# Moisture in Unheated Room



## matt151617 (Jun 26, 2011)

I have a sunroom on the side of my house that's designed for year-round use. It has an electric baseboard heater and new vinyl double-hung windows. The former owners used it as an office and play area for their kids. It's off the living room through sliding glass doors. I don't have any use for it, so I left the heat off and shut the windows. I noticed there's no insulation above the plywood ceiling and electric heat is expensive.

On the cold mornings now, the room is covered in moisture. The ceiling is dripping with water and there's enough condensation pooling in the windows that it freezes into a little ice. The only way I seem to be able to stop this is turning on the heater (which heats it up to about 70 even on the lowest setting) or leaving the glass doors open.

I hate to waste money on heating a space I'm not using, but I don't want the moisture to wreck anything. Any ideas?


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## jburd964 (May 4, 2009)

Open are crack one of the outside windows and leave it, the cold outside air should remove the moisture from your room. I would suggest you inspect the connecting walls, windows and attic looking for heat loss into sunroom. If its that cold where your at, a non heated room should be a lot drier. Heat contacting cold extracts moisture.

I'm not a professional., But I did stay at Holiday Inn Express last night.


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## gregzoll (Dec 25, 2006)

Place a dehumidifier in the space. If you are getting that much moisture in the space, no telling what it is like behind the wall covering. How warm is this space, and you really need to find out why it is behaving like it is, which it shouldn't if unheated. It should be just like a garage that is insulated, but not heated in the Winter. It should not have any condensation in it.

Get a humidistat to find out how much humidity is in the air vs. ambient air temp.


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## jklingel (Dec 21, 2008)

jburd964 said:


> Heat contacting cold extracts moisture.


 MOISTURE, I am sure you meant, contacting cold results in condensation.
OP: Is there any way to better insulate and air seal between the heated and non-heated room? That would sure help, if at all possible. Then you could leave a window wide open and PROBABLY be OK. (That depends on how much air and moisture are leaking out there, of course.)


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## Blacek (Dec 13, 2011)

You need to make sure you have a vapor barrier material installed, especially under the floor. Vapor barrier paint is available as well. Also put down r21 or greater insulation under the floor and r49 or greater in the ceiling. Not sure if you said the walls were already insulated. The warmer moist air of that room is condensing when it hits the cold walls.


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## matt151617 (Jun 26, 2011)

I am in the process of adding insulation above the ceiling. There's no foundation underneath the room so it would be almost impossible to insulate from below.

I have a dehumidifier in the basement that doesn't really need to run in the winter, but I was under the assumption a dehumidifier doesn't work properly when the temperature gets under 40 degrees.

There's no way to insulate between rooms better without sealing up the glass doors. By leaving the door open a little and letting some of the house's heat out there, it keeps it pretty dry except a little condensation on the windows.

Inspected the walls and everything appears in order. Only difference I noticed is the sunroom has plywood ceilings with no insulation as opposed to drywall ceilings with insulation in the rest of the house.


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## Blacek (Dec 13, 2011)

If possible, try to at least insulate the ceiling, r49 or better. That would probably help a bit. Maybe you could have some insulation foam sprayed under the floor? Dont know too much about that stuff, so do a little research first about what it is made of and any possible safety issues (is it flammable, etc). If the foam seems ok, maybe it will double as a vapor barrier too.


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## Gary in WA (Mar 11, 2009)

You need heat after the sun goes down. As you said open the sliding door and live with the results. Or, insulating night-time shutters (R-5-10) on the cold glazing (R-2-5)- my second choice, or, install some thermal mass; http://www.buildgreen.ca/2008/09/an-explanation-of-thermal-mass/
Water barrels would work well, let me know further...

Gary


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## JoJo-Arch (Sep 15, 2011)

I see the problem resulting from two things. One is, the room not being used at all and not heated means the walls and ceilings are extremely cold. Secondly any moist air that enters the room by someone opening the glass doors if only for an instant, will result in condensation. 

