Choosing an ERV
Looking for some input on a 2-bed 750 SF ADU in the walk-out basement under our house. Trying to figure out the best approach for ventilation/ IAQ. In climate zone 3C with an increasingly long “fire season.” Radiant heat in 4″ ins. slab. Kitchen range hood is ductless filtered recirculating. Anticipating 2 occupants max and estimating about 40 cfm. Thinking about 2 options:
1. Panasonic Intelli-Balance 100 with supply at the beds and exhaust at the bath and kitchen.
or
2. Panasonic WhisperComfort 40/20 somewhere “central” and an exhaust fan at the bath.
Some questions I have:
A. With option 1, would you typically install to run on a set timer, or would you wire on a switch to demand circulation (thinking about when you’re using the bathroom or kitchen). Seems hard to find a good spot for that switch if the later.
B. With option 2, I know the efficiency isn’t great with the small WhisperComfort, but when the bath exhaust is running, I assume the ERV isn’t doing anything for energy transfer (but the make-up air is coming through the ERV?)?
Seems like the Intelli-balance is a little over-kill for our size. But I don’t think you can get a MERV 13 or better filter in the WhisperComfort. So very thankful for any words of wisdom.
Cheers,
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Replies
Definitely the Intelli-Balance 100. The 40/20 is not going to be enough - its recovery performance is lousy anyway. Set the IB100 to 60 cfm to start but size the ducts for "boost" mode (full 100 cfm - use 6"). It'll be a bit noisy at 100 cfm but you may want that ability with just a recirc hood on the stove.
Cramer - THANK YOU!
Sounds like I'd wire it for continuous performance rather than on a switch?
Thanks again.
Yes, continuous.
Check out Renewaire EV Premium models too. I'm going with a Large even though a Small could work on our house. The Large has a huge core for great efficiency, especially when dialed way down via the EC motor. It has a continuous and boost mode.
Thank you Michael - those look great.
Keep it simple. Either install a pair of Lunos fans or install the Panasonic Whispercomfort ERV in the bathroom. In your mild climate, there is not much point for spending a lot of money on energy recovery.
In case of the Panasonic unit, I set them up to run on low all the time with the boost input wired to a standard occupancy sensor. This way the boost automatically runs whenever the bathroom is used.
Merv 13 won't do much for fire, not enough to filter smell or PM2.5. To get the smell out, you need a carbon filter, to get the PM2.5 down, you need a hepa filter. The best is a multi stage filter that has a Merv8 carbon pre-filter followed by a hepa filter. Companies offer this as a premade assembly, you can look at Lifebreath TFP3000HEPA or Fantech HS3000. These have a fan built in, but if you use it on the ERV intake, leave it unpowered as the ERV fans are more than enough.
A pair of Lunos e2 is woefully undersized.
Thank you Trevor
The Whispercomfort is great for small spaces. It’s not too expensive and very quiet. But it cannot tolerate high humidity. I had one installed in bathroom in a previous home, and the unit kept shorting out. The soldered in fuse was a bit of a pain to replace.
Akos - I really appreciate that - thank you. I love simple. In terms of cost, seems the equipment costs are similar between the pair of lunos fans, the whispercomfort with the additional inline filter, and the intellibalance 100 (without ducting). Does that seem accurate or am I totally looking at the wrong sites?!
Again - really appreciate the wisdom and guidance.
Cheers
If you want to filter out smoke smell, a multi stage filter is needed whichever solution you pick. This filter can be integrated into your ERV or stand alone.
So the question is, which ERV you want and if you want to include an expensive filter.
I find tenants rarely pay extra for high tech, most would not know what an ERV is. For an ADU, I tend to pick the lowest cost and lowest maintaince option. If a tenant wants a hepa filter system, they can buy a free standing one and take care of the the maintenance.
Equipment cost is one thing but you also have to include install.
A simple exhaust only setup with a bath fan will always be the lowest cost option. The spot ERV would be a couple of bucks more, about the same install.
The Lunos is about 2x cost of the spot ERV and comparable to the Intellibalance but much simpler to install.
The Intellibalance is a great unit and a good deal, it is a more involved install, I would call that the Cadillac option.
Thank you Akos
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My comment is a bit off point. But it is relevant and important to the overall ERV topic.
I’m in an email group of 20 top IAQ professionals. One is probably in the top 5 of mold hounds in the country. She tells us that she’s never tested an ERV core where she didn’t find amplified mold. Then 3 more speak up, having the same experience. Then I had to confess that I’ve found two (2) as well
Of course the conditions inside the core are ripe for condensation. And fun-guys must have moisture to survive. So it shouldn’t be any surprise that mold would develop.
Is there any reason to think an ERV core in CZ 4 or higher would NOT be at risk?
Out of curiosity, the mold you found, was the ERV operating continuously or intermittent? I have an ERV in zone 5 with hot and muggy summers and there is no signs of mold on the core.
I would want to know the fresh air intake location as well. A lot of variables for mold.
My intake is going to be very low to the ground (through rim joist), so I can see an increase risk with that.
The two I investigated were 10 ft and 4 off the ground.
I don’t recall runtimes on the two I investigated. And have no clue about others.
I’m curious about what you mean by ”no signs of mold…” what signs were you looking for?
I was referring to either dark or light spots on the core. After I blew it out with compressed air, the core looked pretty clean.
I can definitely see how this can be an issue especially if the home has high interior humidity. I've been monitoring the temperature and RH of my stale air exhaust and so far it is staying bellow 85%.
Fresh air in tends to have higher RH but it is also much colder, so I can't see it being an issue at least during the heating season.
This may have limited applicability in your situation—and who knows what it’d do to the fan’s life—but I’ve been pretty intrigued by this as an option for the WhisperComfort 40/20 in a small space: https://www.greenbuildingadvisor.com/question/panasonic-whispercomfort-erv-not-necessarily-a-spot-erv-anymore
Additionally, this is a pretty lengthy thread but may have some helpful strategies for mitigating wildfire smoke, particularly the posts about hooking up a HEPA filter to your ERV’s supply: https://www.greenbuildingadvisor.com/question/why-is-our-indoor-pm2-5-and-aqi-so-high-w-merv-13-filters
Finally, if the area of climate zone 3C where you are has dry summers, you might consider inducing a little positive pressure into the ADU during the smoke events. I know that the IntelliBalance will let you do that fairly easily. I’m not sure about the WisperComfort (I don’t think so based on the manual), but there are other ways to do that as well.
Brian - those are great resources and suggestions. Thank you! I have to admit I am very hesitant to cut a 3" hole in that WhisperComfort unit!!
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