It’s early May, and dew points are rising. It won’t be long before each morning, everything outside will be covered with southern dew!
You’re battling the 2nd Law of Thermodynamics. I always tell our clients, “You don’t have NASA’s budget, and I’m not wearing a NASA uniform. We’re going to use common sense to manage this.”
The 2nd Law of Thermodynamics teaches us two fundamental laws:
- Hot always moves to Cold.
- Wet always moves to Dry.
To get a handle on high (uncomfortable) levels of humidity inside your home, we need to discuss where it comes from, what the ideal range is, and how to manage it.
Sources of moisture inside your home, as a result of Stack Effect.
Stack Effect is the movement of air into and out of a building, due to difference in pressure. Its greater in winter, because the temperature difference between your living space and the outdoor environment is greatest. Also, the taller the building, the stronger the stack effect. It’s so strong in high-rise buildings, they use revolving doors at the street. If they didn’t, the stack effect would suck the doors closed!
Comfortable ranges for humidity are in the mid 40% territory. Dryer air creates conditions for static electricity, dry, cracked lips, and dry noses. Higher than 50% RH and the room begins to feel muggy, and AC performance feels less effective.
My Success Formula for many thousands of Atlanta homes
For over 18 years, I’ve had great success sealing houses, by following this formula: Start with the horizontal surfaces, and move to the vertical surfaces. Of the horizontal surfaces, start at the lowest floor.
If your home is on a crawlspace, that is a prime source of huge amounts of moisture drawn upward into your living space. This damp air is loaded with unhealthy trespassers you don’t want to be breathing, 24-7. Remedy: Seal your floor. Use expanding foam to seal every wire, pipe, or HVAC penetration, and seal the large openings under your bathtubs. Seal any framing gaps, voids, and chases. Inspect any HVAC ducts too, while you’re under there.
Some of our homeowners choose to seal & insulate the crawlspace, using spray polyurethane foam to insulate the foundation walls, and a heavy, sealed, poly liner over the dirt. “Closing up” a crawlspace rewards you with dryer, warmer floors, dramatically improved Indoor Air Quality inside your home, and protects your HVAC system from a (shorter) lifetime of damp, unhealthy environmental conditions!
Are you on a basement? The same principle applies as crawlspaces, only you are sealing the basement perimeter walls, and the rim joist. If you don’t have plans to condition your basement, go ahead and treat your over-head floor like it’s on a crawlspace: Seal it.
Now we move to the uppermost horizontal surface: your attic floor(s). You have two basic options here:
- Using expanding foam, seal the penetrations, gaps, voids, and chases like you did in the crawlspace. To safely access all of these points, you’ll have to either remove the current insulation, or rake it around, and restore it when finished. Note: There are many more penetrations to seal in the attic, than the subfloor. See those light fixtures in every room’s ceiling? Do your exhaust fans have working dampers? Seal the ¼ mile or so of top plates too! A top plate is the framing gap where interior walls meet the ceiling. (You’ve got lots of those).
- Or, seal the rooflines using Spray Polyurethane Foam. This protocol seals your attic, and insulates the area too. It’s best to remove the old existing insulation. Think of turning your attic into an insulated, sealed Tupperware!
Sealing the lower and upper horizontal planes in your house will dramatically slow the Stack Effect from drawing moisture into your home.
Take a look at your vertical surfaces. These are the perimeter walls. Windows and doors are the obvious points to inspect. If you’re still using single pane, double sash windows, it’s a good idea to start saving to replace them. We replaced ours, in our 1976 ranch, and I couldn’t believe the improvement over my old windows, even though I had installed storm windows too. I purchased Thermopane windows by Pella, (from Lowes) and my 5 man crew replaced them ourselves in 1 day!
Now that you’ve tightened (sealed) up your house, you’re ready to easily control the RH (relative humidity) inside your home.
Obviously, you know to use your exhaust fans in the rooms that generate moisture. If you can, put them on timers, so they will run 20 minutes after you leave the shower.
Boiling water, and cooking on the stove top? Use your exhaust fan to draw that moisture out of the house.
This is vitally important now, because with the house sealed, those concentrations of moisture and smells that had been marginal, are much more concentrated and detrimental to your Indoor Air Quality.
- Install a noisy dehumidifier in your hallway, and dump the bucket twice daily.
- Run your AC non-stop, and wear layers of clothes because it’s chilly inside your home.
- Best option is to control the RH inside your home with a Whole House Dehumidifier.
The marvel of marvels: the Whole House Dehumidifier (WHD)
I love these simple machines! For about $4000 entry point, you can have the entire process of managing your RH automated.
Some new HVAC systems also control RH really well.
When we install your WHD, we plumb the intake and exhaust airflow into your existing HVAC duct system. This way, it’s sampling and drawing air from the entire zone that this HVAC system conditions. The dry, dehumidified air is plumbed into the SUPPLY side of the duct system.
On every hour, the WHD takes a sample of air – through the RETURN ducts, for 5 minutes. If the RH in the sample is higher than the setting on your WHD, it turns on the dehumidifier, and also turns on the HVAC fan, to move the airflow throughout the duct system and the vents. In a few minutes, the air inside your house is dryer, and your WHD shuts off everything, and resumes the hourly sampling.
When the RH of the sampled air is at or lower than your setting, the WHD waits another hour, and samples the air again, 24-7.
It’s quiet, and the condensate water is drained or pumped to the outside.
With a Whole House Dehumidifier, you can control and manage the moisture inside your home, and enjoy improved Indoor Air Quality.
The Stack Effect, and the 2nd Law of Thermodynamics teach us that controlling RH is a daily battle. By living in Georgia, we didn’t need some science book to tell us that… did we?
Want more information? Call our office and ask for Bob, at 404-538-9168. We can perform all of the mentioned measures for you, and turn your home into a fun & comfortable place to live!
PS: When you seal your home, you must be aware of unintended consequences. Likely, you may need a source of fresh air, to supplement the air inside your home. I have an article about this, here: https://birdinsulation.com/blog/2017/november/part-3-because-we-live-in-the-southeast-u-s-ther/