Ventilating Dehumidifier vs. ERV
I recently watched this video which seems to contradict a lot the GBA conventional wisdom: https://www.youtube.com/watch?v=eLI4D-RzhF0
essentially stating the in humid climates, ERVs misuse budget dollars without saving much energy (and they can’t dehumidify).
Instead, he is advocating a ventilating dehumidifier which pulls in fresh air, filters and dehumidifies it before running through the heat pump.
https://www.natethehousewhisperer.com/blog/bad-ass-hvac-part-6-what-it-looks-like
It also goes against the GBA advice of balanced ventilation through dedicated ERV ducts, in favor of intake ventilation and just using the HVAC ducts for circulating conditioned an filtered air
I’m looking at new construction in CZ6 (2-story house plus finished basement), and I need to decide on:
ducted vs. ductless ASHP
ERV vs. ventilating dehumidifier
balanced ventilation with dedicated ducts, or intake ventilation with shared ducts
what are the pros and cons of each approach?
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Replies
Venting dehumidifier is for warmer climates (zone 3 or 4). In cold climate you want an ERV, the energy penalty of no heat recovery in cold months is way too high.
As for the rest, for a new build you want a ducted unit, ductless can be made to work but has too many issues. Once ducted, usually the simplest is to use the HVAC ducting to distribute fresh air from the ERV.
If you are in an area with a very humid shoulder season, a stand alone dehumidifier might still be needed. This can be something as simple as a budget box store unit in the basement.
I believe Nate Adams is an HVAC contractor in Cleveland, solid Zone 5 territory, and he's reporting a lot of success with the venting dehumidifier installs
I think his argument is that the ERV doesn't recapture that much energy compared to the installation and maintenance cost
Agree about a full ducted system
regarding sharing the HVAC ducts to distribute fresh air, I was deterred by this article
https://www.greenbuildingadvisor.com/article/ducting-hrvs-and-ervs
"Delivering ventilation air through heating or cooling ducts is a bad idea"
I'm in the north edge of zone 5, 7200 heating degree days. Typical house would need about 75CFM of fresh air so in a heating season, the energy used is about:
7200 HDD *24h *75CFM * 1.08 =140 Therms
That works out to 4102 kWh if heating with resistance heaters or 1/3 that with a heat pump. In either case that is very real amounts of money, so even a code min 60% efficiency ERV will have a decent ROI.
You can do the same math and check your ROI based on local energy costs.
In zone 6 you are looking at a hyper heat system for HVAC. All of these have ECM blowers that run pretty much 24/7. There is no energy penalty in using the heat pump to distribute fresh air.
As a bonus in cold climate, it pre-heats the fresh air supply which can get cold even with high efficiency ERV once temperature reaches low single digit range.
If you want better than common simple ducted setup (ie both fresh and stale air both connected to the return), look at hybrid ducted setup. With this you still connect the fresh air to the HVAC return but the stale air pickups are ducted to the house (near kitchen area, basement and most used washrooms). The cost of this bit of extra ducting can be saved by eliminating a couple of bathroom fans. Be warned that 99% of installs are the simple ducted setup, so you might get silly price for anything else.
thanks for the equation
where are you getting HDD? I'm north of you in southern New Hampshire, and I'm getting lower HDD than yours.
6300 HDD over the past 5 years using 65F base temperature. https://www.degreedays.net/
Using your higher 7200 HDD:
4102 kWh / 3 = 1367 kWh with COP 3 heat pump
1367 kWh * 0.24/kWh = $328 per year
I was quoted $4500 for a code-minimum ERV
which is almost 14 years simple payback period.
That's not enough savings to justify the investment to me
Broan's newest AI series 160 CFM ERV is about ~$1800 (https://www.supplyhouse.com/Broan-B160E65RT-160-CFM-AI-Series-Energy-Recovery-Ventilator-w-Top-Ports-67-Efficiency). That's obviously without the install cost, but still, $4500 seems high. It's a 67% heat transfer efficiency unit.
Akos is in Canada, on the edge of Z5 to Z6.
