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Community and Q&A

Dehumidifier in basement: Will it work for the whole house?

JaBK | Posted in Mechanicals on

I own a 3-story home. Basement, ground floor and upper floor. Each floor is approximately 80m2 (860 sq feet large), combined volume of the house is cca 600m3 (21200 ft3).

All stories are heated with floor heating and all have the same inner temperature. Basement is not cooler (perhaps 1F) or more humid.

Given the PHPP (passive house standard) are house falls in the passiv standard albeit we do not live by those standards, so we need a bit of cooling in the summer.

Summers in our country are quite hot at 30-35C (86-95F) during the day, occasionaly even hotter. We have an ERV installed and we heat (winter) and cool (summer) our house with a heat pump. Since we do need a bit of cooling and I am highly sensitive to all kinds of A/C systems (blowing cool air), we opted for floor cooling. Not the best option but adequate and free, since we didn’t need to do any additional installation.

The problem is that floor cooling works in terms of cooling the house to required temperature, but it does not take care of condensed water. I have two portable dehumidifiers (delonghi dem10) – I put one in ground floor and the other one in upper floor and they manage to keep the RH below 65% in the worst conditions. This solution works but I am looking for more automatic solution and there is a lot of talk on American sites about wholehouse an basement dehumidifiers.

The room where I have the heat pump and ERV has installation for direct drainage so I wouldn’t have to manually empty the tank. The amount of condensate is not very big, about 6-8 pints per day.

So how can I “automate” dehumidification of our home?

1) Can I use both of my existant dehumidifiers as an whole house dehumidifier in the basement? I have been told yesterday that moisture will quickly even in my house since it is very air tight and I do not have closed stairways between stories. Additionaly there is an open ceiling (220 sq ft) between ground and upper floor.

2) If those two dehumidifiers won’t work is there hope for any dehumidifer installed in basement and not being connected in any way to the air ducts. I am looking at a 40L (85 pints) dehumidifier but am not willing to buy if this will not work. I am borrowing a 20L dehumidifier tomorrow and will start all 3 (2x10L + 1x20L) dehumidifiers in the basement room where I would like to put a single machine. Will these 3 dehumidifiers perform the same as one 40L dehumidifier and can I assume the same result – that is either failure or success.

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  1. User avatar GBA Editor
    Martin Holladay | | #1

    There are lots of issues here.

    To summarize: You live in a hot country, and not in the U.S. (Care to tell us where?)

    Your house has an air-to-water heat pump that creates warm water in the winter and cool water in the summer. This water is circulated through tubing in your floors -- so you have a hydronic heating system and hydronic cooling system.

    You have just discovered why people don't install hydronic cooling systems very often: You end up with puddles on your floor. Now you need whole-house dehumidification.

    If you lived in the U.S., your house would probably have forced-air ducts. But since you probably live in Europe or Asia, you only have ventilation ducts.

    My advice: Experiment with basement dehumidifiers and see if they work.

    If they don't, your three options are: (1) Install a dehumidifier on each floor, with the condensate piped to the basement drain, or (2) Install a whole house dehumidifier, along with the necessary ductwork; or (3) abandon the hydronic cooling system, and cool your house with ductless minisplits instead.

  2. JaBK | | #2

    I live in Slovenia, Europe. I am aware and was warned beforehand. But since I only need dehumidifiers when cooling and I only need coling 3-4 weeks a year I didn't want convectors to deal with moisture, because they always give me grief healthwise. So your number 3 is a no-go as well. I dread A/C.

    Am doing number 1 right now without the automatic drainage, which I would probably not do. We are done with the house for now and have been liiving in it for 3 years. I see no construction work in near future. So, with that in mind I started googling how people deal with humidity. I was surprised I could only find american discussion sites, Europe obviously does not recognise humidity as an issue. Whole house dehumidifiers do not exist here or at least I was unable to find any. There are standalone dehumidifiers but no disscussion whatsoever about putting one large dehumidifier to deal with the whole house. Hence, I could find noone with any experience on the subject. This is completely new for me.

