Ron's Notes on How to Build Your Own Walk-In Cooler

NOTE: The article on this page offers general home-built cooler-construction techniques.

Below are some links to other folks that have put up links to making a walk-in cooler.


Cooler Building Plans

  • Pack N CoolPack N'Cool CoolBot Trailer Instructions write-up from North Carolina State. This is beautiful -- check out the lower left hand side of the website for links to detailed construction plans and budgets... So well done. I think we have been getting as many requests for trailer-coolers as room coolers lately, and this will certainly help a LOT of people.

    Direct link is here: http://plantsforhumanhealth.ncsu.edu/2012/08/17/%E2%80%9Cpack-%E2%80%98n-cool%E2%80%9D-provides-farmers-with-mobile-refrigeration-solution/

  • http://www.evergoodfarm.com/trailerbuild.htmlAnother absolutely wonderful site done by a CoolBot Customer for how to built a cooler on a TRAILER can be found here:
    evergood trailer
  • http://www.storeitcold.com/DIYrestaurantcooler.pdfA Restaurant in Maine built one of the tightest coolers I've ever seen. Materials for the walk in were about $3,000, the AC was $400, and of course the CoolBot is $299. It's a terrific write-up! Plenty of people have hacked together cheaper coolers (including me) but these folks really didn't waste a dime. It's all in better materials and wall finishes that many people skip in non-restaurant coolers. It's outstanding!:
  • uk cold roomUniversity of Kentucky offers specific home-built cooler plans using stick-built construction. We are calculating that now well over 1000 people that WE know about have used their plans to make a CoolBot Cooler. We love UK! I do recommend using 1.5 inches of poly-isocyanurate insulation instead of the 3/4 of an inch recommended in the article. That's not to say the article isn't great! They are right on with meeting industry standards, it's a GREAT plan. But doing a bit more does save electricity and pay off in the long run. For coolers that don't get a lot of public action the other change that quite a few people have made is to switch the rigid poly-isocyanurate foam insulation to the INSIDE of the cooler instead of the outside of the walls. This saves you another layer of plywood because it can serve as the inside walls (and then you break even on costs, even though you are doubling insulation!) Also it minimizes condensation on the inside of the walls if you DO get air infiltration from outside. These changes are not necessary, the plans are great as they are, but this is a very simple change to make for folks without publicly accessible coolers.

    Direct link is here: http://www.ca.uky.edu/agc/pubs/aen/aen96/aen96.pdf

Please keep in mind that these sites were not put up by someone that makes any money from cooler building (like we do!). They just wanted to share their experiences. PLEASE, PLEASE, PLEASE do not contact them to ask questions as it can be overwhelming and then they'll ask us to take these down. There's already a lot of info in there!


Vapor Barrier Note

Before we get to the actual article, I want to highlight one thing, and that's VAPOR BARRIERS in home-built walk-in coolers. Although we discourage people to build with fiberglass insulation, lots of you still do, and a professor at KSU has designed a CoolBot cooler I link to above that is sort of a hybrid that mostly uses fiberglass insulation and his design is REALLY good. But you can't change or subtract from what he did (you can add, though!). The biggest issue is the VAPOR BARRIER.

As you are building your cooler, imagine that there is a constant spray of water against the OUTSIDE wall of your cooler. low pressure, but constant -- shooting straight sideways. You can't see it, but that's exactly what's going to be happening. Warm air OUTSIDE your cooler contains more moisture than the cold air INSIDE your cooler. This is even true for those of you in Phoenix, AZ! In a normal house, you put a vapor barrier on the INSIDE of the house, and so that's what lots of people do when they are building their coolers. Big mistake!

Use a continuous sheet of polyethylene (carpenters plastic from Home Depot). And when you are putting it up on (between the outside air and the fiberglass insulation) just keep thinking about that CONSTANT side-ways water-spray and protect against that. The KSU document has you put up rigid foam insulation on the outside of the carpenter's plastic and I think he even has you caulk the seams. That's GREAT! Do that! We have to stop that water from getting into the fiberglass.

Okay, that's all... Now onto the regular article :-)

WAIT! NO! ONE OTHER THING! If you build a narrower rectangular cooler, like 4 or 5 feet wide, you need to make sure you are blowing down the LONG way. So... if you build a 4x6 -- you want to blow the air down the 6 foot direction, not across the shorter 4 foot direction. If you have a 6x10 foot cooler -- you need to blow down the 10 foot direction. If you have a 6x20 cooler... you need to buy 2 air conditioners and put them on either end (and 2 CoolBots).

