# HEPA filters and air purifiers for allergy relief?

Mentor
My wife and some of my friends have been experiencing a spike in moderate allergy symptoms (Sx) this past week or two, and I was wondering if adding a HEPA air purifier at home in our bedroom would help. This recent PF thread discussed air purifiers, but not really from an allergy perspective:

Two of my colleagues at work have had good results by closing their bedroom windows at night (problematic now that the summer heat has set in), and adding HEPA air purifier fan units to their bedrooms. Is this a good approach? I'm having trouble sorting out the research from the advertising so far. Thanks!

Last edited:

BillTre
Gold Member
2020 Award
It could be effective.
Its a matter of how fast can your clean the pollen out of the air vs. how fast new air is introduced.
A closed room with an air supply that is fully HEPA filtered would be ideal.
A unit cycling through air from the room will reduce pollen but not as well, but should have an effect.

I have had one going in our living room in a house with poor control of incoming air (family members) and I didn't really notice an difference.

russ_watters and berkeman
I just bought a Honeywell air purifier today, berkeman. I'm not an expert on them either.

I just wanted to quickly say that the one we have has a True HEPA filter, which AFAIK is the most restrictive filter. It removes .3 microns and up of all particles. The regular HEPA filter removes 2 microns and up.

We also upgraded our air conditioning filters from the lowest grade (which removes just dust mostly) to the level above it (to include mold spores)...there are two grades above the one we have. In those, microscopic allergens are also removed. My mom wanted to save money, so we stopped at the second level only.

I think these filters can help remove/trap free flowing particles. But I'm not sure how effective they are at removing everything, as there can be hard to reach surfaces. For those hard to reach surfaces, you can buy a vacuum with HEPA filter (maybe even True HEPA too?). We're looking into that right now. A vacuum with that narrow detachable stick can help get hard to reach places.

berkeman
Tom.G
Three things my wife and I have found quite helpful, and the combination seems to be required:

1) Keep the windows closed.
2) Keep the humidity down, 50% is often cited as ideal but some people are uncomfortable with it that low. Between 50% to 55% works well for us.
3) If you have forced air heating and/or cooling, use air filters specifically marked for allergen control or better. 3M makes some under the Filtrete brand. Best brick-and-mortar prices I've found are at Walmart. Change them every two to three months.

We are in a 700sq.ft. apartment about 6 blocks from the ocean. We installed a 70 pint portable dehumidifier last October and it has helped quite a bit. It does run up the electric bill though, adds $35 to$60 a month which includes increased A/C and reduced electric heat usage. It is plugged into a Kil-A-Watt which currently logs 2480 Hours and 463 KwH. We often turn it off overnite. During humid periods the dehumidifier runs continuously which means we empty the catch-bucket roughly every 12 hours.

Another note. The three electronic hygrometers we have (one in the dehumudifier) all read low. They read 35-40% when a wet-bulb/dry-bulb hygrometer reads 53%. The mechanical one (paper/metal spiral sensor) has a time constant of a few hours.

Cheers,
Tom

russ_watters and berkeman
One question related to the efficacy of purifiers is whether or not you need to run them 24/7 or close to that?

I've seen several online sources saying to do this, but I'm curious about the reasoning behind it (if it actually is sound advice). If these machines do what they say they do, then wouldn't the pollutants and other unwanted particles decrease over time and at some point reach a "stable low point." Other than presumably new pollutants coming into the house (from opened doors and maybe stuff sticking to your shoes/shirt from outside each day), wouldn't the internal air environment be pretty good? If it's just random stuff getting into the house from those sources just listed, is it enough to literally have to run the purifiers 24/7?

I'm not so concerned about allergens as I am mold spores and dust mites.

Mentor
just bought a Honeywell air purifier today, berkeman. I'm not an expert on them either.
Which model did you get?

I'll say this, the machine's out-going air is very powerful and doubles as a fan.

berkeman - I used a combination of Consumer Reports' ratings (both by CR and CR users) + major online big box store retailers' user ratings (Walmart, Home Depot, Target, etc.) to find one to buy. I knew, however, that I wanted one with True HEPA for sure. HEPA wasn't even good enough for me. Then I used the reviews and factored in cost.

The first thing I did with each website was look at the lowest rated reviews to see if a particular purifier had any common significant problems. I do that with all products I buy. I'd rather know the bad before the good. I weeded out ones that had major problems that were brought up by multiple users.