You can pick up an 88% efficient ERV for a lot less ($1600 USD)...take a look at the RenewAire EV Premium L. It has ECM motors and gets efficiency from a relatively large core: https://hvi-1491.quickbase.com/db/bh6688vwb?a=dr&ifv=1&rid=17526&dfid=12
The reason typical HVAC vents are not "recommended" for fresh air circulation is that this would require using the furnace fan motor 24/7 with the energy penalty that would entail. That ERV I linked would use 37 watts at 120 CFM in a dedicated duct setup.
Keep in mind Akos is using just sensible heat in that equation. In summer, the ERV is effectively drying incoming air at around 70% transfer efficiency assuming 120 CFM. In the absence of an ERV with just dehumidification (humid summer day), you'd need to both cool that air, and dehumidify which would be a lot more energy intense vs passive transfer over a core. Yes, you may need to still dehumidify with an ERV, but it would be less for sure.
The venting dehumidifier is also not zero equipment cost or zero install cost.
agreed that both devices have associated cost
trying to decide the merits of choosing one over the other
I would love to buy HVAC equipment at cost, but my builder is quoting $4500 installed. I'm not sure how to save $ here; I'm not going to DIY install
BOM cost is about the same, install cost should be similar. One uses way more energy in cold climate. Plus around me, energy recovery is part of the code.
One in-between option is to install something like Whispergreen spot ERV for each bathrooms. I've had somebody run into same silly pricing for an HRV but upgrading each bathroom fan to the spot ERV was only a couple hundred dollars. These are not the best efficiency but still better than zero.
Tell your builder to just install the exterior wall penetrations with some sort of cap on the inside and then you can install the ERV yourself at a later date. Or you can get an HVAC contractor to do it later without the builder's markup.
One added complication would be if you need a dehumidifier no matter what, because then we are talking about installing both an ERV and a dehumidifier instead of just one or the other. A reasonably priced ERV has a decent payback/ROI in my opinion though. Probably better than upgrading double-pane to triple-pane windows or other similar upgrades you may have already paid for. Just something to consider.
if I understand the proposed system correctly, he is using the heat pump to dehumidify, then reheating with an electric resistance coil
https://www.natethehousewhisperer.com/blog/hvac-20-equipment-wish-list
That heat strip setup stuck out to me as a bit obtuse in a cooling mode/dehumidifier setup. I don't get at all. Using a heat strip is horribly inefficient whereas an inline dehumidifier would be using the evaporator to cool, then the same unit's condenser to return the air to temp. Adding a heat strip after a heat pump coil (in cooling mode) to condition dehumidified air...maybe the worst possible way to do it with respect to energy costs.
he's claiming "the cost to operate electric reheat is between $20-100/year"
Amos and Dennis wood- i think this concundrum really boils down to energy efficiency versus mositure management. Obviously you turn first to an erv in Quebec. Just as obviously you turn to a ventilating dehumidifier in Miami. What do you do however when like over 80 per cent of us who live in an in between climate? I have more heating days than cooling days in zone 4 marine, but not much, and soem btutak weeks where we have 70ndegrees and 75 per cent humidity….very very few heat pumps, even full inverter and variable blowers, can handle that scenario. Unsurprisingly, as this is GBA after all , there is an obsession with energy efficiency and ‘carbon footprint’ , even as readers drive their EVs around that consume 20 barrels of oil just for the manufacturing inputs, or charge their cars at a Tesla supercharger in New Jersey cores by an oil burning electric plant. Way before those considerations must, even on this forum, focus on health, and also comfort. And this means dealing with radon and moisture mold WAY before obsessing about VOCS and passive house standards. If that’s the case, beyond building tight houses and managing bulk water which we all can champion, I would submit you wnat to Strive mightily to avoid ANY mold ….once you get it, it’s there permanently unless you want to tear down your walls and even then hard to remediate. I can’t justify ANY compromise mold defense to saving a few trees in the Amazon. Nor can I cut any corners on radon defame, and that means you mUST strive to avoid negative pressures at all costs. 80 per c Et of the houses probnly exceed their indoor dew points for long enough periods of the year to deposit soem moisture and this mold in thier wood stick houses. It’s really hard to ‘blow’ Il and pressurize all but the most tight houses. It’s really easy to depressurize, even in well designed houses. everybody has a cooktop fan e.g., so stop worrying about positi pressures, a sl positive pressure means you never get negative pressures and no mold amd no radon. Ventilating dehumidifiers Emma you don’t increase the burden on your hvac as you add fresh air and you ensure you house is never in negative pressure. What not to like> low humidity, fresh air, lo radon , no mold. And you CAN use your hvac ducting supply . You cna set it up continuously if you buy one of the larger newer units with fans strong enough to overcome your ducting static pressure or link it to your hvac blower, .
