Ideas for Whole-House Dehumidification
Hi all,
Wondering about a dehumidifier in Climate Zone 4 (North Vancouver, BC).
I’m building a home. Insulated walls, with a target ACH of <1.0, maybe even considering using Aerobarrier to bring it even lower.
Will be using a ductless mini-split for heating/cooling. However I’m also looking for a way to install a whole-house dehumidifier. My energy advisor has told me that I don’t need one in this climate zone, but I disagree (especially with climate change and what I’ve experienced tracking dew point in my old leaky house right now). He states that the HRV will be enough. But in any case….
I’m wondering what product or what way could a whole house dehumidifier be installed without the duct work for forced air heating/cooling?
Any thoughts, thank you!
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Replies
I’m giving your question a bump. Although this reader was inquiring about whole-house dehumidification in Florida, I think this conversation thread will interest you, and there are a few links to relevant articles you might want to read.
great, I'll take a look. thanks.
No doubt that a dehumidifier will sometimes increase comfort. But less clear is if a much lower initial cost portable unit + open interior doors would be enough.
But OK, say you are going for high end, maximum comfort, even with closed doors. For that, I'd review the installation manuals of the various whole-house units available. Honeywell, Aprilaire, etc.
I have a portable dehumidifier but during the shoulder season last year it barely made a dent in my relative humidity. And its noisy!
Using a portable dehumidifier for a whole house is like use a dorm fridge for a walk-in cooler. They don't have enough capacity and they aren't durable or reliable.
I don't have a lot of evidence for this, but I think that if you install a whole-house dehumidifier with very limited ductwork, maybe just one supply and one return, or a few of each, you'll do fine. The biggest advantage of a whole-house setup instead of portable units is that the best whole-house units are much more efficient than stand-alone ones.
As far as whether you need it, the better your insulation, the less the A/C runs, but you still need dehumidification. So if you are going for excellent R-values, you are likely be benefit from having a dehumidifier.
To your primary point, I think one needs a supply to every closed door room. After that, it gets less clear about how much mixing will occur.
> best whole-house units are much more efficient
Aprilaire 1830 70-Pint Whole House Dehumidifier: 2.0 L/kWh
Best/only ES listed whole house (probably 2X over-sized which will lower efficiency): 2.35 L/kWh
A good Energy Star portable: 1.9 L/kWh
Jon, thanks I'll take a look at that unit. Looks promising.
I'm thinking something like UltraAire 98H, at 2.55 L/kWh, or 155H at 3.45 L/kWh.
Agreed, those are better examples. But at say 1280 L/year, the difference is a not-so-much ~$40/year.
Yea, I see Matt Risinger uses UltraAire, so that's good enough for me!
Thanks, I was hoping a single supply and return would be enough. That may be an option. I'm thinking I will have ceiling fans in all the rooms to help move air as well.
Say we agree that the lower operating cost doesn't cover the increased purchase/install costs of whole-house. Then a single supply/return will leave you with just the not-quantified noise difference.
That puts things in perspective.
I am climate zone 6 and working on a new PGH design. With dehumidification being our primary comfort for the summer months. For myself, I am taking the air handler route, but spent several months looking at the minotair and the aprilaire systems very closely. The minotair looks like it can do cooling, dehumidification and the erv function.
The minotair is convenient, but when you actually look at its performance numbers it doesn't look that great to me. But it's a little tricky to know for sure.
Yea, I remember reading about it in a thread somewhere on GBA, but when I looked into it. I don't think it would perform well enough.
Did you just find that having ducts made the most sense due to your climate zone?
The decision for duct work was a goal was to get down to a few appliances as possible. So it an air to water heat pump for radiant heat and an air handler that does cooling, dehumidification. The ERV is to be connected to the air handler because, most of the time it will be just the ERV running, I.e. balanced. With the VFD on the air handler the energy usage should be low. I did the controls for my current system, zone valve control is easy to design and mixing valve just required one call to technical support.
