https://www.ultra-aire.com/

 

High humidity for short periods will not grow mold, but near condensation for more than 24 hours results in actual mold growth. This type of grow is progressive and continues on during damp times. In time it causes extensive damage.
I suggest a whole home dehumidifier connect to the a/c ducts with a control located in the center or dampest spot. Set the control for <55%RH and close the open doors and windows as much as possible during times when the outdoor dew points are withing 20^F of inside temperatures.
Sizing is tricky, but oversizing is better than undersizing. 2,000 sq.ft. of inside space should have 70-80 pints per day capacity and circulation. Installing the dehu return to to the heating duct and blow dry air to the dampest area would be one way.
There could be a better ducting strategy.
Ultra-Aire.com
Keep us posted. This works.
Regards Teddy Bear

 

Thank you both for the advice. I'll be getting some quotes for a whole house dehumidifier this week. As I type this (9 pm), interior relative humidity is 70% with temp of 70. Dewpoint is 63 degrees tonight. We're quite comfortable inside, but I wonder; few coastal homes in this area have A/C. Does everyone use portable or whole home dehumidifiers, or are all the houses around here growing mold?

 

Most homes with+70%RH grow some mold and have musty odors.
Dehu are just starting to catch on. You are going to have fun finding a adventurous contractor to hook up a dehumidifier to your home.
Thanks for the interest. Keep us posted.
Regards Teddy Bear

 

I would contact Ultra-Aire and see if they can recommend someone.

 

Thx again. Does whole home dehumidification significantly increase the temp inside the home? We don't have AC, and our home temp is mostly in the low 70's. Any significant temp increase from dehumidification could be a problem...

 

A dehumidifier that first chills the air to dehumidify it, then reheats the air before sending it onto the house, could potentially raise interior air temperatures higher than desired. There are split system dehumidifiers that chill the air without reheating it, and probably would not overcool the home, since most of its energy would be for removing humidity. Ultra Aire makes both types.

I once was an HVAC service tech in San Diego County. I serviced many homes along the coast, and the heat-only configuration was very common. Mainly larger homes with lots of interior activity (lights, entertainment, cooking, etc.) had air conditioning, along with condo towers. Go inland several miles and a/c was much more commonplace.

 

If you dry the air in the house, you will have more evaporative cooling from your skin, and even if the dry bulb temperature rises, you may still perceive it as being cooler.

Think of what happens when you leave the bathroom after a shower. When you go into the room, the air is dry, and the moisture on you skin makes it feel very cool in there, even though the room has not been cooled at all.

 

You set for the max %RH. When the %RH is exceeded, the dehu operates. If you have a 2,000 sq.ft. home, removing 3 lbs. of moisture in an hour and adds 7,000 btus of heat per hour.
Every degree warmed lowers the humidity 2% RH in the home. A rough estimate is that starting with 70^F, 65%RH, 58^F dew point, 30 mins of operation of Ultra-Aire 70H would result is 75^F, 50%RH, a 55^F dew point. The recycle is dependent on the amount of moisture from infiltration and occupants.
The DEH3000 controller has max temp control which could be set for a max temperature.
During times of not being occupied, the home could be dried down. A dry down every 24 hours will also control mold.
I have not had any complaints on coastal application of dehumidifiers over heating. Keep in mind that raising the temperature 1^F lowers the %RH +2%RH plus removing 3 lbs. of moisture per hour.
Keep us posted.
Regards Teddy Bear

 

Thanks again for the advice. As I was looking at my ducts around the house, I see another potential problem with a whole home dehumidification system: I only have one duct for the entire upper two levels of our home. All the ducts are located in the lower levels (the bedrooms). While the mildew issue seems concentrated in the lower levels, we still have RH >60% in upper levels. With only one duct for the upper two floors, how could whole home dehumidification possibly be effective and efficient?

 

Moisture is desperate to equalize in all direction. Minimal air circulation is required to dehumidify a home. Open door for rooms without ducts is needed.
Regards Teddy Bear

 

I started reaching out to some HVAC companies on this site, and they said I really need an indoor air specialist that will be able to do air testing, analyze if leaks or excess moisture is present, and determine if increased crawlspace ventilation is required with/instead of whole house dehumidification. Do I now call home/inspection and mold specialists for an evaluation and recommendation, then call in HVAC to do the install? Isn't there someone that can do both the analysis and install?

 

How do I assess whether an encapsulated crawl space is required versus a whole home dehumidifier? I have vented crawlspaces underneath the lower levels of the home, and I've heard these can be a frequent problem in hillside SoCal homes.

 

Measure the %RH in the crawlspace. If the space dries out everyday it is not a problem unless you have air movement from the space to the home. I would suggest covering the earth at a minimum. If space does not dry after 10 mil plastic on the earth, close the vents and duct a small amount of the dehu output to the crawl. Important to get dry everyday to stop mold from growing. Any mold growth in the crawl? If not, not a problem.
Keep us posted.
Regards Teddy Bear

 

I checked the crawlspace today, and there is white mold on the open dirt, floor joists, and underside of sheathing. Quite a bit of efflorescence as well. RH of crawlspace is approx 75%. No visible puddles or leaks, just dry, powdery dirt.