The Zehnder ComfoAir Q350 ERV boasts a heat recovery efficiency of 86% and humidity recovery of 73%. That is huge. You don’t get any of that with a venting dehumidifier. And there are some problems with intake-only fresh air like wasted conditioned air escaping your over-pressured house. I’m sure you can do some simple math to figure out the electricity costs differences between ERV-exchanged air and the wasted exhaust air in the case of the vented dehumidifier.
https://www.zehnderamerica.com/wp-content/uploads/2023/01/zehnder-group-nederland-bv_comfoair-q350-erv-comfort-vent-q350-erv_1006vs03_en.pdf
I think Nate makes a lot of sense with his e,mphasis on putting that extra money to work with a good modulating inverter variable speed ecm heat pump,then supplementing with a ventilating dehumidifier. Radon and mold are by far your two biggest concerns, but you’d never know it reading gba and the subscribe obsessed with setting new records for ach 50 and passive houses. But who can afford afford a $15,000 installed zhender systems (esp if a house that needs. Two zhender systems //0. As for pressurization , you never want a negative pressure in a house, and it’s really hard to over pressurize anything but a passive house. And the best best way to ensure you never have negative pressures is to have sl pressures. Subslab Radon is a much greater Health risk than co2, VOCS etc etc.my solution ? Ventilated dehumidifier in basement system to lean on summer Standard erv upstairs to replace bath fans and lean on in winter. Thsi also resolve separate ducting system question-you scavange what would have been a ducting system for bath fans and use it for your erv returns. As for the ventilating dehumidifier, makes sense to use hi hvac ducting . I believe you want to duct your dehumidified outside air into the hvac supply well away from blower. Why? You want to first use your hvac as dehumidifying capability and cycling as long as possible. Your dehumidifier will exhaust cold dry air into that duct, a good dehumidifier a much more EFfic(ent way to deal with water vapor esp during trunk seasons. Of lot of these bias are deeply but subconsciously influenced by your climate , that’s why it can be dangerous to have a guy in Boston do your manual j in Florida and vice versa. Bottom line for me- focus on radon and latent heat ; stop obsessing over positive pressures and global warming esp if you don’t have a leaky hosue.
The error in logic with a ventilating dehumidifier (in my simple mind anyway) is that you have to address the full sensible AND latent heat burden if you're just bringing in outside air. The latent burden on a hot moist day as the phase change occurs from water vapour to liquid will likely require more energy than the sensible differential...something that needs to factored into operating costs. This energy cost will be incurred for the life of the home.
If you can reduce those inputs by 70-80% using a decent ERV (and add some positive pressure if needed), how does that not make sense?
I have 2 erv's in my home. I paid approx $800 cad each for them. And I still think erv's are overpriced for what they are. I installed them, ducted into the return , it's not rocket surgery. Even an HVAC contractor can do it.
