Helpful? 0

Why does my client have ice and frost on the inside of windows and doors?

I have a client who has ice and frost forming on the inside of her doors and windows. The house is only 2 years old. It was built in zone 6 A. This month she had sent me pictures of what was going on,along with a picture of the thermostat showing:
Outdoors: 10 degrees with 30% humidity
Indoors: 69 degrees with 45% humidity.

The house was given a blower door test and to my knowledge...passed.
It was also given a 5 star plus energy rating. We are thinking that the indoor humidity is causing the problem?

Any help would be appreciated! The house is built on the Hudson River.


Asked by Michael Craig
Posted Mon, 01/27/2014 - 16:39
Edited Sun, 02/02/2014 - 07:09


6 Answers

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Helpful? 1

The dew point of 45%RH 69F air is about 47F, so any time a window or door surface reaches that temp you'll get condensation.

The outdoor air's RH and dew point are irrelevant- but it's temperature is, since the heat loss through the windows & doors is what draws the interior temperature down.

The building scientists consider even 40% interior RH as a "high wintertime indoor humidity". Anything above 30% RH indoors is plenty healthy for humans (even 25% is OK, but 20% is uncomfortable.) That means 45% is truly EXCESSIVELY high wintertime humidity.

The dew point of 30% RH/70F air is about 37F, fully 10F colder than your client's indoor air, and perfectly comfortable/healthy.

Most tight houses need active ventilation to keep the indoor humidity down in winter- in zone 6A it's usually in the form of a heat recovery ventilation (HRV) system, that pre-heats the incoming air stream with the outgoing exhaust air. But exhaust-only approaches can work too. Running a bathroom fan under dehumidistat control during the winter may be enough to get the interior RH down to something that's still in the healthy-comfortable range, and below the ice-on-windows buildup temp.

Answered by Dana Dorsett
Posted Mon, 01/27/2014 - 17:41

Helpful? 0

What is the manufacturer and model of windows on this building ?

Can you get her to measure temperature of the condensing surfaces ?

45%RH should condense only if a surface is at or lower than ~45F ,
so either you have fefective windows/doors or a very poor performing model.

Could you link pictures?
Where on the door and windows is the condensation forming?

Answered by Jin Kazama
Posted Mon, 01/27/2014 - 17:48

Helpful? 0

New home, very cold outside, the humidity is too high in the home. New homes do take some time to lose moisture from materials longer than two years.

The client needs to have no humidifier running. The bath fans need to be on more and the heat has to be set high enough. They may have to crack a window this year too.

Get the humidity down and also as this long cold snap ends all will get better.

This has been a long long cold snap.

Answered by aj builder, Upstate NY Zone 6a
Posted Mon, 01/27/2014 - 18:51

Helpful? 0

Dana : 45%RH is not that high in new tighter home ..the more we resolve the leaking problems , the more we are going to see higher RH% during winter time.

Then, if i read correctly ..we are talking about not solely condesation but also ICE formation .
Now i wouldn't have any problem with water, but ice = inside surface temps of lower than 0c.
This points to a major defect on a component of the windows/door , unless they were bought at
local surplus store in deep rebate ...

It is the second time we have discussion about condensating downd to ICE on windows here,
and in both case it blows straight through ...

unless someone can provide with technical explanation why there would be ice or frost
on an interior face of any recent building coponent ( other then its defeciency ) i'd say your client has a probably more complexe problem than thought ...

Answered by Jin Kazama
Posted Wed, 01/29/2014 - 17:43
Edited Wed, 01/29/2014 - 17:44.

Helpful? 0

Jin: 45% is of COURSE not that high for a tight home that isn't actively ventilated, which is exactly the problem.

The building scientists using 40% as a "high" wintertime humidity level is intended as a warning for underventilated homes, since above that the risk to wood sheathed wood framed buildings rises dramatically. If you ventilate to the ASHRAE62.2 rates you'd be at 20% RH or lower most of the winter in any US zone 5+ location, which is lower than what's healthy for the humans. Keeping it in the 30-35% range is a reasonable compromise.

Answered by Dana Dorsett
Posted Wed, 01/29/2014 - 18:01

Helpful? 0

Dana : yes ..but what is the problem with 40-45%? If the "tight" house has goodperforming windows and wall system, condesation should be rare and no problem ( assuming walls have the correct in/out ratio of insulation ) ..i understand that ASHRAE are for "average" and "safe" values.

So if we take it this way, ventilation should be controlled by a humidistat during winter time,
because anything lower means there is infilatration and fresh air is getting in neway.

Still doesn't address the mr Craig's issue with ice and frost.

Answered by Jin Kazama
Posted Thu, 01/30/2014 - 13:09

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