Whole-House Dehumidifier

[TromboneAl]

Anyone have a whole-house dehumidifier?

I continue to struggle against mold in our house close to the ocean.

I thought that I could cut down on our high humidity by using the forced air heating instead of the fireplace, but it doesn't help.

Today the RH is 80% in the upstairs hall. I have some small dehumidifiers in some rooms, the humidity is down to 75% there. I have a normal dehumidifier in the bathroom, and that works fine.

I put the (calibrated) hygrometer on the front porch, and it read 99%!!

Another option I'm considering is buying another normal dehumidifier and running it once a week to cut humidity down enough to kill the mold. Running it all the time would be noisy and expensive.

I run fans along the walls to keep the air circulating.

Any other ideas?

 

[braumeister]

In a previous (non-air conditioned) house we solved this problem with an attic fan.
The large fan was mounted in a dormer up in the attic and had a louvered opening in the ceiling of the second story. The louvers only opened when the fan came on.

The huge air flow through the house wasn't even noticeable but the indoor temperature and humidity stayed in a very comfortable range.

Something you might look into.

 

[Big_Hitter]

Have you tried a window unit a/c? The primary purpose of an air conditioning unit is to remove humidity.

 

[ERD50]

Anyone have a whole-house dehumidifier?
...
Another option I'm considering is buying another normal dehumidifier and running it once a week to cut humidity down enough to kill the mold. Running it all the time would be noisy and expensive. ...

Any other ideas?

Well, we run our Air Conditioner to reduce relative humidity to a more reasonable level, like 55%. But I guess that won't work in your climate.

I don't think there are any good alternatives to a full scale dehumidifier (which is basically an AC unit that just returns the heat to the room rather than pumping it outside). I think that's the price you pay for living in that climate, just like we need to heat in the winter and cool in the summer.

I've heard of silica gel absorption systems that then use solar power to heat and dry them out, and then return them to absorb some more. I'm not sure how big those come, or how effective they are, or if you get enough sun for them in that humidity.

Also, is there generally a time of day where the humidity is lower? Could it make sense to have some sort of whole house fan, or air exchanger to blow the lower humidity air into the house at that time, then close it up, and dehumidify it further? I'm guessing morning is worst, with the ocean fog rolling in?

-ERD50

 

[rodi]

When my sister lived in Okinawa she had 2 dehumidfiers running 24/7... one in the living room, one in the bedroom. They were "portable", which is a fancy way of saying you had to manually empty the water out... the reservoirs would fill up every 12 hours... so this was just part of the routine - empty them before work, empty them in the evening. I spent a summer over there with her and that was one of my chores for the summer to help earn my free rent. If I forgot - the apartment got humid very quickly.

I don't remember it making a lot of noise - but I know it was a power hog.

 

[bUU]

Anyone have a whole-house dehumidifier?

We probably should have done that, but did not. Instead, we upgraded our furnace to variable speed. It works great over the summer, when humidity is at its worse, but in the shoulder seasons, when the A/C isn't running, it doesn't do anything. So we ended up buying a 50 liter standing dehumidifier. It's a pita that we have to manually empty it, but in the shoulder seasons it only generates about 2 1/4 gallons a day (i.e., we only need to empty it once a day).

I have some small dehumidifiers in some rooms, the humidity is down to 75% there. I have a normal dehumidifier in the bathroom, and that works fine.

I've got to say, those small dehumidifiers look like toys. I hope you didn't pay $219.00 for it (the price it is currently available at, according to Amazon.com). We bought one of these for less than that, and although it shouldn't be able to handle the load by itself (we were prepared to buy a second) it seems to be doing the job for our entire 2300 sq ft home (however, to be fair, we're here in the foothills north of Atlanta, not by the ocean).

Another option I'm considering is buying another normal dehumidifier and running it once a week to cut humidity down enough to kill the mold. Running it all the time would be noisy and expensive.

We were moving the dehumidifier back and forth between the office and the loft (i.e., a 10 foot move) whenever we needed to dampen its noise impact, but it's really relatively quiet, and we've actually stopped doing so, since we are only in the loft for 2-3 hours each night, so we just turn it off for that short period of time. The humidity creeps up and then gets knocked back down overnight.

Without the dehumidifier, our interior humidity would regularly climb above 70%. As of this minute, it is 38% here in the office. Last time I checked the meter in the great room (downstairs) it was 43%. I have the dehumidifier set to 45% or 50%, I forget which.

Our electric bills (total) run $4 per day, except on laundry days. During the days just before we received the dehumidifier, our electric bills (total) were $3 per day. You do the math.

I don't think there are any good alternatives to a full scale dehumidifier (which is basically an AC unit that just returns the heat to the room rather than pumping it outside).

I suppose I should be thankful we upgraded the furnace fan to variable speed, then, so that we don't need the dehumidifier over the summer!