Would you believe up to a pint of water condenses from mosit air every hour for a medium size space. Just breating in a cold room will produce droplets on cold ceilings over a period (like if someone sleeps in the room overnight).


To address these two conditions, are you able to insulate the walls and ceiling to stop loss of heat and so you can maintain their surface temperature.
Are you able to seal the room from moist air?
If the answer is no, you need to allow the space to reach room temperature as for the rest of the house. Can you use a different form of heater to an electric radiator system? Surely in such a cold climate, there was provision for house heating, like a fireplace in each room, slow combustion heater or possibly gas. People also install oil heaters, hot water radiators and such like. There is always a source of heat, or people simply woudn't live there. 

Even eskimos are snug in their igloos (ice is a good insulator) and light a central fire. 

If you have no other choice but electricity, your best option is a reverse cycle A/C unit. with split diffuser. These units use 2.5 kW (watts) of electricity to produce approximately 3-1/2 times the heat out put that is around 8 kW.
That's like running 8 bar radiators for the price of 2. 

The larger your house, the bigger the unit required. An 8 kW unit will just do 18-20 squares. It will also give you 7.5 kW of cooling on a hot day. Most importantly, it will remove 3 pints of water from the air every hour its on. 

Today's units have inverters which ramp up or down depending on conditions. When your house is warm, the units work very little and consume little electricity. This depends how quickly your house loses heat, or simply how well its insulated.

Hope you understood the simple physics at play here.
Cheers from Joe in Oz


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## JoJo-Arch (Sep 15, 2011)

I see the problem resulting from two things. One is, the room not being used at all and not heated means the walls and ceilings are extremely cold. Secondly any moist air that enters the room by someone opening the glass doors if only for an instant, will result in condensation. 

Would you believe up to a pint of water condenses from mosit air every hour for a medium size space. Just breating in a cold room will produce droplets on cold ceilings over a period (like if someone sleeps in the room overnight).


To address these two conditions, are you able to insulate the walls and ceiling to stop loss of heat and so you can maintain their surface temperature.
Are you able to seal the room from moist air?
If the answer is no, you need to allow the space to reach room temperature as for the rest of the house. Can you use a different form of heater to an electric radiator system? Surely in such a cold climate, there was provision for house heating, like a fireplace in each room, slow combustion heater or possibly gas. People also install oil heaters, hot water radiators and such like. There is always a source of heat, or people simply woudn't live there. 

Even eskimos are snug in their igloos (ice is a good insulator) and light a central fire. 

If you have no other choice but electricity, your best option is a reverse cycle A/C unit. with split diffuser. These units use 2.5 kW (watts) of electricity to produce approximately 3-1/2 times the heat out put that is around 8 kW.
That's like running 8 bar radiators for the price of 2. 

The larger your house, the bigger the unit required. An 8 kW unit will just do 18-20 squares. It will also give you 7.5 kW of cooling on a hot day. Most importantly, it will remove 3 pints of water from the air every hour its on. 

Today's units have inverters which ramp up or down depending on conditions. When your house is warm, the units work very little and consume little electricity. This depends how quickly your house loses heat, or simply how well its insulated.

Hope you understood the simple physics at play here.
Cheers from Joe in Oz


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## joecaption (Nov 30, 2011)

I think Jo Jo is talking about a mini split unit.
And he's right it works great and cost very little to run. I live in a tiny one bedroom house and I went from gas heat that was costing over $150.00 a month to a small mini split and my total electric bill is about $40.00 in the winter and summer and I have not bought gas in 2, years since I put it in.
(I use gas for my cooking stove.)
The lowest temp. I can set mine is 58 deg.


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## matt151617 (Jun 26, 2011)

Thanks for the info. I've been in the process of putting R-30 above it, it's just very difficult to get to. The rest of the house is also under-insulated. The sunroom was an addition at some point; the wiring is all new and there's no foundation under it. The rest of the house is heated with oil hot water so there's no hot water radiator out there.

