Latest Discussions : Basement & Foundation


03:01PM | 07/26/06
Member Since: 03/03/05
271 lifetime posts
Dehumidifiers are expensive to operate on a monthly basis. Dehumidifiers do not circulate air, so the air quality in your basement can be poor and mold can still flourish. You should consider a Humidex unit. There is a Humidex unit designed for crawl spaces. The Humidex units are excellent and will cost you a fraction of the amount to operate.


06:03PM | 07/26/06
Member Since: 04/25/05
1915 lifetime posts
"There still appears to be an issue with the humidity in the air during the warm, humid summer months. "

That is the source of your problem. The air is loaded with moisture. And the crawlspace is cool by it nature of being partially under ground. Then you add AC in the house.

That made the crawlspace very cool and when the outside air comes in and cools down the RH goes way up. In fact you said that it was 60 degrees in the crawlspace. In many areas that is well below the dewpoint and you will have condensation in there.

You want to seal off the vents. Seal the ground. Just laying plastic down is not enoug. But the plastic has to bee SEALED. Sealed to the foundation and any laps in the plastic sealed.

And the crawlspace walls should be insulated on the inside. That will help warm up the crawlspace. It will also help make the house more comforatable in the winter.

Do a google on Conditioned Crawlspace and also Sealed Crawlspace and you will find a number of details.

Here is a start.


A most likely if you do a good job on the conditioned crawlspace you don't even need a dehumdifier.

The Humidex sounds good until you start looking at the details.

What they don't mention that is it draws in UNCONDITIONED AIR into the house. That is air that is hot and humid. The AC needs to run overtime to cool it off and remove the humdity.

By controly the sources of humidity (ground and outside vents) and warming up the crawlspace (insulation) you have solved the problem.


04:28AM | 07/27/06
Member Since: 03/03/05
271 lifetime posts
Bill, if you do not have any experience with the Humidex units, please do not comment about them. Your post is incorrect in your assumption on how the unit operates. I have real world experience and do not rely on links to provide information.

I have personal experience with Humidex and the system works. By creating airflow, you allow wicking to occur which will not only move stale air out of the basement, but it will remove moisture off surfaces. The Humidex unit takes air from the first floor, that is considered conditioned. Proper placement of the unit is crucial in order to get the desired airflow.

There are ways of dealing with you crawl space, airflow is an inexpensive way to combat your seasonal problem.


07:02AM | 07/27/06
Member Since: 07/25/06
4 lifetime posts
My only concern is the air quality down in the crawlspace once it is sealed - my family

is prone to allergies and I worry about the dust, must and mold down there and the heightened effects if it is sealed. Again, I am not an expert but would think that sealing it off would trap the air down there. Any thoughts?


12:13PM | 07/27/06
Member Since: 03/03/05
271 lifetime posts
I would have to inspect the area to properly give you an answer. I just do not feel comfortable.

I do not like the idea of having any pockets of dampness in a basement. I deal with mold issues on a daily basis and know the negative health affects of mold.

99% of the time if you have sufficient air flow in the area, you will eliminate the moisture and hence the other associated issues.

If you are to insulate, have a contractor use a closed cell polyurethane foam. Closed cell foam will not harbor bacteria. I'm not sure you could find a contractor that would spray a small area...but I';m sure he would come and fill in the crawl space with foam.


05:45PM | 07/27/06
Member Since: 04/25/05
1915 lifetime posts
"The Humidex unit takes air from the first floor, that is considered conditioned."

And that is what I said.

But you are completely ignoring the next step.


You will have to register to read the whole thread, but I am copying and pasting this one message.


From: experienced Jun-13 12:02 am

To: DonNH (4 of 5)

74934.4 in reply to 74934.3


I know the inventer of the Humidex. When I lived in New Brunswick, he lived about 20 miles from me. We were both early in the HRV industry about 1980-1.....he with a manufacturer and I as an vendor/installer. The Humidex was invented as a "dehumidifier" for damp summer basements to replace standard units and run at lower costs.

