Dehumidifier 70 better than 45 ?

[MS]

Would a 70 pint DH remove more water, more quickly (than one rated at

45), or does it merely have a larger bucket?

I am currently running a 45 pint DH in the basement, connected to a permanent drain. When it was filling its bucket, it would fill up every 24 hrs. Its humidistat readout indicates that it now keeps the basement at 60% rel/humidity (RH). The target setting I gave it is

50%, since 60% feels just about ok, but dryer would be better.

The RH sometimes drops to 55%, but not for very long (for about 20 minutes). Sometimes it swings up to 70%, for a very short time (5 to

10 minutes), but most of the time the DH keeps the RH between 60% and 65%.

However, the DH never shuts down. The best it can do is to cycle the compressor off (this is when the RH usually creeps back up to 70%).

The basement does not have any water seeping into it, but only as of last week.

I had discovered a downspout dumping water 2 feet away from the house (onto a driveway) where it was sloped towards the house foundation AND where the ground had sunk - towards the foundation - AND where a 1" crack had opened up. IOW, one downspout was directing its entire output directly into the foundation. This condition existed for years (I recently bought the house) and created extensive basement stucco spalling exactly in the area of this problem. No more! The crack is sealed with hydraulic cement and the slope is fixed (away from the foundation) with some regular cement and sealed with asphalt sealer and the downspout now dumps water further away.

The basement does not feel damp, at 60% RH, as long as the DH is running all the time, but I'd like to get the basement closer to 50% RH. Thanks for any input!

[Joseph Meehan]

The higher rating will remove more per unit of time.

Meters and markings on dials are not very accurate. A 10% difference in the reading of one meter to the next is not unusual.

Why do you say dryer is better? Too dry is just a bad as too wet, but for different reasons.

I suggest you may try turning the setting down on the unit and see if that lowers the humidity.

Shutting down the compressor is really shutting it down. I have not seen one that does that and keeps the fan on, or do you mean it leaves the ON light on? It may just be turning off the compressor to cycle through a defrost cycle.

If it is truly running 100% of the time, then you will need a larger or additional unit. I suggest getting a larger one and keeping the one you have. The larger ones usually are more efficient (cost less to operate) and will take our more moisture. The original unit can be set a little higher for those times the larger one is unable to keep up or fails for some reason.

That should help a lot, You are on the right track.

[Michael Baugh]

The magical number for mold growth appears to be around 55%. Best to keep below that.

[m Ransley]

A 70 removes 70 pintes in 24 hr 45 removes 45 in 24 hr. How much water does your tank hold, measure it and the amount you dump out every day to see if your unit is operating right, it may not be. You dont say basement size. How old is your unit does it have Energy Star ratings. New units use maybe 40 % less electricity. The larger units are more efficient but they all are costly to run. A dehumidifier also warms the air, that may be alot of the discomfort. You could read operating watts or amps and i will guess your unit takes at least 700 watts and costs you 60$ a month running 24x7. at 0.12 kwh. My damp 25 x 25 basement costs 5 $ a month to dehumidify and I live 30 ft from a lake, basement is maybe 5 ft above high water mark, I used a log meter to verify it. That is why I wonder on size and if you units operating properly. Running 24-7 is costly. The humidistat on your machine may be very innacurate leading you to over dehumidify. I have no mold problems at 75 % . One person recomends below 55%, well If I had to keep my house at that level myself and 90% of America would never open their windows in summer, rarely is it below even 60% outside. Are walls painted,floors. This will seal out moisture a bit more.

[m Ransley]

What is the temperature in your basement , Most units can freeze up below 65 some at 67. Sears has a new 70 pt that can run to 45. and their other units freeze at lower temps. Consumer Reports did a good write up. When they freeze most go into a defrost cycle. Or it could mean your unit needs repairing if your condensor doesnt continualy operate. Start by measuring output of water.

[Joseph Meehan]

Note: That is only true under the specified test conditions; temp and humidity. My guess is the test condtions are ideal and few people will match them.

Very true.

True, at least with the ones I have seen.

More costly per unit of time, but not per unit of water removed.

