Window condensation with radiant system

Ken D.

Constantin mentioned something VERY important. High humidity is an indication of a fossil fuel appliance not venting properly. Check you furnace or other fossil fuel appliances.

Kim I

Need help with window condensation

Have a staple up radiant system and have had bad condensation on windows in winter. Raising heat temp. in room doesn't seem to help. Bought a dehumidifier, but is very noisy and bulky. Have an A/C system which is shut off during winter, tried running fan only, but didn't help. Any suggestions?

2500 sq ft ranch, full, partial finished basement, 2 adults, 5 kids, no unvented gas appliances. All vents working properly. Southeast Michigan. Thanks to all for the help and suggestions.

kevin coppinger_4

I have ad this....

issue w/ my last home. Apparently you are producing a lot of moisure inside...do you have a god qualty bath fan and is it staying on long enough? Are you doing a lot of boiling of water/cooking and not veting it outside enough? Do you have any unvented gas appliances ie. gas range, ventfree fireplace? How old is the house? if its new it might take awhile before all the materials dry out.....framing, concrete...you might need to lookinto a whloe house air exchanger to asssit in air quality...kpc

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Brad White

I am with Kevin

Too much moisture and/or your glass is not the best.

Can you measure the RH of the space and what is the glass quality? (Double or single pane? Low-E? As examples.)

I have some charts somewhere which tell you at what RH and outdoor temperature various glass types will exhibit condensation. Regardless you have to measure in order to manage.

Unvented appliances as Kevin mentioned are the general sources. Sometimes unvented dryers, even if electric but especially and more dangerously gas, are huge contributors.

EDIT: Do you have a wet basement of other external moisture sources?

Kim I

Leave the bath fans on until there is no condensation left in the bathrooms. No unvented gas appliances, use microwave fan (vented to outside) while cooking. Condensation usually shows up overnight if the dehumidifier is not going. Will stay all the time throughtout the winter months if don't use dehumidifier. House is 8-1/2 years old. After 8 winters of this, I've tried most everything. Have even thought about changing the A/C only to a heat pump/A/C, but didn't want to spend the money on something unproven.

Kim I

Thanks, have had the window manfr. out and they even replaced half our windows. They are double paned low-E. Window guys insist it is poor air circulation, but, as I said, I have tried leaving the c/a fan on all the time to no avail.

Mike T., Swampeast MO

If a new or extensively renovated home I'd suggest opening some windows slightly for the first season. There are literally tons of moisture that must escape from a typical new home before it achieves reasonably equilibrium.

If not new or recently renovated, unusually warm humid winter weather could be most of the problem.

If none of this applies, start looking for water leaks from the outside, water leaks inside or excessive interior water vapor that is not vented to the outside. Are you perhaps burning an unvented "gas log"?

Steve_35

You have excessive moisture coming into your home.

Are you on a crawl space or basement?

The best bet would be to find and stop the source of moisture entry. Second best would be an HRV.

GW

Could the windows have lost their seal? The window guy may be blowing smoke. Do you have plants next to these windows? So, some windows condense and others do not? Can you narrow down the factors some? You may need a hygrometer to check humidity. Does it condense during mild weather? The more facts you have the better we can help you nail it!

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Brad White

\"Poor Circulation\"

Unless they mean drier outside air leaking in, the term is meaningless when speaking of humidity.

Unless moisture is being removed (absorbed by drier outside air and carried out with the air displaced), circulation is just moving things around.

It has nothing to do with humidity control when it takes place within an open structure. (Lack of circulation may contribute to condensation if the air is stagnant behind thermal drapes I will grant you.)

Low-E glass to me is an indicator of thermal integrity but the fact is, the surface temperature of low-E is no different than a comparable window which is not coated. (The emissivity is a radiant function and the surface temperature is fractionally the same as a non low-E glass.)

Do you have a hygrometer (humidity meter)?

Ted_9

Speculation

We are all guess and there are some great ideas.

Two things I'm also thinking of.

1) The Basement.
2) Is the condensation in rooms that people are sleeping in at night.

Massachusetts

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Darrell

This thread is going to turn into another of those ones that pits scientific theory against practical observation...but, here's my two cents.

Measure the surface temperature of the glass surface of your window. Go back to your highschool science class and remember that air at a given relative humidity will condense on a surface of a given temperature...just like a glass of ice tea. Depending on how cold the surface of the glass is, and how humid your air is...you will condense...it has too...God made it that way.

Now you need to determine if that level of humidity is "excess". It is possible to condense at the surface of the glass and have a RH in the home that is too low for comfort.

Try this. Make the air against the window surface turbulant. A fan will do it...but, so will a simple suction cup for a window decoration...anything to make the falling, (think convection), column of cold air against the glass surface tumble down the glass instead of being laminar. As it tumbles, the cold air at dew point will mix with the relatively warmer air of the room just inches away, and the moisture will be transferred to the "drier" air of the room, leaving the window condensation free. I discovered this the year my boys got dart guns for Christmas...with the darts stuck on the french doors...the condensation cleared up in minutes. Now, we always put suckers on the windows and they stay clear, even at higher RH.

