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ERV, HRV, Dehumidifier retro fit before finishing basement

Wendy D | Posted in Mechanicals on

Hi all, I’m new here. Please bear with me with lots of questions.

I live in Zone 4A, with humid summer (100+ F, at least 3-4 months AC time), cold winter (-10 — 0 F, at least 3-4 months heating), and wet spring and fall. Our house was built about 10 years ago. It has 3 HVAC systems for 4000 sq. ft. and additional 2000+ sq. ft. unfinished basement. Two HVAC systems are located in basement while the third one located in a closet on 2nd floor.

We’re planing to have basement finished with drywall ceiling. Before all the ducts are buried behind drywall, I want to do as much work as possible on the HVAC systems so we don’t have deal with it later. I have contacted several big brand dealer regarding the HRV/ERV. Unfortunately this is quite rare in this region and dealers have only installed a handful systems. They are not familiar with the system design, especially in a retro-fit situation.

I want to have a ventilation system installed. Since we are in the middle zone, all the literature I read says either HRV or ERV works. I have received conflict answers from manufacturers as well. I understand that the main difference between ERV and HRV is the handling of the humid air in the summer. In that sense, probably ERV is preferred.

Meanwhile, I also need to deal with humidity issue in basement once it is finished. Currently, we are using a portable dehumidifier (70 pints) to maintain 50% RH in the summer. We have gone through a couple of broken machines already and I think the machine has to work really hard to reach the RH level. Also, placing the portable dehumidifier in the middle of a recreational area will be quite unsightly once the basement is finished. So, I’m researching on whole house dehumidifier that interlocks to the central air.

Below are my questions:
1. If I opt for a whole house dehumidifier, then would a HRV be preferred because the humidity issue will be taken care of by the dehumidifier?

2. If both HRV and whole house dehumidifier are interlocked to the duct, would the duct system to be too complicated as both dehumidifier and HRV have their own controls?

3. Does a heavy duty standalone dehumidifier work in a closed utility room in the basement? If so, we may not have to hook it to the central air system.

4. We have two HVAC systems in the basement. I was told the HRV can only be interlocked to one system, not both. I guess the same thing applies to whole house dehumidifier. Is it true?

5. HRV/ERV duct design question — we still have full access to all the ducts to the first floor at this time and I understand that fully dedicated installation works the best. My rough thoughts is to draw stale air from the bathroom in basement (part of the finished basement) and probably two other locations of the basement. Plus, is it feasible to convert a return duct from the first floor to HRV/ERV intake duct so the ventilation system also removes some stale air from the first floor? For fresh air distribution, is it possible to hook the fresh air supply duct from HRV/ERV to the supply duct out of the furnace instead of hooking it to the return duct of the furnace, as a partial dedicated system? My intention is to make the HRV/ERV run independently, not rely on the running of central air handler as our blower is single speed.

Your suggestions are highly appreciated. I feel overwhelmed by all the ideas and articles I read.

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  1. Charlie Sullivan | | #1

    I can try to answer some of these, though others are outside my expertise.

    Q1. "If I opt for a whole house dehumidifier, then would a HRV be preferred because the humidity issue will be taken care of by the dehumidifier?"

    You are paying for the electricity to run the dehumidifier. The ERV reduces how much humidity comes into the house, so you have to run it less. So at least for the summer, you'd prefer ERV at least as much with dehumidification as without. You might consider a unit with swappable cores if you want HRV in the winter.

    Q3. "Does a heavy duty standalone dehumidifier work in a closed utility room in the basement? If so, we may not have to hook it to the central air system."

    Only if it's vented through the walls of that utility room. That might be better than hooking it to the central air system, as the central air system dehumidifies as it cools and is unlikely to need the dehumidifier too.

    One general question: Have you done air sealing already? You might have humid air leaking into the basement driving the need for dehumidification, or you might have moisture coming through the foundation walls and/or floors. In either case, you might want to address those problems.

  2. Wendy D | | #2


    Thanks so much for your quick reply.

    Yes, we will have spray foam done for our basement wall and rim joist before drywall.

    I think you have made a valid point that dehumidifier plus HRV probably is not as energy efficient as ERV alone. Thanks for pointing out the swappable core unit. I was not aware of it until your post. Is Venmar the only manufacturer that makes swappable core unit?

    The utility room planned will have Louvered doors and it is next to an open recreation area. Do you think a stand alone dehumidifier will work in such environment? To be honest, I'm a little hesitate to add more component to the central duct system.


  3. Charlie Sullivan | | #3

    A dehumidifier running in a louvered closet will keep the closet dryer than the air in the room outside. It will then have to work harder to extract humidity from that dryer air. If the amount of moisture it has to pull out is low--which we can hope it will be with your walls foamed--that might be OK. So one option would be to try that and see how much it has to run. If it's not much, you are all set. On the other hand, if it has to run a lot, I'd get a ducted duhumidifier, like an Ultra-Aire. But I wouldn't connect the ducts into the system---I'd just run them through the wall of the utility room to the main space in the basement.

    If you haven't pulled the trigger on the spray foam yet, you might want to know that the spray foam now available has a quite substantial global warming impact--the gas they use to make the bubbles in the foam is much worse than CO2 (as in >1000X worse) as far as its climate impact. Another option for basement walls is EPS (beadboard) foam which is >100X better than spray foam in that regard.

    Zhender and VanEE also have swappable-core ERV/HRV units. Happily all three of those companies also have low-electric consumption motors at least available as options. Since that motor may be on 24/7 it's nice to have it be an efficient one. "ECM" is the buzzword to look for for that.

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