Okay, that's REALLY it...


Notes on Home-Built Walk-in Coolers

by Ron Khosla


A "down" economy might be waking the rest of the country up to the importance of savings and DIY, but for farmers working on low margins and high risk, it's business as usual. We built the "CoolBot" because we couldn't afford a real walk-in cooler compressor, and a real walk-in cooler box was out of the question too. So we built our own, and we've since helped many other people build their own walk-in boxes, as well as getting tips and information back from hundreds more folks that have shared what to do (and sometimes what NOT to do) when building a room for cold storage.

If you're reading this article, you probably fit into one of two groups.

The first group has basic building skills and won't think twice about putting up a new shed or barn. Those folks just want to know how much and with what to insulate the walls, what to do about the doors and floors and how to deal with the high humidity levels found in the cool fall night that will be your walk-in-cooler's perpetual reality.

The second group has very little building experience, but can't afford a “real” walk-in box. They need a primer on everything from how to put down a concrete slab to basic framing and roofing questions – and then they get to all the same questions the first group has.

There are plenty of great basic-building resources already out there at (library, Internet, hardware store) on how to build small shed-type structures, so this article won't cover basic building techniques. Instead we'll focus on what's specific to making an inexpensive but energy-efficient walk-in-cooler box.

If you don't have a lot of building experience (or even if you do!) you might find that starting out with a pre-built shed, box trailer, shipping container, or even just the inside corner of your barn or garage might be a huge time and money saver. These structures are already structurally sound and weather-tight and just need to be cooler customized.


Where to Put the Cooler

You know how in the middle of summer it's so much more comfortable in the shade rather than out in the hot sun in the middle of your field? It's the same with your cooler, except instead of dripping sweat, a cooler sitting out in the sun drips dollars – lots of them, each month of the summer you keep it in operation!

Shade:

carolina car port

Site your cooler:

  • Inside an existing building
  • Under a tree
  • On the north-side of a barn
  • Or build a shading overhang onto an existing structure.

If none of those are possible, then at least make sure you have a ventilated shading roof on the cooler box.

Roof:

Flat roofs on a small cooler, may still be structurally sound in wind, rain and snow loads, but they don't protect from sun exposure. Building a standard peaked roof (over the insulated cooler ceiling) will shade the cooler and provide passive ventilation that will keep air circulation over your cooler and save money on cooling costs.

Note:

In a house, heat rises and that's why we put twice as much insulation in the roof as the walls, but in a cooler, we're building a box to keep cold in –and cold just sinks. Keep your cooler roof out of direct sunlight and you can put the same insulation in the roof as you did in the walls and you'll save money both in construction and long-term operating costs.

Ground Up

Now that you know where you want to put the cooler is time to consider the foundation. Two fundamental concepts to remember when building your cooler are:

  • cold sinks
  • water falls

It sounds obvious, but again and again I get calls from folks with converted box trailers or structures built up on decks that did such a great job insulating the walls and roof but then put nothing or half as much in their floor!

perched cooler

Perched Floors:

Coolers built up on a deck, need at least as much (preferably more) insulation in the floor as in the walls. If you build on a deck instead of a slab, you need to insulate the floor to r24.

If you have an untreated wood floor under your cooler, you will need to put in a vapor barrier. This is how we did ours:

  1. We put three layers of carpenter plastic between the styrofoam and our top layer of plywood. (Some people happily report using single pond liners instead.)
  2. We stretched the plastic out into a “bathtub floor” that goes up the walls a couple inches
  3. There it's gathered under “Roof Edge”* that is screwed about 3 inches up from the floor all the way around the wall like metal baseboard trim.
  4. We caulked the entire top of the Roof Edge so the water dripping off the walls won't slip between the plastic and the wall and pool up under the floor.

*Roof Edge is cheap and available in the flashing and roofing sections of all the big box grocery stores.

Concrete Slab:

If you're building on a concrete slab (or dirt floor) and plan to stay:

  • above 45 degrees then insulating the floor will never pay.
  • down at 40F... there's a bit of an argument for insulating the floor, especially depending on your region.
  • in the 30's, you really need to insulate that floor. Even just 2 inches makes such a big difference.

Haven't poured the concrete yet? It's so easy to add below grade (and cheap) I would definitely do it.

