived, in an air conditioned house, for the 24 hours before the wedding, if I build this it sounds as if my flower survival worries will be greatly decreased. Thank you for all of the good information.

    • Debra, you’re braver than I am and I’m sure much more talented. I never even thought about trying a wedding — way too much pressure for my limited skills. I thought of myself as mostly a flower grower and only by necessity a seller — never a florist. I’m sure you will love to have a cooler. It adds a lot of flexibility to the timing of your work. I wish you luck in building yours.

  35. Did you really put the outlet and wires inside the cooler?

  36. This system should have a vapour bearier installed on the inside walls. I know this as I am a refrigeration tech.

  37. Thank you for posting these pictures of the walk in cooler. I have plans to do a similar set up with a indoor cooler.
    This too will be for my wife’s bridal floral business. I want to install the walk in cooler in our spare den room. I would like it to be her actual flower shop.
    My question is, Does the window unit AC push a lot of warm air inside the room?
    Would it be better to install the window unit in a window with a 4ftx8ft so warm air is not in the same room?
    would you of done something different for a flower business?
    Thank you so much.

    • Thanks for writing, Juan. I’m not sure I’m qualified to answer your questions, but I will try. First, I would probably not build a cooler in an existing room in my house because I would worry about water from the cooler possibly getting into the floor or walls. That was not a worry in my basement because it had concrete walls and floor.
      Second, the AC does push warm air into the room, but most of that heat seeped into the cooler from the room to start with, so I think the temperature of the room wouldn’t go up much. I never noticed that my basement warmed up much, although it is a lot bigger than just a room.
      Third, I think that this kind of cooler could work for a floral business because it did for me. The one downside was noise. The AC unit was fairly loud and ran all the time. I think a commercial cooler would have been quieter, though a lot more expensive.
      Good luck with yours.

      • This is awesome. And it is a really nice size room. I been thinking about the same so I am researching the efforts of people like yourself Most of what i have seen so far have been big rooms, but yours is a great compact area with a lot of usable space.. I guess there is no need to go the 200 square foot route.

        One thing I haven’t seen yet in all the coolbot blurb that you mentioned is ” The AC unit was fairly loud and ran all the time.”…. I assumed that the ac unit would cycle on and off like a normal refrigerator or ac unit. meaning that it would run for a while turn off then run for a while etc etc.
        Could you maybe just clarify this point a little… and if it runs all the time is it like expensive to operate… as running ac in a room in summer all the time can be pretty dear.
        Cheers and thanks for sharing such a great set up.

      • Hi, Mike. It’s been about five years since I was in the flower growing biz, and my memory is a little fuzzy. I do remember that it would run constantly, though I think it was the fan that kept going while the compressor would cycle on and off. While I was using it I didn’t notice any big spike in the electric bill, though, as they say, your mileage may vary.
        Thanks a lot for your interest.

  38. Ángel r flores said:

    It was very helful your información.

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