# Forum Home Renovation Heating & Cooling  Do reverse cycle air cond In heat mode act as a dehumidifier (Ie dry the air?)

## DBR

Here goes.. Since last weekends deluge,, I put the air reverse cycle Delongi air conditioner on heat and full pelt for three days straight in an attempt to dry these old house out.... However I was at work today and a workmate said that me doing so would hand actually added moisture to the air and that the only function that will take moisture out of the air is the "dry" mode of the unit.... 
i personally tjknk sge she is wrong and I'm hoping she is wrong.. Interested in your thoughts???   I believe that the best option with full fan  would dry the air out just as much as the dry option.. Only difference is they the dry option doesn't heat or cool so is cheaper to run.. Interested In what you think? I'm hopkng the three days wasn't a complete waste of time..

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## Marc

Heating increases the amount of water capable to stay as vapor in the room. Unless you have a mechanism to vent this water loaded air out, you are not drying much at all. Cooling on the other hand produces condensation of the water that is in vapor state when it heats the cool condenser and gets drained outside making the air dryer.
Of course this is only in relation to water that is in the air. If you have water in carpets or walls, that water must first find 'motivation' to get out of there and in the air. This can happen if the air is dry, or if the air is hot. Neither a quick process.

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## Smurf

As anyone who has lived in a cool and wet climate will be well aware, heating the interior of a structure will in practice "drive out" moisture over time. In some cases even things like roadside electrical cabinets are internally heated to keep them dry in places where it's regularly cold and wet outside. 
How you add the heat makes no difference with the exception of heaters which themselves produce moisture (unflued fuel burning heaters - gas, kerosene, metho). 
A reverse cycle A/C does not directly remove moisture from the inside air in heating mode although the heat itself will speed up the drying of whatever's wet.  
FWIW - the air-con is removing moisture from the outside air in heating mode and you'll find that dripping out the bottom of the unit. That water came from the outside air not inside however.

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## OBBob

There's a dry mode on my RC/AC... don't know much more about it though.

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## havabeer

the dehumidifier we have fills up a 10 or so liter bucket worth of water removed from the air, unless your air con has a big catchment bucket it isn't taking anything out of the air

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## Marc

> As anyone who has lived in a cool and wet climate will be well aware, ...

  Wow now there is a useful statement ...

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## Whitey66

> Here goes.. Since last weekends deluge,, I put the air reverse cycle Delongi air conditioner on heat and full pelt for three days straight in an attempt to dry these old house out.... However I was at work today and a workmate said that me doing so would hand actually added moisture to the air and that the only function that will take moisture out of the air is the "dry" mode of the unit.... 
> i personally tjknk sge she is wrong and I'm hoping she is wrong.. Interested in your thoughts???   I believe that the best option with full fan  would dry the air out just as much as the dry option.. Only difference is they the dry option doesn't heat or cool so is cheaper to run.. Interested In what you think? I'm hopkng the three days wasn't a complete waste of time..

  If you want to dry out any type of enclosure with heating you need to provide venting or some type of dehumidifier. 
Once the warm air in the enclosure is moisture laden it's ability to absorb more water is limited.
So by heating and venting you can remove moisture, providing the humidity of the outside air is not higher than the inside air.
Have you considered hiring a dehumidifier if you can't afford to buy one?
Or putting the A/C in heat mode to get the moisture in the air, then put it on cool to remove the moisture and repeat several times.
I thought dry mode is a cooling mode with a slow fan speed but maybe it does what I said above automatically??

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## Brian7886

Using the heater to try and dry your home out is the worst thing you could do. What you will be doing is giving a better envirnoment for bacteria to grow in the moisture that is present (assuming your home has more moisture than a normal day). When you arent home id suggest either leaving the air con on the cooling mode (which removes heat and lowers humidity anyway) or if the delongi has a dry mode us it. Dont worry about the temp, when you are home you can always flick it over to heat again anyway. Or try to run it on heating with a few windows cracked to get some natural air flow through the home also.

