Crawlspace Dehumidifiers - Installation and Safety Issues

by Anon.
(Rochester NY)

My crawl space is about 900-1000 ft and on an incline, It is maybe 2 feet at the front of the house and gradually gets shallower to 6 inches at back of the house.

The crawl space was originally open to the elements in the front of the house when I purchased it 9 years ago while a small area in the back has concrete block walls. I first had 2 sizes of wire mesh put in the front area to keep out animals, then 2 years ago, had T-111 siding placed over the wire mesh on the exterior and put down 4 or 6 mil plastic over the dirt but it did not go up the ‘sides’ of the crawl space.

This summer, I noticed a musty smell in the living space above the crawl where the T- 111 siding and plastic floor barrier was installed. The shallowest area at the back of the house has always had a musty smell even though we managed to get some plastic over the dirt floor there (but not on concrete block walls).

There has never been any standing water anywhere in the crawl. There are no appliances in the crawl or any ducts into the house. There are return pipes that are part of the hot water heat system.

Questions:

1. Will a crawl space dehumidifier work well in the conditions I described above assuming I close the 2 vents in that space?

2. I’m thinking of placing a crawl space dehumidifier under the house near the bathroom and kitchen plumbing. Is it possible to drain the dehumidifier into that plumbing?

3. If there were ever a plumbing leak in the crawl space, could the dehumidifier be flooded and if so, does this pose a fire hazard?

4. Are there any other safety issues of concern?

5. I live in western New York State where we often have very cold winters. The Santa Fe is listed as ranging down to 49 degrees. What happens below this temp? Does the unit get damaged or just ‘stand by’?

Thanks very much!

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Answers:

I will take your questions in the order you have asked them.

1. I see no reason why a crawl space unit should not be effective. Even the lowest capacity Santa Fe model, the "Compact 2", will have capacity to spare. The area of your crawl space is well within the 1800 square feet maximum area of this model and, because the crawl space is so shallow, the volume of air will be less than a more typical crawl space with the same floor area.

If there is a "problem" it is the restricted air circulation possible in such a shallow space, particularly at the back of the house. I'll return to that issue in a moment.

2. It is possible that you could drain the condensate into an adjacent waste pipe if a suitable junction exists or might be created. I would suggest you consult a plumber to confirm that the configuration of your plumbing will allow this.

A related issue is the position of such a junction in relation to the outlet port in the dehumidifier. Drainage from all Santa Fe models is by gravity feed alone. If the water has to travel "up-hill", or even horizontally for any distance, you will need a condensate pump. A decent model will provide 15 feet of vertical lift or about twice that distance horizontally.

3. If significant amounts of water come into contact with the unit the very least that will happen is that it will short out and will almost certainly be damaged, maybe irreparably. I cannot rule out the possibility of this causing a fire although I would judge that the probability is low.

The Compact 2 is unique among crawl space models in that it can be suspended above the floor of a crawl space using the optional "hang kit". Typically this is done by hanging the unit in between the floor joists. This may not be possible, given the restricted height in your crawl space but the depth of the Compact 2 is only 12 inches so it is worth exploring. This would not only provide protection against flooding but may also alleviate the gravity drainage problem I referred to earlier.

4. The principal safety issue with dehumidifiers is, indeed, the fire hazard. Scarcely a week goes by without a domestic fire being reported which has been started by one of these appliances. This usually involves standard portable models and typically has one of three causes.

a) A manufacturing fault in the dehumidifier. This usually afflicts an entire production batch and results in a "recall" by the manufacturer.

b) Abuse by users. Typically including the use of unapproved extension cables or "tinkering" with the appliance.

c) Poor air flow around and through the unit. This can occur if the clearances between the air input and output vents and other items, most usually walls, are less than those specified in the user's manual. It is more often caused by the user's failure to carry out the simple but essential task of cleaning and/or replacing the air filter that protects the inner workings from air borne particles.

The other safety issue is, of course, the risk of electric shock. This is a risk presented by all electrically powered appliances and normal safety precautions, not least those involving water, should be observed.

5) At temperatures below 49F even the Compact 2 becomes less effective or ineffective. The unit should not be damaged below this level and will either cease operation until the temperature rises or operate intermittently.

A very important point, however, is that no refrigerant dehumidifier, including the Compact 2, should be operated (i.e. switched on) at any temperature below 33F. If zero or sub-zero temperatures are likely to occur in your crawl space the unit should be switched off and securely covered or, better still, removed from the crawl space until more temperate conditions return.

I have tried to answer your questions within the very detailed context that you provided in your preamble. I would now like to make a suggestion that might answer most of you concerns, including any arising from my answers.

My suggestion is that you do not site the unit in your crawl space at all. You could site it in the house or in any built-on extension, such as a garage. This can be done by running ducting between the unit and the crawl space. The unit is configured for ducting and the ducting itself is relatively inexpensive.

Ducting would overcome the "problem" of air circulation (question 1). It is recommended by the manufacturer in any crawl space for more efficient humidity control and would be particularly helpful for you given the unusually shallow depth of your crawl space.

Positioning the unit outside the crawl space would give you different and, possibly, more convenient drainage options (question 2)

It would also ensure that your unit was safe from any flood risk short of that which (God forbid) engulfs the entire house (question 3)

While I would not suggest that you might neglect to clean/replace the air filter you would find it much easier and more convenient to do so outside the very cramped working area in your crawl space (question 4).

Almost any alternative location will be less hostile than a crawl space, particularly with respect to ambient temperature (question 5).

Naturally there are a couple of new issues that arise from my suggestion. First, finding a suitable location; there may not be anywhere convenient. Second, noise nuisance; this type of dehumidifier is not among the quietest.

I cannot help with location but, if there is suitable apace, the noise nuisance can be reduced by enclosing the unit in a suitable closet or constructing an enclosure around it. In both cases the noise can be reduced further by lining the enclosure with sound deadening material.

My suggestion may not suit your wishes or your circumstances. If so I hope that my numbered answers to your questions have provided you with all the information you need to plan and implement an installation in the crawl space.

Tom (Webmaster)