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Community and Q&A

What is best clean & dehumidified air solution?

Barbara French | Posted in General Questions on

Hello,

I am building a two story 5250 square foot, hydronic radiant heated residence in the Monterey Peninsula. The area has high humidity and normal temperature range is 40-70 F. There will be no AC. I am interested in designing the air system to prevent mold and also have good quality air. I have been advised to install an ERV system with a dehumidifier. Is this the best solution ? If yes, what would be the best way to configure the dehumidifier.

Thank you,

Barbara

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Replies

  1. Expert Member
    Dana Dorsett | | #1

    Just because it rains a lot doesn't mean it's "high humidity" , or that you would need a dehumidifier. Far from being high humidity your location has very TEMPERATE humidity, not too humid, not too dry, just about right (almost) every day of the year!

    Pull up a dew-point graph on Weatherspark of say, Pacific Grove, and zoom out to cover a whole year.

    https://weatherspark.com/#!dashboard;q=pacific%20grove%20ca%2C%20USA

    The mean mid-summer outdoor dew point is about 55F, which at 75F indoor temps is a healthy and comfortable 50% relative humidity. Mid-winter mean outdoor dew points are about 40F, which at an indoor temp of 70F is a perfectly healthy and comfortable ~35% RH. It doesn't come any better than that! Health pros suggest 30-50% RH as the sweet spot for human health & comfort, and it's rare day when that would not be achieved by ventilation alone.

    A dehumidifier and ERV would be a waste of money in that climate. With ANY air conditioning at all the interior would stay under 50% RH in summer. Even with no air conditioning and high ventilation rates it would rarely go north of 50%. In winter you can ventilate (even at high rates) with an HRV without excessive drying.

    An ERV + dehumidifier has a better rationale in gulf coast conditions, where outdoor dew point averages can linger in the 70s F for days or weeks on end:

    https://weatherspark.com/#!dashboard;a=USA/AL/Mobile

    THAT would be aptly described as "high humidity", not the Monterey Peninsula.

  2. Barbara French | | #2

    Dana,
    Thank you for the explanation. Your answer explained human comfort level but does that also hold true for mold growth? The area is plagued with mold. Would an HRV system create enough air flow to keep mold at bay?

    Best,
    Barbara

  3. GBA Editor
    Martin Holladay | | #3

    Barbara,
    I'm not sure why the area is "plagued with mold." Does this problem occur in bathrooms? Perhaps in crawl spaces?

    In general, mold grows under conditions of high indoor humidity. In your climate, you should be able to keep mold at bay in your bathroom by using your bath exhaust fan regularly. Mold in crawl spaces is a different matter entirely, but if that is the problem you're thinking about, we can talk about it -- and can guide you to specifications that will produce a mold-free crawl space.

    In most rooms, mold problems are most likely to occur in the summer, during spells of hot, humid weather, especially in homes with no air conditioning. Under these conditions, ventilation makes the problem worse, not better. If you have a problem during hot, humid weather, the solution is to close up your house and operate an air conditioner. If you like to keep your windows open, you can do that instead of operating an air conditioner -- just use good housekeeping practices, and your house should stay mold-free.

  4. Barbara French | | #4

    Martin and Dana,

    Thanks for the responses. In general, there is mold in present in most homes. Although, many are on slab. The home I am building will have raised floors but with minimal clearance and I believe there will need to be an active ventilation system installed. What that is exactly, is part of my question.

    The weather has higher relative humidity than I believe Dana mentioned, in July according to weathersparks, Monterey is between 63 -93% ( 25th -75% percentile) and the weather is mostly cool due to the high percentage of clouds ( in July 72%). Monterey is on the ocean, and experiences morning fog that lasts a significant part of the day, which keeps the temperature lower and humidity higher than would be expected in the region. I am not knowledgeable about this subject but think the fog prevents the ground/ structures from fully drying- thus creating an environment for mold to grow.

    I just want to design an environment inside the home and beneath the home that will prevent mold and create good air quality without over designing.

