You probably don't want a whole house dehumidifier in Maryland. If you have central AC, you want a two speed compressor. If you have a too humid basement, buy an Inexpensive frigidaire or GE unit for the basement only.

Above the basement level, if a house is cooled by the AC but still too humid the problem is an oversized AC.

Whole house dehumidifiers are for wet, mild winter areas. Like Seattle, where some heat with dehumidification is desirable during the rainy season.

Ana I am on vacation I will check when I get home. Don is right my hvac friend put in the dehumidifier and also said having a huge very efficient ac is not the best because it does not run long enough to dehumidify. I love mine and use it on the humid days where it's not really hot enough for ac but also not cool enough and too humid to open the windows. Also I have a rancher so it does the trick for our first floor and basement but maybe whole house dehumidifies are not the best normal 3 story houses

Taking Don and Dave's guidance, I purchased a Frigidare 70-pint

FFAD7033R1 dehumidifier, placing in the utility room in the farthest corner of the basement, adjacent to the in-law one-room studio. My goal is to control humidity and prevent mold from gathering in some parts of the house, esp. the basement's in-law apt and the upstairs bedrooms' closets.

The dehumidifier is having a positive effect on humidity (though the humidity level has been in the moderate 50% this past weekend). However, it puts out lots of hot air which is counterproductive when the house a/c unit is trying to cool the basement area.

The expense of a whole house unit is about $1,500 plus installation costs. The advantage is that it dehumidifies the whole house, and hopefully, the farthest corners of the basement where there's an in-law unit. From your comments, it would have no effect on the A/C usage, except maybe replacing A/C usage in the early Fall and Spring.

I suppose it is fiscally prudent to try out the 70-pint portable dehumidifier.

Would it be even more prudent to give up thoughts of a whole house dehumidifier because it is inappropriate?

Ana

An efficient AC is fine, it's too powerful AC that's the problem.

If AC run time is less than 10 minutes during humid outdoor conditions the indoor humidity will be too high. Twenty minutes plus run time will almost always provide adequate dehumidification in hot humid conditions, except in too damp basements. AC's with short cycle times also use more energy and have shorter lives.

Newer AC can be purchased with dehumidification features controlled by the thermostat. This feature runs the blower slower. Additional features can be added to keep the coil from freezing.

For most houses in in humid areas ( say north of Atlanta?) a mid-priced AC, properly sized and with dehumidification features, will do a good job with above ground level dehumidification in warm weather.

The reality is that most houses have oversized AC because bigger units create fewer performance complaints from the homeowner. Most houses also have inadequate ductwork. If a home AC cools the house fast it simply can't do adequate dehumidification.

For people who want fast home cooling, a large AC with a ducted dehumidifier may be the answer. But this setup will cost more to run, and have more equipment expenses over time. A properly sized AC kept on during warmer weather will be less expensive overall.

A dehumidifier is ideally only considered when there is high humidity but little or no cooling load. A condition where a basement is too damp and yet warm enough to allow using an AC instead of a dehumidifier is unusual. Where I live yesterday was hot and humid. My basement started the day at 72F with humidity in the high 40's. This is good. After the central AC ran for hours, the basement was 68F and humidity was above 50%. Even with the central AC running and dehumidifying, the drop in basement temp was enough to raise the relative humidity to an undesirable level.

So like most people my only choice is to use a dehumidifier in the basement. Even with temps in the nineties and the central AC running all day my basement is cool and too humid. If I put a small window AC in my basement it would remove more humidity, but also continue to drop the temperature further.

As far as analysis, humidity should be quantified. I picked up a couple of $10 acurite hygrometers, and did a simple overnight calibration (google "calibrate hygrometer). All inexpensive hygrometer can be off by 5%. Without a simple calibration it is hard to know the true humidity.

Thank you, Don. Your explanation and guidance are most helpful! You have a great way of explaining the mysteries of the way our houses are designed to support us.

My A/C unit runs about 10 to 15 minutes, about every half-hour, so I'll look into a dual-speed compressor with dehumidification.

The new portable dehumidifier in the basement utility room seems to be helping. But it blows heat into the room, making the room uncomfortable. Is there anyway to direct that heat to a productive use? The unit is adjacent to the hot water tank. Can the warm air blown out of the dehumidifier be captured for secondary use? Or, just siphoned out of the house via a direct vent to the outside?

