Root cellar update: ventilation and humidity

Overall, I am very pleased with the root cellar I built last spring.  It’s keeping temperature well, not showing signs of mold or infestation, and most of the produce is in very good shape.  I have learned a few things and made some changes from the original design, though, and I’ve got some good preliminary data on which arrangement of bins is working best for me.

Outside paneling
With paneling
Insulation up
Without paneling

First, I had to take the paneling off the outside of the cellar before I even put food in it.  This was pressed-wood-fiber type paneling, got cheap at the re-use center.  It was pretty, but even though I took great pains to keep it from touching the floor or walls, it started absorbing moisture and got very moldy very fast.  I pulled it off and didn’t replace it with anything, so the outside wall of the cellar is bare studs and you can see through to the rigid foam insulation.  While my aesthetic side is sad, it doesn’t change the functionality at all, and I really want to avoid starting a mold farm in the basement.

Root cellar ventilation pipes
I've abandoned this ventilation system. Instead, I just let air flow through the holes where the pipes were, or open the window completely.

Second, I’ve abandoned the complicated ventilation system.  It wasn’t letting the cellar cool down enough in the early fall – we’d have a 35 degree night and the temp would only drop from 60 to 58.  Not nearly good enough.  I ended up just opening and closing the window as needed.  That worked really well until about mid-December.  Then I got to a point where having the window open was too cold but leaving it closed was too warm. (The cellar holds around 40 with no ventilation.)  So I took the window out completely and put the board back into the window. (There’s a screen to keep critters out.) This board is about 4″ narrower than the window frame (it had held the vent pipes in place) so it effectively closes off 85% of the window but left it open a bit for some air to get in and out.  I can leave it like that night and day unless we have a series of lows near zero and highs below 15F – then I need to put the window back in or it gets too cold in the cellar.

This hasn’t been much trouble at all.  I have a thermometer with a remote sensor on the kitchen counter, so I can see the temp in the root cellar many times a day as I’m passing by.  This has let me learn its patterns.  For example, I now know that if it’s going to be cold many days in a row, I need to close the window up completely.  It’s a 5-minute chore to open the window, or to swap the window and the ventilated board, so no big deal there.

Third, humidity.  I can’t seem to get the humidity in the room to stay above 50% now that winter has set in, even with bins of damp sand on the floor, so instead I’m trying to keep the local humidity around the produce high.  I’m ok with this – it seems to be working fine, except maybe for beets, and I’ve definitely not had trouble with mold on the walls.  My only concern is that the methods I describe below won’t keep things moist for the whole winter.  I’ll report back in April on that one.

The information on the bins is quite extensive – I’ll post that separately tomorrow.

Published by Emily

I'm an instructional designer and gardener based in Ann Arbor, Michigan. Free moments find me in my garden or the forest, hugging trees and all that jazz.

7 thoughts on “Root cellar update: ventilation and humidity

  1. I just finished building a computer-controlled ventilation system for my parent’s root cellar. It monitors temperature and humidity and opens and closes vents automatically as needed. It also turns on a ventilation fan to quickly cool the cellar down, and includes a humidifier to maintain proper humidity. If the temperature in the cellar drops too low, it turns on a light to raise the temperature.

    If you’re serious about root cellaring and get tired of policing root cellar conditions yourself, you may want to consider building a system like this…it was rather easy to do, though I guess I am kind of a geek. I’m not much of a gardener, but I have enjoyed designing a system that allows my parents to more fully enjoy the fresh produce they grow and love so much.

    1. Wow! That’s really impressive. My concern, as always, is that I want to be building systems that will work when the power is out, and anything the computer is doing is something I’m not learning how to do for myself. I have been sorely tempted to install a fan, though, I admit!

  2. I’ve been tempted to install a fan, also. Just as you said, getting it to cool down in the fall is difficult, even when the nights are cold. I wonder if there’s a way to cause the pipe from outside to suck air in (like a siphon)? Hmmm. I have been thinking of pulling out the 2 liter bottles that we always keep in the freezer and placing them around the room in the fall. (Think pond ice in the future.) I’m also struggling with humidity. I just had a thought, tho: I have a sump which drains a gravel field under the house. What if I actually did siphon the sump water through the root cellar, into a shallow container with holes at the top (to overflow to the drain that’s in the floor) — leaving the water in the container to evaporate… Hmmm….

  3. Well, I’m all new to this and I prefer not to struggle if at all possible. I was thinking about building a root cellar under my deck. It’s 2 feet off the ground and I would dig down 9 or 10 feet. I was thinking about cinder blocks for the walls and painting them with some type of paint to avoid the moisture being trapped in the pores giving mold a solid starting point. I’m not sure if that will be good of bad . Cinder blocks have a natural insulating value due to the dead air space. I’m concerned that the paint may trap excess heat or moisture in and backfire on me.

    I then want to dome the roof. I read somewhere it helped keep condensation from clinging to the ceiling and dropping on your produce. Instead it follows the ceiling to the walls where it runs down to the floor.

    ANY input would be appreciated.

    1. My basement is painted with Killz paint – don’t see why yours would suffer if you paint it. A dome sounds hard and expensive to build – a sloped roof would be easier and achieve the same thing. Though really, you shouldn’t *have* any condensation if you’ve got enough air flow.

      Digging 10 feet down under a deck sounds really tough. Will you just take some boards off for better access while you dig? How will you access the cellar when it’s done? Do you need to be under the deck at all?

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