    You comments are much appreciated.

    Thank you both,
    Barbara

  5. GBA Editor
    Martin Holladay | | #5

    Barbara,
    As I mentioned before, if you want to lower your indoor humidity levels, "active ventilation" can be your friend or your enemy. In cold, dry weather, active ventilation will tend to lower indoor relative humidity (RH).

    In warm, damp weather, however, ventilation makes things worse.

    In most cases, sealed crawl spaces stay dryer than ventilated crawl spaces. For more information on this topic, see Building an Unvented Crawl Space.

    If you are finding it hard to avoid mold with the windows open, the solution is to close your windows, stop ventilating, and to operate an air conditioner or dehumidifier. For more information on these topics, see:

    HRV or ERV?

    All About Dehumidifiers

  6. D Dorsett | | #6

    For mold to take off it takes chronic interior air dew points well north of 58F. The mean HIGH outdoor dew point in your area is 56F at the peak month of August, with a mean low in August of 51F. (Pull up a dew point graph for Pacific Grove.) That means you would able to control the indoor humidity into the low-mold zone by ventilation alone, even during the worst case weeks.

    In your area as long as there is a heavy polyethylene or EPDM vapor barrier under the slab, a slab on grade home would be fine. If you're going to build a minimal height ventilated crawlspace you will still need the vapor barrier over the soil, but it also means you will have to add substantial insulation under floor, which lowers the temperature in the crawlspace, making the joist edges more susceptible to moisture.

    It's a dry enough climate that you can get away with that, but a sealed insulated crawlspace with 1.5" of EPS under a 2" rat-slab and R10-ish walls would make better sense.

  7. Barbara French | | #7

    Hello again,
    I am still struggling with understanding the best plan of action. Most of the time when the fog is present, the air has a cold bite to it. This is most days from morning till early afternoon. When the coverage clears, there is a dramatic difference in the feeling of the air. Maybe the relative humidity chart shows this by the dramatic difference in relative humidity in a day, it can range form 96% - 57%. This is in reference to summer days when there is little chance of rain.

    I am assuming this house will be using the radiant heat most of the year since even in the summer the mean high is 69F, therefore most of the year the interior temperature will be higher than the exterior. From my limited understanding, an HRV or ERV would make sense to transfer the heat to the intake air. The ERV also transfers some of the moisture. Is this a good thing? Would it make more sense to have an HRV with a dehumidifier? The dehumidifier would lower the interior humidity and the HRV would not transfer the moisture from outside to inside like the ERV would. Although, we probably would not want/need the dehumidifier all of the time, since it probably wouldn't be needed once the fog lifted. Is there a controller for a dehumidifier that can regulate and monitor the house humidity to a certain percentage? I read dehumidifiers consume a lot of energy. This house will utilize solar electricity. I have some questions on this subject that I will post later.

    On the subject of the crawl space ventilation- the ground drainage is an issue on this lot. It is beneath a golf course that has a lot of runoff. The ground, several feet down is clay, and does not absorb well. We are having to design a drainage plan that will divert the water around the house. I still think the ground may have moisture issues. Under these conditions would you recommend a slab or raised floor? I had assumed a raised floor would be better but am open to your comments.

    Many thanks to both of you

  8. Expert Member
    Dana Dorsett | | #8

    The relative humidity changes outdoors have NOTHING to do with the humidity levels indoors. The outdoor RH is all "relative" to the outdoor TEMPERATURE, which varies (a lot) over the course of a day. Even 100% RH fully saturated 50F air brought indoors and brought up to indoor temperatures results in perfectly healthy 50% RH at 70F. When it's foggy out, the dew point temperature = = the outdoor temperature. The only time it's of concern from an indoors mold growth perspective would be when it's in the 60sF outside and foggy. I'm sure that happens at least a few hours out of any given year, but it's not a chronic condition in your location. Most of the time it's only foggy when it's cool outside.

    An ERV is only beneficial if you have (and need) mechanical dehumidification of the interior air. If you are trying to dry out the indoors with the ventilation air, an ERV would slow down that process.

