Dehumidifiers: one large or 2 small ones?

[AcidWater]

My downstairs does not have ductwork; except the unfinished part (464 sq ft) which is below grade has one vent. I could cut more... but the AC doesn't run continuously anyway.

The finished part (404 sq ft) is above grade & connected with an open door & short hallway, also containing the stairs.

I'm running a portable dehumidifer located in the finished part and it has a 1 gallon bucket that fills at least 2x a day. It has a 40 pint/day rated capacity.

I _think_ the humidity must originate in the unfinished, below grade portion of the downstairs. The floor of the finished portion has some blue foam insulation under the strandboard floor tiles, then a carpet. So its a moisture barrier.

OTOH I it doesn't really matter if the unfinished part has some humidity, I don't spend time there.

Should I trade this unit in on a larger one & locate it in the unfinished area, or get another smaller on and put it in the unfinished area?

I suppose I should place it in the unfinished area and try to empty it ASAP to figure out how many pints/day I need to remove...

The fan runs all the time, so that costs $$$, but the compressor only runs as required... Don't know if 2 small fans is cheaper than 1 large fan... and if 2 separate units might be more efficient if only one of them usually needs to operate at all.

[skippedover]

I guess the operatonal costs would all depend on the size of the equipment, right? But that's incidental to having mold grow because the humidity level is too high. Controlling humidity in the absence of a moisture barrier is a lost cause. So whether an area is finished or not is really not the issue. The issue is where is the moisture barrier? If you already own one dehumidifier, I expect it would cost less to purchase a second unit. But you might want to consider a whole house dehumidifier that will remove all the mosisture you want in the basement. We've got some potentially damp basements where we've installed them and the customer love them. The basements are as dry or drier that the upstairs. Naturally the upstairs doesn't have AC so it's more humid in the summer but even in winter the downstairs is drier. So they're definitely worth the investment if you can afford it.

[teddy bear]

My downstairs

I _think_ the humidity must originate in the unfinished, below grade portion of the downstairs. The floor of the finished portion has some blue foam insulation under the strandboard floor tiles, then a carpet. So its a moisture barrier.

OTOH I it doesn't really matter if the unfinished part has some humidity, I don't spend time there.

Should I trade this unit in on a larger one & locate it in the unfinished area, or get another smaller on and put it in the unfinished area?

I suppose I should place it in the unfinished area and try to empty it ASAP to figure out how many pints/day I need to remove...

The fan runs all the time, so that costs $$$, but the compressor only runs as required... Don't know if 2 small fans is cheaper than 1 large fan... and if 2 separate units might be more efficient if only one of them usually needs to operate at all.

Does the unfinished part have a concrete floor? If yes, concrete is a vapor retarder. The source of the most basement moisture is the infiltration of high dew point outside air.
Keeping a home dry that has normal infiltration needs to have 4-6 gallons of moisture removed per day. During high cooling load of a proper setup a/c, the a/c will do much of dehumidification. On days when the a/c is only operating a couple hours, the dehu must remove the most of the water.
2 gal. is a start. Get the best dehu you can afford with minimum of 60-90 pints per day capacity. One good dehu 90 pt/day will keep you home <50%RH. The real good ones like the Santa Fe use 50% less energy then the cheap ones. Could save $30-40/month.
Regards TB

[Carnak]

Does the unfinished part have a concrete floor? If yes, concrete is a vapor retarder. The source of the most basement moisture is the infiltration of high dew point outside air.
Keeping a home dry that has normal infiltration needs to have 4-6 gallons of moisture removed per day. During high cooling load of a proper setup a/c, the a/c will do much of dehumidification. On days when the a/c is only operating a couple hours, the dehu must remove the most of the water.
2 gal. is a start. Get the best dehu you can afford with minimum of 60-90 pints per day capacity. One good dehu 90 pt/day will keep you home <50%RH. The real good ones like the Santa Fe use 50% less energy then the cheap ones. Could save $30-40/month.
Regards TB

If they have poly under the slab, then there is a vapour barrier. Concrete itself is pretty pourous. Put a plastic or metal pail on the floor for a day or two. If you pick up the pail and there is a ring of water, it means it is coming up from the slab. No ring then the slab is not a problem.

My father but some special membrane down at his house before he put flooring in the basement. We had no vapour barrier under the old slab. This membrane is like a wick that lets the mositure wick over to where the baseboard trim is in the finished basement.

Blue styrofoam like the Dow Sm does not let much water through, so I hope you have the poly beneath the slab.

4 to 6 gallons per day of moisiure removal because of normal infiltration is sort of opposite to what you normally preach teddy. Thats a couple pints an hour due to infiltration? That would fall right in line with the amount of fresh air you figure a home needs-- usually you like to argue no infiltration in summer the wind is not blowing and there is 'no stack effect'

[teddy bear]

If
4 to 6 gallons per day of moisiure removal because of normal infiltration is sort of opposite to what you normally preach teddy. Thats a couple pints an hour due to infiltration? That would fall right in line with the amount of fresh air you figure a home needs-- usually you like to argue no infiltration in summer the wind is not blowing and there is 'no stack effect'

I preach 4-6 gals. these day. 24 hours X 2-3 lbs.per = 60 lbs./day
2-4 occupants X .25 lbs/occupant X12 hours = 12 lbs./day
72 lbs. /8 lbs. per gal. = 9 gals/day
But put any number down you want. I am sure you can get the moisture out without a dehumidifier. Ok with me.
Regads TB

[Carnak]

What I am saying is now, it would seem there is summer time infiltration if you need to pull out 2 pounds per hour. You go on other tangents and say summer time infiltration is non-exisitent, so that people have to pump in a steady amount of fresh air so therefore they need to buy a dehumidifier to pull out 4 to 6 gallons a day.

[teddy bear]

What I am saying is now, it would seem there is summer time infiltration if you need to pull out 2 pounds per hour. You go on other tangents and say summer time infiltration is non-exisitent, so that people have to pump in a steady amount of fresh air so therefore they need to buy a dehumidifier to pull out 4 to 6 gallons a day.

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You finally got it. Enough fresh air when occupied, to change the air in the home in 5-7 hours is enough to require a dehumidifier in climates where get less than 4-7 hours per day of a/c cooling. You sure have problems getting your head around that.
A wholehouse ventilating dehumidifier with fresh air when the home is occupied is working out well. Our high efficiency dehus are minimizing the cost of maintaining 50%RH. You can turn off the a/c for extended times and have 50%RH at a fraction of the cost of attempting dehumidification by over-cooling the home.
This is all optional and I am sure you know a better way. Ok with me.
Regards TB

[Carnak]

What I get, is no matter what the problem, the solution is the capacity of your product.

I guess it stings a bit when you hit a nerve

[Carnak]

I noticed the duct straps caught your attention. They are a slick product invented by a member here called benncool. They would make a good addition to your ducting kit.