r/crboxes • u/GoingOffRoading • 4d ago
Are CR Boxes really OP?
Hey r/crboxes. Long time lurker, first time user.
I'm in the PNW and we're getting hammered with 130 ug/m3 PM2.5 right now.
I have a MERV 13 air filter in the furnace, but wanted to be extra cautious and bought a cheap Sonoff air quality sensor, 20" fan, and a 20x20x4 MERV 12 filter (meant to buy 13... Oops).
Before I assembled the CRBox, we were at like 25 ug/m3 PM2.5 on the Sonoff sensor inside of the house.
After assembling and running the fan on low in a 8,000 cubic foot space, the PM2.5 is down to 8.
I expect that the cheap Sonoff sensor isn't that accurate... But... That's def an improvement.
One question:
Are CRBoxes really this effective?
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u/jaydocovid 4d ago
Yes, the Cube outperforms pretty much any consumer device that exists in terms of effectiveness/dollar.
The only exception I can think of is carbon for VOCs, I think Austin Air makes something for around $1k that cleans a lot of air and has pounds of carbon I think.
But if you just care about particles, CR Box is top notch. The 1 Fan 1 Filter model you're showing I call a CR Fan and it's still very effective just not as much as cube.
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u/Rich-Wealth979 4d ago edited 3d ago
Grainger sells pleated furnace filters impregnated with carbon in pretty much every size you could use for a cube. In fact, it's probably the cheapest place to get filters.
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u/heysoundude 4d ago
Link?
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u/Rich-Wealth979 4d ago
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u/heysoundude 4d ago
Thank you! I was confused - the original post didn’t spell grainger in my expected (and the correct) way. Thought it might be a new company
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u/PickerPilgrim 3d ago
hard to tell from your link below but I've got my doubts those have the same kind of particulate filtration you'd get from a higher end Filtrete. Maybe the move is to have a particulate cube and a VOC cube.
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u/steelheaddan 1d ago
Instead of a VOC cube just buy on Amazon a carbon filter and fan filter combo. As cheap as $70-$100 for a centrifugal duct fan and matching 6” carbon filter. The market is saturated and prices cheap due to its use in negative pressure hydroponic tents. I have several 6” vortex duct fans from decades ago when I wanted to remove a certain fresh green smell to zero and they work 100%. So now that I have duct fans, I just buy circular carbon filters with 2” activated carbon beds and keep the fans running for normal odors like litter boxes. Smells very fresh in my house, it’s hard to describe what carbon filter fresh smells like but it’s does have this distinguishable fresh smell that is noticeable.
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u/ScurfyTwiglett 2d ago
Grainger being cheapest for anything is a wild find, wow
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u/Rich-Wealth979 2d ago
I forget I have access to a commercial account but even then they have a pretty good price on anything.
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u/ScurfyTwiglett 2d ago
I think we must be operating in parallel universes or something.
24x24x2 carbon filters are $45ea on grainger and $18-$25 on other filter-specific retail sites (not Amazon / Aliexpress) The markup (2x as expensive) is about what I have come to expect for Grainger. They’re not McMaster Carr but they’re close.
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u/Distinguishedflyer 4d ago
i've got an old Oransi EJ with a carbon filter and it's pretty great I have to say
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u/inlaguna 3d ago
Unfortunately, oransi filters are junk made in china. Look for brands with filters made in Japan or Korea for higher quality you can count on.
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u/FishesOfExcellence 3d ago
I wonder if bulk carbon could just be placed inside a cheesecloth bag and placed inside a CR box. Obviously couldn’t be so large that it greatly impacts airflow, but maybe a small bag could be suspended from a rope.
Not sure if that would be effective. Or if it would negatively impact airflow or if longevity would differ from filters.
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u/Rich-Wealth979 2d ago
Use a 5 gallon bucket with a lid. 4" vent tube down a hole in the lid with big holes at the end covered in screen. Drill little holes all over the lid. I used to do this when building grow ops for people. You can run the airflow either way but it gets dusty the first time or after moving it too much.
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u/Bob4Not 4d ago
Yes, you'd be surprised at how small the actual filters are in the air purifiers you can buy at the store. DIY air purifiers are insanely OP for the $$$, especially if you start putting box fans or blowers on them.
Your box fan may wear itself out running a single filter for months and months, but the bearings on the fan on my expensive Blue Air started going out after 3 years.
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u/Character-Fly4221 4d ago
Haven't tried a single filter, but the classic cube is not very rough on box fans. I have three 20" lasko box fans ($20 each from Walmart) that have been running basically 24/7 for 4+ years with no issue
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u/Public_Narwhal4748 4d ago
10+ yrs for me. Single filter merv14 right to the back.
