I am not one of those guys with a lot of letters behind my name. All of what you are about to read are my own thoughts on the subject based on my thirty years of experience in the field of HVAC distribution and you are getting exactly what you are paying for. I have to generalize a bit so your particular HVAC system may not be described in full – the universe is simply too large. Even if you follow this advice, you still might get covid. Forward.
There have been a lot of articles recently about the virus and how it transmits and moves around in air currents, in particular the ones that are created by HVAC systems in your domicile or your place of work. Some of these articles have been pretty decent, and a lot of them pretty dismal. Below are my thoughts on the virus. A lot of this is based on our past experience in the industry when anthrax was all the rage.
There are three main ways to lower your chances of meeting the virus up close and personal, as relates to HVAC systems. These are in my order of preference:
1. Dilute it
2. Zap it
3. Trap it
1. Dilute it – everyone knows you are “safe” if you are outside, even if you don’t wear a mask. Why is this? Because covid needs a bunch of “them” to get into “you” and if you are outside, there are naturally fewer of “them” around because there is so much free air diluting “them”. The fewer of “them” that can get into “you”, the lower your chance of getting the disease. In most single family dwellings, fresh air isn’t introduced enough. In the energy conserving decades of the seventies and eighties, we tightened up our structures and this practice continues to this day. While saving energy, the same stale air circulated through your house eventually is actually quite bad for you, and if you toss in the off gassing of new carpets or floors or drywall, it is even worse. Energy Recovery Ventilators and Heat Recovery Ventilators are code in some parts of the country, but not in most. These devices introduce fresh air into a house, exchanging the heat or air conditioning and exhausting the stale air. Very good items to have, but expensive. If you live in a residence I would highly recommend one if practical. Also, LEAVE YOUR BLOWER ON 24 hours a day. Most modern HVAC systems don’t consume all that much energy and your air filtration equipment simply doesn’t work if there is no air moving over it. In commercial buildings with rooftop units, the economizer is what brings in fresh air into a structure. Many times the economizers are broken and never fixed. Sometimes they are. If you live in a high rise, you have fewer options. If you can, open the windows. Obviously in extremely hot and cold climates, it is harder to make air exchange energy efficient or opening windows practical. In other words, you can’t bring zero or one hundred degree air into a structure for pretty much any reason, to keep it short.
2. Zap it – There are two main ways to kill covid in an HVAC system. I put both of these in the “zap it” category. You can put a UV light in the air stream (again, it doesn’t work if you don’t have your fan on) or put in a bipolar ionizer. UV lights are pretty self explanatory – they have been proven to work on heartier viruses than covid but not actually tested against covid. Also, as you can imagine, demand is intense right now. The other technology is bipolar ionization – on a simple level, these machines create ions that attach themselves to the virus and deprive it of hydrogen so it dies. Demand is also very strong for these. The commercial versions have been tested against covid and are effective.
3. Trap it – I have seen articles in the MSM about MERV 13 filters. The articles are, amazingly, mostly correct, with one very large problem. They are correct in the fact that MERV 13 filters (to keep it simple, MERV is an efficiency rating) will trap the virus (and it will die in a day or two after sitting on that filter). The problem is that demand right now for MERV 13 filters is so high that it is unlikely that you can find one. I work with four filter vendors and as of this writing, their lead times stack up like this:
Company 1 – not taking orders, back orders fulfilled in 12-16 weeks
Company 2 – taking orders, lead time 12 weeks
Company 3 – taking orders, lead time 12 weeks
Company 4 – not taking orders, back orders fulfilled maybe next year
We are recommending our customers who want MERV 13 filters to purchase a full years supply at once and store them. The issue is that the same companies that make the media for PPE are the companies that make media for MERV 13 filters and sell it to the filter manufacturers. Guess what is getting priority?
That is basically it and I am sure I have left out a lot as the HVAC universe is large. You really have nothing to fear from your HVAC system. Face to face contact is a far greater concern. I will attempt to answer any specific questions you may have in the comments. Keep it civil, as I freely delete nasty or insulting comments.
24 thoughts on “Covid and HVAC Systems”
Good stuff, Dan! Thanks!
Our HVAC contractor tried to sell me a UV unit last spring but there are just the two of us here. It would make good sense in a work place or a commercial site.
No reason not to put in a UV unit if practical and you can afford it, Mike. They have other benefits besides just killing covid. Also, UV gets far more complicated in a commercial setting for a variety of reasons, the most important being that the commercial world is far less standardized than the residential one.
Just talked to our HVAC people and they are going to stop out tomorrow and look at adding Calgon ionizers to our system.
Good on ya Jeff. Very easy to install.
Dry climate, the evap. cooler runs with water on the pads during the day but by 10pm the temp’s down to <70° so then I turn it to fan only. 100% outside air. Won't help in the winter, though. Hopefully those MERV 13 filters will be back in stock by late-October.
Thank you. Valuable info.
Also, thanks for the information. Where I work we have 100% outside air 100% of the time because of vent fans running 24/7. When we had to shut off a unit, we had trouble opening doors. So I’m not too concerned for myself.
Some thoughts occurred to me. First, how well will a standard system deal with what I assume is an increase in static pressure?
Second, some of our filters are located in the returns in the ceiling over work spaces. When these filters are changed, they could be classified as bio-waste. This would make changing them and disposal a huge hassle and expense.
Third, a UV system, since it is protecting from a workplace hazard, might come under OSHA and require testing and certification. Dito for the filters as well. I know that systems built to even high standards are far short of meeting bio-containment requirements.
This is not a can of worms that I will be opening voluntarily.
