Window Condensation

ced48

Well I put in a Modcon boiler which heats with 120 degree water, +- baseboard radiation, tightened house up with new windows, doors, and insulation. Great, nice low gas bill, but now I have an issue with condensation on the windows. I assume caused by low heating water temperature, and lack of air movement. Is an HRV unit going to solve my problem?

JUGHNE

Sometime extended use of bath and kitchen exhaust fans by use of timers will clear it up. It has worked for me.

Robert_25

Did you do other remodel work that added a bunch of moisture to the house?  Thinset and sheetrock compound contain a lot of water.  If you did a remodel and just closed up the house and turned the heat on, the condensation may clear up in a few days.  A dehumidifier may also help get things to a steady state.

ChrisJ

You didn't give us enough information in my opinion.

Is it all of the windows?

What's the indoor RH and temperature?
Whats the outdoor temperature?

ced48

All windows, RH 50% +, outdoor temp 35 degrees and below.

Zman

I have found that crawlspaces with exposed dirt or basements with inadequate moisture/vapor barriers are often the culprit.

ChrisJ

50% is probably too high in the winter.  I've always heard 35% is safer.  I agree you need better exhaust fans and perhaps need to bring in some air in general.

But I'm not sure I would expect good windows to condensate with it 35 degrees out either even at 50%?  That seems surprising.

ced48

Getting the humidity level down seems to be one of the issues, but when the humidity outside is even higher than inside, seems like a HRV system would be counter productive.

ChrisJ

ced48 said:

Getting the humidity level down seems to be one of the issues, but when the humidity outside is even higher than inside, seems like a HRV system would be counter productive.

Depends on the outdoor temperature.

80% RH at 30 degrees F is only 18% at 70F.
100% RH at 0F is 6% at 70F.

That's why it's relative humidity. This is also why the windows are condensing humidity. The air cannot hold as much humidity when it hits the cold glass so the water literally falls out of it.

Here's an online calculator you can use to see the relation.

http://www.dpcalc.org/

ced48

So, bringing in outside air with a temperature of 35 degrees and a relative humidity of 65% will actually decrease the the humidity level inside which is at 68 degrees and 50% humidity?

ChrisJ

ced48 said:

So, bringing in outside air with a temperature of 35 degrees and a relative humidity of 65% will actually decrease the the humidity level inside which is at 68 degrees and 50% humidity?

Yep.

This is why drafty houses like mine are dry in the winter. It has nothing to do with the type of heat (forced air vs steam vs hot water) etc. But forced air, especially if installed improperly can make infiltration worse.

JUGHNE

Perhaps a big factor in the OP's house is that he got rid of a chimney vented boiler and went ModCon, probably 2 pipes.
The constant flow of basement air up the chimney caused dry outside air to be pulled inside from various places.
Tightening up the house and losing that air flow would add to retaining inside humidity.

Our house is "superinsulated" with vapor barrier everywhere, minimal exterior wall penetrations. We had to run bath fans maybe 30 minutes per use to prevent condensation on windows.
We have a 6" cold air pipe hanging into the basement for fresh air. Now only with a full house on holidays, will we see moisture.
But all the kids live with heat pumps and feel overheated with our 72-74 rooms, so windows are snuck open when they think I am not looking. So plenty of cold dry air coming in.

Jamie Hall

There's a bit of elementary physics involved here. If we suppose an interior air temperature of 70 F and an interior relative humidity of 50%, then you will get condensation on any surface cooler than 50 F. Which a window is very likely to be if it's 30 outside.

This has nothing to do with the source of the heat which is maintaining the interior temperature (assuming it's not open water, of course -- nothing like a hot tub!).

What happens is that if the house is made tight, the natural moisture from human occupancy and activity will often raise the relative humidity into the critical range -- or even higher. Older, draughtier, houses had much better indoor air quality and much lower humidity -- and didn't have the problem.

An HRV (sensible, not latent) will help by bringing in more outside air and lowering the relative humidity -- but if you want high relative humidity, you will have to cope with the condensation.

bburd

@op I don’t want to worry you unnecessarily, but one of the signs that the combustion fumes from a gas fired appliance are not properly vented to the outdoors is high humidity indoors. 

Are you absolutely sure the exhaust from that modcon boiler is venting out of the house as it should? Carbon monoxide from an incorrectly vented gas fire can kill you, and you’ll never smell it.

If you have working carbon monoxide (CO) detectors and they are not alarming, you are probably OK.

pecmsg

bburd said:

@op

If you have working carbon monoxide (CO) detectors and they are not alarming, you are probably OK.

CO Alarms that are UL 2034 listed are virtually worthless. They will only alarm when 70PPM is achieved or exceeded for between 60 & 240 minuets.

Every home Should Have a Low Level Detector!
https://www.myhomecomfort.org/carbon-monoxide-levels-risks/

ChrisJ

pecmsg said:

@op

If you have working carbon monoxide (CO) detectors and they are not alarming, you are probably OK.

CO Alarms that are UL 2034 listed are virtually worthless. They will only alarm when 70PPM is achieved or exceeded for between 60 & 240 minuets. Every home Should Have a Low Level Detector! https://www.myhomecomfort.org/carbon-monoxide-levels-risks/

I've seen people in here say this repeatedly.
If they are "virtually worthless" why is that the standard that was developed and agreed on?

If that is worthless why do we feel other codes and laws are so important?  

pecmsg

ChrisJ said:

pecmsg said:

bburd said:

@op

If you have working carbon monoxide (CO) detectors and they are not alarming, you are probably OK.

CO Alarms that are UL 2034 listed are virtually worthless. They will only alarm when 70PPM is achieved or exceeded for between 60 & 240 minuets.

Every home Should Have a Low Level Detector!
https://www.myhomecomfort.org/carbon-monoxide-levels-risks/

I've seen people in here say this repeatedly.
If they are "virtually worthless" why is that the standard that was developed and agreed on?

If that is worthless why do we feel other codes and laws are so important?

That level was accepted to cut down on 911 calls!
CODES and Laws are Minimum Standards

ced48

I have run a combustion analyzer, 0. Thanks for the tip.

pecmsg

ced48 said:

I have run a combustion analyzer, 0. Thanks for the tip.

0 What?

ChrisJ

pecmsg said:

I have run a combustion analyzer, 0. Thanks for the tip.

0 What?

I'm going to go out on a limb and assume 0 ppm CO. 

motoguy128

I thought it was a time weighted average and lower levels around 10ppm over 8 hours will still trip the alarm. Where more toxic high level will trip it almost immediately. It’s to prevent nuisance trips form ovens and stoves, and keep the price reasonable to there’s widespread adoption of the devices.

That’s my take.

pecmsg

motoguy128 said:

I thought it was a time weighted average and lower levels around 10ppm over 8 hours will still trip the alarm. Where more toxic high level will trip it almost immediately. It’s to prevent nuisance trips form ovens and stoves, and keep the price reasonable to there’s widespread adoption of the devices. That’s my take.

On the UL Listed CO Detectors? No
69PPM NO zero alarms
70PPM OR above 60 to 240 minutes before alarming. 

ChrisJ

pecmsg said:

motoguy128 said:

I thought it was a time weighted average and lower levels around 10ppm over 8 hours will still trip the alarm. Where more toxic high level will trip it almost immediately. It’s to prevent nuisance trips form ovens and stoves, and keep the price reasonable to there’s widespread adoption of the devices. That’s my take.

On the UL Listed CO Detectors? No
69PPM NO zero alarms
70PPM OR above 60 to 240 minutes before alarming. 

They also detect a rapid rise in co.