    With a foot of clean gravel on top of clay you could move a whole river under the house without creating moisture problems at the slab if there's a code-worthy vapor barrier under the slab. If the footings of the stem walls (or grade beams) are going to rest on damp clay soils, line the concrete forms for the footings with 10-mil poly or EPDM wide enough to reach above slab level to keep them completely dry from any runoff issues. Tape the footing & stemwall vapor barrier to the slab vapor barrier before pouring the slab.

    Slab radiant is far cheaper to implement than installing it in wooden floors. In your climate you'll do fine with 3" of EPS between the gravel and the vapor barrier (with the slab poured onto the vapor barrier. Even at your +37F 99% outside design temperature (see: https://articles.extension.org/sites/default/files/7.%20Outdoor_Design_Conditions_508.pdf ) the heating water temperature requirements would be quite modest (lower than they would be with most wood floor radiant solutions.)

    The heating/cooling balance point of a code-min house is about 60F these days, so even though the summertime mean peaks are sub-70F, it doesn't mean you'll have a very long or very deep heating season. With the thermal mass of the slab fully inside the thermal envelope of the house it'll even-out the solar gains a bit, and even on days that drop to 50F overnight you may not need the heating at all unless it's cloudy during daylight hours.

  9. GBA Editor
    Martin Holladay | | #9

    Barbara,
    A few points:

    1. I agree with Dana that you won't be using space heat for "most of the year." If you build a good thermal envelope, you won't be turning your space heat on until the outdoor temperature drops to the 50s for extended periods of time. The rest of the time, your refrigerator, television, and lights (along with your dog and other family members) will be providing plenty of space heat.

    2. You should be able to design a foundation that drains well and stays dry. If you have any specific questions about foundation details, ask them here.

    3. In your climate, an HRV makes more sense than an ERV. The purpose of your HRV is mainly to provide fresh air to occupants, but your HRV will probably help lower your indoor relative humidity during most weather conditions in your climate zone.

    4. The mold epidemic in your neighborhood is still somewhat of a mystery. Keep your house clean and relatively dry, and you shouldn't have a mold problem.

  10. Charlie Sullivan | | #10

    I agree with Martin and Dana's advice, but I don't think it is quite as easy as they do. If the outdoor dew point is 50 F, and you have humans breathing, showering, and cooking inside, you need a high ventilation rate to get the indoor dew point down to 55 F. Then when the outdoor dew point swings up to 60 F, that same high ventilation rate will bring the indoor humidity up fast. Considering both of those factors, it may make sense to include an efficient dehumidifier. Especially considering the fact that it could help provide some heating when it is 55 F and 100% humidity outside.

    Maybe I should calculate the outdoor dew point at which the HRV fan energy makes it consume the same amount of energy as an energy star dehumidifier per liter of moisture removed.

  11. Stephen Sheehy | | #11

    Does radiant heat make sense in such a climate? Would radiant heat's slow response create problems when, as Dana pointed out, the heat may be off more than on? For intermittent heating needs, I'd think a hot air system would be more responsive.

  12. Joe Suhrada | | #12

    Why wouldn't you heat that place with an electric air source heat pump? Either ducted or ductless. I don't get it. Radiant heat and boiler seems like something you want on the Maine coast, not here. The heat pump would have air conditioning to cure any humidity. The whole system would be cheaper to install and maintain and cheaper monthly bills would result.

  13. D Dorsett | | #13

    Charlie: A 60F dew point in the 2 warmest months when the indoor temps ride the mid-70s is not a significant mold hazard, especially if there is ANY air conditioning used. Unless there are 10 people living & bathing in a 5250 square foot house it won't take a huge ventilation rate to keep the indoor humidity tracking the outdoor averages, which are quite modest. Scanning weatherspark data there were only three times in 2015 when it was 55F or higher at 90%RH for more than an hour or so the night of 6/7 June, and the night of 7/8 June and 8/9 June. The average daily temperature over each of those three days was north of 60F, sunny during the day, cloudy/foggy at night which in a code-min house with ANY solar gain is a cooling load, no auxilliary heating needed. I'm sure if you searched the data over the past 25 years you'd find some days where there was an actual heat load under those outdoor temp & humidity conditions, but designing & building mechanical systems to manage a 0.01% condition that is non-persistent is a bit silly. A typical Net Zero Energy house could easily have a heating/cooling balance point of 55F or lower, and effectively zero heating load under those conditions. Put the real money into the thermal envelope, not the mechanical systems.

