Basement Dehumidifier in Winter

[Vic99]

Got a basement dehumidifier in June to deal with mold growth in my unfinished fieldstone basement.  Seems to be working well.  I'm almost done with the long process of spraying down surfaces with bleach to kill mold.  I realize I probably won't get it all, but am trying to be thorough.  I've also caulked holes in the foundation that I suspect would let moisture in.

1. At what level should I set the dehumidifier's humidity level to prevent or at least greatly reduce more mold growth?  I'm currently using a 60% humidity setting, but the dehumidifier is running ~80% of the time and I'd like to cut my electricity consumption . . . but if I had to choose between reduction of electricity and no mold growth would rather be mold free so I can both store stuff and put the cat litter box down there.

2. Will I have to run the dehumidifier in the winter?  I do not heat the basement. 
before buying the dehumidifier, I have measured temp around 55 degrees.  I heat the whole living space above with a wood stove on the first floor and have natural gas back up.

Thanks.

[BikeFanatic]

I am also interested in this answer. I suppose you heat the basement enough so the pipes don’t burst, I live in similar climate and have gas heat. Keep house at 55 when not home and keeps basement warm due to the furnace working I guess.

[BudgetSlasher]

I keep our basement at 50%. We use our basement for a lot of things (spend considerable time there) so it is probably lower than it would need to be for simply a basement that you don't want musky/moldy.

Our dehumidifier works less and less as winter settles in and often doesn't run at all in the dead of winter when everything is frozen up.

Based on our dehumidifier run time (and other factors, such as inadequate hot water supply) we switched to 80 gallon heat pump water heater running in heat pump only mode. Dehumidification is a by-product of these, though only when they are running and so a dehumidifier is still needed.

Do you know where you humidity is coming from? Is there humid air infiltration, is there a liquid water leak, or is it vapor migration through the concrete. 

[Vic99]

BugetSlasher said: Do you know where you humidity is coming from? Is there humid air infiltration, is there a liquid water leak, or is it vapor migration through the concrete.

I think that it could be wicking up through the concrete floor, but sometimes I find large holes in the foundation that I caulk.  I do not have a musty smell any more.

[Sibley]

Aim for 40-50% RH. Depending on your location, this may be a seasonal problem. I have to add humidity in the winter for example.

Oh, and I'm really sorry to tell you this when you're almost done, but bleach isn't the best product to use to kill mold. It'll get some sure, but more likely it'll just bleach it out but not actually kill it. Or the spores. Get concrobium instead.

[big_owl]

I used to keep mine at 50% in the summer.  My basement came from the builder with some foil-backed insulation on the walls and the HVAC system had 2 small vents in the basement to "condition" it.  In the winter I never needed the dehumidifier (mid-atlantic).  The dehumidifier ran from June-October though.

Then we finished the basement and insulated it properly and I never have to run the dehumidifier anymore in the summer, even though it only has the same small two vents conditioning it.  In fact I was recently going to give my dehumidifier away and tried running it a while back but it seems to have leaked all its refrigerant...now it's just a brick.

[Car Jack]

Can you circulate air from where the wood stove is into the basement?  The stove will pull a ton of moisture out of the air.  I've heated with wood for decades and the problem is that the air is so dry that you have to add a tone of moisture to keep it comfortable.  If you can get this circulation going, you won't need a dehumidifier during the winter.

[Agg97]

Got a basement dehumidifier in June to deal with mold growth in my unfinished fieldstone basement.  Seems to be working well.  I'm almost done with the long process of spraying down surfaces with bleach to kill mold.  I realize I probably won't get it all, but am trying to be thorough.  I've also caulked holes in the foundation that I suspect would let moisture in.

1. At what level should I set the dehumidifier's humidity level to prevent or at least greatly reduce more mold growth?  I'm currently using a 60% humidity setting, but the dehumidifier is running ~80% of the time and I'd like to cut my electricity consumption . . . but if I had to choose between reduction of electricity and no mold growth would rather be mold free so I can both store stuff and put the cat litter box down there.

2. Will I have to run the dehumidifier in the winter?  I do not heat the basement. 
before buying the dehumidifier, I have measured temp around 55 degrees.  I heat the whole living space above with a wood stove on the first floor and have natural gas back up.

Thanks.

1.  There was a study done in the 80s that concluded keeping the indoor relative humidity in the 30-60% at all times of the year.  It's the best compromise of the pollutants involved, and is the standard in the HVAC design industry.  See graphic:  https://www.sylvane.com/blog/wp-content/uploads/2017/05/ideal-humidity-levels-chart.png.  Can't find the source for the study off-hand.  A typical design would be capable of reducing the indoor air to 50% relative humidity at all times, to give some excess capacity (buffer).  If you have a way to verify the humidity is indeed 60%, you can leave it set at 60%. 

2.  As long as it stays in the 30-60% range, you're good.  I don't see the harm in leaving your setting at 60% year-round since it sounds like your dehumidifier is either on or off. 

-Agg97

edit: found the study.  E.M. Sterling, A. Arundel, and T.D. Sterling, Criteria for Human Exposure to Humidity in Occupied Buildings (ASHRAE Transactions, 1985), Vol. 91, Part 1.  Study Link:  http://sterlingiaq.com/photos/1044922973.pdf

[GuitarStv]

If you have forced air heating, you shouldn't need a dehumidifier during the winter.  The forced air tends to dry things out quite a lot.  Our basement is usually in the low single digits for humidity in the winter.  We actually started running a whole house humidifier for that reason.

Do you have water issues (leaks/liquid running down the walls) or something?

[Vic99]

I have forced hot water heating, not air.  Heat doesn't circulate purposefully in the basement because there are no baseboards and the pipes are mostly insulated with a foam jacket.  Obviously some heat gets there . .  I use the natural gas source as a back up or supplement maybe 10% of the time.

The woodstove heat won't directly reach the basement directly.

I have to imagine that the moisture comes in from between the cemented joints in the fieldstone.  The house is 99 years old.  I caulk when I see a hole, but I'm sure that doesn't quite do it.

I have what looks like a few irregular wet spot about 2x2 ft on the cement floor.  Doesn't feel wet to the touch though.  I'm wondering if I should cover these somehow.

I'm going to try that concrobium for mold as well.

[Sjalabais]

Our house is only a little over a 50 years old, but the outside drainage is failing. Very hard to do something about that, as it is impossible to get around the house with vehicles. The moisture is pushing salt out of our concrete walls. No mold yet, but we've been at 75% for long stretches of time, so we bought a dehumidifier and it runs constantly. Lowest I have seen is 50%, but I set it 35% just to keep it running permanently. Energy cost at 200W (or 400W in "turbo" setting) are entirely negligable.