The RH in the house stays around 40%. Works for me...🤷🏻♂️
Jamie
You are overlooking the vast majority of Houses ], even new ones, even tight ones , even with ervs, even with full inverter heat pumps with variable speed fans, will always have a season of at least a few weeks where the the high humidities with moderate temperatures.even with a 3 degree setback.unless you have suitable upscale carrier Bryant with heated dehumidification using the heat strip , most of us need a whole house dehumidifier . Now of course you can size your house exquisitely and ,precisely for cooling but then your heating likely to be inadequate, and you’re using heat strip often in winter. Bottom line most houses south of Boston need a whole house supple,mental dehumidifier along with their ac, and of course they need ventilation. if new and tight. Combine them and you get both.of course you. Tend to get positive pressures or actually always avoid any negative pressures, but that is a good thing esp of u are in a radon area.we spend way too much time on gba obsessing about carbon footprints and marginal energy efficiencies , and not enough ensuring houses are ALWAYS dry in climates where 75% of us live, ervs don’t lower humidity in fact in humid days they ADD to house humidity burden.ervs are a balanced ventilation strategy that mitigates energy costs. Ventilating dehumifier s are balanced ventilation strategy that deals with humidity. I’d much rather have a dry and sl positive pressure house than a precisely balanced one, tripping into negative pressures every time a door is opened , and adds my my houses humidity burden, esp during trunk season when my ac is not designed to handle hi lane t heat in the context of low sensible conditions.
yes I think Nate Adams is more concerned with managing moisture year-round and less on minimizing the absolute energy cost
can you say more about "upscale carrier Bryant with heated dehumidification using the heat strip" - would this be a candidate for me with new construction in Zone 6 outside Boston?
Nate IS more concerned about moisture, as we ALL should be .he has some very interesting real world numbers also to show the concerns about cost are overstated. Bryant extreme evolution and carrier full inverter green speed models allow setting to use heat strip to heat air and ‘fool’ system into staying on during days you have high humidity and moderate temps. Nate is an advocate of ventilating dehumidifiers but first putting your money toward the heat strip implementation. I think you might get away with that in zone 6, but I can’t in mid Atlantic. We had a particularly brutal trunk season this years. Weeks where humidity and temp both in 70s. I have a carrier system, but not one that can implement heated dehumidification (8 years old) it also a]only ramps down to 40 per cent max, not as low as 25% as new units. I a, currently building another house and here is my approach. Really obsessive about keeping mositure out - commercial foundation drainage products, inner and outer drain tiles , xylex and /or dryvit , air tight house . As Bryan Orr insists , in any climate that’s your first priority keeping external load down. I will have an evolution extreme heat pump, and an erv, with a plumbed in vent system to use in basement for additional ventilation and /or dehumidification if my heat pump can’t handle the full years panoply of moisture challenges.
Except for a couple of micro climates, an ERV is the most efficient way to bring fresh air into the house. Doesn't matter which zone and how humid outdoor air is.
As you get towards warmer climate, the energy saved by it gets less and less so eventually the ROI is too high. This would be somewhere around zone 3.
Next question is what is the best way to deal with indoor humidity. A dehumidifier simply converts this latent load into sensible heat, so it isn't all that efficient as this extra heat has to be rejected by the cooling system anyways.
Since most cases a home will have AC, there are many ways to add a bit of sensible heat to use that for humidity control. The strip heat coil is one of option, there are also wall mount units that have built in re-heat and humidity control (Daikin Quaternity).
Another option that works extremely well in a multi story house with separate heat pumps on the main floor and upper floors. You set the upper unit to dry mode and the lower unit to heat. The combination keeps the house from overcooling and the operating cost of the extra bit of heat is very low. I've tried this and it is very effective, side benefit is that it keeps the bedrooms cooler which is perfect.
In my home, the one I found by accident, is heat gain from west facing windows. This bit of heat is enough to increase the runtime on the AC to keep humidity very low even during shoulder season. We have pretty hot and muggy summers and I never see above 45%rh. I also run an ERV so the fresh air supplied is much dryer than outdoor air in the summer.
One more thing about venting dehumidifier in cold climate. The fresh air supplied in the winter would be very dry and you would not be able to maintain reasonable indoor humidity without a humidifier (which also adds operating cost).
Great stuff! What’s your climate zone?
