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Old 07-23-2008, 05:28 PM   #1
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high humidity in basement


My daughter and husband bought a house in May 2008. Very happy initially, but in last couple of days have noticed very high humidity, moisture on floor in basement. No issues when they looked at the house in March /April prior to purchase.
House was built in 2002, has AC, furnace and Venmar air exchanger. They had furnace cleaned, new injector nozzle, filters installed when they moved in. Technician said there was no need to operate the Venmar system in summer.

Last Sunday (3 days ago) noticed dampness on floor and some mold on drywall. Monday we removed all drywall in workshop area, and took bleach to floor and other walls. Have placed some window fans to exhaust the basement air.

We have several questions and hope someone with experience/suggestions will respond.

Should the furnace fan be turned on - or is there a danger to moving any particles/pollutants through the rest of the house?
Should the furnace fan be running just to move air/ventilate normally?

Should the Venmar unit be connected to the forced air furnace?
How should the Venmar air exchanger be operated? None of us has had one and have no experience with its operation.

They are getting a dehumidifier today. Will it help?

Thoughts and suggestions are welcome.

Also, we're in Ontario Canada and have had 22 days of rain in June, and not much less so far in July. Also expecting rain for the next 4-5 days. So outside air is high humidity as well.


Thanks.


Last edited by orange; 07-23-2008 at 05:32 PM.
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Old 07-24-2008, 10:47 AM   #2
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high humidity in basement


I'm not qualified to repond, however check your gutters sounds like water is not being diverted away from the house when it rains. This can cause humid and moist environment in basement even water on the ground. Also is your ac unit drain clogged in the basement. That will back up if clogged. Hope this was somewhat helpfull. Sounds like you should find the source of the moisture and tackle that before anything else. Good luck

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Old 07-24-2008, 11:32 AM   #3
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high humidity in basement


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I'm not qualified to repond, however check your gutters sounds like water is not being diverted away from the house when it rains. This can cause humid and moist environment in basement even water on the ground. Also is your ac unit drain clogged in the basement. That will back up if clogged. Hope this was somewhat helpfull. Sounds like you should find the source of the moisture and tackle that before anything else. Good luck
Thanks for your response. We did adjust the downspouts. They were going into the ground ( could be connected to weepers - we don't know) but seemed to be going to a dry well -pit with gravel. We put elbows above ground and put 8-10' of plastic pipe on each to run the water from gutters down the sloped lawn.

Note house is relatively high with lawn sloped away from the house on all sides.
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Old 07-24-2008, 11:37 AM   #4
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high humidity in basement


I would definitely either have the furnace fan running constantly (if it is capable and rated for 24/7 running) OR have the Venmar running.

The idea, apart from the idea just suggested in the previous post is worthwhile; you have a high humidity problem, the source of which you will have to find, but if you don't find one then you just have high humidity. Maybe coming in through the concrete...could be a number of ways. But one way to reduce mould and musty smells are to increase ventilation in the house specifically in the basement and if possible vent that outdoors.

There is a chance that a previous water accident left mould in the furnace ducts, in which case a good professional cleaning is in order. But your house would have smelled a long time a go if you had, so I would reduce that probability. No I'd say you had -or have - higher than 60%RH conditions with no air movement and thus mould growth.

Clean it up with dilute bleach, put on the air exchanger and get a dehumidifier if you like. Don't do all that much but every little bit helps...
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Old 07-24-2008, 11:50 AM   #5
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I would definitely either have the furnace fan running constantly (if it is capable and rated for 24/7 running) OR have the Venmar running.

The idea, apart from the idea just suggested in the previous post is worthwhile; you have a high humidity problem, the source of which you will have to find, but if you don't find one then you just have high humidity. Maybe coming in through the concrete...could be a number of ways. But one way to reduce mould and musty smells are to increase ventilation in the house specifically in the basement and if possible vent that outdoors.

There is a chance that a previous water accident left mould in the furnace ducts, in which case a good professional cleaning is in order. But your house would have smelled a long time a go if you had, so I would reduce that probability. No I'd say you had -or have - higher than 60%RH conditions with no air movement and thus mould growth.

Clean it up with dilute bleach, put on the air exchanger and get a dehumidifier if you like. Don't do all that much but every little bit helps...
Thanks. They did install a dehumidifier last night and it is working well. Also, they are running a fan in basement window to exhaust air from basement.
There has been no musty smell in the house. I think a big factor is that we have had the wettest June and July in years- and rain is predicted right through to next Monday. It' hard to dry anything with these conditions. And it's raining right now. Seems the Venmar would just bring in the humid air.

Is there any danger of worsening the situation if they turn the furnace fan on at this time?

Last edited by orange; 07-24-2008 at 11:52 AM. Reason: rain
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Old 07-24-2008, 12:05 PM   #6
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high humidity in basement


Is your Venmar an ERV model, or an HRV. Model number will help. Just currious why the tech said it was not necessary to run it during the summer.

I know in Canada, they are desirable, due to ventilation requirements, and it is more likely the previous owner experienced similar problems and dealt with them by installing the Venmar ststem. Some are more elaborate than others, and do offer dehumidification. Try turning it back on, and see if it helps.

Just read your post re. Venmar system... never mind, probably a simple HRV.

Thanks.

