GBA Logo horizontal Facebook LinkedIn Email Pinterest Twitter X Instagram YouTube Icon Navigation Search Icon Main Search Icon Video Play Icon Plus Icon Minus Icon Picture icon Hamburger Icon Close Icon Sorted

Community and Q&A

HRV vs. ERV vs. Dehumidifier – Unique Situation!

bfQLjjpJj5 | Posted in General Questions on

Hi everyone. New member and first-time poser of question. 🙂 Please keep in mind this is FAR from my area of expertise, so talk to me like a dummy; I won’t be offended!

I live in Central-Northeast WI, so our annual temps run from about -40 to 90+
depending on the season. The summers overall I’d say are mild, while the
winters are colder than I’d like. 🙂

I run a home-based business breeding fish and propagating coral and as such,
have a pretty high humidity level (under 90% is pretty rare). I had been
running a dehumidifier in the past but it’s recently died on me so it needs
to be replaced one way or another. It was also costing me $20-30 a month to
run consistently, and even then kept the house maybe a little dryer. It’s a
small 45-pint LG unit, so likely undersized for the chore. I shut it down
over the summer as things were pretty decent temp and humidity-wise, and it
just won’t turn back on now.

I run ~500 gallons worth of heated saltwater, the bulk of that in the
basement (I do have a 65-gal. display in the living room). My issue is that I get
severe sweating on the windows throughout the house, and it’s starting to
affect the wood trim. The corner closets also tend to be somewhat cold and
develop a musty smell. The house was built in 2005, so my assumption is it’s
pretty air-tight.

With my situation (and trying to be somewhat energy-conscious), would an HRV
help alleviate my issues? From the reading I’ve been doing I don’t think an
ERV would solve my problems, as I can’t ever envision a time when I’d need to
add any humidity back to the incoming air. Or would it make more sense for me
to look into a whole-house dehumidifier?

Thanks in advance, I appreciate your thoughts!

GBA Prime

Join the leading community of building science experts

Become a GBA Prime member and get instant access to the latest developments in green building, research, and reports from the field.


  1. GBA Editor
    Martin Holladay | | #1

    Let me get this straight:
    1. You have a tank filled with 500 gallons of heated saltwater in the basement.
    2. Your indoor relative humidity is usually at 90% at higher, even when you run a dehumidifier.
    3. Your dehumidifier just broke.
    4. For years, your windows have experienced "severe sweating," to the point that the trim has been damaged.

    Fred, Fred, Fred -- you are destroying your house. And you're not doing it slowly, either -- you are driving at 90 miles an hour on the Autobahn in the direction of massive failure.

    Your home is a commercial enterprise that needs a commercial ventilation system and a commercial whole-house dehumidifier. It's time to call up an HVAC engineer familiar with the design of such systems. Do it pronto!

  2. bfQLjjpJj5 | | #2

    Thanks Martin, that gets me started.

    Let me say first off, it's not as "commercial" as you'd think. I may have overestimated the total actual water volume vs. the capacity. I'd say in all, I generally have ~300g worth of water going at any time. There are many, many tanks out there that people have as simply their display. I guess I can't say 100% for sure, but I think a commerically-sized dehumidifer would be overkill.

    Let me address a couple things as well, hopefully it will provide a little more insight:

    1. The dehumidifier was a unit purchased refurbished off Ebay. I'm definitely not a repairman, so I'm not sure if it doesn't work due to overuse, old age or something else. I took it apart, and the internals look fine, but the circuit board seems a tad corroded. Not horribly so, but enough that I'd guess it's the issue. I can't say for certain if this is from before I had it, or since I purchased it, as I don't know what the problem that necessitated refurbishment. It's been sitting in the basement not running for about 6 months, so I'm sure that didn't help it either. I'm pretty sure it's not from being overworked. The unit, when I ran it continuously, did drop the humidity to around 70%, give or take a little. But the cost was getting excessive due to constant use.

    2. The only place I've measured humidity is in the basement, and that's based off the now-defunct dehumidifer and a cheap analog gauge I have. I guess it would be prudent to measure the humidity on the main floor as well. I'll do that tonight to see what the humidity is on the upper level, not just the basement.

    3. The window "damage" I may have overstated. It's mostly some indications of mold growth along the trim. The wood itself isn't showing any issues like curling, expanding, bowing, etc. Just some slight discoloration in a few spots (I do sop up the condensation and clean it pretty frequently as well).

    4. I don't have much of an issue during the summer. I generally keep a number of windows open or run the A/C (with them closed) as needed. I didn't run the dehumidifer during the summer this year, hence the sitting for 6 months or so.

