How can HEPA charcoal filter benefit allergies and asthma?

@jeff1047 That's a great question. I can say that my experience with the Foust 160R2 model is that I have usually changed the carbon in it every 9 months to a year. I have also changed it at 6 month. By a year, I can tell that the air doesn't smell as fresh, and I've wondered if some of the dust held in the filter can be shed from the edge of the felt if it gets overloaded. It's not just dust in the air, but also dust that comes off the carbon. This answer needs some context.

The cylinder is made so there is a one inch wide chamber in the perforated wall to hold the carbon granules, and it holds nearly 7 pounds. I repack the cylinder myself which is a very messy dusty job, so I always do that outside and I'm careful not to inhale any dust. Wearing a respirator is advised. That is the most economical way to change the filter. You can also get a pre-packed cylinder shipped to you and return the old one. They are re-packed and resold.

Inside the cylinder is an airspace, and the "filterdown" or HEPA felt material is held against the carbon chamber with springy metal strips and hardware cloth. The HEPA felt is an additional charge, and I always buy that and also get the filterdown they give you for backup supplies. It is easy to cut yourself on the metal springs or hardware cloth while changing the filter media. The industrial type motor on the top lid is connected to the bottom lid by a long bolt with a wing nut on the bottom. Air is drawn first through the carbon chamber then through the filter felt fabric and upward from the center out the top of the unit's blower. If you want to use the filter down without carbon, you can do that. They will also sell you a pleated filter that can go into the carbon chamber if you don't want to use carbon.

I have had these units last a long time (8 to 10 years) before the motor might quit. There are no user serviceable parts, and the bearings can wear eventually causing the motor to get hot. Cooling for the motor is only through some air vents and dust can collect in there which needs to either be brushed out or blown out with air for better air cooling. It all depends on how much you run the motor. We run these most of the time. The unit in the bedroom was run only when in that room at night. I no longer trust a unit that gets hot, so I run that only about an hour before going to sleep and turn it off. When we are away from home, all units are off.

We also have the larger 400 series running all day on the main level of the house. It has a prepacked filter box that lasts a few years. All you have to do is change an outer filter much like a furnace filter that catches the large dust. You can also get this with a UV light, and I've had that bulb burn out after a year, but the filter is fine. I think I've had this for at least 4 years, and the air coming out the top still smells fresh, and I have not replaced the original filter except for the outer one. This unit costs more, but it is so much easier to keep up. Removing the filter is just lifting off the top and lifting the box out. That filter cannot be re-packed and you must buy a replacement. There is no mess. The unit is on casters, so can be moved around. When the box arrives, it's too heavy for one person to lift, so I opened it on the driveway and took the pieces inside individually. This also has a larger industrial motor inside the unit so you don't see it except when removing the outer filter.

I think the company does represent the life of the filters honestly. These are made without glue or adhesives because of people with sensitivities, so they may not be the most attractive air filters you can buy. My 400 series is a solid beige color. The 160R2 units are a metal cylinder (which can rust) with a black industrial motor on top. The 400 series is nicer and easier to maintain, but if you are buying replacement pre-packed cylinders for the 160R2, all the dusty work is done and you just swap out that cylinder. In the long run, filter changes may cost less over a long period of time with the 400, but the unit is more expensive. There are 2 fan speeds on the 400, but they are nearly identical, and the unit is fairly quiet. The 160R2 is a bit louder, but not bad. These filters do a good job of removing dust, smoke, pollen and chemicals like VOCs, fragrances and formaldehyde that may be in home construction materials. On the days when outside air quality is poor due to far reaching wildfire smoke, the air inside my home was safe to breathe. If you have pets, that may clog the filters sooner. They do sell a cover to put over the cylinder on the 160R2, and I tried that, but the motor burned out right after that, so I'm not sure I would recommend doing that and adding an extra load to the motor.

