New Mask Using More Water?

I just switched from my Nuance mask to a Air Fit P10. I use a heated hose and heated humidifier. With the Nuance mask I could get two nights of water use in the water tank. With the P10, there is only a minute amount of water left in the tank in the morning. In fact, the first night I used the P10, the tank was dry. I use the P10 for exactly the same amount of hours as I used on the Nuance. Why would the P10 be using so much more water?

Sleeping Ugly wrote:I just switched from my Nuance mask to a Air Fit P10. I use a heated hose and heated humidifier. With the Nuance mask I could get two nights of water use in the water tank. With the P10, there is only a minute amount of water left in the tank in the morning. In fact, the first night I used the P10, the tank was dry. I use the P10 for exactly the same amount of hours as I used on the Nuance. Why would the P10 be using so much more water?

I also went from a Nuance to a P10, but don't recall any difference in water usage.

Water consumption is more related to ambient room humidity or pressure or leaks than it is to which nasal pillow mask is being used.

I have always had to add water nightly no matter which mask I have been using unless the night was extremely short for some reason.

Has your ambient bedroom humidity changed? Is it cooler now where you live and maybe using a furnace?
Both can mean drier air.

Has your leak rate increased?

I have my heating and humidity settings on fixed instead of auto, so I would not think the ambient temperature would affect it? I have no idea.

As far as the leak rate--no--there has been no increase at all in leak rate. I have a practically non-existent leak rate with both masks.

Curiouser and curiouser.

Actually even with fixed humidity setting of a number the ambient humidity will play a very large part in water consumption.
How the humidifier works is it takes whatever the ambient humidity might be and adds heat so that the output of humidity is what you selected.
It all starts with ambient humidity first. That's the starting point.

I have mine fixed as well at 6 and I vary the hose air temp as the season dictates for comfort. If the ambient humidity is high I won't use much water at all and if it is rather dry I might use almost all the water. I never vary the humidity setting because I nose doesn't like change.
I use more water when the furnace is on than I do if the windows are open. If I used the fireplace it would dry the air out even more and more water would be used. If it is raining outside and I have the windows open I might not be able to see a drop in the water level so little is used.

As Pugsy noted, the ambient room temperature and humidity and hose-mask system circuit leaks are often the main variables for humidifier water usage. However, the mask vent rate will also impact the amount of water evaporated from the humidifier.

Check for any difference in the mask vent rates.

"If" the only variable that changed is the mask type. My suspicion would be that the newer mask has a much higher leak rate. More air leaking from the mask = more air flowing over the water in the humidifier tank and because of that a higher evaporation rate.

Any number of other variables could come into play as Pugsy and others have stated. If you left a tray of water out and the relative humidity is very very low then there is a good chance that that water will be gone the next day due to evaporation. But if the relative humidity in the room is high not much water will evaporate into the air from the tray as the air is already holding a lot of water already.

She's gone from the Nuance gel nasal pillows to the P10 nasal pillows....I doubt that the vent rate has changed unless leaks are massive from mask movement. The vent rates for the 2 masks aren't all that different. If she wasn't mouth breathing with the Nuance I doubt that there would be much mouth breathing leak with the P10.

The most common factors affecting water consumption like I said in my first reply
Ambient humidity (this is probably the greatest factor)
Pressures used (higher pressures will use more water)
Leak rate...large amounts of time in large leak can use up more water. Each to check by looking at the leak graph.

Pugsy wrote:She's gone from the Nuance gel nasal pillows to the P10 nasal pillows....I doubt that the vent rate has changed unless leaks are massive from mask movement. The vent rates for the 2 masks aren't all that different. If she wasn't mouth breathing with the Nuance I doubt that there would be much mouth breathing leak with the P10.

The most common factors affecting water consumption like I said in my first reply
Ambient humidity (this is probably the greatest factor)
Pressures used (higher pressures will use more water)
Leak rate...large amounts of time in large leak can use up more water. Each to check by looking at the leak graph.

