Could Steam Heat Cause Mold/Mildew Around Windows and Mouldings?!

keyserjose

So, I just had the house insulated and "air sealed" through a State-run program that pays for most of the cost. The work was completed in mid-late September and by early to mid-November the 2nd floor unit (I own a 2-family, live on the first floor with hot water heating and rent the 2nd floor which has steam heating) started to grow mold (could be mildew) around all of the windows and on a lot of the baseboard moulding. The bathroom fan is working and venting properly and this mold thing has never happened before. My investigations have lead me to the steam heating as the prime suspect. I've posted on this site once before and found out that I probably need to skim the boiler, but haven't got to that yet. I had a couple radiators spitting water last year, but that doesn't seem to be happening this year. Still I can hear some sounds in the steam pipes that sound liquidy.

I guess my questions are: is there a good way to determine if the air that comes out of the vents is wet enough to make the house this humid (~75% according to my dehumidifier) and is there a good way to dry up the air/steam to try to reduce this issue? Has anyone heard of an issue like this? Thanks in advance.

Jose

Canucker

Not likely that the steam system is leaking enough for condensation to build up. More likely that your home is no longer leaking air since the insulating and air sealing was done. If you haven't installed an HRV or ERV since the work was completed then you are seeing the humidity that is present from your normal activities that used to escape to the outdoors before

Jamie Hall

Your dewpoint is about 62 to 65 under your quoted condition. The excess humidity isn't from the steam heat, though -- that's irrelevant and has nothing to do with it.

Now that you have a nice tight house, you are dumping a lot of moisture into the air just by daily living, and any surfaces which are below the dewpoint temperature will be wet -- and will grow mold. The only solution to the problem is to bring the humidity down to something more reasonable -- around 40% should be satisfactory. Because of other indoor air quality considerations (you're looking at a symptom here) you should, as @Canucker suggests, add a heat recovery ventilator to your house. You are looking at a minimum of two air changes per hour for air quality considerations, and four would be better.

keyserjose

Jamie Hall and Canucker, thanks for the response, though I'm a bit bummed to hear that you don't think it could be from the steam heating system... I live with my wife, a dog and a cat and a lot of plants downstairs and have no problems with moisture at all. I assumed that this was because of our baseboard hot water heating. Upstairs is just two 20-somethings and steam heat. I should add that last year I was dealing with overpressure issues before I spoke with some folks on this site and got it under control, so potentially there are some broken air vents up there. I'm planning to change out any vents that I didn't change last year at least to see if that helps.

A question on air venting - I don't know if the main line vents in the basement are working or not. Would it make sense for me to change those out before the radiator vents or is there a way to confirm that they're working properly? I was also thinking maybe I should make sure they're sized appropriately. I read here that it depends on the volume of the main line piping (not risers) so I measured mine. I have two mains and the south run is roughly 20ft of 2" and 13ft of 1-1/4" pipe. The north run is 14ft of 2" and 10ft of 1-1/4" pipe. So, if the 2" pipe is about 0.022 cf/ft and the 1-1/4" pipe is about 0.009 cf/ft I think I have:
South run = 0.55cf
North run = 0.39cf
and, each run has a, potentially functional, Ventrite #77 at the tee down to the wet return. I've also read here that I should elevate the main line vents at least 6" - I think I can get 9". I'll attach a photo of the vents and near boiler piping. Oh, and in case it matters, I was once told here that my boiler was approximately 260% oversized (it was like this when I got here :-/) and that might be a record for this site. So, I guess I have two additional questions - Do those vents seem appropriately sized? And, am I in first place for oversized boilers?

keyserjose

pecmsg

Youve tightened the house to the point that you need mechanical outside air ventilation.

Whole house dehumidifier with an outside air connection.

ethicalpaul

Canucker said:

Not likely that the steam system is leaking enough for condensation to build up.