    If I can't do this for a reasonable price, it's more economical for me to simply shut down the large portion of water volume in the basement. It's a fun little business, but doesn't really make a ton of money, unfortunately. :)

  3. GBA Editor
    Martin Holladay | | #3

    At a minimum, you need a whole-house ventilation system that includes an HRV.

    You need to keep the indoor relative humidity below 50%. It's possible that you need a whole-house dehumidifier; if you go this route, the person to talk with is Ken Gehring at Therma-Stor Products.

  4. bfQLjjpJj5 | | #4

    Would it make sense to start with one or the other? The HRV units seem to be more cost-effective as far as cost to purchase/install and cost to run vs. the dehumidifier.

    I'm assuming the two could work in conjunction as well? If I start with the HRV and it doesn't quite get the job done, I could look at adding the dehumidifier at some point as well?

    I've found a couple slightly-used HRV units locally for sale that seem like they would fit the bill, but I'll definitely check out the link you provided as well. Thanks!!

  5. GBA Editor
    Martin Holladay | | #5

    I would certainly start with an improved ventilation system. And don't forget to buy three or four hygrometers, and install them in various rooms of your house.

  6. bfQLjjpJj5 | | #6

    Will do. Any recommendation for a good hygrometer? The one I have looks pretty simple if memory serves me correctly. I believe it's a simple dial with some sort of coil on the back. If I'm looking for a few, is there a specific type or brand that is relaiable but won't break the bank?

  7. user941025 | | #7

    This is awesome. I tip my hat to you, sir.

  8. user-626934 | | #8

    You might be interested in reading the recent article from Joe Lstiburek - "In the Deep End" - regarding indoor swimming pools. It's mostly concerns new construction, but it might convince you that you'd be better off setting fire to dollar bills than to continue with this operation in a building that wasn't designed for it.

    A couple of other things...

    1) I wouldn't assume that the house is "pretty air tight". If you have some significant leaks, when combined with your extreme indoor RH%, you could be headed for the rare case of sheathing damage via moisture-laden air leakage.

    2) The moisture load you're adding to the building probably has a lot more to do with the total surface area and temperature of the water than on the total storage capacity. More surface area + warmer water = higher moisture load.

  9. R6EgUpNZE6 | | #9

    If you end up going the ventilation route, you can get units that have "swappable" cores.
    I put a HRV core in for winter, and ERV core for summer use.
    Venmar Constructo 1.0 is one example of such a unit.

  10. user-788447 | | #10

    I share in the others' concern. I work at architecture firms in the Twin Cities and used to frame houses in the early 2000s. Your house is likely constructed of 2x4 or 2x6s, a poly vapor barrier with fiberglass batt insulation and OSB sheathing (i.e. moisture damage prone material). Too little regard was or is giving to actual air tightness with standard construction.

    The chances that you have exfiltration of moisture laden air out of your house at typical problem areas is high. The fact that you are observing sweating windows and have a musty smell in your closets is reason to believe you could have moisture accumulation in your walls that you cannot see.

    This bears repeating, the damage that we are suggesting is possible would not be visible to you.

    Depending on who your energy provider is, you may be eligible to receive and blower door/ infrared camera energy audit for around $100. This is best done in the winter when the temperature difference between the interior and exterior is high. The infrared photography can locate areas with the highest rate of air exfiltration. These would be the areas to investigate to see if the exterior sheathing and adjacent wood framing have high moisture content and therefore the potential for mold growth or even wood decay.

    There might be a moisture meter that can be inserted in these areas with little damage to the walls, but it might require removing some exterior siding to take a sufficient look.

    In the twin cities there are many empty small retail and studio spaces vacant. Why not set up your shop in a commercial building?

  11. bfQLjjpJj5 | | #11

    J - good advice. I'll check with my gas/electric company to see if they offer something of the sort. I know there are other companies in the area that specialize in energy efficiency and do scans for airflow and temp difference.

    Just out of curiosity, what are the options for making a home more airtight if there are some areas like that? I'm guessing they're neither fun nor cheap? I'm somewhat of a DIYer. If I don't know how to do something...I generally teach myself. :)

    Just a couple updates as well to the whole scenario -

    1. Checked my hygrometer in the basement right now - Temp 65, Humidity 72%
    2. Brought it upstairs after that in the kitchen - Temp 68, Humidity 70%

    So it may not be quite as bad as I originally though.

  12. bfQLjjpJj5 | | #12

    Also, forgot to address this one - "In the twin cities there are many empty small retail and studio spaces vacant. Why not set up your shop in a commercial building?"

    Believe me, I'd love to. Retail space around our area is obnoxiously expensive. Any decent place is at least $500+ per month, the vast majority of them are upwards of $1,000 per month. It just doesn't fit in the budget, unfortunately.