He had an idea based on the fact that due to cool summer basements (especially if uninsulated) he would see condensation/dampness in the low corners and at the floor/wall intersection. From this he determined that moisture "fell" to the lower levels of the home and basement. Confirming RH's by psychrometer but by neglecting another variable in RH measurement- temperature- he missed the temp stratification of the basement air from higher temps at the ceilings to lower temps at the floor. Thus he found higher RH's at the floor, lower RH's at the ceiling.... and this proved his theory....albeit wrongly.

So he built the humidex protypes to clean up his summer basement moisture. He found that in some "weather", he needed a fan that would exhaust 200 cfm to do the job. From there he popularized the product locally and it took off.

How does it work .... and not work!!

It works not by dehumidifying (no compressor, evaporator, etc) but by exhausting the lower, cooler basement air with higher RH's and replacing it with warmer air from upstairs and outside. With enough air exchange the basement would begin to warm up slowly and the average RH would be lowered not by having lower absolute moisture content in the air but by having a warmer basement through free heat, a lower RH and a low fan electric bill.

It does not work well or at all in very hot humid weather. You're now bringing in air at 75-95 deg F and 65-80% RH that just needs to be cooled a few degfrees before it will condense on even a slightly cool surafce. The last two summers in our area have been the most humid of my 13 years in this locale. The Humidexs are not working as in past summers. People go to the storage room, bring out the old dehumidifier, fire it up and set the two systems working against each other!!! The dehumidifier actually dries the basement air by refrigeration while the Humidex sucks it out to be replaced by more humid air for the dehumidifier to dry and be exhausted. IGet the idea??? have had a few calls from frustrated homeowners that have two machines running that never shut off and the Rh is not going down- in one monitored case it had gone up!!!

The Humidex "dehumidifier" is like the foil faced foams claiming outrageous R values for 1" like 27- more "smoke and mirrors".

Ture storey: I used to be the provincial energy analyst (wrote the energy regulations) and 1 of 4 public residential energy advisors. As part of the job, we put on public energy conservation seminars around the province. One evening a gent came to ask specifically about why the Humidex was not working in his home.

His basement was a partial basement with a big piece of the local granite bedrock (not much soil cover in some areas here due to past glaciers) forming one corner of the basement. In addition there was a high water table under his slab about 8 inches down. He put his dehumidifier away, started up the Humidex and nothing happed. Since he was so well connected to the cooling effect of the bedrock + high water table, the temp in the basement would not rise much if at all.

He called the manufacturer about his situation. They said to heat the basement to boost the temperature so the unit could then maintain it at a high enough level for the system to work. So in July he fires up his basment wood stove for 2 days!! (free firewood from his own lot = cheapest energy form) Neighbours thought he had lost it. After 2 days all was sufficintly warmed so that the system worked for a few days but eventually lost the higher temps leading to basement RH rise. His money was refunded by the vendor and now he still uses the original dehumidifier.


Now it is possible that the Humidex can work in some conditions and climates. But even in those cases it can probably be done better by other means.

But he is in mid-atlantic area. So I choice Baltimore.

For the month of July the highest dew point has been 75 and the average 67.


Not to mention that it will also draw in more pollen and mold spores.


05:50PM | 07/27/06
Member Since: 04/25/05
1915 lifetime posts
If you get the humidity level down then there won't be an mold.

While the term "sealed" is used, it is not the best term, conditioned is better. But both have been used and thus I used both for your search.

It is sealed from the ground and sealed from the outside. The two external sources of moisture.

But is still much communicate with the rest of the house. That is where the conditioned part comes in.


06:01AM | 07/28/06
Member Since: 07/25/06
4 lifetime posts
What about sealing the floor as Bill mentioned, insulating the walls with the foam board as KV mentioned and then putting a couple of box fans down there during summer months?


02:53PM | 07/28/06
Member Since: 07/17/06
6 lifetime posts
Tell us more.

Is air conditioning used upstairs?

What is the set point temp normally used?

Is the A/C used continuously or intermittenly?

Is there a "wet spring" in the basement?

What the soil clay or loam?

Why does the crawl space stay at 60deg F? Is the ground sloped with a deep basement or flat and consistently 5' deep?

