Should we buy an ozone generator?
February 7, 2019 6:38 PM   Subscribe

We recently bought a house and are preparing to move in next Friday. Until then, we're trying to eradicate a musty/moldy/old cat pee smell in the basement, where two bedrooms are located. An ozone generator seems like a good option for blasting away these things/smells, but it's hard to get a sense for how effective it'd be, or how dangerous. Or if there are other air purifiers we should use instead.

There are not and will not be any pets, people, or plants in the basement at the time when we want to use it. I almost think of it as a single-use tool, because we wouldn't be able to use it after we bring in our considerable plant collection and pets and people--we really just want to blast out any residual animal waste or mold spores that we can't see or reach.

We have already: Removed carpet. Had a professional cleaning company take care of the space. Then my spouse has cleaned floors, walls, shelves, pretty much all surfaces, again, with Pine-Sol and bleach (not together, and with good ventilation). He also removed a cabinet unit that was moldy, and cleaned a spot of drywall that had some dusty mold formations visible.

Our guess is that at some point in the last few years, the hot water heater blew out and there was a bit of water damage that the previous owners didn't clean. At the time of the home inspection, the area surrounding the (brand-new) hot water heater was covered up in stuff; it wasn't quite a hoarding situation, but close. So we were unaware that there was actual mold anywhere in the basement--to me, it smelled about right for an underutilized basement full of stuff. But the smell is still there, although less strong than it used to be.

Anyway, the tl;dr is that I know an ozone generator is not something to use in an occupied space, and that there are a number of health and safety hazards associated with them. But it also seems like a very effective tool for this moment in our home's life. Is it worth it? Are there alternatives that would work?
posted by witchen to Home & Garden (9 answers total) 2 users marked this as a favorite
Response by poster: The particular model in question is this. There is a vast discrepancy in reporting between 5-star and 1-star reviews, almost on the level of "this is a miracle machine that makes everything clean and perfect" (about 2,300 of these) and "this machine gave me and my cat bronchitis and almost burned down my house" (about 240 of these, but those outcomes are...bad).
posted by witchen at 6:50 PM on February 7, 2019

Have you checked the humidity? Our basement has a bunch of smells that disappear once the dehumidifier drops the humidity below 50 percent or so.
posted by rockindata at 7:58 PM on February 7, 2019

We recently removed some drywall in our basement that had had water damage a decade ago. We never detected the odor of mold. We have a rec room down there, and use it frequently. The water damage was because a neighbor (we share a wall with another house) had a pipe leak, and since our basement is dug slightly lower, we collected water on our floor. The baseboards got wet. The plasterboard walls were a little damp where they met the baseboard, but there was no mold anywhere, and with fans, dehumidifiers, and fervent mopping everything dried out. We moved on.

Fast forward to last year. We put in new flooring, and removed the baseboard to do it. There was mold on the back of the baseboard, and when the contractor removed the lowest part of the plasterboard behind the baseboard it was moldy. The back of the plasterboard was covered in mold, but nothing showed on the front. We had lots of mold but had never seen it. We ended up removing the bottom foot of plasterboard all the way around the room, which our contractor patched beautifully. We then had to repaint the entire room. We could probably have tapped the homeowners insurance, but the damage occurred 10 years ago and we hadn't claimed it then, so it seemed a little strange to do it now.

If you have that handy one-year home warranty insurance, though, that might work for you. And I think if your home purchase is fairly recent you might still be able to purchase coverage.

So, if you see mold on the outside of a plasterboard wall, please investigate what might be on the inside surface. A dehumidifier may help, but if you actually have mold it should be removed.
posted by citygirl at 9:10 PM on February 7, 2019 [2 favorites]

I dealt with a somewhat similar issue - cat and dog pee + smoke smell in a fixer upper house I bought. The ozone machine definitely made a difference, but it wasn't a miracle, either. We left it running in the house overnight and stayed somewhere else, then just opened the windows and doors for a bit after we returned.

If you do use one, I suggest you rent - you'll probably end up spending the same or slightly more as buying the unit you linked, but you'll end up with a much more powerful piece of equipment that makes a bigger difference.

