Anyone intalled a whole home dehumidfier?

1,097 Views | 17 Replies | Last: 5 mo ago by TennAg
Ezra Brooks
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AG
We are getting significant condensation at our AC vents - dripping condensation.

Our AC guy didn't have much of an explanation, he felt out ducting was insulated well.

This is a new house for us, and it feels more humid than we are used to, so one thought is that some of the condensation is from the cold/dry air hitting the more humid air of the rest of the house.

Anyone have any experience here?
evan_aggie
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AG
What's the % humidity inside? I'm assuming 50-55%.
one MEEN Ag
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AG
Ezra Brooks said:

We are getting significant condensation at our AC vents - dripping condensation.

Our AC guy didn't have much of an explanation, he felt out ducting was insulated well.

This is a new house for us, and it feels more humid than we are used to, so one thought is that some of the condensation is from the cold/dry air hitting the more humid air of the rest of the house.

Anyone have any experience here?
You already have a whole home dehumidifier installed in your house- your AC system.

Usually when you see too much humidity in a home, the builder or AC man has installed an AC system that is too big for the house. The AC system serves two purposes, cooling off the air and the things inside the house, as well as pulling humidity out of the air at the same time. If you've got too many tons of AC cooling capacity, the system can blast cold air into the house before its circulated enough of the air in the home through the unit. This short cycling can make a home feel cold and clammy.

How old is the house and how 'tight' is the home build? If its an old home that is really loosely built, you could have a ton of humid air leaking into the home causing the humidity spike. If its a relatively new home thats pretty well built (especially if you have closed cell spray foam insulation or glazed windows), the AC system might be too big for it.

Also, the AC man might be giving you the run around because he knows he installed too big of an AC system and doesn't want to fess up to it.
redag06
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I've looked in to it, and right now I plan to hold off till we need a new system.

We have an older home that we have sealed up fairly well, but the walls are still 40 years.
And during the shoulder months we have to run the ac COLD just to dehumidify(Houston)

I'm fairly certain the unit was oversized before we did new windows, doors and insulation. Now the lowest we see humidity is about 58%
Dr. Doctor
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AG
More than likely, you had an adequately sized system. But if you upgraded the insulation, windows, doors, etc., now the system is 'oversized'. Thus the high humidity.

Another culprit could be leakage by the duct/attic area. If your ducts aren't sealed 100%, the cold air acts like a venturi and will suck in other air (usually attic air, which is hot and moist) and come in. The warm/moist air condenses on things (air register cover) and drips.

I have thought about installing a whole house dehumidifier, but mostly because I keep the house warmer than most for my wife, but want to keep the humidity out of 60% range. I also live in Houston (Upper NE side).

~egon
Gary79Ag
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Paging "The Fife"...he's done it IIRC
Mr. AGSPRT04
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I installed a WHD in my 1964 leaky house, but never had the condensation problem. I prefer it at <50% humidity, which I could never achieve in the summer without overcooling a lot. It's doable as a DIY perspective but would not dare spend that kind of time in my attic this time of year.

Condensation on the supply air vents definitely is from cold air meeting warm air. Is it on all vents or just certain ones. It may be in the living space from leaky or open doors/windows, cooking/showering/panting dogs. Or it may be coming in from poorly sealed supply vents from a hot attic. You may try spray foam in a can around the vent boxes and seal other attic penetrations.
The Fife
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I'll echo a few things that others have said. First, sealing up the place nice and tight so there will be less infiltration of humid outside air. For example, the gap between the ceiling drywall and your ductwork (take the register grill off to get at it), plumbing and electrical penetrations, fixtures, and whatever else.

Your system is likely oversized, it seems like just about all of them I've looked at are because 'for (some small amount more) you can upgrade to X tons!' is how a lot of HVAC systems seem to be sold. Anyway if you've done all of these things and your measured humidity is still unacceptable (like 55%+) I'd look into adding a dehumidifier into your existing ductwork. I used a Honeywell DR90 a few years ago and it's worked pretty well and it was an easy install but I've worked around this stuff a bit.
Ezra Brooks
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AG
evan_aggie said:

What's the % humidity inside? I'm assuming 50-55%.
I don't have a % - just going by feel at the moment.
Ezra Brooks
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AG
Dr. Doctor said:

More than likely, you had an adequately sized system. But if you upgraded the insulation, windows, doors, etc., now the system is 'oversized'. Thus the high humidity.

