Condensation on windows: Furnace Dehumidifier?

[battman]

Hello all,

I'm not sure if this is an HVAC issue, but I'm looking for advice and welcome all opinions. Sorry for being so long...

I have a 2000sq ft ranch house in Wisconsin that is about 2.5 years old. The house also has a full basement (just one open room, cement floors, poured cement walls, totalling another 2000 sq ft).

Last winter was my first winter in the house, and there was a significant amount of condensation on the windows when the outside temperature dropped below 35F. At 0F, I would experience dripping levels of condensation from all windows.

When I called my builder (the house was then under warranty) I was told it was just the new house drying out, and to turn on my furnace fan (to run at all times) and run all ceiling fans/bath vents/etc. Additionally, I bought 2 humistats, and found the humidity levels to hover in the 55-70% range throughout the house.

So winter #2 is starting, and the Wisconsin weather has had a few nights in the 30's, and again I'm experiencing some condensation on the windows...not dripping yet...but it's also not that cold yet. My humidiy levels are holding between 55 and 75% depending on cooking/showers/etc.

I have no visible water in my basement or anywhere but the windows...but obviously I have a ton of humidity. I have a small (30 pint) de humidifier that I've had on for a few days. It fills in about 1.5 days, but doesn't seem to be having a great effect on the overall humidity levels. Additionally, I've tried putting it in both the basement and kitchen (so both levels) - and it doesn't seem to matter much. Given, this is way too little de humidification for the size of my house...but before I got buy a bigger one (finally), here's some questions:

Instead of getting a larger stand alone dehumidifier, is anything made that can attach right to my furnace? (home depot wasn't very helpful with this, since they don't carry anything like this) Is this an unusual request/question - or a normal occurance (so any HVAC contractor would know what I need?)

While the above might solve my excess humidity issue - I still am kind of wondering where it's coming from. Can anyone offer an opinion about the house still 'drying out'? I was told 3 years, which seems pretty unlikely to me? I'm also kind of wondering about my cement basement...this might be the wrong forum...but could I be getting excess moisture from my large, poured walled basement? If so, would painting/sealing solve it?

Again, sorry for questions outside of the norm, but thanks for the advice. Jeff

[t527ed]

furnace itself is usually a great dehumidifier. i would get hvac contractor in to look things over. make sure flues are drafting properly, etc. something don't sound right, what is outside humidity? house may be to tight and may need fresh air system.

[deejoe]

check out HUMIDEX. An installation of a Humidex may solve your problem instead of using an electricity guzzling de-humidifier. The Humidex uses approx 35 watts.
http://www.humidex.ca

[billva]

a furnace is in no way a dehumidifier. the relative humidity levels will lower in the warmer plenum and ductwork, but as soon as this air returns to room temperature, the relative humidity levels will return to where they were prior to entering the heat exchanger.

we have installed quite a few aprilaire whole house dehumidifiers, capable of removing up to 90 pints of moisture daily, these can be connected to ductwork or stand alone.

more info at http://www.aprilaire.com

good luck.

[t527ed]

if furnace does not dry out air then why are houses with hot air heat so much drier in winter time than a house with hot water heat???

[pecmsg]

Originally posted by t527ed
something don't sound right, what is outside humidity? house may be to tight and may need fresh air system.

You may want to look into a HRV for this house. 2 ½ years old, you might have gotten a builder that did a great job, and the house is not breathing properly. Call your contractor and ask about a Heat Recovery Ventilator.

[billva]

Originally posted by t527ed
if furnace does not dry out air then why are houses with hot air heat so much drier in winter time than a house with hot water heat???

infiltration.

[t527ed]

Originally posted by billva

Originally posted by t527ed
if furnace does not dry out air then why are houses with hot air heat so much drier in winter time than a house with hot water heat???

infiltration.

oh, houses with hot water heat don't have that??

[billva]

where do you drain all this humidity removed by a furnace?

[t527ed]

Originally posted by billva
where do you drain all this humidity removed by a furnace?

damn if i know were it goes but it sure does dry the house out compared to other types of heat.

[amd]

It's called relative humidity for a reason. Heating systems do not remove moisture - they simply increase capacity of it.

30F outdoor air is @ 60% RH is very dry when heated to room temperature for example. Newer homes have much less infiltration relative the moisture produced by occupants.

Homes with natural draft furnaces tend to be much drier - outdoor air has to displace what goes up the stack.

I would have thought that all hvac technicians grasp the concept of relative humidity. Guess not.



[Edited by amd on 10-27-2005 at 08:13 PM]

[tinknocker service tech]

dumb question
is there a humidifier on the system and if so is it working properly.
what was the level durning the ac season or when you were running the ac

[docholiday]

If I were trying to solve this one, I would merely allow some cold outdoor air in. (fresh air) The RH will drop

[t527ed]

Originally posted by amd
It's called relative humidity for a reason. Heating systems do not remove moisture - they simply increase capacity of it.