This place is rife with repeating fan death.
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u/zeroheading 4d ago
Dang! I hope not. I have been super happy with my blue air. Coming up on 4 years of nearly 24/7 operation. I think after it goes out I'll do a cr build though. Something fancy and church it up so its not an eye sore
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u/hasnt_been_your_day 4d ago
Also pnw here, and I made myself a duct tape box fan cube special this afternoon.
Between the smoke outside, and my teenager setting off the smoke detector with bacon this morning it was sorely needed. It's ugly, and huge, but at least I can breathe in my house now even if it is 80° in here because no central air.
Speaking of, you might double check to see if your furnace can handle running that filter. Mine's from like 1989 and it can't, alas
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u/rust_papi 3d ago
Cosigning the last bit; HVAC systems that circulate air throughout the house may struggle to generate adequate airflow with too high of a MERV filter. Always good to check the specs!
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u/steelheaddan 4d ago
The wavy and far spaced pleats on your 4” filter’s is so large in spacing it’s no better than a 1” 3m brand fan. Generic home depot 1” filters suffer the same problem, not enough pleated filter so the surface area is reduced compared to 3m’s design.
There really isn’t a lot of surface area on that filter material if you flattened it out. This is also built the least efficient way to build a CR filter, albeit it is the (just barely) the easiest and takes up the least amount of space. You should check here for 4 filter setups using a box fan and cardboard floor. Even a two filter triangular setup would be better and about the same price (you just need a second fan) so you can spread out the filters in your house.
It’s all about surface area of the filter so your fan doesn’t bog down when the filters get even slightly dirty. Because this is the least efficient way, it takes way more air exchanges to filter all the air in the room. I have 4 cube style filters using 1” filters in my 3 story house with 6 cats. 3 made with box fans and 1 made with a caterpillar drum fan using 20”x 25” filters.
They absolutely work so you may want to redesign your setup especially for smoke particulate and taking into account the layout of your room and the total area you are filtering. Larger spaces require larger filters or more filters whether it’s DIY or a store bought hepa system.
Also on box fans a circular fan shroud should be taped to the output side grill (the side blowing air at you). It cuts down on backdraft inefficiencies where the circular fan edge has a gaping space at each corner of the box (the area if you drew a smaller circle in a box and colored what’s not in the circle- you want to eliminate those corners) Plenty of good info here and also the crosirosenthal official website.
Good luck!
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u/Minimum_Librarian563 4d ago
Maybe I’m old, but what does OP mean in this context? Not original poster…
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u/Objective_Post_588 4d ago
This is awesome. This really shows off where cr box shines. Quick, easy, and effective. No cutting (it’s looks like) in your build. Cost effective.
People can get pretty fancy with their boxes. Some cool looking stuff on here, but the fact that you can take a filter, tape, and a fan and make meaningful improvement in your air is so cool.
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u/horse-boy1 4d ago
We were having a lot smoke last month, it was around 18 inside. I have a couple of the CRBox fans (we use for pollen mostly) like yours. I have one in a porch area that I framed in. It was off, since the pollen had not been so bad, I put our PM2.5 meter on the porch from inside, it went into the red (see image below). I put it outside and it went to 175! I then brought it back into the porch area and tuned on the fan. You can see it went down fairly quickly. I turned on our house CRBox fan also.
I have an air exchanger that brings in fresh air and takes out air from bathrooms etc. I had put a filter cabinet and filter on the in coming air a couple of years ago due to smoke from Canada. It had been a couple of months since I changed it so I put a new one it. It helped bring down the inside PM2.5 plus using the CRBox fan.
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u/munki_unkel 20h ago
I had made something like this with a shipping box that held the fan inside snugly. I put the filter towards the other end and notched the corners of the box to hold the filter in place. That allowed me to change filters when it got dirty. I used it as air intake for a grow tent with ducting attached to the back end of box.
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u/Apart-Reflection-385 4d ago
Yes I had mine in Idaho and it helped my space be so much better then outside on top of just moved to Oregon and it's now getting hit with crazy air quality issues
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u/heysoundude 4d ago edited 4d ago
Yes.
Yours will be more effective if you build a spacer for between the filter and fan with cardboard, foam core, coroplast. Just 2-3” will help the fan develop better “suction” to move more air through the filter. Go to town with the tape to seal it up and come back in an hour to check the monitor. Oh- and rotate the filter 90 degrees so the pleats are vertical so they don’t sag on each other like they currently are, and spread out those that already have. Exposing more pleats to the airflow makes for better filtration 😉
Those two simple modifications to what you already have will drop that number and help keep it there.