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## Smurf

A bit off topic but to illustrate the point: 
There are light poles near golf course that have heaters in each and every pole. The ground is always damp, the location is near the river and condensation inside the poles was a problem. 
Electrical cabinets (eg rail or traffic signals) sometimes have a heater installed inside to keep them dry. Never heard of that being done on mainland Australia but I know that it is done at some locations in Tasmania if inspection of the cabinet finds the moisture level to be too high. 
There's a power station on the West Coast of Tas (an extremely wet climate in Winter) where, if the units are out of service, standard practice is to put a canvas cover over the machines with a heater under it to keep the alternators dry. That's a lot easier than trying to dehumidify the entire interior of the power station if it's not running. No problem when it's running of course since the alternators get warm of their own accord. 
At a previous address I had a heater in the garden shed set to turn on at 5 degrees. It was literally dripping wet in there at times, water condensing on the roof and dripping down, but the heater fixed the problem. Nothing fancy, just an electric heater on a thermostat.

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## rod222

Opinion:
I agree with your friend, "dry" mode is only available in cooling mode. 
What you are dealing with generally, is the "dew point", if the outside air is lower than the inside, condensate will form on the inside of your windows.
often seen on the underside of uninsulated tin,  (carports garages etc) 
Often the biggest problem is to seek out the main source of moisture.
I have been battling condensate for 5 years in my property,  I have improved the best I can so far, (sheeps wool insulation, insul blanket under new corrugated roof, replacing perf ceiling sheets)
This morning is around 4-5 degrees and I have minor cond inside windows, my last hurrah, will be underfloor exh fan. 
I live on a slightly sloping block, sandy rubble topsoil for about half a metre, then hard clay,
during rain, water filters down from the surrounding area and passes over the clay, If I dig down at the bottom of my block, during heavy rain, I can actually see
the water passing over the clay.
It is noticeable inside, my jarrah floorboards in winter get a faint curling aspect from moisture underneath, I have alleviated most by French drains etc,
and the last job is to install underfloor venting.

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## phild01

> Often the biggest problem is to seek out the main source of moisture.

  Wouldn't that be normal humidity.  My air con can easily pull a bucket of water from my living room in a day, it being natural air moisture, not structure borne issues.

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## SlowMick

dehumidify the air in a room you generally need to heat it and then cool it. you heat up the air, the air then has a high capacity to hold water vapour.  you then cool the air past dew point and the moisture condenses out on the coil.  dry mode is probably an alternating use of heating and cooling.  you can't use cooling to dry out a room as the oonly way it can dry stuff ut s by evaporation.  while blowing air over something will pick up a little moisture it works better if there is a temperature difference to drive the evaporation.  :2thumbsup:

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## ringtail

Do the windows not open ?

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## Marc

:Stooges:

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## mudbrick

I never knew we had so many scientists in the room.. 
Heat increases the vapour pressure so increases the rate of evaporation / humidity in the air. 
As said above the problem that poses is if you are heating a damp confined space all you end up doing is increasing the humidity in the room which is not going to help. Although in reality your house is not really airtight and you are not trying to dry a swimming pool.s
The second way is to pull humidity out of the air via a dehumidifier or the dry function on your AC. 
Moisture in the room then evaporates more quickly into the dryer air than the into the moist air you had to begin with. The best way would be to heat the space and run a dehumidifier at the same time but you're not going to like your next power bill.  
Apparently philips make great dehumidifiers that look like a little portable AC and have a bucket inside. They fill the bucket in a day and cutout when its full. i Can't remember if they carry 10 or 20 litres but one of those would probably make a good investment.

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## Marc

> Do the windows not open ?

  I think we need to start a contest in this thread. Who can post the most entertaining reply coupled with a covert insult to the others. 
MM
Letseee ...  To dry a room, one can ... open the windows, (preferably when it is not raining) ... wait for summer ... take the roof off and let the sun shine in the room ... lite a fire ... run the aircon in cooling ... hire an industrial heater and run the aircon in cooling at the same time.  
Life is hard ... even harder if you are stupid.  _​John Whine_

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## OBBob

> ... hire an industrial heater and run the aircon in cooling at the same time.

  That's a winner.   :Biggrin:

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## ringtail

> I think we need to start a contest in this thread. Who can post the most entertaining reply coupled with a covert insult to the others.

  Certainly not intended to be a covert insult but if it has been perceived as such then it's a win  :Biggrin:  .

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## Marc

Nee, not directed at you. Actually open the window is perhaps the most sensible answer yet.
...short of heating and cooling at the same time of course  :Smilie:

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## OBBob

Well as far as I know the industrial carpet dryers just blow air (not added heat). You can hire them too.

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## Marc

Aaaaah but you fail to take into consideration the vapor pressure of the left handed molecule who hook up with the H2 and get stuck with the O who then can not let go of the carpet unless it stops raining and the window is open ...  :Rofl5:

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## OBBob

True

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