So your ERV and dehumidifier and the air handler all share the same ducting?
I don’t know your local conditions but I see Canada and think month sub freezing weather.
When it is cold outside the HRV will have no problem lowering the indoor humidity as it will be discharging moist air and brining in very dry air.
I would say yes you need dehumidification if you were someplace like Texas and had several months where the outdoor temp was very close to the desired indoor temp but the outdoor humidity unbearably high.
When you are paying for expert advice overruling the expert tends to sour the relationship. You need to decide if trust this expert or not.
Walta
Walta,
The OP is in Vancouver. The climate is the same as coastal Washington State. Wet, not cold.
You can connect your dehumidifier to your hrv ductwork. This way you'll be able to handle your latent and sensible load indepedently which is worth it in my opinion. No more cold air to handle the humidity during the shoulder seasons which are quite long in Canada especially in Vancouver. Matt Risinger talk about that in one of his video.
If you install an dehumidifier, you should definitely pick an ERV instead of an HRV in order to not waste all the energy you spent dehumidifying the house.
Alex,
"you should definitely pick an ERV instead of an HRV in order to not waste all the energy you spent dehumidifying the house."
Can y0u flesh out the logic behind that a bit? Why would an HRV waste the energy?
As you probably know, there are two types of heat : latent and sensible. If you have a dehumifier and a heating system, you are able to handle both types of load in a controlled manner. So you pay an energy price to remove sensible and latent heat. If you have an HRV, you only retains the sensible work you did not the latent work. All the work you did to lower the latent temperature is dumped outside. Why doing it when you can retain some part of it by having an ERV instead of a HRV?
Of course, that is presuming the latent temperature is higher outside than inside which is usually the case if you are dehumifying (unless you have some kind of interior pool). An HRV can also be cheaper and more effective but in general I would say an ERV make more sense on the long term. I could be wrong though.
Alex,
As Charlie said, the periods when you may need dehumidification in Coastal BC are rarely when it's hotter outside than in.
I think that in the climate in question, the common shoulder season conditions is that the outdoor absolute humidity is right around where you want to get to, and it's primarily the internal humidity sources that you need to combat. In that case, ERV vs. HRV doesn't matter. Then when you get to slightly lower humidity outside, the HRV will do the job alone, easily, whereas the ERV wouldn't do as well.
Ok I'm not familiar with the humidity level in the Vancouver area so that makes sense. Some days the HRV might be better than an ERV I guess just like sometimes running an HRV in bypass mode is more economical.
But what about the summer when it's humid outside? You are still paying to remove that latent load no matter if it's the mini split or the dehumidifier handling it.
My point is the equipment choice to handle the latent load removal or addition doesn't matter. What's important to me and some others may disagree is that if you are managing the humidity level in your house, then you should try to recoup some of that energy cost by using an ERV. Some days it could probably be cheaper to swap the ERV for an HRV core if it was possible but on a year round basic the ERV is the better choice in my opinion.
Of course, if you are not managing your humidity level, then the choice between an ERV/HRV may be climate dependant and depends if you are air conditionning your house or not.
Alex,
The problem is probably mine, but I still don't understand. Both ERVs and HRV's recover energy from the outgoing air. The difference between them is the ERVs also transfer moisture. How is that a good thing when you are trying to dehumidify the indoor space?
Hello Malcolm
If the incoming outside air is more humid than the inside air because you are running your minisplit or dehumidifier, then you want the moisture in the incoming air to transfer to the air you are dumping outside. This way the air entering the house will be less humid and you don't need to dehumidify it as much.
Off course, this is only true if the outside air is more humid than the one inside but this is usually the case in summer unless you live somewhere very dry like in Arizona.
Alex,
Ah - finally got it. Thanks.
Great discussion.