Yes a dehumidifier creates sensible heat, but isn’t that what your strategies do also? Ie turn on basement system heat? Ie we take moisture out of the air a create sensible heat so ac continues to run, nit cycle, coil in ac stays cold and water cont*nes to condense . Also, dehumidifier is optimized/set to emphasize latent Removal; hvac systems, esp hi seer due to their manipulation of pressures to achieve those seer ratings do not. I guess a full modulating system can have a Sufficiently flexible algorithm to adjust to that and alter ratio appreciably in trunk season situations, but can’t imagine this is common. Also can you expand on what is ‘dry mode’ amd what is dry mode ? Assume you have ducted full inverter better/variable speed fan system(s)? If so you set upstairs humidity set point low , but what heat setting do you use downstairs? Just high enough to fool thermostat? But how to determine that //? If you r system not equipped with heated dehumidification, without such a set up how do you set thermostat above ambient temp and still get coil to cool? / ?
North edge of Zone 5.
The units are ducted mini splits. So fully modulating units with inverters. Most (all?) have a dry mode where the unit lowers the evaporator target temperature and runs the fan on low. This improves humidity removal but there is still sensible cooling. The downstairs unit is simply set to heat at target room temperature ~72F.
A dehumidifier is about a COP 2.5 space heater. You get the heat from the compressor electrical use as well as the heat from the water condensing. This heat now needs to be transferred outside which means you also have the cost of running the AC.
With the above setup, the latent heat and compressor heat is dumped outside. The bit of sensible cooling and heating is now provided by the heat pumps, during shoulder season these are running above COP 5, so very little energy is required. I haven't done the math overall on efficiency though, not expensive to run whereas as stand alone dehumidifier does spike electricity use. The benefit is that there is no extra equipment required or additional condensate drains to deal with.
Akos, a question. A dehumidifier has an evaporator coil first cooling the air, then the condenser coil heating it. I would assume then that there should be a net increase (heat) limited to mechanical pumping inefficiency, cooling the electronics, compressor and fan motor. I have a basement dehumidifier running at about 325 watts with the compressor on, however I'm pretty sure it is not adding the equivalent of 325 x 2.5 = 812 watts of heat to the room that it runs in. Can you clarify what you mean?
When water vapor condenses into liquid water it releases heat. It's about 1000 BTU per pint. That heat goes into the cooling coil and is expelled by the dehumidifier. So the dehumidifier produces more heat than the electricity consumed, about three times as much. Dehumidifiers are very efficient space heaters.
A dehumidifier that produces 72 pints per day will produce 72,000 BTU/day, or 3,000 BTU hour, plus the heat from the electricity consumed. If it has a coefficient of performance of 3 it will consume 1500 BTU/hour of electricity --- about 440 watts -- for a total of 4500 BTU/hour.
When it comes to ventilation, I want a balanced recovery unit.
When it comes to dehumidification, I would also want a dehumidifier if I needed it.
When you're in the business of designing or building high performing new systems, my opinion is that the HRV/ERV is a for sure, and the de/humidifiers are an additional consideration if needed based on your climate (as you've been driving home).
However, when you're in the business of making money working with average people in their existing houses. You know that +5k quotes won't get jobs to fix whatever people's hvac problems are. But you also know that ~2k is a lot more tolerable. So push just a ventilating dehumidifier, basically a square peg in a round hole. It's good enough and it works, right?
This website it not called Grey Renovation Contractor. It's called Green Building Advisor. Its about the highest function and energy performance, and is populated with some pretty smart and experienced people (I'm not one of them, I know I'm pretty dumb because I'm spending time responding to this...) So I suggest taking what they have to say, ponder it, and use it or don't.
Personally, I'm a big fan of having multiple smaller fancoils in a house. Basically one on each floor to really handle the temp variations from stack effect and differing window packages based on the use per floor. And of course, systems that support these are modulating ducted miniplits that when sized appropriately, run long times and condense for long times. I can't wait for hydronic systems to proliferate, where multiple smaller fancoils become more the norm, then we really won't need dehumidifiers!
Just my thoughts. I'm just some jackass on the internet.