@jenniferhunter
Thanks for the info. I looked at the product page for the 400 series purifier (https://foustco.com/all-products/air-purifiers/air-purifier-units/series-400-air-purifier/) and found that the HEPA and carbon tray are separate assemblies. In the last paragraph of the description they say that the HEPA will “last for years” but the Media Tray only lasts for 6-9 months. You have been able to go for 4 years without changing so I am wondering if your home is very low in VOC’s or if there is something special about their carbon mix . Their ‘Standard’ mix is 40% potassium permanganate and it may be that the permanganate is absorbing any odors that are coming off the carbon. I use a 50/50 mix of AllerAir Vocarb and Exec charcoals in mine and am pretty sure that neither one has permanganate. I may give Foust a call in the next few days to learn why they added permanganate to their charcoal in the ‘Standard’ mix. If they are willing to talk openly about their product I will also see what I can find out about their lifetime specs.

I am familiar with tube-style filters because I ran them in my lab and apartment in the early 90’s’s. The ones I used didn’t have a HEPA but it didn’t matter because I had terminal HEPA’s in the lab AC and a free standing HEPA in my apartment. In those days you could go down to the local filter supplier and buy a 25 lb bag of virgin coconut shell carbon for a few dollars a pound. It was easy to change out the carbon in the tube and I always took it outside so that the dust wasn’t a problem. You could also get refillable flat panels in those days and I had another unit with two squirrel cage motors and a panel on the front. I usually taped a prefilter over the flat panel to keep it from getting dusty.

I built a house on an Atlantic barrier island (< 1/8 mi from the ocean) in 1992 and put a 2” refillable charcoal panel in the fan/coil unit. That system had the same terminal HEPA filters as my lab, a reheat controller that kept the humidity near 60%, and a MERV 11 V-bank pre-filter on the outlet of the fan/coil unit.

I changed the charcoal in the lab and house every few months but didn’t know enough in those days to check it more often. I believe that the apartment charcoal got changed more often but don’t remember how the period between changes.
I am not sure why we are getting different lifetimes for our media but am going to spend some time trying to find out. For the past 10 years I have been spending over $2500/year on carbon and would love to find a cheaper way to keep the VOC’s out of my work area and bedroom.

I am extraordinarily sensitive to mold and control my symptoms by practicing strict avoidance. (I talk about the reasons for this in another post at https://connect.mayoclinic.org/comment/1172607/.) I have found that stand alone units with < 400 cfm help with my symptoms but don’t reduce them to the level that I need to stay healthy. I currently use 2’x4’ HEPA’s (https://www.camfil.com/en-us/products/housings-frames--louvers/terminal-housing/clean-room-ceiling-modules/slimline-dcm-ducted-hepa-filter-module-_-47742) in both of my ‘clean areas’. The work area has 3 filters and the flow rate with the motors turned all the way up (2100 cfm) should give me two air changes per minute. I’m not sure that the returns are positioned to reach the theoretical max but I am pretty sure that I get >1.5 changes per minute.

I have also created microenvironments around my desk and bed by attaching shrouds (thick cotton sheets) to the outside edges of the filters. The flow inside the shrouds is similar to that in a filtered production workstation and the number of air changes per minute is significantly higher than in the entire room. I usually feel a lot better when the shrouds are in place.

Thanks again for your response. If I come up with a plausible explanation for the differences that we are seeing in activated carbon lifetime I’ll let you know. If I can’t come up with an explanation I’ll probably buy one of the 400 series filters with the 0.3 micron HEPA and to see how the charcoal performs in my work area.

@jeff1047 You brought up another good point. My house is low VOC. We worked with a builder and did everything we could to reduce formaldehyde that is common to a lot of building materials. We used formaldehyde free insulation and put in prefinished hardwood floors everywhere except the foyer and bathrooms that are tile. That was over plywood which did have glue containing some VOC, but I seal coated the plywood floors with Safecoat (consistency of painting with milk) before the hardwood was laid. I wasn't able to coat the bottom side of the plywood that formed the floor. The builder wouldn't allow seal coating the plywood before installation, and they wanted an unreasonable amount of money to do this extra step. We had a flooring company come in after we purchased the house to install the hardwood over existing plywood. The raw wood staircase and banister were stained and varnished with polyurethane. We have no carpet.

