Any experience with high capacity dehumidifiers? I have a 50 pint Walmart Energy Star dehumifier which runs continuously in my basement but still doesn't keep the humidity low enough  (old house, lots of cracks...). So I am interested both in using less energy and keeping the humidity under better control--but these are expensive.

Posted By PastTense on 27 Sep 2010 10:14 AM
Any experience with high capacity dehumidifiers? I have a 50 pint Walmart Energy Star dehumifier which runs continuously in my basement but still doesn't keep the humidity low enough  (old house, lots of cracks...). So I am interested both in using less energy and keeping the humidity under better control--but these are expensive.

If your walls are not sealed and you have high outdoor dew points, you're basically trying to dehumidify the great outdoors.  Air sealing the foundation, foundation sill, and rim joist, along with better backdraft controls on any clothes dryers, etc. as well as minimum sizing on any flue openings, etc can make a signficant difference in the infiltration rate.

In addition to air sealing, using silane-based masonry sealers on all foundation walls & slabs, can cementing all cracks big enough to get a knifepoint into can limit the ground moisture transport into the semi-conditioned basement.   If you have a dirt floor, 10 mil poly vapor retarders are called for, mastic-sealed at the edges to the foundation (overlap 12" and mastic seal seams between multiple sheets where necessary.)

Unless you have regular bulk water intrusions, air transported moisture is by far the biggest factor raising humidity in a basement.  If your eave overhangs are short and the foundation stays wet, providing for better drainage & splash-rejection on the above grade exterior counts too. (Masonry sealer above-grade, and foundation waterproofing below grade as well as a French drain along the drip line may all be necessary, if not sufficient.)

If the coolest part of the basement is kept below 60% relative humidity (monitor it!), you won't get much of that musty basement smell going as long as you keep all paper & wood off the cool basement floor.

I would work on reducing the moisture sources before I added a larger dehumidifier. A perfectly sealed room with no internally generated moisture needs practically no dehumidificaton to remain dry.

What jonr said.

If you're going to all the trouble to put in a half-ton (or bigger) dehumidifier, you might as well use an R410A mini-split heat pump that has a dehumidify-mode. It's efficiency as a dehumidifier will be comparable, and it can be employed to fully condition the basement as a separate heating/cooling zone.

But you can usually air-seal a basement for less cost than the cost of a half-ton dehumidifer (or mini-split).

For several reasons, basements tend to become wet, and this wetness is the perfect atmosphere for biological contaminants to thrive. Even more serious, poorly-installed or poorly-maintained utilities and appliances in our basements may leak dangerous gases, as the basement is a particularly susceptible “gateway” for toxins!

They become wet for several reasons, and when they become wet they breed contamination such as mold. This occurs because they tend to be less insulated than the other areas of the house we spend our time in. When we use outdoor hoses, we may be unknowingly allowing water to seep into our basements. And when carpets or stored items in the basement become wet, we tend to keep them there, which perpetuates the problem.

One proven way to prevent mold growth is by installing an air filtration/ventilation system. The RecoupAerator® influences both temperature and humidity to keep mold spores (and other dangers) from surviving and multiplying.

In addition to investing in a product solution, there are other simple steps you can take to prevent dangers to air quality:

Move down spouts away from the foundation of your home.
Insulate basement walls.
Throw away wet items from basement.

The economics are that sealing is the first order, then a moisture proof insulation such as foam panels. Figuring out how to direct surface water away from the house goes a long way.
When it comes down to dehumidifiers, 2 smaller units are better than 1 big one. You keep them apart to facilitate moisture removal and you can shut off the second one when the need reduces.