Thread: Issues with natural materials

The dryness is the RELATIVE humidity not how the air is heated or cooled. The Hot air can hold way more water. When air is heated the water isn't removed from the air, it is able to hold much more so the relative amount changes.

When air is cooled it can't hold as much and that is why condensation is formed. On a hot day your favorite cold beverage container sweats. That is because the air surrounding the can is cooled and can't hold as much water. It then condenses on the container.

I dunno, you can find a lot of hot air in the desert and there seems to be not a lot of water in it. It may be able to hold more water but it has to get it from somewhere. You can heat air with a low RH and you won't find it going up in RH value unless you add water to it usually with a humidifier. It is not getting any moisture from the air that is used in combustion as that goes out the stovepipe as part of the flue gases.

Bob

Originally Posted by 32t

The dryness is the RELATIVE humidity not how the air is heated or cooled. The Hot air can hold way more water. When air is heated the water isn't removed from the air, it is able to hold much more so the relative amount changes.

When air is cooled it can't hold as much and that is why condensation is formed. On a hot day your favorite cold beverage container sweats. That is because the air surrounding the can is cooled and can't hold as much water. It then condenses on the container.

Now that finally made sense to me. So if I understand correctly; say the humidity in my house to start is around 60% at 65° and swmbo tends the fire all day. She keeps the main floor over 100° cause she refuses to open a window because its 30° outside, and the fire being as hot as it is 900° +/-. The air being heated so much makes it so there has to be drastically more moisture to maintain the same humidity in the house.

So if I were to run a humidifier on top of the 10 gallons of water being heated on the stove a day. The humidity should be more reasonable.

Originally Posted by BobH

I dunno, you can find a lot of hot air in the desert and there seems to be not a lot of water in it. It may be able to hold more water but it has to get it from somewhere. You can heat air with a low RH and you won't find it going up in RH value unless you add water to it usually with a humidifier. It is not getting any moisture from the air that is used in combustion as that goes out the stovepipe as part of the flue gases.

Bob

The relative humidity is the amount of water in the air compared to what it CAN hold. The amount of water in the air does not have to change but the amount it can hold will change depending on the temperature. Heating dry air will just lower the relative humidity. A solution as you state would be to evaporate more water into the air such as using a humidifier. Or water pots on your wood/coal stove.

The reason that I brought up the moist air from the chimney as being from the combustion is because that is not "stealing" the water from your house or heated space. It is a separate act. So whether you use coal, wood, or LP the resulting low humidity is not because of your fuel used.

Originally Posted by meleii

Now that finally made sense to me. So if I understand correctly; say the humidity in my house to start is around 60% at 65° and swmbo tends the fire all day. She keeps the main floor over 100° cause she refuses to open a window because its 30° outside, and the fire being as hot as it is 900° +/-. The air being heated so much makes it so there has to be drastically more moisture to maintain the same humidity in the house.

So if I were to run a humidifier on top of the 10 gallons of water being heated on the stove a day. The humidity should be more reasonable.

I think that you got the general idea but I would ignore the stove temp itself unless you were measuring the 800 degree air 1 inch from the stove.

If you really want to get confused check this out. Psychrometrics - Wikipedia, the free encyclopedia

Originally Posted by 32t

The relative humidity is the amount of water in the air compared to what it CAN hold. The amount of water in the air does not have to change but the amount it can hold will change depending on the temperature. Heating dry air will just lower the relative humidity. A solution as you state would be to evaporate more water into the air such as using a humidifier. Or water pots on your wood/coal stove.

The reason that I brought up the moist air from the chimney as being from the combustion is because that is not "stealing" the water from your house or heated space. It is a separate act. So whether you use coal, wood, or LP the resulting low humidity is not because of your fuel used.

Yes, I'll go along with that. That low RH house air when heated will hold even more water and it will suck what moisture it can get out of any natural materials that have any moisture content in them even faster.


Bob

By Jove! It's all coming together now! DRY air! No wonder those things never happen here! I constantly run the A/C in my car and home/office just to get the humidity out all year long! Good work, Gents! You guys are very smart!

Originally Posted by sharptonn

By Jove! It's all coming together now! DRY air! No wonder those things never happen here! I constantly run the A/C in my car and home/office just to get the humidity out all year long! Good work, Gents! You guys are very smart!

I have a hard time with you wondering if you are being a smart alec or not.

I have to work hard to get rid of my preconceived notion that all you people in the Lone Star State live in the desert

Originally Posted by 32t

I have a hard time with you wondering if you are being a smart alec or not.

I have to work hard to get rid of my preconceived notion that all you people in the Lone Star State live in the desert

No, seriously, as pertinent info was disclosed, the culprit has been identified! I have not ever had to deal with it (dry), but down here by the coast, it is always humid! Amazing what has caused this, but in retrospect the explanations are clear. So. A humidor for razors and brushes? Never thought I would ponder THAT!

I don't think it is the level of humidity, but the fluctuations. Even if you put a solid piece of ivory in such environment it will crack. If you change the humidity slowly it would propagate from the surface into the volume and back and the whole object will expand and contract. If you change the humidity too fast the different expansions on the outside and inside can lead to mechanical stresses high enough to propagate a crack.

Alternatively, if you have two materials with different expansion coefficients bonded together then no matter how slow you change the humidity the mechanical stress at the boundary between the two will increase. With high enough stress you can break either the boundary or the material(s) depending on their relative strengths.

If you just leave it be the crack in the brush also means that further cracks are unlikely to develop. With the crack in place that part has room to respond to the mechanical stresses and it's harder for them to build up to the level necessary to create further breaks.