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Root Cellar Venting and Wall Material Questions

 
Steve Sherman
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We have a small room (6'x8') which is in the NW corner of our barn, at the basement level. Two walls are concrete foundation in direct earth contact (with moisture barrier on the outside), the other two are insulate 2x6 stud construction. Ceiling is insulated 2x joist construction. We have been using this room to store root crops for a few years before it was finished, and it has worked somewhat. There were issues of it getting below freezing when it was very cold out, and it tends to be drier than one would like for storing many root crops. I expect the temp thing to be solved once all the insulation is up. But before I do insulate, I need to run some vents.

I've read a few articles/books on root cellar design, and l am planning an intake vent at the floor in the NE corner and an exit vent at the ceiling in the SW corner. Most of the books suggest a 3-4" diameter size for these vents. However I am wondering if I can/should perhaps use something smaller, like 2" diameter pipe. We are located in the foothills W of Denver-Boulder CO. Climate here is ag zone 5a (-20F min temps) and it is quite dry and windy most of the winter. I am less concerned with exiting excess moisture than I am over venting and pulling in too much cold air and freezing the vegies. The only downside I have thought of for the smaller vent size is a slower cool down of the cellar in the fall, which I think I can compensate for by running a small fan on select cold nights.  

What do folks think?

The next question will be what to use for covering the stud walls and ceiling once the insulation (fiberglass) is in? Sheet rock is cheap and easy to install, but likely will not hold up well to moisture (not that it will be that wet in there in our climate). Does anyone have anysuggestions for material that will hold up to moisture and be cleanable?

Thanks.
 
Gilbert Fritz
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Location: Denver, CO
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Hi Steve,

Welcome to Permies!

I'm also in Denver, and I'm interested to see what answers you get. I have to say that I think fiberglass and sheetrock are bad ideas due to water and mold damage. But I hope somebody who knows a lot about this topic chimes in!

If you don't get an excellent answer in another day or so, you can go to the tinkering with this forum thread and invoke the 48 hour rule.
 
Mike Jay
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Location: Northern WI (zone 4)
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I'm not an expert but I have a root cellar in my basement.  My vents are 4" and I have a fan on the inlet to help cool it in the fall.  Since it's in a house (in a cooler room of the basement on the North side) I may have more trouble getting it cold enough in the fall.  I bet I run the fan for a month (when the temp is lower outside) to get it finally cold enough each fall.  I'd put in 4" ducts, you can always partially block them if you wished they were smaller in the future.

Last winter there were a few weeks where it was getting too cold so I cracked the door open a bit to let it warm up to 34 degrees.  My vents are next to each other (not high and low as recommended by the books) so very little air circulates if the fan isn't running.

My root cellar has a block wall against the exterior on one side and poured cement on the other three sides (I didn't do it, the guy before me did).  But I do like the cement walls.  I would definitely avoid sheetrock.  When/if you get it damp enough for your roots, the sheetrock will probably start to get soft or gross.  You might want a vapor/moisture barrier between the root cellar and your studs to contain the humidity and protect the wood.  A building sciences person will probably chime in to correct or amend this but that's the way I'd be thinking.

I'd probably use milk house paneling as my interior finish.  It's plastic and designed to be washed down.  Caulk or seal the joints to protect the wood studs.

Our "solution" to a lack of moisture is a $9.95 atomizing humidifier that uses a water bottle as its supply tank.  It's so cheap that it doesn't turn off when the humidity gets to 50%, 60% or wherever fancy humidifiers stop.  So it can get us up closer to 90% if we keep it filled.
 
Destiny Hagest
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I merged your stuff with the following thread. I hope that is okay by you.
 
Alex Sonnenschein
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Location: Whittier, California
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I am not completely sure where you are coming from with your post (in terms of concepts).

So before I am able to provide with an idea I must ask questions.

I am assuming your understanding of a root cellar is based on the purpose of storing harvested roots.
If so, why do you really need to build a cellar for keeping roots, and any available space not sufficient for it?
Roots, harvested or growing, should be agreeing with their environment regardless of artificial prospects.
So what is the concern requiring a specialization for root storage? Wherefore comes the concern for building an insulated space?
A healthy environment should be facilitating storage naturally for the people that it is able to feed.

If, by another measure, the cellar's purpose is to somehow "age" the roots, and not simply to store them, could you describe that envisioned process with greater detail?
In thinking of animal life and their intelligence by relating to abundant food I have in my mind how squirrels are able to transform, or "age" acorns by burying them (often becoming soil fertilizer even if recovered and nibbled by them), but then again acorns aren't roots naturally made to be underground, so it seems odd that you would have to return them underground when supposedly they would be ready for animal use.

Could you clarify any of those questions? They could possibly lead for the appropriate decision making in proceeding with your roots.