Ana

Your welcome, gooddog.

You can't vent the heat and keep the dry air. You may want to try raising the humidity level. Hot and humid is unlikely in a basement.

If you want to vent the utility room to the apartment, there are several choices. I just leave the utility room door open and blow the dehumidifier exhaust out the door. All other ways, done right, probably cost more money than buying an additional dehumidifier.

The least expensive way to dehumidify the other part of your basement with a closed utility room is to add another dehumidifier. If that setup is unacceptable, the next choice is to vent your utility room into the larger part of the basement. This needs circulation both in and out of the utility room . If you have non-electric furnace or water heater in your utility room, you must ventilate in a way that does not cause negative pressure in that space (you can't just add one exhaust fan). If you have gas/oil burning appliances in the basement, you hopefully already have one or two carbon monoxide detectors on that level.

The air needs to move both in and out a low at low volume. I'm assuming that the your utility room and the basement apartment share a common wall.

First, I would investigate controlling the whole setup with a line voltage humidistat like the Honeywell H46C 1166. This device simply turns power on and off to humidifier and ventilation fans based on humidity. The honeywell would be placed in the apartment on the common wall. I haven't used this humidistat, but based on specs it would be my starting point.

Most/all dehumidifiers save their setting during power failure. This allows these devices to be remotely controlled by simply cutting power. I'm assuming your dehumidifier has a continuous operation setting, and this setting is saved when power is cut.

The choice for ventilation is one fan and a large vent, or two small fans running in opposite directions. The vent option would let more noise into the apartment. SInce these fans would run many hours per year, the most expensive fans provide the best economics. Panasonic 70 cfm through the wall fans are ~$170 each and very quite. The only issue is needing a finished looking vent cover on both sides. You could also investigate less expensive Suncourt products. People with wood stoves use these types of products to circulate air to adjoining rooms.

You may think "spending this money, why not put in a whole house system in the ductwork". Expense aside, the problem with a whole house ducted system is dehumidifying the basement with the windows open upstairs. Running a central dehumidifier with the windows open is attempting to dehumidify the world. In a houses with basement humidity problems, the lower level needs its own system. In new construction a damper system could be installed in the main ductwork to only dehumidify the basement when the AC if off. But in new construction the correct approach is to adequately dampproof the outside of the foundation wall so that no special basement dehumidification is needed.

It is worth listening to an HVAC company for their proposed solution based on your specific house, ductwork and climate.

If running a second dehumidifier in the apartment is acceptable part of the day, an appliance timer could be used. Or an occupancy sensor could be used in a space to only run a dehumidifier when the space is empty.

Don,

The humidity issue is throughout the basement. The basement has three rooms, a small utility room (150 sf) opening to an in-law apt (300sf) which, in turn, opens to a larger recreation room (500 sf).

House windows are only opened during the early morning when humidity and temperature are low. I've got fans running in every room upstairs and down, for long hours, some constantly, to supplement the air vented from the air conditioner. The fans have greatly improved the air quality.

The dehumidifier has been placed in the utility room, which, with the dehumidifier's heat output, is now about 10 degrees warmer and the temperature of the adjacent in-law room is probably 4 degrees warmer too.

I'll definitely look into the the Honeywell H46C 1166 line voltage humidistat. What a neat device! And the through-wall Panasonic 70 cfm fan sounds interesting, as well, as a means to circulate air from the utility room to the in-law room.

But I do not want to circulate the warm air generated by the dehumidifier. I want to circulate the less-humid air so the in-law unit gets the advantage of dehumidified air without having a noisy, heat-venting machine.

I have been discussing this thread with my neighbors and one showed me his heat pump hot water heater in his fully underground basement. The HP hot water heater quite effectively dehumidifies his basement. Have you experience with a setup that uses a HP to dehumidify?

gooddog, what setting are you using on your dehumidifier?

I recently use the Frigidaire 70 pint (found it here), quite quiet and i love that it have auto shut off when the temperature go too low (where i live the temperature going down quite fast at night).

Good dog sorry it took me so long to get back to you. It's a 90 pint Honeywell dr90a2000. I love it and it does the trick no matter the season. Just can't use it in winter but I do not have humidity issues in the winter

just seeing this post- who did the installation? We are wanting to get this done but can’t find any hvac companies that do dehumidifier for the whole house.