Also true. In fact warming it will contribute to reducing the humidity. Temperature differences may be part of the original writers fluctuation of humidity.

It can be. Depending on the situation, it may not be all that costly in real life, as running it will not need to play catch-up to remove the moisture that would have been removed if it had not been running. However I agree, most of the time it would be cheaper to turn it off part of the time and allow the humidity to go up.

Or under dehumidify. My two machines only say more dry and less dry. I good idea in my opinion.

I tend to agree. It is difficult to suggest a specific % of humidity that will protect from mold. There are far too many variables.

[m Ransley]

I just got a new sears 50 pt and have a 2 yr old sears 65pt. I looked up test results because I was suspicous of its operation. Consumer Reports verified result for ratings at [I believe] 70 f 70%rh I duplicated this and got 50 pt on my new 50 pt. Yes cooler and less humid will pull less but, im guessing 80 f 85% may even pull more [ im guessing ] A new sears unit has 6 hr or 3 hr or continous operations so short cycles can be reduced. My 50 pt pulls 5.7a , 65pt 6.5a. Accuracy of humidistat on either is off be 5-10% , I calibrate my large Taylor humidistats. I also see most analoge humidistats new in stores 5

- 25% off. People realy dont know what their humidity is unless they calibrate them. How many do.

[m Ransley]

Digital humidistats are more accurate in general but you still need a baseline off a calibrated analoge to base your digital to know if its accurate.

[MS]

Thank you for your replies, everyone!

Couple of clarification notes:

The basement temperature has cycled from around 53/54F to 60F, but we've been having a cooler than normal spring, so far.

The basement is about 25' x 30' with painted walls. I have an oscillating household fan going 24/7 in the opposite end from the DH to circulate the air.

When I say the unit "runs all the time," what the DH actually does is cycle the compressor on/off, but the fan never stops. My father's older DH (and I believe his new 50-p Sears) actually go to sleep for a while.

I figure my Fedders 45-p DH is barely keeping up with the moisture supply and has only enough time to maybe defrost, when it needs to (and keeps the fan going through that process), but by the time the defrost is done, the RH has crept up to 70% and the compressor kicks back in. This cycle is a 24/7 event, right now.

I've tried setting it lower - to 35, 40 and 45%, but that makes no difference since it can't seem to extract enough water to ever reach below 55% RH. I realize its humidistat could be off the mark, but the two-fold bottom line is that this DH has extracted a LOT of water from the basement - it would feel terrible w/o it - and I still want the basement to FEEL just a bit dryer.

All told, I am looking for a 70-p Sears model. Thanks again for your comments!

MS

[nicksanspam]

Maybe it needs some paint on the floor, eg UGL Drylok, and maybe some rugs to avoid foot traffic abrasion.

I have a similar situation. I think the slab was installed without a vapor barrier underneath. The UGL ap engineer said Drylok has a low water vapor permeability, but it isn't used on floors because it has a low abrasion resistance. He said the slab was probably wicking water up from the ground and evaporating it near the surface. I suggested putting poly film on the floor surface and rugs over that to protect it from foot traffic, but he said that could cause mold growth under the film and water might seep out at the edges. A much more expensive epoxy paint would also work, but the Drylok should also work, even if some wears off in high traffic areas.

The Building Science Corp web site has an interesting basic 18 page pdf on "Insulations, Sheathings, and Vapor Diffusion Retarders"...

...a cubic foot of air containing 2 trillion molecules of water in the vapor state has a higher vapor pressure (or higher water vapor density) than a cubic foot of air containing 1 trillion molecules of water in the vapor state. Moisture will migrate by diffusion from where there is more moisture to where there is less. Hence, moisture in the vapor state migrates by diffusion from areas of higher vapor pressure to areas of lower vapor pressure...

...in a hot-humid climate [exterior at 74 F dewpoint and interior at 75 F and 50% RH] over a one-week period, 1.5 pints of water can be collected by diffusion through [a 4'x8' sheet of] painted gypsum board (about 5 perms); 14 pints of water can be collected through air leakage through a 1 in^2 hole under a 5 pascal air pressure differential...

Nick