The RH of the air in your living space is directly related to the temperature of the air. The air against the window surface has its own little weather pattern.

With other types of heat...FA or even HWBB...there is a mechanically induced rising column of warmer air against the glass surface which does two things...it lowers the RH/with the corresponding higher dew point, and it makes the air turbulent, disturbing the "little weather pattern." Radiant heat is very stable, no moving air, allowing the "little weather pattern" to develope fully.

Do the math...you'll be surprised how low the RH has to be to prevent condensation.

Try the suction cups...you'll be surprised at how simple it is to work with the physical properties occuring rather than fight with them.

Roughly speaking, with standard good windows at -10 outside and no moving air, the ambient RH inside will have to be less than 15%...and that is too dry. Doctors say to live in ai between 40 and 50% RH to strike a happy medium between viruses and bacterias.

burninben

Kim I where are you located?

Steve_35

Where do you live and what is the outdoor temp when you

notice condensation?

gary bettcher

Airexchanger

Get a airexchanger for your house and the windows will be clear .

Constantin

Water on windows is not normal...

I'd go and look for the source.

• Is the basement dry? Test the air with a Hygrometer, they're $15 at Radio Shack. Then test the walls/floor as described over at buildingscience.com with some polyethelyne taped to the wall and floor surfaces.
  
• Are all the heating appliances (water heater, boiler, etc.) venting properly to the outside? Is the chimney flue blocked perhaps?
  
• Are there bathrooms without properly working fans, roof leaks, or other sources of internal moisture?
  
• Do you have a humidifier? Does it run? (Mine tried to run way too much)
  
• Unvented appliances like gas log sets in fireplaces produce a lot moisture also.

Our house took some time to dry after all the construction, etc. was done. All that water vapor in the wallboard skim coat, the paint, etc. We have a pretty efficient air circulation system that I cycle every 40 minutes for 20 minutes so the air inside the house remains fresh.

Andy_17

> Have a staple up radiant system and have had bad

> condensation on windows in winter. Raising heat

> temp. in room doesn't seem to help. Bought a

> dehumidifier, but is very noisy and bulky. Have

> an A/C system which is shut off during winter,

> tried running fan only, but didn't help. Any

> suggestions?



check the bath fans venting,I've come acrossed many units that are not vented to the exterior. Also if you have access to attic look @ the plywood check for moisture build up or mold. There may not be enough attic venting

Bernie Riddle_2

Condensation

When we first fired our radiant system up a few years back the moisture and condensation was unbelieveable. Its a 1500sq ft slab and was poured 3 months before the system was turned on but there must have been alot of moisture left in the concrete. If I remember correctly there was condensation on the windows the whole first winter, but eventually went away.

Maine Doug_52

In my studio

I have about 400 sq.ft of thermal glass


Measure the surface temperature of the glass surface of your window. Go back to your highschool science class and remember that air at a given relative humidity will condense on a surface of a given temperature...just like a glass of ice tea. Depending on how cold the surface of the glass is, and how humid your air is...you will condense...it has too...God made it that way.

Kim I

Have gotten a lot of good suggestions. House is in Southeastern Michigan, 2500 sq. feet, full partially finished basement (no radiant tube down there). 2 adults, 5 kids in house, bath fans run until windows are clear or longer after bathing. Occasionally got condensation on basement windows, but discovered the cause down there and eliminated it. Condensation is primarily in the kitchen (I run the microwave fan that vents outside a lot), but will show up on any windows if it gets cold enough. I have tried leaving the blinds open a couple of inches at night to keep air circulation back there, and that seems to help until it gets really cold. Have measured humidity with a humidistat, center of room keeps in normal range. No gas logs, no humidifier. Will try the suction cup suggestion, but will probably wind up getting the exchanger.

Brad White_9

Kim- Please define normal humidity range?

Summer "normal" may be 45-55% or higher without AC.

Winter "normal" without humidification added might be 15-20%. 25-30% could be a problem.

Your kitchen- are you sure the microwave hood vents outside and is not recirculating? What night is pasta night? I will be over

Kim I

Absolutely positive that the micro vents to outside--I had to go buy the vent kit when we were building. Have checked it to make sure it is working properly. The gauge I used only had "dry, normal and wet" on it. Probably I should spend the $15 at Radio Shack that someone suggested.
PS--Everybody knows that Wednesday is Prince Spaghetti Day!

Bob Gagnon plumbing and heating

quick fix

a friend of mine left his bathroom fan on 24/7 and it cured his problem. He says the heat bill didn't go up. His problem was a wet basement. You have to watch the mold if the windows are wood. Bob Gagnon

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realolman

Dishwashers add a lot of humidity also.