  1. First layer, put down gravel
  2. Second, put down a plastic vapor barrier
  3. Then below grade rigid foam insulation. 2 inches is even fine, four is great, but 2 inches is absolutely enough.
  4. Next Rebar or mesh
  5. Lastly, pour! We mix in fibers to make it stronger
how to insulate concrete floor

How To Insulate the Floor:

Whether you're building up on an existing trailer deck (or above a basement) or on a slab you do NOT need to frame out a floor.

Simply...

  1. Place rigid foam directly on the floor
  2. Lay plywood painted with porch paint/ exterior paint directly on top

The plywood spreads the load out enough over the rigid foam that even after 10 years, our foam still looks fine.

Thermal Bridges:

Studding out a floor is not only slow, but fitting insulation between the studs generally leaves leaks and allows for thermal bridging through the framing studs. Save time, save money and do a better job -- how often does that happen!

Drainage:

Tilt the floor towards the door so that any water that gathers (due to condensation or dripping veggies) can naturally drain out. Don't forget to site your structure so the water has someplace to go once it leaves the front door.

If your building on a trailer or a deck-type floor, this is obviously easy to do. If you're pouring a new slab, just build it above grade a bit and put your form-work a barely noticeable “off-level” towards the door.


Insulation

The industry standard for walk-in coolers is an R value of 26. Going up to R 30 will save even more money especially if you are keeping your cooler at 40F or below. It's probably not financially worth it to insulate above that.

Rigid Foam:

R Values can vary based on the different kinds of foam and the age of the foam. No vapor barriers are required with the use of rigid foam.

3 Types of Rigid Foam Insulation:

polyurethane

Polyurethane:

  • Pink or blue
  • R Value of 7-8
  • After 5-10 years: R Value of 5-6 where it stays
  • Best choice for the floor
  • Comes in 4x8 sheets

Use at least 4 inches in the walls, floor and ceiling and you'll be fine.

polyiso

Polyisocyanurate:

  • Grey or yellow
  • R Value of 6.8
  • After 5-10 years: R Value of 5.5 where it stays
  • Best choice for walls and ceiling
  • Comes in 4x8' sheets
  • Available at Lowes and Home Depot

Use at least 4 inches and if it has foil back then be sure to face that towards the outside. This product can be irritating so be sure to wear long sleeves.

eps

Expanded Polystyrene (EPS):

  • White beaded
  • R Value of 5
  • Retains its R Value over time
  • Comes in 4x8' sheets
  • Available at Lowes and Home Depot

Discovered in 1839, this is the same stuff your bean bags are stuffed with. Never breaks down but has the lowest R Value so be sure to use 5-6 inches.

Spray-In-Place Foam:

This is a professionally applied polyurethane product that can turn leaky barns or sheds into well-insulated walk-in coolers in a short amount of time. R Value and cost can vary drastically. Depending on your location this may be a practical solution for you, check with your local installer for costs. Four full inches are necessary to keep your cooler below 40F.

Fiberglass insulation:

DON'T USE IT! Regardless of whether or not you have a vapor barrier, moisture seeps into the fiberglass insulation, becoming not only a moldy nightmare but decreasing your insulation value. This results in higher electricity bills since you a/c has to work constantly to cool your cooler since the cold air is leaking out through the now uninsulated walls.

University of Kentucky Cold Room:

HOWEVER if you want to use fiberglass then use the excellent plans from the University of Kentucky. This hybrid system uses rigid foam panels to protect the walls from water in the air condensing inside them.

Modifications to the UK plans:

  1. Use more rigid foam. Instead of 3/4 inch, use 1 1/2 inches. This will save considerable money in the end
  2. If you put the rigid foam on the INSIDE of the cooler you MUST use at least 1 1/2 inches of rigid foam and be sure the vapor barrier on the outside is solid.*
  3. You could put 3/4 of rigid foam on the inside and 3/4 of rigid foam on the outside

* If the foam is on the inside you can skip the inner layer of plywood. If it's not a cooler that is going to be open to the public and won't be subject to bins being thrown around and puncturing the foam, this is a great way to save money... well... you'll actually break even, because you'll save the money on the plywood, but then you'll spend it on the extra foam insulation. But it's worth it!

Basement Builds:

A concrete block has a .5 R Value at best. If your average underground temperature is 52-62F and you want to be 52-62F then you don't need insulation. If you want to be lower than that though, you will need some sort of insulation, otherwise you'll be spilling out all the "cold" through the walls into the ground.