  13. user-788447 | | #13

    72% RH is not as alarming as 90% RH but it is still elevated over expected averages (around 55% I would guess) and the fact the the elevated humidity is constant rather than periodic I think causes more of a concern.
    One question is how long have you had this setup in your house? In terms of moisture dynamics over time what is of concern is that during the winter moisture laden warm air is escaping through the building assemblies and condensing when it hits colder surfaces - a wetting process. In turn-of-the-century housing stock with little insulation and made mostly of solid lumber this would be much less of a concern because solid wood can handle wetting better and there is much more potential for the assemblies to dry (one reason being the heat escaping through the walls because the lack of insulation). The way your 2005 house is constructed the drying potential of the assemblies is reduced and the wetting effect can accumulate year after year leaving moisture prone materials moist and ripe for fungi.

    If you did perform the energy audit, even if you air tightened spots you located there is no guarantee that you would have addressed all compromised locations. Addressing a humidity problem with increased air tightness doesn't address the source of potential problems. The proper solution is as you started with to increase ventilation or dehumidify to evacuate the humidity to a reasonable RH level. I don't have the expertise to determine which is the most cost effective route.

    One relatively easy thing you might do to investigate whether any damaged has been caused by the conditions created with the fish tanks is to look in your attic assuming your attic floor is insulated and your roof structure is visible along with the roof sheathing visible from below. In the winter if you see a lot of frost on the underside of your roof that is a sign of moisture escaping from the home and hitting a cold surface. Frost on the underside of the roof doesn't necessarily mean damage because an uninsulated roof has greater drying potential versus an insulated wall assembly. Still you can inspect the roof rafters and sheathing for visible water damage that may occur in areas hit with a greater amount of air escaping (typically around chimney or plumbing stacks going up and out the roof.)

  14. bfQLjjpJj5 | | #14

    So just a few minor updates here:

    1. My hygrometer reading in the kitchen has been at around the 62% mark for a few days now. So I guess sort of good that I overestimated my humidity levels throughout the house. I'm planning on moving it to the other end of the house to see how that fares.

    2. I got a line on a couple HRV units. So by the end of the year I should have one running to see if it makes a difference.

    3. I'm looking at a couple options for moving the bulk of my operations out of the real down side to this at all!

    I'm planning on checking for any other signs in the atthic this weekend. More details to come. Appreciate everyone's input, you've been extremely helpful!

  15. yzerham19 | | #15

    Hello, I am a first time poster and wanted some advice for my basement on whether to forego adding a dehumidifier in lieu of an HRV/ERV. I am located in Westchester County, NY climate zone 5. 1957 Cape Cod; 2400 sq feet on 3 floors with walkout basement. Before finishing basement had a few waterproofing companies come out. One said that if I had no water come in last March (2011) during the once in a 100 year storm that I won't have to worry about flooding from the outside. He said I should just add a dehumidifier to take out the moisture and protect against mold.

    My question is whether installing an ERV/HRV in my climate zone can play a dual function in bringing in fresh outside air while at the same time reducing moisture/dehumidifying the basement.

    Any advice would be appreciated as well as recommendations on HRV/ERV models.

    Thank you.

  16. GBA Editor
    Martin Holladay | | #16

    HRVs and ERVs are usually used to provide fresh air to occupied spaces, not basements. Here is more information:

    Designing a Good Ventilation System

    HRV or ERV?

    The reason that you can't depend on a ventilation system to provide dehumidification is that outdoor air is often more humid than indoor air, especially during the summer. Ventilating during those circumstances will only raise, not lower, the indoor humidity level.

    Are you sure that your basement has a humidity problem? If you are sure that it does, the best solution may be a dehumidifier.

  17. BobHr | | #17

    what if he built a room inside the basement but line instead of drywall use poly. The walls and cieling of the room would not be touching the existing structure. Then run a vent fan to the exterior keeping the area at a negative pressure to the rest of the house.

  18. GBA Editor
    Martin Holladay | | #18

    I'm not sure what your point is. You propose a hypothetical construction -- is that a proposed solution to Michael's dilemma or a building science riddle?

    If Michael builds a room in his basement, and installs an exhaust fan so that the room is at negative pressure with respect to the basement, then basement air will enter the room through cracks in the walls. The effect will be to make the humidity conditions inside the room about the same as those elsewhere in the basement.

    If the exhaust fan is very strong, it will pull exterior makeup air through cracks at the mudsill into the basement, and thence into the partitioned room. This will lower the basement humidity during the winter, and raise the basement humidity during the summer.

Log in or create an account to post an answer.


Recent Questions and Replies

  • |
  • |
  • |
  • |