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Vent the Crawl
200 Gatewood Circle
Athens GA 30607

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Crawlspace Ventilation

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Zeus Crawl Space Ventilator
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Frequently Asked Questions

Quick Links: (click any question to be directed to the answer)

  1. Why shouldn't I seal up my crawl space?
  2. Do you use a humidistate to control the system?
  3. How can you be so sure that venting is the right thing to do when it comes to moisture problems?
  4. Every motor has some vibration, what about Vent the Crawl?
  5. What about noise?
  6. Why does Vent the Crawl use a 24 hour timer anyway? Aren't they expensive?
  7. Why is moisture a problem today when it was not twenty years ago?
  8. How do the Moisture Scrubbers work?
  9. Why cover the earth with plastic Sheeting?
  10. How much money does Vent the Crawl cost to operate?
  11. How many units will I need for my situation?
  12. To vent or not to vent? That is the question. 
  13. What should I expect in my crawl space once your system is set?


1. Why shouldn't I seal up my crawl space?

This is an interesting question. The variables involved with sealing the crawl space are immense and difficult.

Success will depend on the age of the structure, the location of the building, materials used, diligence of the workmen, and how much money you are willing to spend.

The age of the structure is important.

The older houses used brick and cinder block for the foundation walls. These products wick water and were not normally sealed from the exterior against water penetration. Older homes crawl floors are situated lower than the surrounding earth and water heads that way. Older homes were built closer to the earth making accessibility very difficult. The HVAC system is normally located in the crawl and must be dealt with.

The location of the structure is important.

If your house is in a low area you will have more problems with water entry. The side of a hill can make stopping the natural flow of water impossible. A sump pump and a sealed crawl is a ticket to disaster. Radon gas and any earth born gases should not be caped off in this fashion. I have a problem with stail air, for that reason alone I would have issues with a sealed crawl.

The materials that are used is very important.

Cheap materials will not hold up to foot traffic. One hole and you have a problem.

Enough said.

You will need a lot of it.

In summary; I have sold quite a few systems to people that sealed their crawl space just to find out it did not work.

Why not try our system first and see if you are satisfied with the results?

2. Do you use a humidistate to control the system?

No. We do not use a humidity device to override our system. I tried humidistates early on (1982) when I first started working with exhausting the crawl space air. The problem with humidity is that you could not stop it. Moisture is coming into the crawl from two different areas, the earth and the air. If you cannot stop something, the next best thing to do is to get out of its way, or help it along. I chose to help it along.

By moving the air on a consistent basis we have dried out crawl spaces for years. Moisture levels rise in the summer, but not beyond tolerable limits. If the ventilation system shuts down due to high relative humidity outside, the moisture will come in anyway due to air pressure. So your crawl space sits with elevated moisture vapor that now has time to soak in. Dead air and high water vapor levels are exactly what the mold is looking for.

With the introduction of Moisture Scrubbers (2003) we now are controlling the level of moisture allowed into the crawl from outside air. With the scrubbers in place, even condensation on the HVAC ductwork is a thing of the past. The scrubbers perform another beneficial task as well, by removing mold spores from the incoming air.
While humidistates sound good, they just will not get the job done.

3. How can you be so sure that venting is the right thing to do when it comes to moisture problems?

The simplest way to explain this is with an example we all know something about. Houses built on the ocean beach, are on top of very wet earth and the air is normally very moist. These houses are elevated to allow storm surge water beneath them, so they are on piers with little or no underpinning. Even though these houses have the potential for moisture, mold, and Radon below them, they are not troubled due to the exchange of air. It is the masonry skirt wall that creates the retention problem of moisture then mold and Radon. Our goal is to move enough air to provide your house with beach house benefits.


4. Every motor has some vibration, what about Vent the Crawl?

We have vibration like all the others, but we do not transmit it to the structure. By not "hard mounting" our unit in place, we prevent any vibration from transferring to the structure. The edge of the unit that rests behind an existing vent is foamed in place with expanding foam, and the other end of the unit is supported from the floor system by fiberglass belts. By cradling the unit it remains suspended in air. The foam also ensures that we get 100% exhaust, something most of the competition can not claim.


5. What about noise?

Our system is very quiet due in part to the size of the fan. We are using the largest fan on the market for two reasons. One is to move a lot of air and secondly, the pitch of the unit is a lower tone than the competition's. So our unit sounds more like your HVAC coming on than a higher pitched smaller fan. Our unit is also mounted in such a way as to direct the majority of the sound that it does produce to the exterior of the house. The quiet operation is one of our proudest selling points, thanks for asking.


6. Why does Vent the Crawl use a 24 hour timer anyway? Aren't they expensive?

The timer allows us to turn the motor off which allows for cooling. We use continuous duty commercial grade units, but I do not believe any motor can run continuously and not overheat and then lock down. By allowing the motor to remain cool, its life is greatly extended. The adjustable on-off pins in the timer also allow for the adjustment of running time so we can increase the air flow at first and then back off once you have a handle on the problem. This system can be set to run for 20 hours per day, and I have one set that way just to see how it handles it. The unit was set at 20 hours per day in 1998 and it is still going strong. Bottom line, the timer is expensive but it gives us options, control, and confidence our system will be running long after you have forgotten it is even there.


7. Why is moisture a problem today when it was not twenty years ago?

Air-Conditioning. With the increased use of central air, we are cutting back on natural ventilation. We are sealing every crack and replacing leaky windows and doors, and then we beef up the insulation. When was the last time you opened your windows in the summer for a breeze? Moisture that used to travel through the structure and out is now being trapped. Our homes are like jars inverted on the earth. Try that tonight, invert a jar on the ground and see what is inside your jar in the morning.