Christian Egli_2

The quaint look of fogged up windows at Christmas

Not trying to be particularly helpful here, but humidity is a problem in modern hermetically sealed homes. Furthermore, radiant heat introduces no costly air leaking problems and sadly this all traps home moisture indoors... good or bad.

Thus, a modern home such as yours may need an automatic air changing scheme. Seven people adds a lot of life to the home.

Supposing your home is super air tight, all the sucking of the bathroom and kitchen fans may not pump the required air load. Following Bob Gagnon’s suggestion, try cracking open a window, the kitchen window perhaps, when running the fan. This might allow fresh air in while humid air leaves, giving you the air changes you want. Check to feel a draught coming in, you’ll know if it’s working. It might also reduce the noise of a fan trying too hard to suck something out, just like a vacuum cleaner stuck on the drapes.

ALH_4

ventilation

Ace Hardware online sells some inexpensive digital hygrometers. The best, least-expensive plan of attack includes knowing exactly the nature of the problem before attempting the fix. Placing the hygrometer in different areas of the home and observing how the humidity varies with time will tell you a lot.

Heat recovery ventilation systems are the ideal solution to a "too-tight" house. You may be able to retrofit, depending on how partially-finished your basement is.

Mike T., Swampeast MO

Kim,

Again, is this a new house or is this the first heating season after an extensive renovation? If so, all you may need to do is slightly open a couple of windows.

jp_2

replaced windows?

Hmmmmm.

if they have replaced that many windows, my guess is that the rest of the windows aren't far away from needing relacements.

are you sure all condensation is happening on the inside surfaces and not between any of the windows?

what kind of insulation is in the house? 5 kids sounds like a lot of showers, laundry, cooking...breathing.

burninben

C'mon, open a window? You guys know better than that. Kim, you need an air exchanger. Do you have a co detector? If not, get one just in case.

Weezbo

many people have foods they have enjoied for years that

require quite a few gallons of water a day to prepare..there is nothing abnormal about that it is just something that blows right by them sorta like the noise from a clock or a refridgerator...maybe the daily cooking is adding gallonage into the air..some pinner exhaust fan is unlikely to be removing all of it...

there are some pieces of equipment ,called HRV's and ERV's that do a signifigantly decent job of ventilating the home... that would be the best plan..have someone over to the house to do a blower door test...then listen to what he tells you about what the numbers mean in adequately ventilating and controling your environment... go there...you will think it well worth the dollars it may cost up front...controlled ventilation is a key to your long term well being and comfort..

Kim I

That's been suggested before, and methinks that's probably the ultimate answer. Yes, got the CO detector and it's plugged in. Tested it today, since you reminded me...

Kim I

House is 8-1/2 years old, have had the same issues since it was new (and only had two toddlers and a baby). Have recently noticed that the primary condensation points are on the North side of the house. I think the lack of direct sunlight on these windows may be a factor?

Kim I

Seals broke on the windows on West and East sides of home, but not on North or South. Think the North side is the worst for condensation, maybe the lack of sunlight to warm the panes has a lot to do with it??

Mike T., Swampeast MO

Lack of sun could be part of the problem but not the real problem. Frequent condensation on the interior of windows is a symptom of excessive moisture. Both interior and exterior sources of moisture are potential culprits. Cool but unusually humid weather can cause such but weather like that [usually] doesn't hang around for too long.

Jeff Lawrence_25

What kind of CO detector?

If it's one you bought at a box store, you may not be protected as well as you thought.

JimMullins

Condensation

From a carpenters point of view, that sounds like way too much moisture. At 8 1/2 years old your house could be built that tight. Most homes are designed to release the moisture through exhaust fans and attic ventalation. If not, a HRV unit is installed. There are homes that are designed poorly of course. But before I went to the big expense of a HRV unit I would rule-out other possible causes. Quite a few times I have been on jobs where the attic insulation was stuffed into the vent area at the eves so that the warm moist air from the house could not vent out and have seen bath fans vented right into the attic. A clogged dryer vent would do it or a dryer hose came loose from the back of the dryer or in the wall where it goes through. My 2 cents, good luck.

Ken D.

Condensation

Constantin mentioned something VERY important. High humidity is an indication of a fossil fuel appliance not venting properly. Check you furnace or other fossil fuel appliances.

Mark Hunt

Kim


See if you can find someone to perform a "blower door tect" on your home. This will dertermine just how tight the house is.

Moisture issues generally occur with tight homes. Also, if the house is VERY new, this issue may completely go away by the end of this heating season. I would still recommend the blower door test.

IF you do need to mechanically ventilate the house, the blower door test will reveal how much ventilation is needed.

Mark H

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joel_19

testing

i would suggest you hire a member of the Comfort Institute to perform testing on your home.

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