Unless it is

Jamie Hall

On main vents -- do you have a low pressure gauge? if so, it's rather easy to tell if they are adequate -- never mind working. Watch the gauge as the system fires -- if it rises to no more than a few ounces and then sits there for a while after it starts to boil -- on a small system like yours, for perhaps 10 to 15 minutes -- you're fine (it may rise again after that, as all the radiation fills up). Otherwise, if the pressure just keeps rising, you need more (or functional!) main venting.

A serious steam leak could contribute to high humidity -- but you'd likely be aware of that in the water usage of the boiler.

The downside of a tight house is excess humidity, and there is an odd -- or perhaps unexpected -- thing about it: humidity generated in one area (in your case, your plants!) can happily condense somewhere else. Unless not only your house is tight, but the separation between upstairs and downstairs is tight, that somewhere else could very well be upstairs.

Rob_40

Off topic, but is that pigtail installed properly? Seems it could fill with water and reach the guage. I really dont know.

keyserjose

Jamie Hall said:

On main vents -- do you have a low pressure gauge? if so, it's rather easy to tell if they are adequate -- never mind working. Watch the gauge as the system fires -- if it rises to no more than a few ounces and then sits there for a while after it starts to boil -- on a small system like yours, for perhaps 10 to 15 minutes -- you're fine (it may rise again after that, as all the radiation fills up). Otherwise, if the pressure just keeps rising, you need more (or functional!) main venting.

Yes, thanks to the good people of HeatingHelp (might have even been you) I was walked through the installation of a low pressure gauge to supplement my existing gauge. Currently, the boiler goes through a handful (4-6?) of cycles between 0.5 and 1.5psi before satisfying the thermostat. I don't know if that's because the boiler is oversized or if the vents aren't working or something else. I just removed the main line vents and ran some water through them and was able to blow through them OK and then put them back on.

Jamie Hall said:

A serious steam leak could contribute to high humidity -- but you'd likely be aware of that in the water usage of the boiler.

I have an automatic water feeder, so I'm not sure I would be aware of excessive water usage. Is there another way to tell?

Jamie Hall said:

The downside of a tight house is excess humidity, and there is an odd -- or perhaps unexpected -- thing about it: humidity generated in one area (in your case, your plants!) can happily condense somewhere else. Unless not only your house is tight, but the separation between upstairs and downstairs is tight, that somewhere else could very well be upstairs.

I don't believe that any sealing was done between the two apartments, so there could still be air moving between the two units. But, I was assuming that in order for our air to go upstairs their air would need to be leaving as well... but, I'm not an airologist. One more thing to consider anyway.

pecmsg said:

Youve tightened the house to the point that you need mechanical outside air ventilation.

Whole house dehumidifier with an outside air connection.

Is this something that typically gets installed in a well-sealed house? Sounds expensive to install and to operate... let's hope it doesn't come to that, but it beats a mold infestation.

Jamie Hall

No, unhappily, adequate outside air exchange is not commonly provided. It should be, but isn't. And actually, it's not all that expensive. It's a lot easier if there is any ductwork, but can be done without.

Hap_Hazzard

Steam heat makes my house so dry I have to run a humidifier. I guess I'm fairly sensitive to dry air; my nose bleeds from November to April. I do get some condensation on my windows, but I blame this on the windows. Some are worse than others, but they all get condensation when there's a cold wind blowing on them. One of these years I'm going to replace them.

Canucker

ethicalpaul said:

Canucker said:

Not likely that the steam system is leaking enough for condensation to build up.

Unless it is

Anything is possible. Perhaps someone is misting the windows each day with a spray bottle,

ethicalpaul

one or more leaks could easily be putting a gallon or more of water per day into the house, so I'm just saying it's not that unlikely

keyserjose

Rob_40 said:

Off topic, but is that pigtail installed properly? Seems it could fill with water and reach the guage. I really dont know.

