I measured a 15% decrease in air flow compared to a 6 month old mostly clean standard air filter. I think it's a given that if you have smaller pores with the same amount of surface area there will be some flow reduction. I've been using my Bosch 6092C for about a year and it hasn't clogged but I plan to change my cabin filter again soon.

 

Yeah when I used the Bosch on my 4 Runner immediately I could tell the ac wasn't blowing as hard. Returned immediately.

 

Yeah, I think that’s to be expected with the smaller pore size in the filters. Doesn’t bother me, though. I can’t remember the last time I used the max fan setting on anything I’ve owned. I usually set it to automatic and let it do its thing.

I measured a 15% decrease in air flow compared to a 6 month old mostly clean standard air filter. I think it's a given that if you have smaller pores with the same amount of surface area there will be some flow reduction. I've been using my Bosch 6092C for about a year and it hasn't clogged but I plan to change my cabin filter again soon.

Tht’s good to hear! Just out of curiosity, what do you use to measure airflow?

 

Filters with smaller pore size should have additional pores to make up for the loss. Cleanrooms run HEPA or better and recirculate 80-90% of the filtered air. The more the air is recirculated the cleaner the air according to the data.

 

One way to do that is to have more or deeper pleats, or simply have a larger filter.

Tesla HEPA filter $275.00:

 

Wow. I always new they used a larger filter to compensate, but I only assumed double that of a filter like ours. That's huge. Props to them for not cheaping out and doing it right tho.

 

I wonder how much of a difference this would make for us that live in and around this insane wildfire smoke and driving in it for several months out of the year.

 

During some local fires I recall smelling the fires in class 100 and better cleanrooms. These cleanrooms used HEPA filters and were strictly monitored for performance. I am guessing you will smell the smoke. Note that these filters are not specified as absolute and even of they were then some of the smaller smoke particles will get through. Best bet is to always use the recirculate mode.

 

I'm wondering if the hepa filters in vehicles are enough to lessen the PM2.5 and PM10 in the air we are breathing in the cabin.

 

I'm sure this offers some improvement over the stock filter, but if the fit is anything like most cars I've seen, stuff will still get past it. While the filter meets HEPA specifications, what's often overlooked (e.g., with vacuums) is that's just half the picture - the system providing the filtered air must also be HEPA-rated to ensure that air can't easily bypass the filter. Gotta wonder, if the HEPA filter is noticeably reducing airflow, you might even be getting more unfiltered air leaking past it (although I'd expect the net effect is probably still positive).

 

Your are exactly correct because air will take the easy path way, AKA path of least resistance. Same thing happens with surgical masks that are not sealed around the complete perimeter. NASA once looked into these issues but I can no longer find the information on line.

 

Not going to search for the post but someone else who lived through wildfire smoke said it helped a lot. Yes there will be some bypass but if I were in a fire smoke area I would use it. When I bought the HEPA filter it was more for experimental purposes and I really don't need it so I already have a non-HEPA regular cabin filter I will use. After that I might go back to HEPA - hard to say, but the great thing is that we have choices. It's like how some people use a simple surgical mask or cloth, and others use an N95 (which also can bypass if not properly fitted). Your choice. I use an N95 sometimes and a regular surgical mask at other times depending on what my exposure is.

I don't think the system is under strain - surprisingly a restrictive filter can actually make it easier on a blower, except when reduced air flow causes the motor to heat up, but the HEPA is not nearly THAT restrictive. Another consideration is the deposits of particles throughout the system after the filter, like on the squirrel cage itself. Cleaner air getting to the fan is better.

 

Damn it guys lol. Now I want one again to see if it helps. My main focus is not the smell, its the nasty VOC's and PM2.5 and PM10 particles that I want to filter out. Plus both my wife and I have serious allergy issues when we travel back to the Midwest when pollen is high. It sucks that RockAuto refuses to ship to me

 

It is, likely, better than the OEM filter for smoke particle filtration. I recall having to change the HEPAs in the cleanroom because they held the smoke odor and continued to add the smell to the air. The filter is not that much more expensive to not try it out.

 

Anyone know if this filter will fit a 2018 CrossTrek as well?

Answered my own question. It will not. You will need the 6038C for the hepa filter for those wanting it for the CrossTreks's.