Twenty years ago, this was a new neighborhood under construction, and I would get a headache if I visited inside a neighbor's house within an hour, and I was fine in my own home. It lessened my allergies a lot. I do have other allergies here, because we have a river with wetlands behind the house, so I think mold counts are always higher in the area, and I can get sinus and asthma issues on days when mold counts are high outside. The water levels fluctuate with rain fall, leaving a lot of plant surfaces to grow mold.

If you talk to Foust, you can order bulk coconut carbon with the permanganate to try. Why not put that in your existing filter systems to see if the permanganate helps? I think it does help. When it is spent, the little permanganate spheres turn from purple to brown. I talked to them when a motor on a smaller unit died, and they suggested looking for some used units because they don't fix them and replace the motor. I bought 2 that I found on ebay, and Foust didn't mind selling me media for those. They have always been helpful and answered questions. I guess I haven't been paying attention to changing the media tray. Perhaps after 4 years, I should do that. The air coming out of the 400 unit still smells fresh, so I haven't thought about it. FYI, the size of the media and HEPA filter box for the 400 is 12" x 12". I'm not sure how deep it is without taking the unit apart. Here is the page about carbon choices from Foust. https://foustco.com/carbon-choices

@jeff1047 and @jenniferhunter - as I thought this was such a great conversation about HEPA/charcoal filters and how they can impact allergies and asthma, I made it into its own discussion in the Asthma & Allergy group.

@jenniferhunter

Buying loose Standard mix from Foust is a great idea!!!

I would not recommend the level of HEPA/charcoal filtration that I have described to anyone who is not incredibly sensitive to mold and/or allergens. It's also important from those reading my posts to realize that filtration is only one facet of my environmental control measures.

If someone wants to start practicing environmental control I would recommend reading through text and watching the videos at (https://www.aaaai.org/tools-for-the-public/conditions-library/allergies/indoor-allergens-ttr). The only thing that you should ignore is the statement in the second video that "for the most part molds don't cause human disease." This is clearly not the case and is contradicted by several articles in JACI and JACI In Practice (the journals published by AAAAI).

If they want to see if room-sized particulate filters work for them they might want to start out with a Corsi-Rosenthal Box. It doesn't have any charcoal in it but it is much cheaper than the Foust and AllerAir units that @jenniferhunter and I have been talking about.

There is detailed info on the box (including instructions on how to build one) at the Corsi-Rosenthal Foundation website (https://corsirosenthalfoundation.org/ ) and a video interview with Jim Rosenthal at (https://www.iaqradio.com/jim-rosenthal-chief-executive-officer-tex-air-filters-air-cleaning-filtration-and-the-corsi-rosenthal-box/)

@jeff1047 Jeff, this is great information. I like the Corsi-Rosenthal box. It's such a simple idea. We do use the furnace filters with the highest level of particulate filtration available. I also used to work in a research lab doing histology work, and the professor was very fussy about a dust free work space because if dust got into a microscope slide, an image of that tissue could not be published. This was long before digital photography in the days of film and darkrooms. He was wrapping the air registers with filmy fabric to catch dust.

During the beginning of Covid, when people were sewing masks because none could be purchased and limited supplies were needed by hospitals, I was looking up how well fabrics would filter smaller particles like an N95 mask or respirator. I read that denim fabric does pretty well, and I tried making a mask from it. I do keep a respirator with me when driving for those times when my lungs reactive to outside air. I also have run my Foust air filter in the car, but it is big and bulky and can fall over with starts and stops. They do also make a small model for vehicles.