"Wave" or Ventilation Type Dehumidifiers

by Bill
(NJ)

I've read quite a few testimonies of how these and home made equivalents have worked for some.
Any comments?

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Answer

This type of appliance uses a fan to expel air from your basement. The reduction in air pressure in the basement draws down air from the upper portions of the house, replacing the basement air.

Since the air in the upper part of the house is generally warmer than the basement air, and warm air holds more water than cooler air, this reduces relative humidity in the basement.

The advantage of this type of appliance is its lower operating (energy) cost. The most immediately obvious disadvantage is the high unit cost of the system, about $1700 being the commonly quoted figure.

These systems, and home made equivalents, appear to work for some and not others. There is no obvious pattern although it would appear that the system works more effectively where air con is operating in the home although reports are not entirely consistent on this point. There would obviously be concern about venting conditioned air from the house.

The system inevitably draws air into the house from outside. In areas with periods of high ambient humidity this would appear to be self defeating. The differences in ambient humidity levels across the country may explain some of the inconsistencies in the reported effectiveness of this system.

My own view is that the claimed advantages of this system depend on the frequently asserted theory that adequate ventilation will solve moisture problems in the home which is often expressed in terms such as "you don't need a dehumidifier just leave your windows open".

In cold conditions this is impractical. In warm, humid conditions it is counter-productive. In warm dry conditions it may be effective in controlling humidity although it makes air conditioning a waste of money.

This system allows ventilation without having to have windows open. In cold conditions it would be drawing cold air into the house, increasing heating bills. In warm, humid conditions it would be as counter-productive as open windows as it would draw moisture into the home. In warm, dry conditions the system would appear to be working against the air conditioning system and the extra load on the air con must, surely, cancel out some, at least of the energy savings.

Two other factors cause me concern. First, the system may take up to a month to eliminate the effects of excessive humidity. Second, the system causes reductions of air pressure in the home which may involve some risk with appliances such as boilers and furnaces located in the basement.

My own view may be described as "healthy scepticism", not least because of the apparent ease with which some enterprising souls seem to have fabricated a fair equivalent of this type of system at a small fraction of the price being charged by manufacturers.

I have not formed a hard and fast opinion about this type of ventilation as an alternative to dehumidifiers and will continue to assess the evidence. For the time being I remain to be convinced.

Tom (Webmaster)