 

Pretty sure there's plenty of evidence to show that "upgrading" filters in HVAC systems, mainly when they haven't been designed to tolerate the pressure drop from a high-MERV filter, can cause a variety of problems (including possibly reducing the lifespan of the blower motor). I have a large HEPA unit from Blueair and they caution that its blower can be damaged simply by running an old, clogged filter too long. Of course, they also want to sell you filters, but I don't doubt that damage can be done under certain conditions.

 

In general, a HEPA filter is designed to remove most particles that have a size of 3µm or larger. A few larger particles will almost always get through. As a filter traps particles larger than their pore size, in this case 3 µm, some of these larger particles will block off part of the 3 µm pores thus reducing their effective size to something less than 3 µm. This pore can now trap a particle less than 3µm. But, there is a trade-off because the flow rate is reduced and the back pressure increased. This back pressure air begins to look for other paths of least resistance and when found will route unfiltered air around the filter when possible. As I have said many times, running in recirculate mode is worth considering.

Another consideration is to use a brush attachment on a vacuum cleaner to suck the upstream side of the filter and remove some of the trapped particles. This may be useful if the filter is releasing smoke smells into the cabin. Filter companies sometimes resist this as an option but...

 

I'm going to backtrack on an earlier unqualified comment I made about a restrictive filter not harming motors.

If you increase fan voltage to compensate for a 15% flow reduction from a HEPA filter then to the extent that "running harder" wears out a motor faster, yes it will cause wear of the blower motor. It has to use more power to spin faster to push the same amount of air into the cabin. But if you can tolerate a 15% air flow reduction, the added back-pressure is causing no damage to the motor.

Then again poor filtration will leave deposits on the squirrel cage blades and coat the insides of the blower motor, which is why it's a bad idea to run with no filter at all - yes you get more air flow but is it better for the blower motor? Nope.

When your circumstance demands better filtration during pollen season or during wildfires I think it's a bit overblown to worry about motor fan life. If you're that worried about it have a HEPA filter for seasonal use and a more porous filter when it's not needed. HVAC blower motors do fail but are generally easily replaced at home - I've done it once in my 2005 Legacy GT and in the 2009 Honda Fit. While it's possible that in the Gen 6 it's more difficult I doubt it. Both cars always had cabin filters in place but the blower blades had deposits on them. Fan blades do get nasty.

So my take on the situation is to use whatever filter meets your environmental needs instead of worrying about the blower motor. If you need to change your $10.00 HEPA filter more often then it's not a budget buster, but I have used mine for 6 months with no appreciable decrease in flow since it was installed, but I'm a frequent filter changer and will be changing it at the end of the month with a non-HEPA because my environment doesn't require it. I might switch back to a HEPA filter in 6 months.

 

Ok, so I'm going to order one to experiment with. I hardly need to blast the AC here despite the heat and this wildfire smoke makes both myself and my wife rather ill with sinus issues from just being out in it for short trips to the store or to the office. I thought we had Covid and we got tested last night because the symptoms were getting so bad, but both were negative and the doctor said she has been having tribes of people coming in sick because of the AQI being 150-180 in my area for weeks on end. It's normally 30 this time of year. So I think it may be worth tho 10-12 bucks to order one in and give it a go!

Well if I can find one to order that is. RockAuto is annoying and won't ship to me.

 

Yeah, probably not necessary to worry much about blower wear, but I think it would at least be prudent to avoid using the max fan setting with a HEPA filter installed. While it may not be a big deal to replace (the OB is likely easier), getting to the blower motor in my 2006 Impreza OBS required an unsettling (to me) amount of disassembly.

 

Blower motors are expected to be robust and most likely made to run past the expected life of the vehicle. The Japanese are known to be demanding of their suppliers and require reliability data to support expectations. Having abused cabin filter changes in the past, I can say this, back pressure, is not an issue with some Toyotas.

 

Sometimes you can buy the assembly that includes the blower motor and the piece above it attached together for cheaper than the blower motor+fan assembly alone. When that happens I buy the cheaper whole assembly and then remove the blower and install just that part. Much simpler install.