Closing the vents will increase the condensation. To improve the efficiency of the A/C, circulate the 60F crawl space air through the a/c coils. A/C Intake at 60F will make for an efficient A/C and also remove the moisture from the air. Make sure the A/C drain is clean esp for the first couple of weeks. Using the crawl space as an air intake for the A/C will not be effective unless the a/c is run a significant portion of the time. As the A/C cycles on and off, RH will automatically cycle out of control. Select a room thermostat with a small deadband. In cold weather, install a corn stove and use the basement air as intake for the combustion air of the corn stove. Drying out the crawl space during winter makes RH of the crawl easier to control in summer. The soil will already be dry and the crawl will already be warm.

CAUTION: It takes two weeks continuous operation to observe full benefit of this arrangement.

When the ambient temp is above 60F, a steady increase in air circulation through the crawl space will stabalize and increase the temperature of the crawl space and thus decrease the condensation. See the duscussion of wet bulb and dry bulb temp on


10:49PM | 09/05/09
Member Since: 09/05/09
1 lifetime posts
I have now owned 3 of these. Two in my previous house . 0ne in suite and one upstairs .(no stairway or opening in floor to downstairs. It got rid of condensation and mold,midew issues on windows and walls, especially on alluminum double pane. In my new house i bought another one and because i have a duct to the basement it does the whole house. Its a simple machine and it works period. You do not lose any heat if installed correctly. I call it a low cost air exchanger. It works and i am one happy repeat customer. I bought mine for $ 400 canadian and installed it myself. Highly recommened.


06:51PM | 09/06/09
Member Since: 03/03/05
271 lifetime posts
I have plenty of happy clients using these units for years without problems. You are correct, they are simple yet effective. I strongly recommend them to anyone wishing to put a workout area in the basement or have a finished basement. The difference in air quality is night and day.


09:51AM | 10/17/11
Member Since: 10/17/11
3 lifetime posts
I was also told that I needed to get one for our crawl space. I don't really know why so can someone explain it to me further? Is the moisture in the crawl space doing damage? I was told about this website that has a specific Crawl Space Dehumidifier. Is that the type I should be looking for? Sorry for all the questions!


10:51AM | 03/20/13
Member Since: 03/20/13
1 lifetime posts
I have owned a Humidex model 209 since March 2000 and I am totally amazed how well and efficient they work vis-a-vis less than $400 cost versus ten times the cost for a $4,000 HRV.

In the winter, I use it as a air exchanger and in the summer, I use it in conjunction with my dehumidifier to remove excess dampness from the cold concrete floor.

This Humidex does what I expected it to do - expell cold air.


12:22PM | 09/11/13
what should the relative humidity of a crawl space be? 30-50%? One place told me it need to be below 20%! Is this correct?


10:53AM | 02/03/14
Hi I am getting all kinds of mixed information. I have a room in my basement that is located under my front porch, which is slab concrete. During the condensation from the heat of the house hitting the cold of the porch creates water drops the ceiling of the room below and then drips onto the floor area. The room always smells slightly moldy. Should I get a dehumidifier to change the environment in the room or the Humidex? I have already wasted money on a basement waterproof system that did not solve the issue at hand..... Please help me with honest suggestions to solve the problem, as I am female and have no knowledge about what I am being told from the various vendors I have spoken to.

Duane, Moderator

10:14PM | 02/05/14
Member Since: 11/14/13
90 lifetime posts
Va homeowner,
I deal with crawl space issues in eastern VA, the best way forward is to seal off the existing foundation vents and install 8 to 10 mil polly ( this will not tear easily when work has to be performed in crawl space) the poly should wrap up the sides of the foundation leaving a gap between the plastic and sill plate ( wood on top of block/brick foundation) the gap should be at least 2 to 4 " for termite inspection. The next step is to determine the square footage of the crawl space, this will allow you to size the proper dehumidifier.
I recommend April Aire 70 pint per day unit, this will require 8" round duct work that will be 10' to 20' long. This style unit moves air throughout the crawl space preventing stagnant air pockets.
You can also install a remote sensor and install it in your house so you can monitor the crawl space humidity levels. This is also based on the fact that you have solved the ground water issue.

Duane Cotton expert moderator


12:07AM | 05/12/20
should the gap between the sill plate and the foundation be sealed with a thin bead of foam gap spray inside the crawl space?

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