    What baffles me now is my experiment and how relevant it may prove. As of tommorow when we are expecting high temperatures again I will plug in 3 dehumidifiers. A couple of 10L/day with air flow of 100m3/h and one 20L/day with unknown air flow volume 200m3. My question remains (if it can be answered): Is this the same as one latge dehumidifier with capacity 40L/day and air flow volume of 260m3/h. Can I simply sum the litres or is it not that simple? How about air flow volume? Can those be summed and 3 humidifiers are better?

  3. Steve Knapp CZ 3A Georgia | | #3

    I have a whole house ventilator dehumidifier. It is rated at max blower of 320 CFM and will remove 98 pints of water a day at 80 degrees (F) and 60 percent relative humidity. It is not a ducted install, so I depend on a combination of stack effect and an HVAC air handler for air mixing. This works for the most part but is not ideal during the shoulder seasons.

    At the moment, outside it is 88 degree (F) with 62 percent humidity. Inside it is 76 degrees with 40 percent humidity. Indoor humidity normally stays between 38 and 41 percent at this time of year.

    I don't know how standalone dehumification would work in your home without mechanical ventilation. As Martin suggested, you should experiment.

  4. User avatar
    Dana Dorsett | | #4

    Slovenia doesn't have nearly the outdoor humidity issues found in the south eastern US. Compare the humidity graph (a bit more than half way down the page) of Ljubljana to that of say, Mobile Alabama:

    As long as there is at least some open convective or mechanically driven air flow between floors a small dehumidifier in the basement of a tight house that size will keep up with the humidity in the rest of the house, as long as you don't have excessive ventilation rates during periods when the outdoor dew points are high (say 16C or higher.) In fact, just one would do it for most homes. For most houses that size, a whole-house dehumidifier would be like using a cricket bat to swat mosquitoes- way more capacity than would ever be needed.

    The key is to reduce the ventilation rate on the ERV on days when outdoor humidity is high (dew point of 16C or higher)to avoid taking on humidity from outdoors, increase the ventilation rates when outdoor humidity is low (dew point of 15C or lower) to purge humidity from the house. That will use a lot less electricity than relying solely on the dehumidifier.

    For most houses that size a whole-house dehumidifier would be like using a cricket bat to swat mosquitoes- way more capacity than would ever be needed unless high ventilation rates are desired.

    Dehumidifiers convert latent heat (moisture) in to sensible heat (hot air), raising the cooling load on the house. Modifying the cooling system to allow for a chilled water air coil for dehumidification may be the best solution, but it would require a bit of design and rework. It's probably not going to be worth it in your climate.

  5. JaBK | | #5

    The ERV is set to cca 150m3/h, this is as low as possible before I start complaining about stale air. That is about a quarter of the whole net volume of the house. Usually it is set to 300m3/h.

    I want to use only one dehumidifier, but before I buy, I want to know if these two options are comaprable:
    1.) 3 dehumidifiers: 10L + 10L + 20L
    2.) 1 dehumidifier: 40 L

    I am trying out the first option right now. and if it works, can I assume one 40L would worka as well? tahe same, better or worse? That is my main concern, I cannot borrow a 40L anywhere right now.

  6. JaBK | | #6

    So, I have been running my 3 dehunidifiers in my basement throughout the latest "heat peak" which will hopefully end in a couple of days (outside dew point above 18C) and been able to keep the RH in the house below 60%.

    Now I am waiting for the postman to bring me my brand new 50L dehumidifier. perhaps it will be strong enough to work nights only - that is when the electricity is cheaper, outside dew point is as low as it gets as well as temperature, so my ERV will go on bypass and exctract some of the heat produced by the dehumidifier. There is an exhaust duct in that room. Will see how that experiment goes. But mostly I am happy I will not have to hear or see that thing till the rest of the summer when I will unplug it.

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