Either of these might be effective in reducing risk even if they weren’t perfect but that is not the regulatory regime we live under.
MCS – Excellent observation re static pressure moving to a MERV 13 from a lower efficiency. Yes there will be an increase. In most systems this hasn’t been an issue. However, these filters, being so efficient load up much quicker (creating big static problems), causing them to have to be changed more frequently and they are expensive relative to a MERV 8 as an example.
First I have heard with the filters being treated as bio waste or osha with uv certification. I think they have bigger fish to fry but you never know.
Back closer to when all this started, I remember reading something along the lines that HVAC filters, even regular efficiency ones, would be potentially contaminated and would need to be treated as bio-waste. Nothing since but there is a logic to it. As you say, the virus trapped should die within hours, although there seems to be supposed evidence that it could be longer, and any viable viruses should be fairly well trapped. It would still be something potentially contaminated with a hazardous pathogen. I know the filters used in bio-containment rooms and hoods where hazardous pathogens are an issue are treated as such.
As far as OSHA becoming involved, that’s not any sort of stretch. Any engineering control that is used to mitigate a workplace hazard is required to show proof of efficacy. This includes both the device and the installation. Any duct leaks that would let potentially contaminated air bypass the filters or disinfectant would be a problem. Hasn’t been my area but I bet the standards are already written and in force. The difference is when you have to consider all of the workers as a source of contagion instead of a particular patient or process. I’m a little surprised that the idea of making it mandatory hasn’t been floated anywhere I’ve seen outside of the British press.
Remember, we live in the time of: “if it only saves one life”.
I don’t disagree with you MCS. But as a sort of anecdotal note, I haven’t heard of the bio-waste or OSHA things from a single customer and we have literally thousands working in commercial markets every day. I would think that if something was happening on that front I would have heard at least something from someone. Again, not to say that it can’t happen in the future.
I haven’t heard anything from a much smaller group than you have access to. I just have faith in how the regulatory mind works. I also have faith that the health and safety drones are working on something that combines astronomical expense with complete uselessness.
I’m also waiting to see the first wuflu liability lawyer billboard since I no longer watch commercial TV. Unless the feds preempt it, which I don’t think has happened yet, it can only be a matter of time. Texas isn’t prime hunting grounds for those jackals anymore since punitive damages have been limited here.
If they start classifying filters as bio waste, that will certainly add an astronomical amount of money to a simple filter change. It might work in reverse as businesses may say go with lower efficiency filters to avoid the bio waste designation since those wouldn’t trap covid. Ugh.
Just ordered 2 Calgon iwave-5 ionizers for work and one for my house. Should be installed next week.
Pretty cool how they work!
What you’re talking about already played out in the regulations for used engine oil. It started out that it would be classified as hazardous waste. When it became clear that that sort of overhead was going to keep the whole thing from happening, common sense prevailed and a special classification was adopted that avoided most of the burdens. A rare case indeed.
New engineers, especially, have a tendency to try to be “tough” when they start to write specs. Usually one of two things happens. Someone with more experience takes them in hand and explains that specs are intended to be as minimal as possible while insuring function or quotes come back that cause the eyes of whoever is writing the checks to glaze over and ways are found to reduce the cost, sometimes by reducing payroll.
Neither is likely in government, and most especially regulatory government. First, there is unlikely to be anyone with real world experience. Second, it’s not going to cost them; so who cares?
Have a friend who has the PE letters behind his name. He comments that most hospital’s maintenance workers do not like to change the UV bulbs in the systems, when they lose efficiency.
How long do the UV bulbs last?
I did a quick search:
They’re essentially fluorescent bulbs with no phosphor coating, The UV excites the phosphor that makes the white light from conventional fluorescent and LED bulbs. It lists 10,000 hours and above. This is likely burnout, so effective life would be somewhat shorter. One chart I saw showed a decrease of 5-20% over 10,000 hours depending on the exact type of bulb. High output T5 were the best and the older T12 the worst. So for 27/7, replaced every year or two. Don’t know why it would be particularly disagreeable.
We sell two and three year bulb models. I’m not sure why this job is disagreeable either to be honest. It’s quite simple. Unless if they have to dispose of the bulbs in some sort of odd osha/hospital fashion which creates paperwork/hassle.
There’s another type of bulb you can use. Mercury arc come in ratings above 1KW. The heat they generate can make them very hard to remove without breaking and then there’s the mercury part. Installing them is tricky because any surface contamination will shorten their life, sometimes explosively.
If you’ve ever seen a CFD model of air distribution in a lab, you’ll quickly realize it’s a crap shoot that the room will be ventilated satisfactorily (even at 25 ACH of outdoor air) and that the virus might actually make it back through the returns (where the system isn’t 100% outdoor air) to the air filters.
It is more likely that most of the virus particles will eventually fall to the floor.
I would guess that hospital staffers changing bulbs are exposed to airflow from the system, and that the duct they’re working in may still be passing germs from the entire hospital. While COVID is the flavor of the day, there are plenty of other airborne infections you wouldn’t want to enjoy. The actual risk may be minimal, but so is their medical training.
I bought a bunch of MERV 12 filters for my home furnace on clearance last year. Until I run out, they will be good enough. Reading your post reminded me to check my filters. I was SURE I replaced them in June. Nope, they still said March.
Write the day you replaced the filters on the filters with a sharpie. It helps you to see when you need to replace them. And if you have multiple filters to replace, you can confirm you replaced them.
We have electronic air filters on our two HVAC units at home. Does that help or would we still need one of the 3 suggestion above?
Thanks btw. This is very informative.
Ozone generator at air intake at a level below what the human nose can detect.
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