Jamie
Jamie - I have to demur. A strong g case can be made for positive or at least no negative pressures, whole, house dehumdification , and of course ventilation. De signing an hvac system in. Any climate I would submit the priorities , in descending order , . are, even for GBA enthusiasts
1) radon mitigation -why? It’s the only contaminant that’s proven to kill you
2) moisture- why ? If you can control moisture, you can tolerate a very broad range of temperatures ‘ also if you can control moisture, you can avoid mold, the next most serious health threat in any house atmosphere
3) temperature
4) fresh air/low VOCS etc.
4) efficiency -why last ? My family’s comfort and health should always take precedence over Green attributes.
If you are in a hi radon zone, or high air pollution, or forest fire prone area, you never want your house to depressurize. The best way to avoid that? UNbalanced ventilation. . All houses even tight ones leak. Modest positive pressures make up for the air leaking out of the house.
A plethora houses in the USA have moisture/mold issues they don’t know about or ignore. Most houses have too large sensible cooling capacity, so they are very vulnerable in trunk seasons. Even a couple of days of humidity over up per cent even 60 per cent will results in mold growth . Good luck eliminating that once it gets into your wall assembly. You never want your house to get above 60 % rh for more than a couple of hours a week, at MOST! Very few houses meet that standard without whole house dehumidification . So new houses should unequivocally lean toward sl positive pressures (in order to b e certain they o have me pressures)and have whole house dehumidification. A ventilating dehumifier does that. I’m not against ervs, indeed I have one in my house, but unless you have a new, tight well insulated home with a perfectly sized hvac system and life in zone 4 -5 -even 6 I think i can make the case your first dollar is toward a full inverter variable speed fan that isn’t too high a seer (that rating being achieved usually by manufacturers manipulating pressures; some seer22+ units unless fully modulating , full inverters and variable speed fan that n ramp down to say 25 % capacity and have their algorithm shift to latent e over at those levels, . tHEN a ventilating dehumidifier, then an erv.
Minisplits aside from being ugly, poor filtration and high maintainence, often don’t deal with humidity well-surprised pleased to see your units can be adjusted adequately to achieve to emphasize latent loads if desired.
I wonder if the simplest solution would be a super-sized version of the Build Equinox CERV
If you could size it to meet the heating and cooling load, it already provides all the filtration, mixing, CO2/VOC control, dehumidification in a single box
You're describing the "magic box" that is used in some European locations. See Martin's article here: https://www.greenbuildingadvisor.com/article/a-magic-box-for-your-passivhaus.
There seems to be some options available in the U.S. but I have no experience with them. In general, I think you should design each system separately so that they can be as efficient as possible and focus on their singular task. This also provides redundancy so you are not dependent on one single device. There definitely are some potential efficiency gains by chaining the systems though, so I get where you're coming from.
I looked closely at cerv it’s got soem great attributes, but your loads /house have to be carefully designed implemented , it’s not cheap, though neither are street installed prices for full modulating inverter/variable speed ducted systems, my take ? You have to design your house with cerv in mind, sort of designing around cerv. Soem will argue that they aren’t a big company, but try the big boys to honor a warranty issues 9.5 years after install. I would to design a house with cerv in mind. Others will say, who will service it? I say, have you tried to find a quality hav a company these days with stable, experienced and curious staff? The company is a pleasure to work with and know what they are doing.
DC, energy added by the state change does make sense..thanks. This fellow measured both power use and water accumulated to get to a COP of 1.5 ( http://www.iwilltry.org/b/heat-your-home-with-a-dehumidifier/ ) … it follows that your actual and target RH will have a large impact on actual heating from dehumidification. The heat released from that phase change complicates the ERV vs dehumidifier/vent calcs as my understanding is that in an ERV core, most of the humidity exchange occurs as vapour. They don’t need a defrost strategy until -10C or so. The energy efficiency “system” gap then in a humid/cooling climate situation would be even worse for venting dehumidifiers vs an ECM ERV with supplemental dehumidification.