Build it Tight

Building your walk-in cooler air-tight is just as important as the amount of insulation you put it! The bigger the temperature difference between the inside and outside air the FASTER your expensive cold air flies out.

greatstuff

Using several bottles of spray foam and caulk be sure to close up:

  • cracks
  • seams between insulation sheets
  • under the door
  • around the air conditioner
  • every corner

It takes less time and makes more of a difference than you might think!

using great stuff

Over Not In Between:

Tack the rigid foam up on the outside of the studs. Cutting up your insulation to go in between studs will not only leave a few gaps and holes, but no matter how careful you are, polyisocyanurate and polyurethane will shrink a bit over time.

Stagger The Seams:

None of the big box stores sell rigid foam insulation 4 inches thick, but you can use that to your advantage! Buy two layers of 2 inch foam and overlap the seams to keep things sealed up.


Electrical

There is no need for special electrical work.

However sometimes a vacuum effect can be caused by the warm outside air being sucked in through the back of the outlet box, by the cold cooler air.This can result in moisture gathering and could cause the circuit to trip.

The Solution:

  1. Take the cover off the outlet
  2. Find where the wire enters the back of the outlet box
  3. Using silicone caulk seal any gap where the wires enter the box so no air can move through
  4. Replace the cover and thats it!

Note: Besides silicone caulk, clay or feldspar can be used to seal up the gap


AC and CoolBot Placement

taos cooler

Eye Level:

The AC will preform at its best when installed at eye level. Cold sinks, so the higher up the better. This also makes maintenance a lot easier.

Longest Way:

If you have a space that is less square and more rectangular in shape, then the AC should be mounted on the small wall so that it is blowing the longest way possible. For example, on a 5x10 room, the AC should be mounted on one of the 5 foot walls.

Side By Side:

The CoolBot should be mounted inside the cooler next to the AC. If there is a troubleshooting issue, you have to have the CoolBot and air conditioner right next to each other.

Note: If it's an issue of wanting to know the temperature from outside, there are pretty cheap ($19) wireless temperature sensors you can get from Amazon -- I've regularly seen them on sale for $12 from WalMart/Home Depot, and more expensive ones ($80) you can monitor on a smartphone or online.

Also, CoolBots can't be in direct sun, so if you still decide to mount it outside, you'd have to protect from that as well.


The Door

I've seen really beautiful home-made doors that do an excellent job, but unless you've got great building skills, I don't recommend it.

exterior door example

Pre Hung Insulated Exterior Door:

It's cheaper and faster to buy a standard pre-hung insulated exterior door. This is because the key to the door is that it seals up tight and that's not so easy to get right! If you leave the smallest gap in your door, much of the effort you put into insulating and sealing up the rest of your structure will be wasted.

Customized:

Heres a few tips to get the most out of your door:

  • Make sure your door opens to the outside world (make sure the cooler is up a bit from the surrounding ground level so the door can swing freely)
  • Glue another layer of 2" rigid foam to the inside of the door (it'll break down in the sun on the outside).
  • Remove the bottom metal piece of the pre-hung doors so it doesn't dam up the water inside your cooler (and that means you have to cut the sides of the door down so the bottom stays flush against the floor). inner floor.

Inner and Outer Sheathing

Many people just leave the exposed insulation on the inside of their coolers. If you don't have employees and you're careful, that's fine. We have aggressively destructive employees and our cooler is open to a public I seriously suspect to be drunk most of the time by the way they ransack the place.

Inner Sheathing:

Our inner walls are sheathed with $7/sheets of "OSB board." We could have used plywood, it was just more expensive. There are proper, water-proof inner cooler siding materials but they are over $1/square foot and our neighbor built his walk-in cooler in 1985 with OSB board he painted with white porch paint and it's still completely solid 24 years later!

Outer Sheathing:

If your cooler is built inside an existing structure you don't need to sheath it, but if it's outside, it has to be protected from the sun or the insulation will start to break down.

We did this by ripping cheap half-inch 4x8 sheets of “CDX” plywood into 1x8 foot strips to make home-grown overlapped siding! We live in a registered historic district and we are often in trouble with the village elders for not taking their “hysterical” district as seriously as we should, but our cheap plywood siding solution (properly stained a dull green) apparently looks nice enough from the road that it's one thing no one has ever bugged us about!


Building your own cooler can be much more cost-effective than buying a ready-made cooler box and since you can add extra insulation, the extra time you put in building it can also pay off in long-term energy savings down the road.