    When your dew point AVERAGES are north of 60F with no or low AC load for weeks on end, then it's time to at least think about bigger deal dehumidification systems, but that's not a central CA coast climate. High-R / low gain houses on the shores of the Gulf of Mexico, sure.

    Stephen: The diurnal temperature swings in that location average something less than 20F, and rarely exceed 30F. (Temperature swings at ground level on a peninsula are moderated by the thermal mass of the surrounding ocean water.) The response rate of heating with radiant slabs can easily be managed with such modest swings. If a 1-2F under/overshoot on a rare day is really a concern, a thin above-slab approach such as Roth Panels is about as responsive as panel radiators (but more expensive than using the slab as the radiator.) High dry desert/mountain locations that commonly see 40F or higher diurnal temperature swings can sometimes be problematic for radiant slabs, but even those are usually tamable with better controls.

  14. Barbara French | | #14

    Wow! Thank you all for your responses.

    Mold is definitely an issue in the area, I can only guess that somehow the weather averages don't paint the entire story. So assuming, that somehow the conditions are naturally favorable for mold growth- given the data available--What would my best solution?

    My requirements are that it would work quietly, be self regulating and provide healthy environment for humans but not mold- while the house was occupied or if left unoccupied for long periods of time.

    Ok, So Martin is suggesting I install an HRV system which would run continuously. Would anyone agree with playing it safe adding a self regulating dehumidifier?

    My reason for choosing radiant heating is that it is silent and comfortable on the feet.How noisy is a heat pump? Could I use the same ducts for the heat pump and the HRV?

    My foundation choice of raised floor over slab was chosen primarily from fear of having moisture seep into the slab. Although,It seems having a raised floor raises possible mold issues in the crawl space which will need some kind of active ventilation. Which solution would you recommend?

    Thanks again

  15. John Clark | | #15

    The reported humidity levels are strange indeed.

    I've been to the Monterrey Peninsula and if I remember correctly it was an endless cycle of dense fog or cloud cover almost every night which would burn off by noon.

  16. GBA Editor
    Martin Holladay | | #16

    Barbara,
    I'm going to summarize what's been written.

    1. You told us that you are building a house with hydronic radiant heat.

    2. You told us that you are considering installing an ERV.

    3. Dana Dorsett and I informed you that, in your climate zone, an HRV probably makes more sense than an ERV.

    4. Stephen and Joe questioned your decision to install hydronic radiant heat, and suggested that ductless or ducted miniplits (which provide space heating, air conditioning, and some dehumidification) might make more sense.

    Here is my advice:

    (a) While an HRV makes more sense than an ERV, you don't need an HRV in your climate zone. A simpler, less expensive ventilation system is all you need in Monterey. I would start with an exhaust-only ventilation system, and see if it met your needs. For more information, see these two articles:

    Designing a Good Ventilation System

    Are HRVs Cost-Effective?

    (b) I'm beginning to suspect that the mold problem in your neighborhood is outdoor mold, not indoor mold. You haven't given us any examples of indoor mold -- for example, green bathroom ceilings or moldy furniture. In every part of the U.S., the first step (if you want to control the conditions inside your home -- and you do) to having comfortable indoor air is to build your thermal envelope to be as airtight as you can make it. The second step is to keep your windows closed and to condition your indoor air when necessary.

    (c) In your case, your heating system will keep your indoor air dry during the winter, ensuring that your home is mold-free. Your air conditioner will keep your indoor air dry during the summer, ensuring that your home is mold-free. If you don't need air conditioning in your climate, you can buy a $250 stand-alone dehumidifier after you move in if it turns out you need it.