It looks like it did in my 2005 Legacy GT - three screws and an electrical connector above the passenger footwell. Easy.
Image below is for a Gen 6:

72223AN00A - Motor. Blower, Air, HVAC - Genuine Subaru Part

Genuine Subaru Part # 72223AN00A - Motor. Blower, Air, HVAC. Fits Legacy, Outback

parts.subaru.com

 

I would think these blowers are designed to run with a lot of back pressure due to plugged filters. After the newness wears the majority of owners are going to forget to change a filter that is working. Therefore, Subaru has made accommodations for filters with restricted flow. That said, If you change a HEPA filter annually your blower will likely be under very little stress. If I put in a HEPA filter I will continue to set the controls to FULL AUTOMATIC but willing to manually speed up it to max when needed for comfort.

 

Like so many things, it seems a speculative argument exists both for and against. The choice is yours.

 

I have no measurements, but I can tell you that there is a dramatic difference in my 2016 Outback during heavy wildfire smoke when using the Bosch HEPA cabin air filter. Not perfect, but good enough not to wear a mask in the car when I'd definitely wear an N95 outside.

 

It does seem silly to ruin your lungs because you're worried about blower motor life.

 

Folks, be aware that a HEPA filter is not magic. If you are recirculating the air, the amount of good the filter does is the flow rate X the efficiency. The allergen reduction will depend very heavily on how much external air is coming into the car other than through the filter. It might be best to use external air to keep the car under positive pressure, but the problem with that is that your are not filtering out exhaust fumes, which will exacerbate allergies. As a longtime allergy sufferer, I can tell you that there are no magic bullets, just the possibility of some mitigation.

The other thing I noticed when I replaced the cabin air filter on my '18 OB is that the filter frame and seating is not so great, so there is a lot of opportunity for air to bypass the filter.

 

The beauty of recirculate mode is that air that might have bypassed the filter will go back in and get filtered. A better filter is a better filter, and Tesla's famous biohazard mode is literally just a combination of recirculate mode and a HEPA filter, albeit one that's probably 6 square feet while ours is less than one square foot. But a HEPA filter large or small still has the same pore size. With the Tesla filter it will take just that much longer for it to clog, and there's probably less chance of bypass when such a huge filter creates very little pressure differential. It would take a lot of small HEPA filter changes to add up to the cost of a single $500.00 Tesla HEPA filter upgrade.

2012-2020 | Model S HEPA Air Filtration Upgrade

Upgrade your Model S with HEPA Air Filtration for the freshest cabin air available. This package includes Bioweapon Defense Mode firmware as a feature of the HEPA system and comes with a new HEPA filter. For more information, visit the Tesla Blog. Note: Compatible with Model S vehicles with...

shop.tesla.com

 

Not all HEPA filters are the same. They come in efficiency ratings from about 95% to 99.997%, and various pressure drop ratings. In addition, a HEPA filter is useless if you can't push any air through it. The effectiveness depends not just on efficiency, but on flow rate. If the blower is weak, HEPA might decrease effectiveness.

If you are in a hermetically sealed enclosure, recirculated air will be totally cleaned eventually. Also, you will die from lack of oxygen. New air that enters comes with new impurities. The result is that the impurity concentration eventually plateaus asymptotically at some value that is a function of the rate of entry of new impurities, the flow rate through the filter, and the filter efficiency.

In the case of allergens, you can be exquisitely sensitive to the tiniest amount of allergen, so in many situations it is very difficult to achieve a plateau value that eliminates symptoms, although you can mitigate the symptoms.

 

It’s been a few days and I’m quite pleased. Yesterday I got stuck behind an old garbage truck that was belching black smoke, but I didn’t smell a thing even though recirc was off. That’s a first for me; I’ve never had a filter that took care of diesel smoke that well. Today it was 98° and the A/C had no trouble keeping up with things.

 

All homes leak a lot and that's a good thing. I live in northern Calif so we have a verity of air cleaners, best are the electrostatic which ionize the plates at 9KV, but even they have slots for activated carbon filters on the output side. The others are all different forms of mechanical filters. Bottom line is really good ones are expensive, but to me worth it. But, be carefull one of them says "HEPA" on the box but in the book states the size/% blockage and it's nowhere a real HEPA. The Homedics from Costco have a UV feature and seem to work well but the filter as a seperate buy is almost the Costco price for the whole thing.

 

At one time I had a 1000 cfm filtration unit with a 99.7% industrial HEPA filter that kept my small apartment under positive pressure. I still had allergy symptoms. Then, I had occasion to visit a class 10 silicon fabrication clean room. My allergies completely disappeared within a few minutes. IIRC, Class 10 means there are on average 10 impurity particles per cubic meter of air.