In the end, for cost and quality, this was the best one that I found (it's $130.00 only). There were much more expensive ones with lots of bad reviews and common significant problems listed by various users. This one didn't have any really bad reviews (I mean, they all have a few low ratings, but I mean like lots of low ratings and commonly brought up big problems) and was very economical. russ_watters Mentor My wife and some of my friends have been experiencing a spike in moderate allergy symptoms (Sx) this past week or two, and I was wondering if adding a HEPA air purifier at home in our bedroom would help. This recent PF thread discussed air purifiers, but not really from an allergy perspective: https://www.physicsforums.com/threads/would-buying-an-air-purifier-be-helpful-for-home-apt.947592/ Two of my colleagues at work have had good results by closing their bedroom windows at night (problematic now that the summer heat has set in), and adding HEPA air purifier fan units to their bedrooms. Is this a good approach? I'm having trouble sorting out the research from the advertising so far. Thanks! It really should make a big difference, though closing the windows is probably a lot bigger of a difference than using an air purifier. Stopping particulate at the source is almost always easier than filtering it after it gets in. It's worth considering air conditioning rather than leaving your windows open. berkeman russ_watters Mentor We installed a 70 pint portable dehumidifier last October and it has helped quite a bit. It does run up the electric bill though, adds$35 to $60 a month which includes increased A/C and reduced electric heat usage. Could you clarify what you are doing there a little? Are you running a dehumidifier and an air conditioner in the same space at the same time? Why? Doesn't the air conditioner achieve 50% RH on its own? russ_watters Mentor One question related to the efficacy of purifiers is whether or not you need to run them 24/7 or close to that? I've seen several online sources saying to do this, but I'm curious about the reasoning behind it (if it actually is sound advice). If these machines do what they say they do, then wouldn't the pollutants and other unwanted particles decrease over time and at some point reach a "stable low point." If it is strictly pollen that you are worried about and you keep your doors and windows closed, then yes. But if you are concerned about other particulates generated inside the house, then there isn't a "stable low point" but a "stable high point" -- the very thing you are trying to correct! kyphysics Tom.G Science Advisor OK, here is more info than most people want, but since you're in the business here goes. Are you running a dehumidifier and an air conditioner in the same space at the same time? Yes. With the dehumidifier running (567 Watts,measured), two people at rest, two LED lamps (ea. 100W equiv.), one refrigerator, one tower computer & display (350± Watts), misc 60± Watts, there is a >15°F rise above outdoor ambient. Indoor temp 78 to 80 depending on which thermometer and rising, with humidity at 51% (dry 80F, wet 67F). It is 11pm with estimated outdoor temp in low to mid 60s and perhaps 80% humidity (long Beach Ca., ½ mile from the Pacific Ocean. weather.com says 64°, 86%). Dehumidifier is set to 40% and regulates to 50+%, running at 95+% duty cycle right now. (varies w/ outdoor humidity) Doesn't the air conditioner achieve 50% RH on its own? Not even close. It seems to be way oversized, but we haven't had a heatwave yet. Thermostat setpoint is 78F, just switched on at 79F, off at 77F. Run time: 9min. 20sec. Dry/wet = 78/65F. Edit at 12:30am: Cycle time: 61mins. 11:50pm now. I was waiting to determine cycle times. weather.com says 64°, 88% If the outdoor temp drops a couple degrees and the computer is off, the air conditioning will stay off and heat will come on in a few hours at 76°. Cheers, Tom Last edited: berkeman marcusl Science Advisor Gold Member Berkeman, I suffer from hay fever and have found this spring was particularly bad. I run a Honeywell HEPA filter in my bedroom at night and it makes a big difference—to the point that if I leave the bedroom for some reason, I get runny within about 5 minutes, whereupon it takes 20 minutes to clear up again upon return. Calculate the volume of your room and size the unit for 6 complete air changes per hour. Most units have a low-med-high fan setting. To get the air volume you need for effectiveness, you may need to run at med or high which has the downside of being noisy. The sound doesn’t bother me but my wife wears foam earplugs in the spring. Also there’s no point in running it all day if you aren’t in there—just turn it on 40 minutes before bed. berkeman If it is strictly pollen that you are worried about and you keep your doors and windows closed, then yes. But if you are concerned about other particulates generated inside the house, then there isn't a "stable low point" but a "stable high point" -- the very thing you are trying to correct! Random question for you, Russ. Or anyone else. We found out we have mold and fungus in our crawl space. We had multiple people in our house getting skin rashes and infections lately (me, younger sister, and dad - oddly, not my mom) and we had that mold issue, etc. Anyhow, the guy who inspected it and showed up pictures said that 50% of the air you breathe in your house is from your crawl space. Didn't think anything of it, but then was like really (after he left)?! Do you happen to know if this is true? Why would your crawl space's air go up into your actual house? And does the air in your house somehow escape through the walls and ceiling, etc. too? I thought houses were sort of "sealed." *continued above* - Also, assuming crawl space air travels up to your house and inside of it, does the reverse happen, where air inside your house can go into your crawl space? Got me thinking of how mold spores might be traveling. BillTre Science Advisor Gold Member 2020 Award Air flow from a crawl space into a house's living spaces would depend a lot on the details of the house's construction (and therefore age) and where its air system (if any) takes its air in from. You should probably contact your (or the other people's) doctor(s) about any possible connection between the rashes and infections with the mold if that concerns you. I have been told by contractors involved with cleaning out fungus in walls of campus buildings that it is best to leave it alone if the wall is sealed up nicely. I tried air filters, but they can only work if you seal your house up during the nice seasons. So I ended up feeling confused when I'd have the filter running and my windows open. Tom.G Science Advisor Here is an update on energy usage of that 70 pint portable dehumidifier. I connected it to a "Kill A Watt" electrical usage meter. The device draws 567W when running, was almost always turned off at night, and had just 'a few' hours usage during the winter months. Code: Data Collection Time: 8760 Hours (March 2018 thru March 2019) Total Energy: 1347kWh Ave. Energy: 154W per hour, 112kWh per month, Run Time: 2376 hours per year, or 27% duty cycle At the USA average electricity cost of$0.132 per kWh the annual bill would be \$178 USD, concentrated in the middle 2/3 of the year.

See posts #4 and #13 above for installation and environment data.

Cheers,
Tom