HRVs vs. ERVs: Why I Ditched My DIY HRV and Bought an ERV Instead 

Hi all! I’d like to mention that even if you live in the desert, you may still need a dehumidifier to supplement your ERV! Even arid regions can get humid during certain times of year.

100% agree with you. I don’t understand why the industry advises the opposite in all their specifications. I just finished a new house and installed 2 ERV’s with resistance from the HVAC supplier. Fortunately I have taken classes in physchrometry over 20 years ago and that knowledge is still paying off.

You can make an ERV by using plates that are air barriers but vapour permeable, rather than plastic. Materials like Ametalin vapour permeable wall wrap might work for DIY

Outstanding content - thanks! One idea you may not have explored: In the event that you are building a new house or doing a deep remodel, you can elect to use clay plaster (not lime plaster or drywall). Clay-based plaster is an ancient technique that has been used to passively control humidity for thousands of years. It was recently revived by Geoff Lawton in the Greening the Desert project in the Dead Sea. By replacing 80% of the lime in plaster with Bentonite clay, the walls act as a hydric buffer (not my terms, honestly it's the engineers who name these things). When the air is damp, the highly hydrophilic clay particles in the wall absorb moisture like a sponge. When it is dry, the walls dry, releasing moisture into the surrounding air. Result: the indoor humidity settles in at around 45% to 55% regardless of the humidity outside or inside the home. This technique is used in Japan (a very humid temperate rain forest) where the problem is atmospheric humidity, and at the Greening the Desert project in Jordan, with an annual average humidity of less than 20%. This technique produces a lovely wall (decorators call it "Venetian plaster" it's quite on-trend at the moment). The largest challenge is finding plasterers. Plaster on lath is cheaper than drywall (materials cost) but more expensive labor costs (it takes longer and you need a higher level of skill). But, it's still only about 10% to 20% more than level 4 drywall, and you don't have to buy or power expensive mechanical humidity control equipment. To my mind, the set-it-and-forget-it nature of a passive self-regulating system that never needs maintenance or power, makes it worth the extra up-front cost. I would love to hear your take on this technology, as well as other recent tech revivals such as GAHT (ground to air heat transfer) systems, rocket stove wood heating, and Russian masonry wood fired heaters.

You are an honestand and admirable to admit you learned and needed to course correct. Kudos to you! I am curious if your horizontal orientation prevented any partial condensation and drain off as all the commercial ERV/HRVs seem to orient the core vertically such that gravity can drain any condensation in channels as the dew point is hit.

I'm enjoying digging through your videos as I recently purchased an Aranet4 CO2 monitor and realized my bedroom CO2 levels can approach 2000 so now I'm working on bringing those levels down. I may get a broan or panasonic ERV, but am considering first trying the fresh air intake option on a santa fe ultra dehumidifier. In the winter they can operate in fan only mode to bring in fresh air through a merv 13 filter, and the rest of the year can dehumidify fresh air. It wouldn't provide the energy saving aspect of an ERV, but if already needing a dehumidifier it could be worth starting with that and then if an ERV is still needed they could even be ducted together.

Moisture control is an interesting topic. In a tightly sealed construction like a passivhaus (or similarly built), I hear that even with an ERV it's not enough to regulate moisture. That's often because the minisplits that are typically used to condition and heat such buildings can't remove enough moisture as they are sized correctly for the passivhaus type cooling load, but that sizing will make them undersized for the moisture removal requirements. So they can't deal with it by themselves, and one does wind up needing a dehumidifier for the humid climates. But the resulting advantage is that (with some effort) the end result is a house microclimate that can be quite precisely controlled.

I was finally able to install and run my Broan ERV on Friday, waiting for a break in the rain to install the inlet and outlet through the side of the attic. Since my heat pump's air handler uses 500 watts to run I gave the ERV a simple dedicated duct system, pulling stale air from the two upstairs bathrooms and sending fresh into the hallway between the three bedrooms and near the upstairs HVAC air return so when the heat pump is on it will help circulate fresh air through the house. To keep from having to constantly change tiny filters I installed a larger insulated in-line filter to the fresh air supply coming to the ERV. ~100cfm only takes 44 watts per hour. It was so nice watching bedroom CO2 drop from 1600 to the 700s. I installed a Tamarack Perfect Balance air return in the bottom of one bedroom door so far and will be doing the rest soon to help keep air moving through the house even when doors are closed. Thanks for sharing your setup and helping me feel like setting up an ERV would be worthwhile even without having ductwork go to every bedroom.

Thanks for the video here we have 82% humidity all year round so head exchange probably wouldn't be the best

thanks for the video, really very helpful ;-)

Good follow up video. My house is good for humidity, but my chicken coop is too humid and I'm working on solutions to that now. Dehumidifiers are a tricky bet there because of all the chicken dustiness.

I'd say a mixture of the old rotating ERV should be possible with your same design or similar. But yea the new ERV are using membranes that actually let about 50% of the moisture pass through the material.. so that type of material isn't feasible for regular people to get. At least no long term lasting stuff. You could build one out of cotton I guess, but it'd have to have much lower air flow and be much bigger unit lol

Ouch! Yeah, living in the uk we know all about damp air :( . Lots of older houses that have been 'half fixed' ie made 'warmer' by using double glazing and sealing drafts appear to be suffering with damp issues.. We certainly are. So HRV is definitely not a solution!

Would this introduce the same amount of humidity as putting a fan in front of an open window? Or more ?

I work in the building HVAC arena (P.E.), specializing in energy reduction and comfort improvement for K-12. Yes, everyone should know more about psychrometrics - but it will never happen.

10 grains per pound = 1.42857 grams per kilogram