Sorry, I must have missed your post the other day. What I don’t know about steam heat could fill volumes, but I do know that if my pigtail is functioning properly it is filled with water. A liquid water barrier protects the gauge from the steam that would be much hotter than the water can get. I’m sure the Jamie Halls of this site can elaborate if needed. 

keyserjose

@Jamie Hall you mentioned the dew point in my house was probably 62-65. I’m curious where you derived that number from. I’m also curious if you think condensation could be forming within the walls causing mold where I can’t see it.

Jamie Hall

keyserjose said:

@Jamie Hall you mentioned the dew point in my house was probably 62-65. I’m curious where you derived that number from. I’m also curious if you think condensation could be forming within the walls causing mold where I can’t see it.

Kind of winging it. You mentioned a relative humidity (75%) and I assumed a temperature (70) and then just ran the standard dew point calculation from that. There are calculators for that on the web. Plug and chug...

Condensation within walls is one of those topics. The short answer is, it depends. If there is some sort of vapour barrier as part of the interior wall, probably not. In really good modern construction, this might be heavy polyethylene, carefully sealed electric light fixtures and sockets and the like are particular villains!). This might also be closed cell foam. In older construction, plaster over lathe does pretty well. Sheetrock or plasterboard, however, doesn't. Middle aged construction with fiberglass batts with a vapour barrier also work pretty well -- if they are carefully installed. Without a vapour barrier, however, somewhere in the wall thickness condensation will occur -- unless the wall cavity can breathe enough from the outside to keep the humidity in the cavity pretty dry. Some types of walls it just isn't a problem -- brick, stone, concrete (not cinder) block, poured concrete. Old construction, where your wall is basically clapboards, sheathing boards (not plywood), air space, lathe, plaster is not a problem.

It's a matter of balancing dry (cold) air exchange and heat loss...

keyserjose

Thank you everyone for your input. I’ve got a few HVAC guys coming by to look at installing an HRV. I’m also considering a mega bathroom fan that would run full time (or maybe on a smart switch). I may try that first depending on the costs I get for the HRV. 

motoguy128

Stack effect! Or sometimes called chimney effect. IF you have a 20’ tall house. Hot air rises, so warm air rising creates a positive pressure at top causing air to leak out and that results in a negative pressure at the bottom….. both relative pressures to the outdoors.

IFyou have lots of plants downstairs you are creating moisture from evaporation and normal activities. In colder weather dryer air leaks in downstairs and the humid air then leaks out upstairs.

I have a steam humidifier for my 3600sqft brick Victorian with original windows. I can often be 30% RH downstairs in colder weather and 35% upstairs even though the humidifier is only installed on the downstairs system.

dabrakeman

Maybe 20 somethings produce more humidity than older folk Given the oversize of the boiler just double check that the radiator vents upstairs actually close when the radiators are full of steam (when steam reaches the vent). Increase the temperature a few degrees and then after the boiler has been running maybe 45 minutes or more check with a mirror that the vents are not releasing steam.

keyserjose

Just wanted to follow up on this humidity / condensation issue to let you all know what I ended up doing. I ended up researching and installing a ~105 cfm (max) HRV that's probably really moving 65-75 cfm through my flex duct work. I ran it 24/7 starting in maybe early Feb and within a day or so the humidity was under control. I still don't know the true cause for sure, but at least I have a 40W solution that only needs to be run from November to April (less than $10/mo probably). In my research I probably made it all the way to the end of the internet and couldn't find anything recommending how to install an HRV in an unconditioned attic in norther New England, so I'm just kinda rolling the dice. I happened to have a copper pipe that someone installed straight from the attic to the basement along the outside of the chimney, which I used to direct the condensate. I also used a short run of heat trace tape to keep the condensate drain from freezing in the 0 degF attic, but ended up removing that after finding out that the HRV wasn't sending more than a few drops of condensate into the pan (I actually think most of the condensation was occurring within the ductwork prior to the stale house air getting to the HRV. Not sure what I'm going to do about that yet. Anyway, I have a solution that works for now that I may need to tweak later. Thanks to all that helped!