 

[travelover]

......... It's a pita that we have to manually empty it, but in the shoulder seasons it only generates about 2 1/4 gallons a day (i.e., we only need to empty it once a day). ...

Some dehumidifiers come with a pump so you can run a small line to a drain. Or you can add a condensate pump to an existing dehumidifier.

The tiny dehumidifier that Al linked won't do much to move the needle, you need a larger compressor type for an issue of his scale.

 

[bUU]

Some dehumidifiers come with a pump so you can run a small line to a drain.

Ours will drain continuously through a hose. We just chose not to set it up that way because it would restrict where we could place it.

 

[travelover]

Ours will drain continuously through a hose. We just chose not to set it up that way because it would restrict where we could place it.

Right, that is the purpose of the pump. With a pump, you can run a long line up and over to a sink or other drain.

 

[bUU]

Right, that is the purpose of the pump. With a pump, you can run a long line up and over to a sink or other drain.

Our concern was that the hose would be visible running across the house to a room with a drain.

 

[travelover]

Our concern was that the hose would be visible running across the house to a room with a drain.

Sorry to hear that but maybe my suggestion will be a help to others including the OP, Al.

 

[Walt34]

Some dehumidifiers come with a pump so you can run a small line to a drain. Or you can add a condensate pump to an existing dehumidifier.

That's what I've been doing for years. We run a standing dehumidifier in the basement that during the summer months runs pretty much 24/7. From about mid-October to mid-April it is idle.

The one we have did come with a pump but that died the day after the warranty expired. Really. So I just got the condensate pump and ran a line to that.

 

[TromboneAl]

Today I rolled our old, reliable Kenmore dehumidifier

(looks like this:

)

from the bathroom to the upstairs landing, and ran it all day. It dropped the humidity from 80% to 63% after a few hours, and it's stayed there.

One option is to buy a big-a$$, noisy dehumidifier and run it once a week on a timer. Get the humidity down enough to kill the mold. That would avoid the continual noise and high electric bill, but I don't know if it would be effective.

Sometimes I lock that in one of the rooms, and get the humidity to 45% or so.

 

[ERD50]

Today I rolled our old, reliable Kenmore dehumidifier

(looks like this:

)

from the bathroom to the upstairs landing, and ran it all day. It dropped the humidity from 80% to 63% after a few hours, and it's stayed there.

One option is to buy a big-a$$, noisy dehumidifier and run it once a week on a timer. Get the humidity down enough to kill the mold. That would avoid the continual noise and high electric bill, but I don't know if it would be effective.

Sometimes I lock that in one of the rooms, and get the humidity to 45% or so.

IIRC, you have a central heating system. Why not get a big a$$ central dehumidifier and hook it into the central duct system. Run it a few hours (or whatever) every day, and keep the humidity low enough to eliminate the conditions that allows the mold growth. I would bet a central unit would not be that noisy at all.

You've been posting to this forum for years about your mold problem, and lately you said you wanted to loosen the purse strings, so why not just fix this on-going problem, and stop with all the band-aids.

You live in a humid climate - deal with it. For you to do w/o a dehumidifier running a good part of the time, and expecting mold problems to stop would be like me trying to get away w/o heat in my climate, and expecting that my house would stay comfortable. Not gonna happen!

-ERD50

 

[JoeWras]

OK, so I haven't read up on Al's humidity problems, and hence I don't know if this will work for him, but here's what we have in the southeast.

My Carrier units (that is, the whole house A/C) have "Super Dehumidify" modes on them. Here's what it is: a mode of A/C that runs the fan ridiculously slow. So, the A/C comes on, but the fan runs slow with the idea to really give time to let the air hang on the coils and wring out the humidity. The A/C will even come on up to 2 degrees below my set point to make this happen.

But the problem is it is A/C. It does help if your house is at 68 degrees and you have the A/C set at 70. It won't come on. I presume this high humidity it at lower temps. If so, this won't work.

 

[pb4uski]

Our house is spray foam insulated and very tight. So tight that we need to have an air exchange system that pulls in fresh cold air from outside runs and exhausts warm stale air from inside. It runs through a heat exchanger to try to retain some of the warmth of the air.

We originally had a version that did not dehumidify and were getting too much moisture in the house. We then replaced the core with a different unit that dehumidifies as well. initially I just had the water run into a gallon jug and would empty it as needed but later I plumbed the water into our waste system.

It works fine for us but am not sure if it would work where Al is.

 

[bUU]

But the problem is it is A/C. It does help if your house is at 68 degrees and you have the A/C set at 70. It won't come on. I presume this high humidity it at lower temps. If so, this won't work.

That is precisely our situation, down the the detail of it being a Carrier unit (see posting above). Relying on just the variable speed fan or other A/C dependent measures in humid climates is not sufficient, simply due to the shoulder seasons.

 

[travelover]

Today I rolled our old, reliable Kenmore dehumidifier ........