For Vancouver the dew point mean is :
May 2020 9.1C (48F) - temperature is 13.7C
Jun 2020 11.5C (52F) - temperature is 15.3C
Jul 2020 13.1C (55F) - temperature is 17.6C
Aug 2020 13.5C (56F) - temperature is 18.0C
Sep 2020 12.9C (55F) - temperature is 16.3C
Oct 2020 8.0C (46F) - temperature is 10.5C
I would like to keep my indoor dew point below 12C (55F) at all times.
With the house being so tight, and the contribution of internal gains in the latent load wouldn't a whole house dehumidifier be useful to have during these months?
I can see the benefit of an ERV with a dehumidifier during these months though. And the rest of the year running an ERV would help keep moisture inside.
I have a question though: what if the ERV exhausts from the bathrooms and laundry room? Would an ERV be a good choice, or would I just not exhaust from these areas if I am using an ERV?
With the HRV I was thinking exhausting from the bathroom and kitchen would save me from having another exhaust fan in the bathrooms and laundry room and save on having penetrations in the air barrier as well.
Any thoughts?
@Hawnes, regarding #45:
With the air tightness and insulation levels you've described, either an HRV or ERV should be able to handle moisture in your bathroom as long as the unit has some kind of boost function. Separate bath fans shouldn't be needed.
This issue came up in a recent BS + Beer conversation around the 1:15 mark:
https://youtu.be/tvFylYqP07Y
Ideally you'll have supply ducts going to bedrooms and living areas for fresh air, and then exhaust ports in kitchen, bathrooms, and laundry room.
In regards to bathrooms (or kitchens for that matter), you get the immediate benefit of a 'boost' function during and after a shower, but also the continuous air flow (for us it's about 24cfm in bathrooms, 36cfm in the kitchen) throughout the day since the ERV is running 24/7.
Can you point me towards that video?
I've been told the dehumidifier can't be used by the HRV ductwork?
I couldn't find the one I was thinking of but he talks about it in "ERV/HRV vs Dehum - What’s the difference?"
Did they tell you why they can't do it? Otherwise, a solution is to duct your dehum to a big common open room like a living room. Technically, it wouldn't be connected to your hrv ductwork but would still be able to dehumidify the incoming air.
https://www.greenbuildingadvisor.com/article/ductwork-ervs-dehumidifiers-forced-air-heating-systems.
See the section "The ERV and the dehumidifier can share ducts"
Great thanks, reading now and definitely helps me understand the issues.
There is a thing called a "Conditioned ERV" (C-ERV) that is an ERV with dehumidifier. One brand is Equinox -- https://buildequinox.com/
I have no firsthand experience.
That's cool. I didn't know this product existed. Thanks!
I wouldn't actually call it an ERV plus dehumidifier. It can only actively transfer heat between incoming and outgoing streams and can't do it passively like an ERV. It's great that it can do all the different functions but I'm not convinced that the efficiency achieved is as good as you can do with a mini-split plus an ERV.
Thanks DCContrarian. I've emailed BuildEquinox, but due to their "smart ventilation" which is something I've looked into as well. Will ask them about dehumidification as well.
What R-values are you planning for your house?
Typically it's the combination of Passive House (or something close) levels of air tightness and insulation that prompts the need for whole house dehumidification, at least in the case of high performance homes.
In Passive Houses the cooling loads are so low that the heat pump won't run long enough, or hard enough, to remove the latent load, even as it has no problem maintaining comfortable indoor temperatures.
You can read about our experience with excess humidity towards the end of this blog post just above the TOH and Risinger videos: https://kimchiandkraut.net/2019/02/21/hvac-for-passive-house/
When I was designing my HVAC system in 2016/17, much of what I read suggested an ERV - heat pump combination for a Passive House would have no problem with latent load in my climate zone 5, here in Chicago. Direct experience suggested otherwise. We couldn't keep humidity below 60% without the use of 2 portable dehumidifiers (one on our main level, the second in the basement).
Spring and fall, apart from a random day here or there, haven't been the problem. It's always been a combination of temperatures over 80º with high outdoor RH in the summer that causes a spike inside our home.