What finally got rid of the seeped-in pet smells and smoke smell was actual removal of offending materials where it had soaked in (like you did with the cabinet, and in my case, drywall), as well as a professional odor treatment using chlorine dioxide. Consider a professional consult/remediation since your situation involves mold and actual air quality issues, not just smell. Good luck!
posted by drawfrommemory at 9:16 PM on February 7, 2019 [5 favorites]

This is a good podcast that talk about the effectiveness of ozone products (spoiler - they don't work)
You'll find something, but don't waste money on O3
posted by PistachioRoux at 3:39 AM on February 8, 2019 [6 favorites]

there are a number of health and safety hazards associated with them.

Perhaps you include this in the list, but just in case it is not on your radar and would affect your decision, be aware that tropospheric (ie, surface-level atmosphere) ozone is a potent greenhouse gas. It's not talked about much, both because it's not generally produced directly in the troposphere and because it's a very good thing to have in the stratosphere, but if you would avoid CFCs and old aerosol cans because of their effects on climate change, you'd probably want to avoid this solution as well.
posted by solotoro at 8:25 AM on February 8, 2019

We had smoke in our kitchen (a literal pot of beans, my mistake) and rented an ozone generator from Cresco, though I'm sure you have your own local place that specializes in renting equipment for just below the cost of buying. I would check the capacity (measured in grams per hour) because the commercial one produced 10x what the home models did, though. The smoke was acute, but it took a solid 4 days to get a smallish kitchen smelling back to normal, so consider what you'll need to get your space deodorized. And the usual caveats apply about plastics and rubbers, which can get cracked very quickly at high concentrations. That said, it really worked, and with tape and thin plastic sheeting (like for painting) the smell of ozone itself outside the sealed area wasn't bad at all. We didn't remove any of the appliances and they are all fine years later.

As far as ozone as a greenhouse gas, the half life is about a day. It just spontaneously decays. So in an enclosed space, half the ozone will be gone within 24 hours, 99.9% in 10 days. There is no chance that it will make it into the atmosphere. Polluting ozone is generated by nitrous oxides reacting in the atmosphere, not the direct emission of ozone. And in any case, the industrial pollution that would result from you tearing out the drywall, disposing of it, and repainting the room would far outweigh any ozone-related environmental issues. Ozonate away!
posted by wnissen at 8:58 AM on February 8, 2019 [1 favorite]

Ozone is a health risk. Sorry about that last link, the EPA has a 1251 page science assessment with more details. The national ambient air quality standard is set at 70 parts per billion, which may not be enough to solve your problem. Ozone does have a short half-life, and you may not occupy the room, but it will diffuse to all the other parts of your house and breathing space that are not sealed off perfectly or under negative pressure. And, holy crap, that unit you linked to puts out 6000 mg/hour if I'm reading correctly? That's 100 mg/minute. That equates to...46.72 ppm every minute?!?!

We're talking about 46,728 ppb of ozone. That's 667 times the standard, above which it is considered unhealthy. In my state, it hasn't gotten higher than 131 ppb of ozone in ambient air in the last 10 years. During high forest fire conditions. The levels you're talking about may very well raise the ozone levels in your home to unhealthy conditions.

Don't do this. And, as a rule, I would say, you should never buy an ozone generator and use it in a space that is enclosed and near people unless you also buy an ozone monitor. The cheapest handheld monitor that's meaningfully accurate that I'm aware of costs around $500. The ones we use at work to measure ambient levels for the public cost $8,000.

Follow the advice to seek other solutions to your problems. I don't think an industrial ozonator inside a living space is a good idea. The oxidizing effect of the ozone will also oxidize volatile organic pollutants that are in your breathing space, too. Some of them will be destroyed, but some of them may degrade into more harmful versions of themselves, too. You don't know what volatile organic pollutants are in your house (and I will bet money there are some), so you don't know what will happen. That VOCs sample to find out what's in your house would probably cost at least $180 if you wanted the answer to that question.

Air science is complicated and expensive. There are better ways to solve your problem than polluting your living space with ozone.
posted by Strudel at 7:35 PM on February 8, 2019 [3 favorites]

I did an hourly calculation of the steady-state concentration and got 800 ppm, 80,000 ppb, for what it's worth. Assuming a 1000 sq ft basement with 10 ft ceilings, a weight of 1.3 kg / m^3 of air, 6 g/hr of ozone with a 24-hour half-life.
There has also been some research on the effectiveness of tape and sheeting, apparently it reduces air exchange from roughly one change every 3 hours to every 6 hours. So there is significant infiltration.
posted by wnissen at 9:45 PM on February 9, 2019

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