Well water/ pump room convert into passive cellar?

Hi — I’m new to the forum and have really enjoyed reading everyone’s posts. Wealth of info here! So, without further ado, here’s my situation:

I ran out of room in my wine fridge and am temporarily storing overflow in my heated garage — temperature 55 degrees +/-. I live in NY, Hudson Valley and the garage will be too warm in the summer.

I can either invest in another fridge or I can modify my well room into a passive cellar which would be optimum.

The well room (concrete block walls, no windows) runs the length of my finished/heated basement. It shares an insulated wall with the basement and has a door into it from the basement. The other three walls are underground and are outside the footprint of the house’s living space. The ceiling is underneath a concrete slab (old entry to home) that is now hidden by a large deck / covered porch.

The temperature in the well room was just over 40 degrees all winter —humidity 65%. Since I wasn’t planning on using this room for wine storage until now, I have no idea what the temperature will be in there during the summer.

I can add a small heating unit with a thermostat that should keep winter temps at 55 degrees. In the summer —if needed— I can add a portable AC unit. I am also thinking of insulating the ceiling with 100% wool which supposedly helps regulate humidity — it absorbs water when humidity is too high and releases water back into the air when humidity is too low.

Since I’m only interested in short term storage (no longer than a year after purchase) I’m inclined to just ‘go for it’ and move all of my wine into the well room, and heat/cool/humidify/dehumidify as best as I can manage.

Million dollar question: what’s the worst that could happen?

I read Gold’s book and have searched for answers on converting a well room like mine into a passive wine cellar — but found nothing conclusive so far.

Thoughts and advice would be much appreciated.

Sounds like it should be fine.

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Am sure others on here are more knowledgeable than I am, but as I created a passive cellar, can share what I did when building it out.

RE: What’s the worst that could happen - temperature rises and drops rapidly that can impact the wine or too much moisture could create mold.

I converted part of an under-house garage into a passive cellar where the top 2 ft of the walls are above ground. Goal was to insulate as heavily as possible inside on top and sides and just let the floor be the passive manager without adding any heating/cooling electrics.

Outside, I dug down 4ft, then inserted a sheet of R-10 rigid insulation & backfilled w/ soil. Inside, for top part of wall which was wood, I had R-20 batt, topped w/ R-10 rigid and then added another layer from floor to ceiling of R-10 rigid (so top portion has 3x layers, concrete wall portion has 1x layer) - then I covered everything w/ sheetrock. Ceiling had R-20 batts & covered w/ sheetrock. Door to space has weather strip type insulation around door to seal.

Am located in Seattle and in winter we get down to 18 and in summer can get over 90 and touch 100 once in awhile. Wine room temps range from a low of 48 in winter in the winter to a high of 63 in the summer and all changes are very gradual over a period of days, so no sudden temperature jumps.

Because all your walls are underground, shouldn’t need to do anything outside. Inside, you may want to consider using rigid foam insulation on the walls/ceiling. This could help the temps in your space w/o having to get heating or a/c.

Hope that helps.

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Hope so! Thank you for the encouragement.

We have similar temps here – brutal cold snaps and 100’s on occasion. Insulating as you suggested should really help. Thank you!

If I had a passive cellar, I’d be concerned if the wines could potentially freeze or go over low 70°s (at which point, I might introduce some sort of cooling). If I used that for overflow and put in daily drinkers, I might not do anything.


Completely understand apprehension around passive cellars which is why I went with as much insulation as possible. I believe wine can freeze if exposed to temps of 15F to 20F for some time (not sure if that’s X hours or what). While we can get those temps outside here in Seattle, my passive wine space has never gotten that cold.

I suppose it all depends on where you live and what the temperature ranges are. Not sure I’d do a passive cellar in Alaska or Phoenix, AZ, but here in the PNW it seems to work well.

Depending on how big the space is, passive cellars with minimal active cooling can be just fine.

@MChang - what app do you use for temp monitoring?


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So to update and elaborate a bit: the space is a bit over 4’ wide and 20’ long with 7.5’ ceiling height. My well pump pressure tank and water feed pipes to my house are at one end, wine storage will be at opposite end. The room has never gotten below 38-40 degrees.

As an experiment I put an oil filled radiator / heater in there (temporary solution) and set it on the lowest possible setting. Within 24 hours the temp in the room went up to 55 and humidity lowered from 72% to 62%. Two days later the room was still at 55 and is holding.

Outside temps have been all over the place this winter in NY, but averaging around 25 at night and low 40’s during the day. But I’m pretty confident I can properly regulate the room temperature during the winter no matter the outside temps . I will install a more sophisticated /efficient heating unit with a thermostat and plan to insulate ceiling this week.

Summer remains to be seen. I’m probably going to need to cool the room at some point. So far so good though!

Thank you for this! Interesting.

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Mold and power failures are your two most significant risks. Both are easy to resolve

Power: Put anything critical (pumps, etc.) on a SINE-WAVE-based UPS; You can get these at any decent computer parts store or Amazon. You want the sine wave, as that is the filtered power. Unfiltered power has spikes (which can be square waves), which will stress the power supplies of the less expensive units you use. We live in an area with an unstable power supply and regular storms - and the UPS/Surge Protectors work overtime. We have had zero issues since making these small investments. Our fridges, freezers, and all computing equipment are on individual units.

Mold: An easy fix here is to keep a shallow tray (several if need be, depending on the size of your “cellar”) full of the cheap white vinegar (aka…acetic acid) that you can buy at Sams/Costco for a few $. This keeps the air acidic and prevents the growth of mold. We keep these above our wine cellars (we have enclosed 500 bottle units), and while the room has a slight “vinegar” smell - that is a LOT better than the mold, which will be present otherwise.

I do have a generator powerful enough to run my whole house, so no problem with power failures.

But I will try the vinegar mold solution you mentioned. Before I insulated the ceiling in the well room (soon to be wine cellar) I did use vinegar to eliminate a light coating of mildew that was growing on the plywood ceiling right above the entry door that the well room shares with my finished basement – the warmer air from the basement was leaking into the well room at the top of the door and created a mold /mildew growth environment there.