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How To Manage Moisture In The Humid Southeast

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The Struggle is Real

We’re here today with Nikki Krueger, a Building Science & Business Development Manager from Santa Fe Dehumidifiers. We love talking to Nikki, she’s been a go-to resource for the deep dives into ventilation and dehumidification, particularly here in the Southeast for high-performance homes! 

Moisture management issues in high-performance homes

Our buildings are getting tighter which is great for energy efficiency and comfortability, but in the humid Southeast, we also need to manage for moisture.  If you are building tight, ventilating right, but recently experiencing humidity or moisture issues — this blog is for you!

It used to be that when a dehumidifier was needed it meant someone did something wrong, but the reality is that it’s inevitable in the Southeast. If you’re building a tight envelope, bringing in mechanical ventilation to keep homeowners healthy, and sizing the HVAC system correctly, you are doing everything right — almost. Having a strategy dedicated to moisture management is the next level up to truly be a high performance builder in our humid climate zone.

Checkout the full Podcast Interview with Nikki!

The Warning Flag: Condensation

How do you know if you have a moisture management issue?  Condensation is the most obvious sign that there is a problem — either too much water in your air or you are overcooling an area. 

Where do we see it?

  1. Vented Crawl Spaces:  We see a ton of condensation here because air does not simply come in one vent and automatically go out the other. — Stay tuned for another segment on vented crawl spaces and how they’re always going to be a challenge — (“I don’t like them, they’re always a risk,” wise words from Jamie).
  2. Basements: These are also always going to be a challenging spot because any time you’re going down into the ground, you’re going to have vapor pressure and because it is cooler, not a lot of need for air conditioning. Cool surfaces + moisture laden air = condensation.
  3. Whole House: Leaky homes let that humid, southern air sneak in wherever it can, creating moisture issues in all kinds of places. Tightening up the house gives us control over where air gets in and out — but also means less run time on our air conditioners –great for energy efficiency, but not so great for managing humidity.
Vapor moisture from cooking
Occupant lifestyle habits can contribute to moisture management issues

“But I don’t actually see any condensation!”

You might have a mold issue and not even see condensation! High relative humidity in a house means there is not only moisture in the air, but we are also moisture loading the home’s materials.  This means all of the materials in the house — like furniture, drywall, wood, that spray foamed attic — are absorbing moisture and can be wet enough to support microbial growth.  So you may actually end up with microbial issues because of high relative humidity, even if you don’t see it. 

It’s also a lifestyle thing — we all breathe, cook, take a bath. A builder can do absolutely everything correctly and there are still a lot of little components that add to the relative humidity.

Digital hygrometer measuring humidity
Digital Hygrometer, Image courtesy of Hideya HAMANO

Monitoring is Key

Monitoring is how you will know if you have high relative humidity. Some thermostats do measure relative humidity – but sensors throughout the home are the way to go. Typically, you don’t want a homeowner going out and just buying the cheapest thing because those sensors can be way off. So look into a good monitoring system and make that part of your package. As a homeowner, having a builder say, “We care about your indoor quality. We care about your comfort. We’re going to monitor,” says a lot.

What is relative humidity? Relative humidity (RH) measures water vapor RELATIVE to the temperature of the air. For health and comfort, the recommended RH for 72F is 55%.

Managing Moisture: Ventilation, Filtration & Humidity Control

These are the holy grail for controlling moisture. Ventilation and filtration provide the health aspect while dehumidification not only provides the health, but you also get the comfort, sustainability, durability, as well as the reputation and liability protection that goes along with those.

  1. Control your thermal envelope
  2. Bring in new air for indoor health
  3. Manage the moisture
Matt, building performance expert, from Southern Energy Management holding sill seal and foam gasketing material on site for wall top air sealing
Check out our resources on air sealing strategies!

Dehumidification is a strategy you NEED to have a plan for

Air leakage is the number one contributor to humidity so tighten up that building envelope and control where you are exhausting and supplying air. We know that if we can control the way air comes in and out of the house, then we’ve got a better chance of creating a healthier environment by being able to manage the moisture in that air. 

Pro Tip: Variable Speed AC Systems Need Support

What’s important to understand about variable speed is that even with the ability to ramp down, it’s still going to be trying to go towards the temperature more than anything. So you’re not necessarily getting better dehumidification with that system. A tight, well insulated building envelope maintains air temperature for long periods of time, meaning less run time for your air conditioning system — saving folks energy and money, but not managing the moisture.

Tighter buildings also leak less air, meaning all the moisture generated inside by people breathing, bathing, cleaning, washing, cooking, etc… is trapped in the building.  Providing consistent dehumidification and ventilation is no longer the job for the heating and cooling system in a high performance home.

Ventilating the Right Way

In a humid climate, exhaust should not be the ventilation strategy.

It can be the most economical, but it’s the most risky. Some of our leading organizations that determine our ventilation practices are even looking at not allowing different types of ventilation strategies in certain climate zones. 

What we worry about is negative pressure. When we are constantly exhausting out of the house, what we’re relying on is that the air finds its way in some other way. And because we’re sealing everything up really well, it’s going to find the path of least resistance. We don’t always know what the path of least resistance is, which means you could literally be pulling humid air in by accident. 

Adding Positive Pressure

We have so much negative pressure because of things like our bath fans, kitchen hoods, and dryers. It’s important that we try to get a little bit of positive pressure in there. As we bring in fresh air for the occupants, we want to control it and pay attention to what it’s doing to the rest of the house. If we are truly ventilating for the health of the people inside, we don’t ventilate based on conditions outside.

Pro Tip: Balancing Pressure

Typically in the Southeast, a slight positive pressure is what we go for. If you do balanced ventilation (an ERV), then add a dehumidifier for the entire house. ERV’s are not designed to manage humidity, especially in our climate. If for some reason you cannot do a whole house dehumidifier, we recommend at least one for the basement / underneath the house. If you can just get a good handle on controlling that moisture and then monitoring the rest of the house, that’s a great place to start.

Integrating a Ventilating Dehumidifier

Ventilating dehumidifiers tackle the job the A/C can’t do — provide fresh, dry air for the people and the home all year round. For a deep dive, check out the full podcast of Jamie and Nikki’s conversation at the top of the page! 

Here are a few pointers to get started:

  • Provide a dedicated return from the house directly to the ventilating dehumidifier.
  • When connecting to your HVAC System – tie it to the supply side.  If you tie the dehumidifier to the return side, you risk picking up moisture from the a/c coils and reintroducing that moisture right back into the house. This is a common mistake often made by contractors new to integrating dehumidification equipment. 
  • Add a backdraft damper where the dehumidifier connects to the supply side of the HVAC system. This prevents the air from coming back through the dehumidifier when the AC is running. 
A properly set up dehumidifier
A properly set up dehumidification system

In Summary...

Planning for dehumidification and ventilation strategies early in the project will help to ensure moisture is managed to create healthy, comfortable, and durable homes. Proper air sealing and adding in dehumidifiers are a few ways to mitigate the indoor humidity problems we often see in the Southeast. HVAC sizing is also important to make sure that the selected equipment is capable of maintaining comfortable humidity levels. As experts in efficiency and building performance, we’re always excited to educate and help builders and homeowners get the most out of their homes.

Still have questions about this strategy? Give us a call or schedule a meeting! We’d be happy to help you get on track. 

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