Another culprit could be leakage by the duct/attic area. If your ducts aren't sealed 100%, the cold air acts like a venturi and will suck in other air (usually attic air, which is hot and moist) and come in. The warm/moist air condenses on things (air register cover) and drips.

I have thought about installing a whole house dehumidifier, but mostly because I keep the house warmer than most for my wife, but want to keep the humidity out of 60% range. I also live in Houston (Upper NE side).

~egon
I'm in your neighborhood - King's Point actually.

The house was built in '89/'90. There are areas where it's closed up pretty well and areas where there is certainly outside air getting in.

To the best of my knowledge, windows/doors are original. AC units aren't original, but aren't new. Two 4-ton units on a 3,500 sq. foot house. I don't know if that's oversized or not.
Ezra Brooks
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AG
Mr. AGSPRT04 said:

Condensation on the supply air vents definitely is from cold air meeting warm air. Is it on all vents or just certain ones. It may be in the living space from leaky or open doors/windows, cooking/showering/panting dogs. Or it may be coming in from poorly sealed supply vents from a hot attic. You may try spray foam in a can around the vent boxes and seal other attic penetrations.
I need to take a closer look at this idea to see if it helps with the condensation.

Will attacking the problem from the "vent side" be that effective vs. from the "attic side". Some of the vents with heavy condensation are areas where I don't have access from the attic.
Dr. Doctor
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AG
Ezra Brooks said:

Mr. AGSPRT04 said:

Condensation on the supply air vents definitely is from cold air meeting warm air. Is it on all vents or just certain ones. It may be in the living space from leaky or open doors/windows, cooking/showering/panting dogs. Or it may be coming in from poorly sealed supply vents from a hot attic. You may try spray foam in a can around the vent boxes and seal other attic penetrations.
I need to take a closer look at this idea to see if it helps with the condensation.

Will attacking the problem from the "vent side" be that effective vs. from the "attic side". Some of the vents with heavy condensation are areas where I don't have access from the attic.
Yes. You just need to stop the mixing of the air. Weather you do that from the front or back, as long as you block it, it should help.

A thought would be to use the yellow can "Great stuff". Be careful; it really does expand. A lot. Like, way more than you think if you haven't used it before. You can fill in the gaps (with the grates off), let it dry, and then cut the excess away and put the grates back on. Bonus: you can wash the grates and get 10-15 (or more) years worth of dust off! I've run mine through the dishwasher.


And I live in Sand Creek, so yes, near you in a 1987's built house.

~egon
Throwout
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AG
My humidity consistently runs high--currently 67% on our downstairs unit and 68% on our upstairs unit. Our house is just over a year old, so I'm guessing that we've got oversized units (feels good to type that for once). It's rare that our humidity is below 55%. It's sounding more and more like we need to go the WHD route.
redag06
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So 3 of the posters with over sized units on here are in kingwood.
Maybe we can get a group buy on whole home dehumidifiers
91AggieLawyer
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Where exactly do you spray the great stuff foam?
Mr. AGSPRT04
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Around the edge of the box where it meets the drywall on the attic side.
https://www.greatstuff.dupont.com/how-to-air-seal-hvac-ducts-and-penetrations.html
Ezra Brooks
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AG
Our AC guys was out on Tuesday to fix an issue (whoever installed the last AC unit decided that it was easier to plumb the primary drain via a drip line outside of the house instead of into a plumbed drain line, thus creating a muddy mess on one side of the house)

My wife was discussing the condensation issue with him and he mentioned that an over sized unit may not be helping the situation.

He suggested sealing the vent boot with mastic, but I think Great Stuff will be just as good.
TennAg
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Are you running your fan in "auto" or "on"? If your fan's constantly running, that will somewhat negate the dehumidifying effect of the ac system. Try auto and compensate with ceiling fans if needed.
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