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Community and Q&A

Old, empty house — preventing mold

Sue Park | Posted in Energy Efficiency and Durability on

I have a small, old house in Transilvania (Romania) that is empty. The windows do not close well,
and the house has two very old masonry heaters w. gas that are extremely inefficient. The house will stay “as is” until spring time. The climate is quite cold, outdoor RH usually varies between 65-95%. Temperatures vary between 50 to -13 F. The total surface of the house is 65 sq m (around 585 sq ft). A friend is airing the house once a week. The pipes have been emptied, the water is shut down. The 2 masonry heaters cannot be used unless someone goes there at least twice a day to fire them up and then turn off the gas. Trying to heat the house w. them is also very expensive.

I am trying to figure out what my best options are to minimize spending while preventing mold. I considered maybe keeping all doors open and buying a dehumidifier with a thermostat and/or a radiator w. a thermostat. But there are so many variables that I do not know what to consider as a safe option that can run without supervision and that will not cost an arm and a leg. If I buy a dehumidifier, I do not know if it will prevent mold and if I have to stop having the house aired periodically.

Any advise will be appreciated.

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  1. GBA Editor
    Martin Holladay | | #1

    One option is to do nothing. Simply close the doors and windows, and then air out the house when you return in the spring. There is a small chance that there will be a few spots of mold, but it may simply be easier to clean the mold in the spring than to worry about the house all winter long. (This is the traditional approach used for seasonal houses; it's an approach that has worked for hundreds of years.)

    If you decide to install a dehumidifier, you don't want to open the windows. Just keep the house sealed up.

    In the long run, if this problem continues to trouble you, you might consider installing a modern heating system and repairing the air leaks in the windows. If you did that, you might be able to keep the house at 45 degrees F or 50 degrees F all winter long. Needless to say, that approach would be more expensive than doing nothing.

  2. Jon R | | #2

    I'd let it go (no airing out) but have someone check for mold odor now and then during warmer weather. If there is a problem, then you can add a dehumidifier.

    Would be interesting to see discussion of the use of ozone as a more energy efficient method of mold prevention in unoccupied buildings. Say timed release also based on temperature and humidity (ie, only as necessary).

  3. Sue Park | | #3

    Thank you very much for the quick and helpful answers. I am very happy if I do not have to do anything, just have someone check from time to time, but not even air the house. This house is in real bad shape, so if I can avoid spending money with it until I can sell it in the spring, would be great.

    If the temperature outdoors is very cold for longer stretches (goes well below freezing), will it make a difference (from the perspective of mold)? Should I keep all interior doors opened or closed? What is the outdoor temperature (in the spring) when it's better to leave a window open all the time ? Is it better to just open windows periodically or to leave a window open? Thanks again.

  4. GBA Editor
    Martin Holladay | | #4

    Mold does not grow when the temperature is cold. Mold grows when the temperature is warm and conditions are humid.

    As I advised, leave the windows closed for the winter. If the house is occupied in the spring or summer, you can open some windows at that time if you want. You should leave interior doors open.

    If your plan is to sell the house in the spring, don't do anything until you're ready to put the house on the market. At that time, give the house a thorough cleaning.

  5. Sue Park | | #5

    Thanks again for taking the time on a weekend to help. Very much appreciated, I will follow advice.

  6. Sue Park | | #6

    One more question, if you do not mind - when you have the time. If by chance a dehumidifier would be needed (the house starts to smell like mold), what "parameters" should the unit have (such as L/kwh, pints/day, etc.) for the 585 sqft not heated house for the winter?

  7. GBA Editor
    Martin Holladay | | #7

    Almost any type of dehumidifier will work -- around 50 pints per day (about 20 liters a day) is fine. If no one is at the house to empty the bucket, you'll need to connect the dehumidifier to a drain.

  8. Sue Park | | #8

    Thanks for the all the expert advice. I hope there will be no need for a dehumidifier, but I am prepared.


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