Here's the humidity readings I got:

Inside the house, 62 degrees, 56% RH
Outside the house, 30 degrees, 68% RH
Inside the sunroom, 46 degrees, 88% RH

It sounds like I'll just leave the glass doors open and get the insulation down asap. The house air seems to provide enough warm air to limit the condensation to only the windows and not enough to cause any pooling of water.


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## ccarlisle (Jul 2, 2008)

I'm interested: what do you mean exactly by the room "has no foundation"? Do you mean it is sitting directly on the ground?

I am sure that, by now, it has occurred to you that surpressing the source of heat in that room isn't really a viable option as it is the heat that controls - or keeps in check - the moisture level. So, where is that excess moisture coming from?

It seems that the room was built as a three-season room insulation-wise - but was forced into being a four-season room with the addition of the electric heater...as in trying tp get the best of both worlds. In our climate, that's almost impossible. You either build the room to be a four-season room with the proper level of insulation etc - OR you must be prepared to heat an under-insulated structure. By adding insulation on the roof part, you're about to lower your heating costs by a bit - but you'll still need to heat it. And unless you fix the moisture issue, you'll also still need to heat it, no matter what insulation level you have in there now - or later...

The heat will warm the interior elements and keep the ice-formation from happening; it will reduce the RH too at the same time. But you're stuck, IMO, with either having to heat it or dehumidify it one or the other.


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## matt151617 (Jun 26, 2011)

Yes, as in there's no basement under that part where there is in the rest of the house. I'll try and see if the walls are insulated, but it probably doesn't matter much, since most of the room is windows.

I noticed on my electric bill history the former owners were using 4 times the electricity I use now... probably due to the fact they were heating an uninsulated room...


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## ccarlisle (Jul 2, 2008)

Ah-ha, I see; ideally, there would have been a vapour barrier right on the ground (underneath the room) and ventilation at a minimum. But you may have neither...hence the source of humidity.

I don't think there's much point in checking for insulation on the walls; it would make little sense if there was, and probably there isn't. Either way, the moisture is coming from under there - and that's your #1 issue at this point. 

Yes, moisture could be coming from the inside every time you crack the doors, but my money is on the constant, cold-temperature-driven release of moisture from the ground up. There is pleanty of advice on crawl space insulation around, but most of it assumes you have access to the area underneath...if you don't have that access, I'm afraid your choices will be limited to keeping on a minimal amount of heat and ventilation to keep the condensation at bay.


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## gregzoll (Dec 25, 2006)

Or, they could have been the types to leave every light on in the house, run the hvac at cooler temps during the Summer, and higher temps during the Winter, and tended to leave doors open a lot along with Windows to let outside air in.


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## pyper (Jul 1, 2009)

Find a way to spread a plastic sheet on the ground under the room and I bet your problem is (at least mostly) solved.


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## Evstarr (Nov 15, 2011)

Try putting a sheet of plastic down on a section of the floor. Tape it down all the way around to seal it. Lift it up the next day and see how much moisture is under it or on top of it. Should at least give an indication of where the excess moisture is coming from


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## matt151617 (Jun 26, 2011)

I finished insulating the ceiling with R-30, and added weather stripping to the door, and both made a huge difference. However, even with the glass doors open, I'm still getting enough moisture off the windows to make a small pool on each sill. Am I at the point where I need to run a dehumidifier constantly? It got to the single digits here last night and is still only in the teens. The temperature is in the high 40s/low 50s in the sunroom and 60 inside most of the time. RH is 51% inside, 53% outside.


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## ccarlisle (Jul 2, 2008)

_"Am I at the point where I need to run a dehumidifier constantly?"_

What you are witnessing is ambient air at 51% RH at the gauge, but in effect you have 100% RH at the window itself, and hence the condensation. Now what you could do is put a fan on in there to make the 100% RH at the glass come down. Then the condensation will go.

So, yes to answer your question, you can run a dehumidifier in there constantly and what you'll get is a lowering of the RH in the room to levels dependent upon the machine you use. But you'll only be dehumidfying the surroundings, like the soil beneath. You'll get rid of the condensation alright but you'll be emptying the tank fairly frequently and the machine will struggle keeping the RH down at dry conditions...

