Why does my apartment require so much water from my humidifier to increase the humidity

Factual Questions
1

I’m not sure if this is the right forum, but here is the situation.

My apartment is small, maybe 175 cubic meters. At around 70F air can hold something like 18 grams of water per cubic meter at 100% humidity, so thats 3150 grams of water total for the entire apartment at 100% humidity.

Without the humidifier, the humidity is about 25%. With the humidifier the humidity is about 40%. So on paper shouldn’t that mean I would only need to add about 470 grams of water to the air to increase the amount of humidity from 25% to 40%? However my humidifier is using something like 6 liters of water a day, so 6,000 grams.

Why is it requiring so much water to slightly raise the humidity in a small apartment? 6,000 grams or so of water is double the entire humidity content of the apartment twice over, at 100% humidity.

I’m not sure if my math is off or something though.

2

Your apartment is not airtight (as evidenced by the fact that you are alive), so some of that humidified air is constantly being lost to the outside, and unhumidified air from outside is replacing it.

3

Does your apartment share a forced air heating system with other areas? If so, then the humidifier will also be trying to humidify a larger area.

4

I understand that, but how much air has to come through to use up that much water? Wouldn’t that imply that 13x my apartment’s volume of air passes through my apartment every day? that seems excessive.

5

The EPA says a home should have at least 0.35 air changes per hour. That’s a minimum of 8.5 per day. So 13 per day doesn’t seem unreasonable.

6

Older homes can easily have 2-4 air exchanges with outside air per hour.

And remember that any heated air coming in is replacing air going out.

7

It makes more sense if you think about the reverse.

My Austin friends often run de-humidifiers and are pulling gallons of water out in just a few hours during bad spikes. The ambient atmosphere is going to come in, unless you’re fully sealed (which, as stated, is a bad idea).

Another metaphor for this time of year: why do I have to keep heating my house/apartment/cardboard box? Because since it’s not perfectly sealed and insulated, it is slowly reaching an equilibrium with the outside. If you don’t keep putting energy/water/etc into the system, you’ll be back to ambient sooner or later depending on the strictness of your seal or insulation.

8

That’s incredibly aspirational though. The Passive House standard, the toughest building standard in the world can be passed with 0.6 ACH. Modern building codes tend to mandate somewhere around 3ACH and older houses would often have 15 - 25 ACH.

9

Measuring air humidity alone doesn’t take into account the humidity of everything inside the house. Things like wallboard, furniture and bedding will absorb and give up moisture in addition to air.

10

Other folks have commented on why you’re using more water than expected; but I figured I would confirm that your initial math was correct. (I get about 3020 grams at 20°C = 68 F, and the small difference is probably due to how vapour pressure increases with temperature.)

11

Anecdote time:

In my last house, I put a fair amount of time, effort and money into comfort and indoor air quality, speccing an expensive HVAC system and whole-house humidifier (and filter).

The whole deal struggled mightily to achieve reasonable indoor relative humidity levels, burning out two 220V units in the first 8-10 months. And each new humidifier took days and days to get the RH back to the setpoint.

Somewhere not long after that, my house filled with smoke. Our neighbor – about arm’s length away – had installed a smoker (barbecue-type) on his patio that was just feet from my house. When I went outside, I found the issue that caused both problems.

The HVAC contractor who did the initial install put in a fresh air duct – maybe 6" in diameter – that wasn’t called for by the manufacturer’s install instructions. In residential, most current HVAC systems don’t introduce (much, if any) fresh air into the house.

Without me doing the math, it was the equivalent of leaving an X square foot window Y% open … all the time. In the very dry climate of the Rocky Mountains.

It was – and would continue to – also literally sucking the smoke from the neighbors smoker into my house.

Good times.

And @Shalmanese makes a very important point: ACH figured on older dwellings are often the equivalent of my example: you left a window open.

It’s one reason that so many older homes in this country don’t really have mold in their walls, despite a climate that fosters its growth.

Which leads to another OT topic … how “tight” is too tight for a residence. In today’s ultratight houses, you “build tight and ventilate right,” but we’re probably getting more chemical exposure than in the olden days where we all contributed to both heating and cooling the entire neighborhood :wink:

I think it was also mentioned upthread that your system may somehow be tied into the HVAC of the rest of the building. Even if not, though, the inherent leakage of your unit means that, to some degree, you’re sharing their air. Particularly if not everybody is using humidification, you’re basically chasing that ‘open window’ effect.

12

Depending on your heating/cooling system you could have a significant amount of water condensed on vents and other cool spots in your apartment. Not gallons of water, but a thin film over enough area adds something to the total used by your humidifier. If you have A/C running there’s probably condensed water draining someplace from the unit.

13

Kinda. If the humidifier is successfully holding humidity constant, those other objects will have net zero flow of moisture in or out. The air and the stuff is in equilibrium.

OTOH, if the humidifier isn’t keeping up, or is overcompensating, then yes, those other things will contribute to the balance. But that does not seem to be the OP’s case.

14

I have an old house so it cycles pretty quick with outside humidity. I use to try to humidify it but gave up. I just need it when I sleep and the CPAP machine takes care of it.

15

When I was a young teen, one of our neighbors were a couple of retired musicians. As in, retired from playing at the Boston Symphony Orchestra level of musician. She was a violinist primarily, he was a clarineticist, though both also played other instruments for fun. Some obvious additions (viola, oboe) others not at all (bagpipes!, trombone!). Plus both were damn good pianist. Theirs was the only home I had ever seen that had TWO grand pianos in the living room, and any number of other instruments just casually perched on or against chairs and couches and racks and hung on the walls.

Truly, between just the two of them they would have been an amazing band.

Anyway, they did a lot of traveling, and my first ever job was as “water carrier” while they were away. They had three huge stand alone humidifiers, one in the living room, one in the dining room on the lowest level, and one on the balcony/hallway that ran along besides the top floor bedrooms. (It was a split level house.)

Those things went through water at an unbelievable rate. I made two visits each day, and put at least one three-gallon bucket’s worth of water into each of them at each visit!

The couple kept the house fully heated and airconditioned to a steady 75F, 24 hours a day, 365 days a year whether they were there or not. It was VITAL to the condition of their instruments, they stressed this to me, over and over, even after I’d been caring for them for several years.

There were other instructions, too. “Emergency Instructions.” Who to call if there ever was a power failure that lasted for more than twelve hours. Who to call if I fell ill and couldn’t handle the water delivery. Who to call if the furnace or air conditioner stopped working. (They had ‘arrangements’ with their service providers, basically sizeable bribes to take care of their needs FIRST if something went wrong.) What to do if the house was burglarized or a tree fell on it! On, and on.

Those instruments were their babies.

At the time I didn’t really think about it, but now I shudder to imagine what their utility bills must have been like.

Anyway, the point of all this is that the house was never excessively humid. Despite all those gallons of water daily, it never felt dank or sauna-ish or anything but absolutely comfortable. So, yes, houses (this one was built in 1964) can go through an amazing amount of water.

16

I don’t think that’s ever been legal, or the type of thing a builder would even want to do in the first place.

17

Apartments and buildings used to have shared vents to common air shafts. Don’t know if that’s still done.

18

it’s pretty common that bathroom exhaust / air vent systems in apartment buildings are a common air shaft to the roof. With one shaft for each stack of bathrooms. Often with a fire-damper type of louver that will should close were a fire to be pushing smoke & hot air up the common shaft.

But shared forced-air HVAC is not something I’ve heard of in a residential context. It’s pretty common in office buildings.