    (d) While the house is unoccupied, you may need to condition the indoor air with space heat or AC, but you usually wouldn't want to operate a ventilation system.

  17. D Dorsett | | #17

    Ductless heat pumps are about as loud a refrigerator (and don't have a rattling compressor sound, only a DC-drive blower with no hum.) Old school ducted heat pump solutions are comparable in noise levels to gas-fired hot air systems. Ducted mini-split heat pumps modulate the air flow over a wide range, and will run at the lowest/quietest speed most of the time.

    Your location has temperatures that allow for very high efficiency with modulating air source heat pumps like mini-splits. But there is a bit of a capacity hit related to defrost cycles during high outdoor RH days when it's below 40F that the designers need to account for.

    The original question was targeted at mechanical systems, but it's important to review the relevant construction issues regarding mold in the context of the local climate. This is a climate where mold issues in walls can be induced by suboptimal wall stackups, given the amount of rain& dew wetting of the exterior occurs.

    Things that increase risk are:

    * A vapor barrier like 6 mil polyethylene anywhere in the wall or roof stackup will limit the rate at which moisture can leave, and should be avoided. This includes foil & vinyl wallpapers. Standard latex interior paints are preferred, since it allows moisture to migrate to the interior as water vapor, and purged from the house by ventilation rather than letting it build up in wall assemblies.

    * Siding that it tight to the wall sheathing provides a capillary path for dew/rain moisture to migrate toward the interior, and slows the drying rate of the siding itself. If the siding is anything but vinyl (which is inherently back-ventilated), make sure there it at least 3/8" of air space between the siding and the housewrap or whatever the next layer is, ventilated at both top and bottom to allow convection to purge any moisture that gets behind the siding quickly. This type of siding construction is commonly referred to as a "rainscreen". This has for years been a code requirement in foggy-dew western British Columbia, which has many comparably foggy locations, if lower temperatures than yours. Your higher temperature fog is more mold & rot risky than in cooler B.C., but that solution works pretty much everywhere. There are plenty of details & discussion about rainscreen construction on this site, which I'm sure Martin can point you to more quickly than I could.

    The roof/attic assemblies need to be reviewed in these terms as well. What were you planning on for wall & roof types?

  18. Charlie Sullivan | | #18

    As for the question of why the neighbors have mold, my guess would be that they don't have active ventilation systems, and maybe have poor insulation. The outside air is dry enough, once it is heated to 70 F, to avoid mold, but without at least bathroom exhaust fans, used regularly, the humidity inside could get higher than outside due to moisture sources inside the house. In a less mild climate, houses without active ventilation do better because, for one thing, the temperature difference drives a lot of stack-effect driven air flow, and for another thing, it takes a lot less air change to remove the same amount of moisture when the dew point outside is 30 F rather than 50 F. (3.5 X less, if you are starting at 60% inside humidity.) So air changes through accidental leakage can be enough in colder and/or dryer climates, but you'll want mechanical ventilation.

    A simple exhaust-only system is all you need. A Panasonic Whisper-Green exhaust fan is as quiet and energy efficient as the name implies. An HRV would save you heating energy. Your climate is mild enough that the exhaust-only ventilation strategy is fine, assuming you make sure you don't have a moldy crawlspace--you wouldn't want your ventilation air coming from a moldy space. The moisture control effect of HRV and exhaust-only ventilation is identical, so the decision is only whether you want to spend the extra money on the HRV in order to save a little heating energy, and perhaps get better fresh-air distribution.