Try a cheap oscillating fan, about a 14-inch or bigger, first to see if that'll clear the windows. Cheaper than a dehumidifier


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## matt151617 (Jun 26, 2011)

I tried the fan and it helped a bit, but there's still condensation. I brought the dehumidifier from the basement up, but the compressor isn't running very much. I think it's too cold and the coils are freezing. 

So far the only solution I've found to really dry it up is supplemental heat. I hate doing this when I'm already heating the rest of the house and not even using this room.


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## ccarlisle (Jul 2, 2008)

Well then, you've given it your best shot...and sure there's more you could do and farther you can go - but everything in due course.

Let's look at it from a moisture point-of-view here a minute: what you have is moisture in the form of water vapour entering that structure (it comes from _somewhere _after all) and it is sitting in the air in that form. Now when it meets a surface cooler than the Dew Point, it condenses and turns into water... Now there are a number of ways you can minimize the appearance of condensation and one of them is to heat the air. In doing that, you don't change the amount of moisture in the air - you just change the appearance of it in the form of water. 

You already tried to increase the ventilation of the moisture but again that'll only displace the appearance of the moisture. Same thing with the dehumidifier; there you actuallly removed the moisture in the air - but yours didn't seem to work (not sure why. Freezing coils, eh? something's wrong there...).

So your only remaining course is to heat the room. As I said, that'll make the appearance of the moisture dissappear, but it'll still be there. So, the long-term solution is to deal with the water that is coming in. 

You haven't addressed that by adding the insulation, sorry. You've just made it easier for whatever heat that is generated in that room to stay in the room and not escape to the outside, but you still have the moisture issue left. 

Now the moisture could be coming in from below - or just from the outside. Outside, right now up here, it's 63% RH so there you go: that's where some of your moisture is coming in from.

Electric heat - apart from supplying convection currents (similar to the fan) - has a drying effect on RH, so you can expect the RH in the room to drop.


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## matt151617 (Jun 26, 2011)

For some reason only the fan was running on the dehumidifier, the compressor was barely coming on. After a couple days, now it's working great. I'm getting about 18 pints a day out of the air. The sunroom's humidity is now equal with the house, and there's no more condensation anywhere. We had a lot of rain yesterday, and now it's in the 20s, and the windows and walls are still dry. I don't have a forced-air system (baseboard hot water heaters), so the humidity stays up during the winter.

Thank you very much for all your help.


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## ccarlisle (Jul 2, 2008)

Ah-ha, well OK then...

18 pints of water eh? That's huge. Just shows you how much - in terms of volume you can measure - is in the air we breathe every day. As time goes on, that volume will go down a bit, so you won't have to be having to empty the reservoir as frequently.

You might want to consider having the electric heater to come on at about 45-50 deg F or so just to help out a bit; it will create a convection current up from the floor and against the window glass, provided it has a free channel to do so but if you have a lot of glass, it won't keep all glass clear. 

Glad it's sorted! Good luck.


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## JoJo-Arch (Sep 15, 2011)

Hi!,
Carlisle's advice is spot on. Two things you may or may not have looked at are, did you check the ground under the floor if it's moist? and can you put a vapour barrier to isolate moisture coming up from the ground?. 
Also, is it possible to double glaze the window/s? This should help to keep the inside surface temperature of the glass above the dew point.

If you need to see how condensation works and occurs in seconds, put water in a kettle and allow it to come to the boil. Get a small metal saucepan and fill with cold water. Hold saucepan a few inches from spout of kettle. Instant condensation on the saucepan surface. Now replace the cold water in the saucepan with hot water, and no more condensation.

Air holds water in suspension as a gas. Provided the temperature is above the dew point, this moisture is invisible. Lower the temperature, and the dewpoint is reached, so the water in the air condenses, hence we have dew on the ground every cold morning, even if it hasn't rained.

Cheers! from Joe in Oz.


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