30F outdoor air is @ 60% RH is very dry when heated to room temperature for example. Newer homes have much less infiltration relative the moisture produced by occupants.

Homes with natural draft furnaces tend to be much drier - outdoor air has to displace what goes up the stack.

I would have thought that all hvac technicians grasp the concept of relative humidity. Guess not.



[Edited by amd on 10-27-2005 at 08:13 PM]

still does not explain why hot air furnace dries house out more than hot water boiler. both draft up chimney.

[Edmund Forsthe]

if you dont have storm windows try putting one in and see if it helps with that one window

[t527ed]

Originally posted by Edmund Forsthe
if you dont have storm windows try putting one in and see if it helps with that one window

O P stated 55-75% humidity, don't think its a window issue.

[battman]

Thanks to everyone for the replies thus far...

To answer the questions I saw: Yes, there is a 30pint dehumidifier that's been on for a few days (I think 4 days this year...but I tried the same one for awhile last winter too)...it fills and needs to be emptied, but it seems to have zero effect. I don't know much about dehumidifier capacity, but I think it's rated for a house about 1/4 sq ft of mine (when you include my basement)...

There was another comment about opening a door for ventilation. I actually tried that last year...and a window...the issue of course is that quickly I get a very cold house (I did this on the worst days - it was probably 1 degree out)...no matter how much heat I seemed to waste, it didn't seem to have much of an effect (if any) on the window condensation...

Thanks again, looks like the repeating suggestion is to get an HVAC guy in to look at bigger humidifier or some type of ventilation system...

[mister freeze]

tinknocker, not dumb. I was thinking the same thing. should have a tech check it out, and if there is a humidifier have them install a humidistat.

[Carnak]

The first winter after new construction there is moisture, but ventilation should take care of it. The ventilation would work hard the first winter.

Dehumidifiers are designed to work the best in summer time, they will not be effective when you need to be pulling the RH down in your house to be low enough to stop window condensation in the dead of winter.

You seem to realize that cooking and showers create humidity, and as a dumb sounding suggestion, make sure you are not hang drying laundry in that big basement.

I would assume that there is a vapour barrier under the basement floor slab. Easy test would be to place a pail on the slab, go back a day or so later and pick up the pail and see if there is a ring of moisture under it.

Most likely you need to ventilate, exhaust some humid air and replace it with cold dry air to dry out the home.

For a house your size you would need a system capable of moving 180 to 200 CFM. This ventilation system could be controlled by a dehumidistat to turn on when RH rises. The setting will depend on how cold it is outside and how good your windows are. I would initially try a 35% setting once the outside temp falls below freezing.

If the system maintains 35% and there is still condensation, then lower the setting. You may find that a higher setting of say 40% will work as well. This depends on the quality of your windows.

Your house sounds fairly tight so exhausting a large amount of air could make chimnies spill. You should make a provision for a way for air to get back into your house.

Exhaust fans with a make up system will work. The Humidex mentioned by others are just a packaged exhaust fan.

Our group's leading dehumidifier salesman has recently suggested a good test and I am going to plagerize him here and now. Since it is not overly cold out right now, crack open a couple windows and run the clothes dryer on 'air fluff' for a few hours and see if RH starts to drop off. Other wise try a couple bathroom fans continuously for a day or so. Do this when it is in the 40s outside.

You mentioned that you opened windows before and were concerned about all the cold air at 0F. You may be interested in a heat recovery ventilator or HRV as pecmsg
has already suggested. This is a successful system used in Canada and other northern states.

This system exhausts humid indoor air through a heat exchanger, and at the same time it draws in cold dry air from the outside. The exhaust air heats the fresh air and recovers 60 to 70% of the heat that would otherwise be going straight outside.

In your case if it was 0F outside and 70F inside, an HRV could recover 65% of the heat you are exhausting.

There is a 70 degree temperature differential between indoors and outdoors so the system could recover 70 x 0.65 = 45.5 degrees. The fresh air coming into your house would get heated from 0F to 45.5 degrees, so your heating system would not have to work so hard to compensate for the ventilation.

Another fine edit as I really need to use spell check and the 'preview post' option more frequently





[Edited by Carnak on 10-28-2005 at 01:24 AM]

[dan sw fl]

Originally posted by deejoe
check out HUMIDEX. An installation of a Humidex may solve your problem instead of using an electricity guzzling de-humidifier. The Humidex uses approx 35 watts.
http://www.humidex.ca

"
WHAT YOU GET WITH YOUR HUMIDEX:
10-year warranty on all parts.
Lifetime warranty on cabinet (against rust or corrosion).
Vented outside like a dryer no heavy buckets of water to pour out, no filters to change or wash.
Installation time 1 to 2 hours, complete with assembly kit and instructions. Quiet operating fan (55dB).
Powerful - able to process 205 cfm (independent lab test)."

WHAT YOU GET is
a SIGNIFICANT, additional ~20% heat loss ! ...
Q = 1.08 * dT * CFM
__= 1.08 * 40 * 200 = 8640 BTUh

REAL cost $200 annual +