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Hi all, what would be the desired indoor humidity level for a house with a central HVAC system. I live in North Carolina if climate factors into that.
The reason I ask is because my HVAC is still under warranty and I noticed the "dirty sock" smell when the cooling cycle is on. The service company came out and said that it is the beginning stages of mold growth at the air handler. He told me that leaving the fans on "circulate" and not auto is what can cause that. I told him that I had just installed new thermostats and just noticed that setting 3 days ago and turned it on during our cold spell that pushed through.
In any event, looking online it says that your indoor humidity should be either under 50% or 60% (depending on if you're going by the CPSC or the EPA). My house is consistently above 60%. So I'm wondering if the HVAC is just not removing enough moisture and perhaps that's what's causing the mold growth. Since I'm under warranty I want to call the company back but I want to make sure my reason is valid.
Humidity levels are very subjective and could vary depending on an individuals health, sinuses and other medical conditions.
The general recommendation is somewhere between 30 & 50%, however others prefer 60% and I would say that is definitely at the higher end of the comfort level for some individuals. Best to find your most comfortable range and do what’s needEd to maintain that level and you might find it to vary depending on the season.
So, assuming that your question is about now (cooling season), the answer will mostly depend on the system (the whole system- air handler/blower, ductwork, and the air tightness of the house and insulation/vapor barrier).
Depending on the rh, it’s capacity to remove moisture from the air is limited by a few factors. So, the end result maybe short of that desired 50-60% range.
The position on running the fan/blower constantly is a regional one. The dryer the air, the less likely to promote unwanted mold spore/mildew growth. At one time, there were a few manufacturers that programmed their systems to continue the blower for several minutes after the condenser had been shutdown- the purpose was to “dry” the evaporator. I don’t think that is employed much anymore- it was basically just putting moisture back into the house when you’re trying to remove it!
Agree regarding running the fan and I understand that. I only ran it for 2 days when the cooler weather moved in and the A/C itself was off.
My question is more along the lines of - could the mold be related to an equipment issue? My only reason for asking is because my warranty is up in December and if it is something covered I'd rather it be taken care of.
If it's just a part of life, that's fine too - I just don't want to spend $1-2K on a UV package when it was something with the system itself (i.e. not removing all of the moisture).
Certain times of year, your AC might not go on enough for it to remove humidity. I don’t know what the weather is like where you are, but spring and fall tend to be the steamier times of year because it’s not really warm enough for the AC to kick on enough to remove moisture. I know I’ve gone on vacations during these times of year, had my dehumidifier fill, and got home to humidity in the house at 70%. This was when the temperatures in the home were between around 62-78 or so and my system was not set to run. Even with a good AC, I still use dehumidifiers.
Certain times of year, your AC might not go on enough for it to remove humidity. I don’t know what the weather is like where you are, but spring and fall tend to be the steamier times of year because it’s not really warm enough for the AC to kick on enough to remove moisture. I know I’ve gone on vacations during these times of year, had my dehumidifier fill, and got home to humidity in the house at 70%. This was when the temperatures in the home were between around 62-78 or so and my system was not set to run. Even with a good AC, I still use dehumidifiers.
This is when a combo humidistat/thermostat can rectify the "problem". We have the same conditions here in the ATL.
This is when a combo humidistat/thermostat can rectify the "problem". We have the same conditions here in the ATL.
In the case of my old upstairs AC I had a dead spot in my coil and the system was 20 years old. I needed to run not only the AC but a dehumidifier as well as a portable to keep up on 90+ days. Without the dehumidifier it was hitting 70%+.
Replaced the unit and it stays around 50% RH when running now. During hot and humid days the condensate drain is obvious with water pouring out. Last few days with the AC in a transitional state (too cool out for it to run much) and the RH is still below 60% overall. Atlanta suburbs. Indoor temps set to 72.
OK, I just wanted to make sure before I call them back. So perhaps it may end up being a combination of the UV light inside the air handler and possibly look into a dehumidifier.
You're in GA and I assume that you get similar weather to us here in the Raleigh area - can be some darn muggy days.
I posted a few weeks ago regarding humidity in my crawlspace (that's a separate downstairs air handler) so that's a 2K fix on top of the 1K + for the UV bulb in the upstairs unit.
I think the cheap fix would be buy a cheap hygrometer and dehumidifier and run it near the HVAC return or in your "wettest" room. Our leaky 1950s built house typically sees 40-70% during the summer without any intervention, and 35-60% during the winter months. Running our old 5-ton AC during a typical summer day for 6 hours will produce 5-gallons of water in the condensation pipe (I've routed it to our rain barrel); it brings the indoor humidity from 65% down to a more comfortable 50%.
I break out our $100 dehumidifier during those muggy days/evenings to keep things comfy.
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