The last couple of summers we've been averaging 30-40 days when the dehumidifiers are necessary. Definitely not an everyday need, but we're glad we have them when we do need them.
In Passive House consultant training this past summer I brought up this issue, worried that I had screwed up my HVAC set-up somehow, but the instructor confirmed that dehumidification is a legitimate concern for most climate regions. He said he recommends a combination of ERV-heat pump-dehumidifier. He also added that when clients ignore this advice, it's not uncommon for a whole house dehumidifier to be added post-construction when comfort issues arise --- a much bigger hassle than having it installed during construction.
If I had it to do over, I would've installed a ducted whole house unit during construction. At this point, as long as the 2 portable units continue to work, I don't think it's worth the bother, even with an energy penalty since these units are less energy efficient.
These are the units I bought off Amazon:
https://www.amazon.com/gp/product/B073VBWKJZ/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1
As Jon and Charlie point out above, you'll also want to consider your layout when it comes to how you duct the dehumidifier. Rooms with closed doors, or separated spaces, will likely suffer. In our case, a single unit on each level works mainly because of our very open floor plan. We have oversized doorways between bedrooms and living areas, but the barn doors for these bedrooms can and do remain open when the dehumidifier is running. Same scenario in the basement (few walls down there). Each level is 1500 square feet.
In the training we were told to dump the heat from the whole house unit into the basement, or directly outdoors. In our case, each unit is set-up about 8 feet away from an exhaust diffuser, so the heat from the units has never registered as any kind of problem.
The CERV and Minotair units, since they're newer products, come with some risk. How confident are you that someone in your area will be able to service the unit should issues develop? Are you ok working through technical issues on the phone with a company rep should it be necessary? What will you do if the company goes out of business and issues then come up?
Trevor apparently had to deal with this kind of situation a while back:
https://www.greenbuildingadvisor.com/question/erv-recommendations
If something catastrophic did happen, could you afford to change out the system post-construction for something else --- something else meaning a separate heat pump, H/ERV, and dehumidifier --- since you'll be depending on a single unit for most/all of your HVAC needs?
Someone with an engineering background will likely weigh the risk/benefit ratio of trying a new product differently than someone with no background or interest in engineering. It's probably fair to say that most homeowners would not welcome the idea of opening up their 'magic box' to tinker with it in the hopes of repairing it should they be unable to find a competent service person in their area. It's something to consider.
Hi Eric, thanks for your experience. Super helpful. Our R-value is aimed to be at 40 (not sure what the effective would be). Also ACH 1.0 or less.
Yes, I have been worried about having to install a whole-house dehumidifier post-construction, so I have been pushing my builder to install one. They were hesitant at first but I think they are convinced now! Or just fed up with me haha.
80F with RH of 60 outside places your dew point at 65! That sounds gross.
Thanks for your blog post, really useful information. I'm not trained in construction or building at all so really useful explanation and pictures.
I think right now I'm planning to either install a ducted HVAC system or have a simple single duct supply and return for the dehumidifier with ceiling fans to move air. It will depend on cost for me.
That hOmeLabs dehumidifier. Is it loud?
It's not quiet. Roughly comparable to the noise produced by a fridge, maybe even a little louder.
After they've been on for a couple of days in the summer they become background noise to us, but I can understand if someone else found them to be too loud.
They also run intermittently, so the noise isn't constant, which some might find even more irritating since, unlike a white noise machine, you can't get used to a constant mechanical hum.
Similar issue with heat pump water heaters. We don't find our Rheem unit to be especially loud, but others online have expressed some irritation with the level of noise that it produces.
> In the training we were told to dump the heat from the whole house unit into the basement, or directly outdoors.
A good idea, but looking at typical whole house units, I see no option to control where the heat goes - it gets mixed in with the dry air. So what is meant by this?