I'll take your word for it and won't argue the difference in CO2 vent rates between the two masks since I do not have the data for them and I'm too lazy to look them up.

However, please forgive my being so nit-picky -- but pressure is not a significant or even "directly" what causes greater water use. A higher CPAP pressure results in higher vent and/or leak rate (or airflow which is the true reason for increased water usage).

Please allow me to explain:

1 atmosphere (ATM) unit of pressure (the mean global standard atmospheric pressure at sea level) is equivalent to 1,033.23 cm of water. Therefore an increase of say 20 cm of water within a CPAP pressure circuit would result in an average change in pressure of less than 2 percent in most bedrooms exposed to atmospheric pressure. Now the standard is at "sea level" and clearly not everyone lives at sea level although about 40% of the US population lives within 30 feet of sea level and one would have to go to the top of Mt. Everest to experience a 25% decrease in atmospheric pressure. Nonetheless, the 2% change due to 20 cm of water in CPAP would be more or less still relative to whatever land altitude of said bedroom atmospheric pressure.

Furthermore, based on pure physics, the fact is that evaporation actually increases with a "decrease in atmospheric pressure" and evaporation decreases with and increase in atmospheric pressure (an inverse correlated function) assuming all other variables are kept constant (Thermodynamics 101). But again, a 2 percent change is relatively insignificant to make a difference in evaporation rate either way.

Now let's take a look at the more significant evaporation variables: temperature, humidity, airflow, and surface area. Well right off the bat we can disregard surface area for CPAP use because the size and shape of the humidifier container is a constant.

An increase in the water temperature due to heated humidifier unit will increase the water molecular kinetic energy and thus increase evaporation. Likewise, an increase in air temperature would increase the molecular kinetic energy of air molecules (including water in vapor phase) and thus increase the evaporation rate. Decreases in temperature of water or air decreases evaporation rates.

Now the room ambient humidity plays an important part because it's a function of the room's temperature and "vapor pressure" (the equilibrium of the gas vs liquid phase of water in the air -- or more simply the amount of water molecules already in the air). In other words, a high room/ambient humidity will decrease the amount of evaporation (because air is saturated with water vapor) while low room humidity increases the amount of evaporation (plenty of room for more water vapor molecules).

However, when we take airflow into consideration, removing the humidified air from the room allows for more water molecules to go into gas vapor phase which increases rate of evaporation ... the same is true for the CPAP humidifier chamber, removing the humidified air from the chamber (via CPAP CO2 vent or leaks) with increased airflow will also increases the rate of evaporation in the humidifier chamber. But do keep in mind that the CPAP humidifier chamber is not a closed system and so we have ambient room air as input into the CPAP circuit and output back into the ambient room ... so airflow within the room also has an impact.

So actually it is the increase in "air flow" caused by CPAP pressure that increases water usage/evaporation and not the pressure itself. (I know it's a small detail and we've had this debate before ... but what can I say)

Pugsy wrote:Actually even with fixed humidity setting of a number the ambient humidity will play a very large part in water consumption.
How the humidifier works is it takes whatever the ambient humidity might be and adds heat so that the output of humidity is what you selected.
It all starts with ambient humidity first. That's the starting point.

I have mine fixed as well at 6 and I vary the hose air temp as the season dictates for comfort. If the ambient humidity is high I won't use much water at all and if it is rather dry I might use almost all the water. I never vary the humidity setting because I nose doesn't like change.
I use more water when the furnace is on than I do if the windows are open. If I used the fireplace it would dry the air out even more and more water would be used. If it is raining outside and I have the windows open I might not be able to see a drop in the water level so little is used.

Ohhhhhhhhhhhh! OK. THANK YOU for explaining this! I totally understand now.

As far as leak rates being a factor, I would have to say no. My charts show only teeny tiny minute leak rates on occasion. I have not had any significant leaks with either pillow mask.