 
Mark Zielinski
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I also live in the Rocky Mountain foothills and used 4" PVC for the two vents in a 12' X 12' root cellar in one corner of our basement. Both pipes were placed in holes drilled through wood just above the concrete basement walls, so both holes are right at the ceiling of the root cellar. The air intake was piped down to maybe 6" above the concrete floor, the air outlet is just a straight pipe at the ceiling. The specs I've seen say the pipes should be larger for my size root cellar, but the 4" pipes have worked pretty well. What I did buy is a rounded cap for 4" PVC and, to keep warmer air in to keep things from actually freezing, I cap the outlet pipe in really cold weather, the type of cold that tries to freeze the water pipes in my basement. Most winters, that's only a few days total at most (so far!).

The typical non-Summer temperature in the root cellar is in the low- to mid-40's. The highest I've ever seen it is 60 degrees during a real hot spell during the record-hot Summer of 2015.

The two walls that are not concrete walls are standard woodframe sheet-rocked walls sprayed with maybe a 1/2 inch of insulating foam. Ceiling is also sprayed that way.

good luck, this is a fabulous project, you won't believe how great it is to be able to store all kinds of fresh and preserved food in stable coolness.
 
Mark Zielinski
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Alex, for many food products, storing them in temperatures in the 40's in a root cellar is tantamount to free refrigeration, even better actually because the storage can be drier than what you get in a fridge. And once the root cellar is built, that "refrigeration" is free going forward. Think of all the money and resources that are consumed on this planet by refrigeration.

If one lives anywhere with a short growing season, then you really want a cool temperature place to store lots of the things you raised in the garden during that short growing season (e.g., onions, carrots, potatoes, garlic, etc.) You want those things to last into the growing season of the following year, and a root cellar can make that happen. It is also a fabulous place to store foods canned from that short growing season--they will last for many years with no spoilage. So all those strawberry, blueberry, and raspberry preserves we put up this year will be with us for as long as we can resist devouring them or giving them away as gifts.

Also, if one is a baker, milled flour lasts very nicely in cool storage, and whole grains are likely to last for one's lifetime.

Did I mention: I really like root cellars and find them extraordinarily valuable! It's very unfortunate for all of us that they have "gone out of style."
 
Steve Sherman
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Alex, let me also try to answer your questions:

The term "root cellar" refers to a below ground (or partially so) room where vegetables and other food stuffs are stored. It typically is designed to keep temps slightly above freezing, and can be high or low humidity, by design. The term is generic in its usage; root cellars can be used for storing root crops of course, but are useful for many other foods too, such as cabbage and apples and other above ground items, Sometimes even smoked/cured meats and cheeses are stored in them. As Mark said, they are a low energy input means of refrigeration really (actually far better for storing many items than modern refrigeration).

It is true that in some warmer climates, one can store root crops outside in the ground over winter, perhaps with a layer of straw to protect them. Not here. the ground will be frozen 2' down in winter and covered with snow typically, making outside storage unusable.

As it turns out, my intended use is primarily for storing fruits and vegetables. I would like to manage this room to stay at 34-40F. Really no aging or fermenting of foods should be going on in here, just a long term, cool and dark storage place.



Mark:

Thank you for your comments. It is reassuring to hear that your root cellar has been working in this same locale.

So judging from your numbers, 4" diameter pipe vents works for a 144 sq foot cellar. Since my cellar area is roughly 1/3 the size of yours that would point to a vent size of roughly 1/3 the area or a pipe diameter of between 3" and 2" (2.3" diameter to be more precise). Of course that does not take into account increased resistance to flow from the higher wall to overall area effect of smaller pipe. So I think that going with the 3" pipe is the right choice.

If I can ask a question Mark, what sort of rain cap to you use on the "exhaust" vent? I have been debating whether I should use a U-turn of pipe at the top to keep rain/snow out, or the more traditional "chiminey" type cap. The concern being that a U-turn might present too much resistance to unpowered air flow.
 
Roberto pokachinni
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I have been debating whether I should use a U-turn of pipe at the top to keep rain/snow out, or the more traditional "chiminey" type cap. The concern being that a U-turn might present too much resistance to unpowered air flow.
  A 'T' shaped fitting can provide the airflow and the protection.

you really want a cool temperature place to store lots of the things you raised in the garden during that short growing season (e.g., onions, carrots, potatoes, garlic, etc.) You want those things to last into the growing season of the following year, and a root cellar can make that happen. It is also a fabulous place to store foods canned from that short growing season--they will last for many years with no spoilage. 
  It should be noted that many of these things require specific storage conditions that are not always compatible.  For instance, I would personally never store garlic and onions or canning in the same cold slightly damp space that I would store carrots or potatoes.  Garlic and Onions store extremely well in a warm dry place.  While canned food can take the cold, the dampness of a cellar can cause rust on the metal lids and compromise the jar seals.  
 
Steve Sherman
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Yes Roberto, various crops have different storage needs. Different temps to some degree. Different optimum humidity levels is often a big one. And also issues with outgassing, for example apples tend to give off ethylene, which will cause potatoes to sprout.

We typically store winter squash in a cool place in the house, as they need 50F and dry. There are some "tricks" to meeting the different needs for the cold storage crops in the same room (which I have not tried myself yet, but will once the cellar is completed), like putting apples up high near the vent so their ethylene exits before it can interact with other vegies.

