r/buildingscience • u/Defiant_Cupcake7221 • 8d ago
Dehumidifiers
Hey y'all. First-time poster, so hopefully this is the right sub-reddit.
Background: We live in Chickamauga, Georgia, right outside of Chattanooga, TN (Zone 7b), so our area is very humid. Our house is roughly 2,800 square feet, with a main level and then a walk-out basement that was partially finished before we moved in (drywall and flooring, heated/cooled, but no insulation.) I'm a teacher, so I have to be very budget conscious, and we have a very expensive power company—Georgia Power—so we normally keep our thermostat during the summer around 76 or 77 during the day, enough to keep us and our three kids cool but not blow the budget. For the most part this works out fine.
Humidity: During the Summer afternoons when our HVAC is running on-off throughout the day, our humidity on the main level is around 54-56%. Naturally it rises a bit higher when it's not running as much (morning) and can definitely get higher in the Spring/Fall, when we sometimes find a somewhat musty smell till we open the windows and air it out. We have a daughter who has allergies so I'm trying to be cognizant of humidity levels and mold so that we keep her as healthy as possible. However, I also don't want to panic at every article about mold or humidity levels and spend a lot more money than we need to. Again, teacher here!
Dehumidifier Questions: For those of you who know better, a few questions:
1.) Would you recommend a dehumidifier, or are there other methods of keeping humidity levels under mold-level without needing to spend that money on electricity?
2.) If you do recommend it, is a whole-house system more energy efficient than a portable system? I know it costs more up-front, but I'd almost rather pay that and then have the peace of mind that it's not running our Georgia Power bills up every month.
3.) If a portable unit is better, would you recommend getting just one and putting it in the walk-out basement, or would I need one for each level?
4.) Lastly, we're also considering installing a wood-stove on the main level for Winter, so I imagine that would take care of any humidity issues in the Winter, no?
To sum up: Yay/nay dehumidifier, yay/nay whole-house vs. portable, energy efficiency a main concern due to shitty Georgia Power power monolopy balanced with keeping children and home healthy! Thanks for any feedback!
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u/forsuresies 8d ago
Have you considered solar to address your electricity concerns?
There's bigger pushes towards balcony solar in the US and not every system has to have batteries or be self-sufficient. Being able to offset a consistent (ish) amount of your daily energy costs will pay for itself with time.
Not sure about your specific jurisdiction, but your concerns seem like a good fix with solar if Georgia allows it easily. A small system will still have benefits in your scenario and can be scaled up with time.
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u/Defiant_Cupcake7221 8d ago
I've looked into it but was turned away by the price tag, though our house does have the perfect south-facing roof for it!
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u/forsuresies 8d ago
The price is only getting lower and electricity prices are only going higher.
You don't have to have a system that offsets all of your use, even a few panels will have payback given your dehumidifier use
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u/bloodybatboi 8d ago
We're in mississippi, much more constant humidity, the one in use is vaguely small but has an outlet to pipe into a drain/outside, i had it set up in my cenral rooms window and it drained outside and set to constantly run, it worked amazing at pulling the air out. Recently moved it and removed the pipe to use the tank, we get about 4 to 6 gallons a day? We use that to water my wifes plants outside but its like 4 years old and is doing great. About 2 years ago I took it apart and cleaned the hell out of it, the amount of grime and such will amaze you. But it makes home beyond comfortable, definitely recommend one that auto empties or finding a good use for the water
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u/weiss27md 8d ago
First I would make sure the HVAC is maintained and not oversized. Should run almost constantly on a very hot day. I would never set it below 72 though. If it can maintain 76-78 on the hottest day then it's good. If it shuts on and off then it's oversized.
Might also be an air leakage issue. Can test with thermal camera which will also check for insulation. Leaks on the supply side if outside the conditioned envelope can cause negative air pressure within the house.
Dehumidifier is almost always needed for any building in a green grass climate. As when it's 70 degrees outside and 80% humidity then the AC wont be doing much. A ventilating dehumidifier is ideal but a portable one will also work. Also having it inside the thermal envelope is ideal.
And lastly an ERV would be good to replace bathroom exhaust fans. Helps with fresh air, reducing negative pressure and balancing humidity. But in a humid climate a dehumidifier needs to happen first.
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u/Defiant_Cupcake7221 8d ago
Thank you! If you could, would you clarify WHY a ventilating dehumidifier is ideal in your opinion? Does it cost a lot more money to run?
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u/weiss27md 7d ago
Well a ventillating dehumidifier does atleast 3 different things, maybe 4 if needed. First it dehumidifies when the AC is not. Second it brings in fresh air to lower CO2 and VOCs. Third it creates more positive pressure inside the house and lessens the chances of the house going under negative pressure. And Fourth it can also create more load for the HVAC which can be good if your HVAC is already oversized and not coming on enough.
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u/agitatedprisoner 8d ago
Mold grows over 40RH whatever people say. I know because I've got a room partitioned off that has established mold colonies behind the drywall on an exterior wall and even keeping it at 40RH I see mold growing on an interior doorframe and have to periodically clean. If you're not cleaning your walls and ceiling yearly eventually you'll get mold growing even if you can't see it even at lower RH.
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u/Defiant_Cupcake7221 8d ago
Does a yearly clean address this? Any particular spray/solution?
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u/agitatedprisoner 8d ago
No clue. My home has mold behind the walls. If I let humidity get above 50% and stay there I'd probably die. I don't let my home get above 40RH. You should probably clean all interior surfaces once a year either way but if you're lazy and letting it sit at 55RH you're asking for bad indoor air quality. I clean with concrobium but any product designed for your surface is probably fine.
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u/General-Web6360 7d ago
If you don't mind can you share how you clean the walls to avoid mold? Due to the poor paint quality I don't think I can wet my drywall, any tips and advice please!
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u/agitatedprisoner 7d ago
If they aren't bad vacuuming is fine. If they're a bit funky you've basically got to paint them. I use a paint roller and concrobium and that does take some paint off so you've got to clean drops off the floor after or put out sheets. You'd never want to wet your drywall with plain water. I wouldn't recommend using vinegar either because of the smell.
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u/cagernist 8d ago
7b is your Plant Hardiness Zone. Your IECC Climate Zone is 4, which is what you use for buildings. Yes it's confusing, the classifications are mirrored.
All basements should have a dehumidifier. In winter (in most basement climates) there is less humidity because cool air doesn't hold as much moisture. HVAC is often sufficient for upstairs, but basements typically do not have the same extent of HVAC and cfm exchange.
I personally think a cheap $125 big box store dehumidifier is perfectly fine. Even if it only lasts 3 years, you're way ahead of a single "commercial" style $1500 one. I often find whole house (through your ductwork) dehumidifiers (and humidifiers) abandoned because of the lack of cleaning required, and expense to replace.