The amount of moisture air can hold increases with temperature. Outside air at 32F, holding 3.78 g of water/kg air has 90% humidity (because it can only hold 4.2 g/kg at this temperature). Inside air at 75F holding the same 3.78 g/kg has 20% humidity (because it can hold 18.63 g/kg at this temperature).
take a look at this calculator: https://www.lenntech.com/calculators/humidity/relative-humidity.htm
What this means is your moisture is not coming from outside in the wintertime, but building up inside while not being allowed to escape. You'll actually be better off in this situation if you increase the amount of outside air getting into your house.
Is this new construction? Vapor barriers, door seals, caulking and new windows have all combined to reduce leakage of air from inside homes to outside homes. This is great for energy efficiency, but if your house can't "breathe" to the outside air, it can't lose moisture to the outside.
Other than the large moisture loads you said you don't have, where is moisture coming from? Mostly the occupants. Attached is a table of moisture generation for different size houses. The chart assumes two people for the first bedroom, and an additional person for each additional room.
Here is a more in-depth discussion: https://www.fpl.fs.fed.us/documnts/pdf2001/tenwo01c.pdf
So....you want to crack a window.
If you go back to the calculator, you'll see potential problems during shoulder seasons - spring/fall. For example, if it's 59F outside with 90% relative humidity, bring it inside and heat it up to 75F, you'll have 51.7% humidity.
You raise some interesting points. If I maintained the house at a higher temperature in spring/fall/winter, it could reduce my relative humidity. E.g. on a 65F spring day like today with 90% relative humidity outside, I would turn on the heat to raise the temperature from 68F to 72F, reducing relative humidity from 77% to 60% per the calculator. I could NOT use my thermostat's scheduling function and would instead keep the house warm full-time.
At some point above that level, I'd run the AC to cool and dehumidify. So there would rarely be a point in time when either the heat or the AC is not running, and maybe both in the same day. However, if incurring that cost means not buying a dehumidifier, it might be cheaper in the long run.
It's not a recent construction, and in fact we've been finding and patching huge air leaks for years. I wonder if the complete lack of wall insulation, combined with not running the HVAC very much, creates cold spots near the walls on the floor where moisture can condense. That is where most issues have occurred.
I don't think the refrigerator would do enough to be noticeable. But I also don't think a floor-standing dehumidifier should cost more than about $200.
So far $229 is the lowest price found for a 50 pint model like I would need. With tax that would be over 250.
https://www.homedepot.com/p/Frigidaire-High-Humidity-50-Pint-Capacity-Dehumidifier-FFAD5033W1/312546305?MERCH=REC-_-pipinstock-_-310365942-_-312546305-_-N#product-overviewIn conjunction with the calculations above, I wonder if it would be more economical to run the 545-watt dehumidifier or the whole-house 13-SEER heat pump to keep the house maybe 4 degrees warmer (72 instead of 68) when it's not summer. The rule of thumb is costs increase 3% for every one degree of change. So for a 4 degree change as in the example, the heating portion of my electric bill might go up 12%. That might amount to $5 or $10 a month on average, which is probably less than the dehumidifier.
The flip occurs when it starts getting hot, and we have 95+F days with 80-90% humidity. The calculator says my indoor humidity would be 377% at 72 degrees, not including the effects of the AC removing water from the air of course :)
As we can see, there's a gap between the weather where I could run heat to raise the water carrying capacity of the air, and weather where I could run AC to remove water from the air. E.g. on a day when it's 72 outside and 75% humidity, neither the heat nor the AC is going to drop my indoor humidity below potentially dangerous levels. I could narrow that gap by using the heat below 72 and the AC above 72, but I don't know if I'll ever eliminate it because the heat and AC would cut off after a short time. Perhaps this gap is where the dehumidifier would be necessary?
I have two large open rooms in my basement. I bought two 50 pint dehumidifiers. Drain one into a floor drain and one into the french drain system and now my humidity never goes above 45% (it used to get up to 70%). FYI- they say they are rated for 3,000 sqft but I'd imagine that would only work in a 3,000 sqft space with no walls. Sucks to have to pay for extra electricity but wayyyy better than dealing with mold remediation.
@GoCubsGo how much higher is your electric bill since you installed the dehumidifiers? Sounds like you're doing twice or three times the capacity I'd need, since I'm not in a basement and I'm looking at doing only one 50 pint unit.