Last edited by 8 Ball; 07-24-2008 at 12:10 PM.
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Old 07-24-2008, 12:21 PM   #7
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high humidity in basement


8Ball,

System is Venmar Constructo 1.5 Model 43110 Installation date Nov 2004.

Does this help?

Is there a procedure for running/setting this?
Thanks
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Old 07-24-2008, 12:29 PM   #8
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Well, it sounds as if the Venmar just brings in new air from outside, runs it through the furnace and the exhausts it. OK, that's fine too. At least it's moving...

If the RH outside was constantly above 60% at 21 deg C, and the same conditions were inside your house but there was little air movement, then mould would grow wherever it found food. Mould growth can be reduced by: 1) reducing the moisture content of the air; 2) increasing air movement or 3) increasing the air temperature (either the general space temperature or the temperature of the walls and floor).

Either high humidity or temperature can be the major factor in a mould problem. A humidity sensitive mould may not respond well to increasing temperatures, and conversely a temperature-sensitive mould may not respond very well to increasing ventilation. So try both increasing the temperature down there and reducing the humidity by increasing the ventilation.

If the relative humidity near the middle of the basement is fairly high (e.g., 50 percent at 20 deg C), mould or mildew problems in the room are likely to be humidity level-sensitive. If the relative humidity near the middle of a room is fairly low (e.g., 30 percent at 20 deg C) mould or mildew problems in the room are likely to be temperature sensitive.

Good luck!
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Old 07-24-2008, 12:30 PM   #9
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high humidity in basement


there may be a small leak.... look at the bare concrete.... a leak is not a big deal... it can be fixed easily most of the time.... not knowing/and finding it is....
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Old 07-24-2008, 01:28 PM   #10
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high humidity in basement


ccarlisle..

Is this a probable case of ground saturation? Does saturation increase w/depth of the soil, or is it less. I know she has stated that the ground is sloped away from the house, but without knowing the depth of the basement vs. the depth of the slope, at what point do you consider improving the terrain vs sealing the entire basement?
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Old 07-24-2008, 06:30 PM   #11
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Yes, I think it is a saturation issue, thankfully a temporary one. I didn't ask if they had a sump pump, it may be there isn't one and that their house is close to - or now at - the ground water table. But the drainage issues are always IMO the first fix before tinkering around indoors...indoors you just see the effects of inadequate-fix causes outside.

So the downspout directed away from the foundation is a good start unless you can be absolutely sure the water goes deep enough into the weeping, the weeping isn't blocked and the proper sock around it and that that runoff is properly connected to the sewer. There are a lot of "ifs" and I'd just rather see a 8-foot pipe taking the runoff away from the house altogether. They have that...so fine.

That's all part of positive-side remedies. On the negative-side i.e. inside the house, I like to apply a silicate sealer to concrete. If that's not feasible (and most times it is), then you can always do what's happeneing here: manage the humidity levels to provide a safe, mould-free living environment. I personally think fans should always provide adequate air circulation, and the Venmar is just one I like.

Saturation increases with soil depth.
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Old 07-25-2008, 07:22 AM   #12
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high humidity in basement


The house does have a sump pump. It has been working during the actual rain, but after the rain the sump pit is pretty much empty. I have a feeling there is some saturation next to one wall - under the front porch. The plan is yo remove some porch floor boards and see what the grading is like, We think this may have been saturated because of all the rain and the way the gutter drains were set up.
The dehumidifier is working great. RH is in 69-70% range.

Prediction for today is sunny with no rain !!! Maybe we can dry out a little.
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Old 07-25-2008, 12:16 PM   #13
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Well, well, orange, you're from my home town! Was born in Rockcliffe Park.

RH of 70% at say 17 deg C is OK, but still a bit high. Can't do much else but to run the dehumidifier because outside it's probably 75%RH at 22 deg C. But as soon as it gets to around 55%RH at 23 deg C, then open doosrs and windows, run the Venmar because then you'll be removing the moisture naturally. The the mould problem will go too.

Nice and sunny here today! We're about 125 miles apart
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Old 08-04-2008, 09:56 PM   #14
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After installing a dehumidifier and some ceiling fans RH is now about 53-55%.
Things seem much better.
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Old 08-05-2008, 06:12 AM   #15
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Good...the next things you'll want to look into is continuous air movement down there - which you may already have with the Venmar - and removal of sources of mould growth i.e. anything with cellulose. Ceiling tiles, gyproc, wood studs, natural-based carpet (wool or cotton), cardboard, wood panelling,etc. I know that's a long list and turning your basement into a plastic jungle isn't an option, but the combination of low humidity constant air movement and lack of food will eventually rid your basement of mouldy and musty smells.

In the meantime, a shot of diluted 1:1 bleach here and there in dark corners, on concrete, even on joists, studs and panelling just might lower the problem to acceptable standards. I found a 8"x8" cover on a anti-backup valve made of plywood to be the main culprit in the last house I did. This cover was sitting on a plywood box that literally stood in 1" of water for years. Cleaning that out and replacing the cover with a metal one did the trick...

Keeping the RH at 55% at temperatures around 18degC is "normal"; at lower temperatures, the %RH will go down, which is even better. On the other hand, if the temperature goes up to 21degC and the RH is still 55%, that's just on the borderline for growth, so something extra is needed.

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