Like refrigerators, newer dehumidifiers are more energy efficient. If you run it a lot, it might be worthwhile to buy a new, energy efficient model.

This link might be of use.

 

[MichaelB]

I continue to struggle against mold in our house close to the ocean.

Being that close to the beach it's a surprise you don't have more issues with salt.

Perhaps some ceiling fans might help in the smaller rooms. At low speeds they consume much less electricity than a dehumidifier, you can leave them on for extended periods.

 

[bUU]

Like refrigerators, newer dehumidifiers are more energy efficient. If you run it a lot, it might be worthwhile to buy a new, energy efficient model.

This is so true. Although no one can foretell the future, but I wonder what the C/B looks like for a new unit that will last X years versus 1.5*X years. As I mentioned above, we just replaced two HVAC units that were 10 years old. The impact of increased efficiency is clearly evident in the attached image. We went from averaging $12-$14 per day to $3-$4 per day. I bet dehumidifiers have also gotten more efficient.

 

[ERD50]

For those talking about A/C units optimized to dehumidify, IIRC, T-Al doesn't use A/C at all. His climate is cool year round. I think he uses his wood burning stove something like 10 months/year.

That's why I keep talking about a dedicated central dehumidifier, maybe coupled with some kind of air exchange unit.

...
Perhaps some ceiling fans might help in the smaller rooms. At low speeds they consume much less electricity than a dehumidifier, you can leave them on for extended periods.

With the kind of humidity levels T-Al is talking about (80% plus), I really don't think a little air movement (just moving around the same wet air) is going to do the trick. He needs to dry that air out.

-ERD50

 

[TromboneAl]

Yes, this thread's main purpose is to see if we should put in a whole-house dehumidifier.

>Being that close to the beach it's a surprise you don't have more issues with salt.

We do. Rust. Everything here rusts at an alarming rate.

I'll try a few more things, then look into the whole-house. One option is to have the entire interior repainted with mold-proof paint. I did that many years ago in the shower, and it's worked great.

Thanks for the ideas.

 

[ERD50]

Yes, this thread's main purpose is to see if we should put in a whole-house dehumidifier.

.... One option is to have the entire interior repainted with mold-proof paint. I did that many years ago in the shower, and it's worked great.

....

Mold proof paint sounds like another band-aid.

The root problem is humidity, the paint might knock out the mold on those surfaces, but what about inside drawers and everywhere else you've talked about over the years?

I'll bet that this will be one of those things that, once you fix the problem, you are going to kick yourself for not doing it years ago, and wasting all your time on ineffective band-aids.

We do. Rust. Everything here rusts at an alarming rate.

Rust isn't just a function of salt. Humidity plays a big part. My basement will get very humid in summer, and if I let it go, everything will start rusting down there (no salt water around here). But before it gets that humid (which normally is in sync with our hot weather), I'll run the A/C with vents open in the basement to dry it out. Sometimes, I do this even if we maybe could get by upstairs w/o the AC on. It's worth it.

So fixing the problem will also help your rust problems. Paint on the walls won't do that.

-ERD50

 

[TromboneAl]

My rough estimate is that if I run the whole-house heating and dehumidifying system enough to keep things under control, it could cost $6,000 per year as oppose to about $500 now. Propane is expensive here and so is electricity.

The fans alone for the propane furnace suck 500 watts. As we get into the higher tiers, the electricity costs more. We would be paying to heat rooms we rarely visit.

That's why I want to consider alternatives before going to a whole-house system. Maybe I'll run the heat for a month, and see how much that would cost.

>So fixing the problem will also help your rust problems.

The rust issues are in the garage (tools, etc.) which is not heated.

 

[ERD50]

I'm not understanding how propane fits into this?

A whole-house dehumidifier (as opposed to using AC to dehumidify) would add heat to the house w/o any propane use - they would have both the cooling and the heating coils in the duct, basically the same as a stand-alone dehumidifier. Dehumidifiers aren't moving the heat away (which is what the AC units do), so you gain heat by whatever energy the unit uses.

Sounds like it might only need to run a few hours a day to bring the humidity down - would it really cost that much? I know our AC unit will bring the humidity down from high 70%'s to ~ 55% in just an hour or two. And it is not fully optimized for dehumidifying, it is balanced between cooling and dehumidifying.

And someone mentioned they run the fan on a very low speed for this purpose, so likely less than 500W running (the fan that is, the dehumidifier compressor will take more).

And I really don't think running the heat will dehumidify anywhere near as much as an actual dehumidifier. The lower humidity is just a minor secondary effect of heating. Raising the air temperature allows the air to absorb more water, so relative humidity goes down, but you have not actually removed any water. The dehumidifier removes the water. Big, big, difference!

Rust only in the garage? I seem to recall a photo you posted of nails rusting right through the drywall in the house (maybe that was a bathroom)?

-ERD50