    I argued that a dehumidifier might be useful to get ride of moisture generated inside rather than making the ventilation rate high enough to get rid of that moisture purely through ventilation. Dana argued that the ventilation rate needed isn't high. Moisture generation rates in residences vary all over the place, but one standard is 8 liters/day for a one-bedroom residence, 12 for two, and 14 for 3. Just taking 10 liters per day as an example, and assuming you want to maintain 55% humidity with and outdoor dew point of 50 F, I calculate that the required ventilation rate is 260 CFM. That's toward the high end of available residential HRV units. It's perfectly feasible, but another option would be to size the HRV (or exhaust-only ventilation) for your fresh air needs, and use a dehumidifier if and when needed. With 10 liters/day moisture generation, and 260 CFM ventilation, your indoor humidity would average about 5% higher than would be expected based on the outdoor dew point. You could get away with cutting that ventilation rate in half and allowing the indoor humidity to be 10% higher, or you could control your indoor moisture generation carefully, so you don't necessarily need 260 CFM.

    The ventilation options work, but using a duhumidifier could be as a efficient, and having a dehumidifier available could avoid needing as large an HRV system. Here's how the energy use comparison works: If you have an HRV that provides 1 CFM per watt (typical for induction motor fan based systems), and the indoor air is 5% higher humidity than what you'd settle out at with the outdoor air ventilation (e.g., again 55% indoor humidity, 50 F outdoor dewpoint), the HRV is providing moisture removal at 1.6 liters per kWh consumed. That's lower than the 1.8 liter/kWh energy star standard. So a basic energy-star dehumidifier has a slight edge over upping the ventilation rate (or hours run/day) in an HRV system. You can get more efficient dehumidifiers and more efficient HRVs, but the comparison would probably still be neck-and-neck.

    So my summary is that I agree with Dana and Martin that you can do it with just HRV, or even just exhaust only ventilation, but using a dehumidifier is not crazy--the energy use would be similar. If it gives you peace of mind to have a dehumidifier that can automatically knock off any peaks in humidity, the energy use of that solution is not any worse than the HRV solution. And it could allow you to use a normally sized HRV, rather than upsizing it to be able to deal with the moisture load.

  19. James Morgan | | #19

    Somewhere on this thread was the question of whether the local mold problems were indoor or outdoor, and I don't think that question was answered. Mold on outdoor walls in such a climate would not be surprising, and would be mitigated by the rain screen construction already mentioned and by keeping tall vegetation well away from the walls. It's been many years since I've been there but my recollection is that dense vegetation around the homes is a popular landscaping style in the area and this may be the source of the problem.

  20. James Morgan | | #20

    Question for the experts - might a home in this climate benefit especially from the hygric buffering properties of cellulose insulation?

  21. D Dorsett | | #21

    The vapor diffusion rates through 5 perm paint isn't going to make cellulose magically control the interior relative humidity, nor is it going to fix the exterior moisture drives of a wall built without back-ventilated siding. The clearer benefits of the hygric buffering capacity of cellulose comes in much colder climates, where the sheathing temperatures dwell below the interior air dew points for months, with a high potential of loading up on moisture from interior moisture drives. In this climate that doesn't happen.

    Without re-doing the math, Charlie's numbers sound like the right range. Note, 55% RH & 70F is not a mold hazard, far from it. But it is modestly higher than the 50% upper bound the health care community cites. At higher than 50% RH dust mites can reproduce fast enough to become a potential hazard to those with allergies to dust mites, but mold & fungus doesn't take off until it's north of 60% RH, and don't really soar until it's in the 70% RH range or higher. Most people in the eastern half of US spend most of the summer in homes with an RH higher than 50% (some much higher.)

    It's pretty easy to monitor the interior relative humidity, and adjust ventilation rates up or down as needed, or to use room dehumidifier to take it down even lower.

  22. Barbara French | | #22

    This has been very informative and thank you all for contributing.

    The exterior is board formed concrete, stucco and some stone veneer on pillars. The roof is a low slope membrane with aluminum fascia.

    The house is a modern design with 38% glass.I am considering some high priced thermally broken aluminum window (Blomberg) and door manufacturers (La Cantina) and also fiberglass ( Marvin or Milgard). They seem to have similar energy ratings but a dramatic difference in price. I am also weighing using the fiberglass for the windows and aluminum for larger folding doors. I am curious to know your opinions.