With our Mitsubishi heat pump and Zehnder ERV set-up, dehumidification would have to be a stand alone function, as opposed to connecting a unit to the existing ductwork of a gas furnace. There's no way, at least that I'm aware of, where the 3" Zehnder tubes could be used directly in combination with a dehumidifier.
The whole house dehumidifier would be ducted to main areas of the house in order to pull humid air back to the unit (in the basement or 1st floor mechanical room typically), where the heat produced by the unit could be allowed to exit directly into the basement/mechanical room, or be ducted directly outside. https://www.sylvane.com/how-to-duct-dehumidifier.html
I see no option at that link to duct the heat anywhere without the dry air going with it. Do any indoor units allow you to direct the hot air separately from the dry air? Like the expensive Ultra Aire SD12, but no outdoor part.
@Jon R: Not that I'm aware of.
In class, the discussion was:
Excess humidity will likely be a problem...
Add a whole house dehumidifier...
A dehumidifier produces heat, adding to sensible load...
Expel it into the basement (where occupants won't notice a slight increase in temperature) or directly outdoors.
Have you looked into the Daikin Quaternity mini-split? The head has two coils so you can run one cool, one heat for dehumidification, or both heat or both cool.
No, haven't heard of them. Will take a gander.
The thing to keep in mind is that dehumidifiers are also really efficient space heaters. They remove water vapor at room temperature from the air, and exhaust it as liquid water near freezing. All of the heat they extract -- in addition to the heat from the electricity they consume -- is put into the living space, and it's done with the COP of a heat pump.
So a couple of observations:
If you are running AC, you don't want to be running a dehumidifier unless the AC in its "dryest" possible setting can't keep up with the humidity. You'd be heating air just to cool it again.
If you need a dehumidifier, a heat pump water heater is a no-brainer. Put that excellent space heater to work!
Yes, we will have a heat pump water heater. I was thinking of placing it in the laundry room, but with solar panels I've been told there's an issue with not placing it with the mechanical room. Don't know. Will require more discussion.
Hi Eric, regarding your #51 (it won't let me reply anymore),
I remember in a BS + Beer show someone saying that they don't duct exhaust of the ERV/HRV from the bathroom or kitchen so that the core doesn't have to handle the moisture.
I may be remembering wrong though.
What do you think of that?
Also I remember hearing one of the shows with Ken Nelson (https://youtu.be/p_pDNFc5KVk?t=3350) where he talks about having the supply and exhaust in the great room?
I think Travis was asking about whether there's any risk to the core if it sees moisture (long term), but this shouldn't be a problem.
In addition to the filters (at least for Zehnder) at the main unit for incoming fresh air and stale air returning to the core, there are also smaller filters at exhaust ports.
The Zehnder core is also washable. I've found that about once a year is plenty in order to prevent the core from seeing too much dust and dirt build up. Even with a MERV 13 filter for incoming fresh air, some dirt and debris will find its way around the filter to the core itself where it will collect. Same is true for the two fans that run the unit. They're easy to wipe clean once the main unit is opened up.
I imagine these units could really suffer in a mechanical and performance sense if the filters and core aren't cleaned for months or years. Passive House and Pretty Good House designers and builders have increasingly stressed the importance of supplying the homeowner with a user's manual for the whole house, but especially for HVAC since it's fairly distinct from conventional HVAC systems. These systems can only perform as designed if they're well maintained.
You can remove the face of the main unit to access all of these areas for an annual cleaning. It's a little nerve racking the first time you do it, since you don't want to break any parts (at least it was for me), but it's actually relatively painless to do.
Zehnder was designing system layout for all supply and exhaust diffusers, so hopefully they still offer that as part of the purchase price. Even if they don't, it's relatively straightforward: since it's a balanced system, you need equal amounts of cfm entering (supply) and exiting (exhaust) your home.
For instance, this would mean a supply in a bedroom and an exhaust for an attached bathroom, or supply in a family room and an exhaust in a nearby kitchen. On our first floor we have one more exhaust port than supply in our laundry room. In our basement we have two supply diffusers (main area and an office) and one exhaust (rough-in bath area).