Other solutions include having two rooms in the cellar, a "wet" one and a dry one.

 
Mark Zielinski
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Steve Sherman wrote:
If I can ask a question Mark, what sort of rain cap to you use on the "exhaust" vent? I have been debating whether I should use a U-turn of pipe at the top to keep rain/snow out, or the more traditional "chiminey" type cap. The concern being that a U-turn might present too much resistance to unpowered air flow.


Steve, I am lucky to have the inlet pipe under an eave and the outlet pipe under a carport, so no rain or snow problems (again, at least so far!). Roberto's comment about a t-shaped fitting sounds great. Also, definitely figure out a way to put screen over the outdoor openings on these airflow pipes so the bugs, shrews, etc. stay outside.
Mark 
 
Chad Anderson
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Location: Dawson Creek, BC, Zone 2a
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There are a lot of variables at play, so I doubt anything but "wait and see" experimentation will answer this. I live in northern Canada between Rocky Mountain foothills and prairie, and in our case, 4 inch vents don't seem to be drop the temperature early enough or keep it low enough long into February / March / April, even though nighttime temperatures are well, well below freezing. Some of my variables: ours touches an uninsulated foundation of the house (soon to be insulated), and the vents are not in particularly exposed locations, and not aligned with the prevailing winds.

If it's near enough to the house, a $15 battery-powered weather station with a wireless transmitter is a handy way to monitor the temperature in the root cellar. Plug the vents, partially or completely, if the weather's getting too cold.

I'm going to be using a timer outlet to run an in-duct fan on the vent at night - with the addition of an thermostat to shut off the fan before everything is frozen solid. (Inkbird ITC-308.) With the fan, timer and thermostat, I think I should be able to keep the place at ideal temperature well into April and probably even May, given our cool nighttime temperatures. It's a little too high-tech for my liking, but should keep us in root vegetables until we're planting next year's crop. If it works well, I'll have a 12 x 14 foot refrigerator for a microscopic fraction of the electric bill that would otherwise require.

(I THINK you could use two of the Inkbird thermostats in series, to run the fan anytime it's cooler outside than in the root cellar, but I can trust overnight cool temperatures, and already have the timer.)
 
Steve Sherman
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Interesting data point Chad. I wonder why 4" was enough for Mark but not so in your location. Perhaps subtle details on the thermal siphon your vents setup or don't.

I actually just installed a wireless temp sensor for the root cellar (had to find one that had the temp probe remote from the transmitter as there is no reception with the transmitter underground in the cellar. It will be handy for following the temp changes.

I think what you are looking for is a differential thermostat. Similar to the ones used in solar hot water systems (but setup for cooling rather than heating). A differential thermostat has 2 temp sensors, and will turn something on (say a vent fan or open a vent closure) when there is sufficient difference in temp between the two sensors and when the main sensor is not at a good temp (too warm say for a cooling one). If the main sensor is cold enough or if the outside isn't cool enough to make a difference then it does not turn on the fan/vent. These are a bit more sophisticated than just wiring in two regular thermostats, and should help with only running your fan or opening your vents when it will really so some good.
 
Roberto pokachinni
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two different people I know open their cellars up (with a screen door to keep critters out), to let cold night air in, when (or before) storage begins to get the temperature down.  I was thinking of having a couple large vents in the ceiling to do the same thing.  These would be closed off with insulated shutters when the proper temp was reached; after that the smaller vent tubes would be the only ventilation.
 
Brett Hammond
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The area of the opening in a 4 inch pipe (12.6 sq in) is almost twice the area of a 3 inch pipe (7 sq in) so I suspect 3 inch or smaller pipe will be much too small. Also, the additional drag of the disproportionally larger walls of the smaller pile (as compared to the volume) will further reduce airflow, but don't know the math on that. I am not sure what affect the "chimney effect" will have on a smaller pipe.

Square inch area of a circle is 3.14 x R x R (where R is half the pipe diameter in inches).

3.14 x 2 x 2 = 12.6 for a 4 inch pipe.

Cubic inch volume of a pipe is area x length in inches.

I wish I had a root cellar. Best of luck! 😀

UPDATE: I just noticed you said the area of your cellar is 1/3 the size, so please disregard my comment. 😀
 
Steve Sherman
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Roberto, I too know people who open their cellars up prior to get them cool more quickly. It seems to depend on two things:

First that it is cold enough in your location outside to be able to significantly lower the temp of your cellar. In some places it is just not cool enough yet outside at harvest time.

Second thing is that your openings are sufficiently large and at the right locations to allow good air exchange. If not, then I have seen a small fan used to create the necessary air movement and cool things off at night, like what Chad mentions above. I plan on doing this because my cellar door does not open to the outside.

I would be concerned that two ceiling vents, even if they were good sized may not move the air all through your cellar. If your regular vents are positioned one high and one low, then you might do better using a fan for a short time to bring the temps down at the start.
 
ronie dee
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I would rather have my vent too big and have to reduce it than make it too small and have to increase it.
 
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