8. How do the Moisture Scrubbers work?

Maybe the best way I can explain the way the moisture scrubber works is to go over something we have all seen. When it is cold outside and warm inside and moisture condenses on the glass widows and doors. If the problem is pronounced, the water drips down and stains or even rots the sash or sill.

We demand that the warm moist outside air be introduced into the cool crawl space after passing through our unusual window. As warm moist air is pulled through our cool scrubber, by the action of Zeus, the moisture in the air condenses on the interior of the scrubber. As the water drips and pools inside the scrubber, it moves down hill via gravity to the exterior.

The air comes out of the scrubber dry. Zeus pulls the air through the crawl space drying out the entire area.

SIDE BAR; With our system in place, the moisture will be removed from the above "wet windows" example, along with further damage to the window and trim.
ONE MORE SIDE BAR; the fact that the interior of the moisture scrubber is wet, allows the scrubber to capture unwanted mold spores. The spores stick to the wet surfaces inside the scrubber and are expelled with the accumulated water.



9. Why cover the earth with plastic Sheeting?
  The majority of the water vapor that accumulates under a structure comes from the earth itself. Applying 6-mill. Polyurethane sheeting over as much dirt as possible reduces the evaporation rate into the crawlspace. I have never seen a crawlspace that was to dry, so cover it all and lap the plastic by several feet and then tape the loose edges. I like to take gutter spikes and stake the corners down so the plastic does not move around. You can live with a few holes. By the way, the water that accumulates under the plastic is a good thing. It is not in the air.
10. How much money does Vent the Crawl cost to operate?

The 24 hour timer clock costs about $0.20 a month to run. The unit's motor while in operation is pulling less than 1/2 amp. The power company in Georgia charges $0.09 per Kilowatt (Jan 2020) with our 12 hours running time per day would it consume 20 Kilowatts each month, which would give you a cost of $1.80 per month. The total cost to run would be under $2.00 per month in Georgia.


11. How many units will I need for my situation?

Normally, only one of our units is needed to exchange the air 20 to 24 times per day.

First you must determine the square feet (sq ft) of your "foot print" (the area your crawlspace covers)now multiply that number by the height to determine your cubic feet.

Let's say you have a 1,500 sqft foot print and about 4' head clearance. The jousts have space between them so we will count that as well. We have 1,500 x 5' = 7,500 cubic feet of wet air that we want to move out at the rate of 20 to 24 exchanges each day.

Our system moves 510 cubic feet per minute (CFM)and we preset the timer with four cycles of three hours each, which gives us 12 hours exhaust time each day. 12 x 60 (minutes in an hour)= 720 minutes x 510 CFM's which = 367,200 cubic feet moved each day at this setting. This is about double the amount of air exchange to do the job and that is good. 40 exchanges per day will dry out the area fast and keep it that way. 20 to 24 exchanges works well once the area is under control.


12. To vent or not to vent? That is the question.

If you have an existing house that is over a crawlspace and you smell a musk/earthly smell, you have too much moisture. 90% of the time, it is from the earth your house is resting on.

You have two choices: (1) Seal the area up as some authorities recommend, or (2) Vent the Crawl.

From personal experience, sealing the crawlspace will not work. The water from the earth wicks up on the concrete foundation wall and evaporates moisture into the crawlspace. The next suggestion the authorities have is to insulate the foundation wall with something, usually foam. This is an attempt to control temperature differences between the exterior and interior of the wall. This sounds reasonable until you realize that termites would love this situation and your pest control provider will not bond your house with something like this in place.

Possibly you could seal a crawlspace adequately in new construction before everything is in place, but even then I see no way to guarantee that no moisture would gain access and then be trapped; maybe in a lab setup but not in real life. Besides, what is the plan for the trapped Radon gas if there was any?

Venting is the only reasonable approach to handling elevated moisture and any unwanted gases under your house. But you must move enough air to do any good. Moving just a little air will not work. By experience and others, you should exhaust the cubic feet of crawl space air at least 20 to 24 times each day. Moving less is a waste of time, when it comes to controlling moisture in this area. Moving more is even better and we like to see 40 exchanges each day.  You must be careful though, you do not want to exchange the air down there much more than this.  If you approch say, 60 exchanges each day you will warm the crawlspace up in the summer time and nullify the effectiveness of the Moisture Scubbers. 

Click here to read more information on this topic.


13. What should I expect in my crawl space once your system is set?

 It depends on the condition of your crawl space and the time of year.  If you have a lot of water in the crawl, it will take some time to remove it.   From one week to one month may be needed to gain control, each crawl is different.  And while removing it, the relative humidity will elevate.  Our system works by removing the water vapor at the top of the crawl space atmosphere, your floor system.  Until the existing water has had a chance to evaporate (below 72% RH) and vented out, your relative humidity will be quite high.  Once the water has evaporated the relative humidity will come down, into the 60% range.  

Now for the time of year: During the summer the air is hot and the heat (energy) holds the water vapor suspended in the air.  We would pull hot moist air into the crawl space when Zeus turns on, but we have Moisture Scrubbers.  During the summer your crawl space is nice and cool, we use that to our advantage.  We place Moisture Scrubbers, as needed for good cross ventilation, at the vents for the makeup air to come in though.  The Scrubbers are cool and the warm wet air touches its cool surfaces, and condensation occurs inside the Scrubber.   The air passes though the Scrubbers and into the crawl, dryer and cleaner.  As the outside air cools, in the Fall, Winter and Spring, it is much easier for our system dry things out, the air holds less moisture.   Once our system runs though a winter, you should not encounter relative humidity above 65 percent.  80 percent is too high and 50 percent is too low.  Museums work very hard to stay between 58 percent and 68 percent relative humidity.  They have paper, antiques, paintings, you name it, and in this range you do not get mold and you do not get dust.


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