Does Heating Air reduce moisture content? (For HVAC Folks...and other smart people..

[GTS225]

Re: Does Heating Air reduce moisture content? (For HVAC Folks...and other smart peop

Heat always rises, it never goes sideways (which is why gable vents are no longer used).

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Sorry, Beef.....the inaccuracy of this statement bugs the crap out of me. I gave you five days to correct it, but now I just gotta "out" you on it.

The form of energy that we call heat emanates in all directions from it's source. Heated air rises. I know perfectly well that it's a very common misconception that "heat rises", but it makes a difference in the industry when it comes to clarifying what might be needed in a given situation.

Roger

 

[dolluper]

Re: Does Heating Air reduce moisture content? (For HVAC Folks...and other smart peop

Think Pink check the insulation sites,,,,outside wall needs BREATHABLE membrane all inside walls must have vapour barrier between insulation and the wall finish period...to stop mold or mositure build up .....accoustic caulk is used to seal vapour barrier meeting joints Air is vented over ceiling through attic to aid in cooling and heating not to dry wet insulation come on now

 

[levittownnick]

Re: Does Heating Air reduce moisture content? (For HVAC Folks...and other smart peop

Infiltration of cold outside air with a low amount of moisture and then heating it causes the relative humidity of the heated air to be less even though the total amount of water vapor in the heated air is a constant. Most dwellings constantly exchange outside air with the heated inside air. As this process goes on the relative humidity of the inside air decreases since warm air can hold a higher percentage of water vapor than cold air. Thus outside air that may have a RH of 30 could be less than 10 once heated to room temperature. This is the reason you need humidifiers in the winter to be comfortable. If you want all the boring formulas go to your local library and get a copy of the ASHRAE handbook and get yourself really confused about it works. Condensation on cold surface is caused when conditioned air is cooled to a point where the film of air on the surface falls below the dew point.

Let me say up front that this post was 2 pages long when I started it and I didn't read every response as thoroughly as I would have liked...But as for the original queston "where does moisture go when something is heated"...From an AC perspective no where...Relative humidity is just that relative...If you have a cup of water in a two cup measuring cup you essentially have 50% relative humidity(I know assuming the cup of water was actually a percentage of moisture vapor in a certain amount of air)...When you warm up the air, the airs capacity to hold moisture increases...So essentially if the measuring cup is two cups at 60 degrees it would be more at 70 degrees...So at 80 degrees it might be 4 cups and your relative humidity would be 25%...The amount of water didn't change, but the container that holds it gets bigger and smaller...

Moisture in the air is called latent heat and the only way to get rid of it is by moving it into a medium that is colder(Thats what AC units do)...

If you notice that at 70 degrees your house is 45% Relative humidity and at 80 degrees its its 38% you still have the same amount of moisture in the house...Your house can just hold more moisture at the higher temperature...

BTW one of the byproducts of combustion is water...So the steam or moisture coming out of a flue on a furnace isn't(exactly) the moisture in the house...

dwco5051 post #8 and the above quote (#30) have the question that was asked correct. As long as you don't go down to or below the "Dew point" the ammount of moisture in the air does not change by simply heating the air BUT the "Relative Humidity" does decrease as the air is heated because the quantity of moisture that air can hold increases with increasing temperature.