    Would you recommend a single string inverter, microinverters and power optimizers for PV design? My initial thought was that the single inverter would have a longer life because it, unlike the other options, it is not subject to the elements and the heat form the panels. Is this an issue? The other options I believe also have their benefits with data available from each panel not just a string.The system is approx 9000W ( 330W with 28 panels).

  23. Expert Member
    Dana Dorsett | | #23

    OK, we know the outer layers, now we know what's between the board formed concrete & stucco layers and the interior paint? Is the board formed concrete also the structural wall?

    Both stucco and concrete wick up significant amounts of dew & rain moisture, then release it at a fast rate when the sun hits it. This makes a rainscreen type structure to purge that moisture critical to keeping the wall assembly dry.

    Inverter designs are a rapidly moving target. Micro-inverters have about the same warranty periods as other equipment, and if one should fail it's one panel that's down, not the the whole string. Temperature-wise your location isn't a tough environment compared to hot desert locations. Equipment is designed to live out in the elements should be able to take it. The evolution of the equipment is rapid, and there isn't a lot of published data on failure rates or failure mechanisms.

  24. Eric Habegger | | #24

    Having lived intermittently in coastal areas of California it's not clear to me that all facets of those climates are being accounted for in the advice to Ms. French. I'm not saying the physics that has been described by those answering her questions isn't correct. But those models may not be modeling all aspects of what is going on in her climate. There are other regions of California that are similar to hers, such as the Sunset District of San Francisco. This is a notorious microclimate that sees almost no sun that are ensconced in fog or low clouds most of the year. The town of Pacifica is another. These towns and regions of California are microclimates that see very little radiant energy from the sun. So, while the humidity may be modeled well in climate charts these microclimates can deviate drastically from nearby areas. I'm not sure individuals who aren't acquainted with these microclimates appreciate that.

    There is also another aspect that I haven't seen adequately described. Humidity changes cyclically daily in all climates. However in those climates that see much less radiant energy (on average) from the sun it seems to me that there will be much less drying of moisture from those times when the temperature was below the dew point outside.

  25. Expert Member
    Dana Dorsett | | #25

    Eric: Ever lived on the edge of temperate zone rain forests in WA or B.C.? There are a few locations in CA as foggy-dew and lo-radiant as that, but not many. The rainscreen approach to siding works well there, as does HRV ventilation.

  26. Eric Habegger | | #26

    Dana, good point. Most areas of CA don't require rainscreens so we don't think much about them. A lot of those coastal towns here that these conditions apply to don't even have particularly high annual rainfall amounts. It's easy to forget that there are other things besides annual rainfall amount, cold temperatures, and humidity that make a rainscreen necessary. I would suggest that areas like Monterrey with merely average rainfall, temperature, and humidity would benefit from a rainscreen. In other words, there maybe a fourth condition that make it a requirement - high levels of overcast year around with frequent dips below the dew point at night.

    I'd say this is a good day. I learned something.

  27. Adam S | | #27

    Has anyone created a map for HRV vs ERV territory? Planning to build a house in Guilford, CT and am curious which system is appropriate. https://weatherspark.com/#!dashboard;a=USA/CT/Guilford
    Also, if this is poor etiquette, I apologize for posting on Barbara's thread. Thanks.

  28. Expert Member
    Dana Dorsett | | #28

    Adam: in Guilford CT you can use either. Latent loads are often higher than sensible loads in our part of the US, but still pretty modest. Mechanical dehumidification is really the only way to hold the line at 50% RH when there is little to no sensible load but still a latent load, which is pretty common. Frost damage to ERV cores is sometimes an issue in this climate- my inclination is to go with HRV.

  29. GBA Editor
    Martin Holladay | | #29

    Adam,
    The idea that the choice between an HRV and an ERV should be based on geography is a fallacy.

    For more information, see HRV or ERV?

  30. Barbara French | | #30

    Thank you all for your help.

    Can anyone recommend an HRV manufacturer for my application?

    Best,
    Barbara

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