As long as you have balanced cfm entering and exiting and they're in areas that make sense, you should be fine.
In kitchens you need to be careful about the exhaust port being too close to your stove/range hood. It's a good idea to keep your exhaust port about 6-10 feet away to avoid cooking grease and oils getting inside the exhaust port or the ductwork.
It's also helpful to remember that these are relatively small rates of cfm entering and moving through rooms, so more like a cloud of smoke slowly making its way through a family room before it exits through an exhaust port in the kitchen. Even in boost mode it won't be an airstream making a straight line from your supply diffuser to the exhaust port.
With brands other than Zehnder you'll want to find out what your options are for diffusers/ports (how are they adjusted, style, suggested placement), as well as the ductwork options (who will install it, where in your structure will it be located).
With Zehnder, the white 3" comfo tubes can fit in most areas, even in 2x4 walls without a dedicated chase, which can be helpful when planning layout for HVAC equipment. The only thing that we found they don't do well is make quick 90º turns (you need some space to make a more gentle turn).
They also have more options now than when we built our home: https://www.zehnderamerica.com/air-distribution-systems/
Zehnder is more expensive than other brands, but to us it was worth it based on the history of the product in Europe, in terms of performance, as well as allowing us to install it ourselves to avoid the cost and space requirements of traditional ductwork.
I see, I assume he meant that he has a bath exhaust fan that runs based on the RH detector at the fan.
Then he exhausts air from the "great room" (the room where everyone spends time) and I assume the supply is into the bedrooms. This way the "great room" has the air there diluted.
This avoids all the moisture and dust from the bathroom and laundry room entering the core.
I think this would also avoid re-introducing the moisture from these rooms back into the house if the humidity outside is lower. But this may be beneficial as well if the humidity outside is too low.
With the Zehnder if I push the button for 'boost mode' in one of our bathrooms it increases the cfm supplied to the entire house at all the supply diffusers. This also means it's then sending more air towards all the exhaust ports, pulling moisture laden air in the bathrooms back to the core, but ultimately outdoors where you want it. It won't harm the core. It's simply doing the job it was designed for.
There's also a double layer of defense for the core: filters at the exhaust ports themselves, as well as a dedicated filter at the unit before stale air can return to the core before being finally expelled outdoors. As long as the filters are maintained, along with the core, the system shouldn't have problems in this regard.
The basic idea is to supply fresh air to living areas (bedrooms, family room, dining room, home office, etc.) while pulling stale air out of the house from areas associated with moisture and unwanted smells (bathrooms, kitchen, laundry room).
It was a little odd at first realizing that boost meant increased cfm for the whole house, rather than just limited to a single bathroom or the kitchen. Having lived with the system for almost 3 years, I really appreciate the way this works.
One quick example, we like to roast garlic, but as long as we use the boost function, combined with the fact that the ERV runs 24/7 even when not in boost mode, we've never had any lingering smells.
That's a big advantage of this balanced, constantly running system (assuming no one unplugs it) is that even when not in boost mode areas like bathrooms and the kitchen are receiving a supply of fresh air and then that air is expelled via the exhaust port 24/7.
With a traditional bath fan someone has to turn it on and remember to turn it off (unless it's on a timer). The other issue has been no one usually remembers to clean the unit itself on a regular basis, so even if it has sufficient power it tends to get clogged with dust over time. And when it's off it's off, so there's little airflow through the space. Most of the bath fans that I've lived with previously supplied more noise than actual function.
Also, with an ERV you benefit in the winter when it adds some moisture to the fresh air supply (at least here in Chicago where winters are notoriously dry). In the summer it's supposed to be sending this excess moisture to the exhaust stream, but there are limits since the unit is constantly supplying fresh air. This is why dehumidification is sometimes necessary.
A Zenhder sounds great, but its way out of my budget. But I'll have to see my overall budget once the plans are done.