Home Ventilation Advice from HVAC Researcher Jeffrey Siegel: How Many CFM is Ideal?
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- čas přidán 28. 09. 2022
- Spoiler alert: Corbett's wearing a retainer. Yes. You don't have to comment about it. Video forthcoming, as a matter of fact.
Jeff Siegel is a superstar of HVAC research, and you can learn more from him in his original interview with me ( • HVAC IAQ Mythbusting w... ) and at his research site (civmin.utoronto.ca/home/about.... We're in the University of Toronto's rooftop climate chamber, shooting the bull about how many air cleanings per hour (aka air changes per hour, which is confusing to blower door folk) we should aim for in our living spaces.
Take my Ventilation Training and learn all that I know about this complex topic: buildingperformanceworkshop.c...
Learn more about specific ventilation strategies at:
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HVI.org
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"i'm allergic to standards", absolute gold 😁
One topic that interests me is best practices for location of equipment and ducts (in new construction). These best practices would be valuable for giving appropriate attention to making equipment accessible for maintenance inspection, future replacement or with modular replacement parts, able to be retrofitted with future controls, monitoring… I think there is a lot to improve there
Word. I want to put ducts into a new construction build to future proof it. It's so easy to do this for electrical - run conduit through inaccessible areas instead of Romex, and pull more wire later. What are the options for ventilation if I don't want to spend $20k on a system today and the stud bats are accessible?
@@ThisIsNotAVideo You could build a plenum (when you are ready) under the ceiling in the rooms, and run ducts through the plenums and though adjoining interior walls. That's one option to not open the walls studs later. This puts ducts in the conditioned space (and not in the attic). This worked for me in a renovation of a single story 650sf 1930's home. Would work even if you want to maybe add a system later and you're doing new build now. You could account for the plenum space if its a new build so that you avoid the common complaint plenum being in an awkward spot.
I’ve seen the relative humidity go up pretty high in houses when they keep the fan “on” their thermostat. When the AC kicks off, the fan continues and pushes the water vapor off of the evaporator coil causing humidity issues indoors. Just my 2 cents.
In theory yes, but that’s how my HVAC runs in Atlanta and our RH is locked at 45% at 76F with a 120pint dehu.
@@HomePerformance Absolutely. The dehumidifier makes all of the difference. Air circulation is vital, but unfortunately when done through the HVAC you go through filters monthly. It’s totally worth it though.
It’s also amazing, might I add, the feeling of sitting comfortably in 76 degrees with low humidity. People look at my thermostat and are like what the heck?!
If you're going through filters monthly, then you need to look at the source of what is getting filtered. The only way they can clog that quickly is with a constant very small particle source.
@@christopherhaak9824 Absolutely keeping a house clean is important. One big problem is HVAC returns being installed at a low level. Carpet is a big issue too to contributing to dust and contaminants.
That guy in the video doesn't know what he is talking about.....
A lot of the comments thus far are great get at a much larger issue. Our buildings are systems. Changing one thing doesn't always have the intended consequence. Trying to ventilate and maintain a positive or negative pressure inside is really hard if you don't have a really good enclosure (trying to inflate a leaky balloon is the appropriate analogy). Using an ECM fan (or, quite honestly, your entire air conditioner) when you have a constricted return ducts is not going to work out well. That is the fun and the challenge of what we do: every building is a puzzle that you have to figure out and it often plays out differently in seemingly similar buildings. Pressurizing in a cold climate has a higher chance of leading to a moisture problem in the enclosure when the exfiltrating warm moist indoor air hits a cold surface. Depressurizing in a humid climate is going to introduce a big latent load to your air conditioner (which probably isn't able to deal with it). Overall, I generally like the idea of pressurization with filtered and dehumidified air, but your enclosure has to be designed for it (more of a challenge as it gets colder). Separate issue, for those asking about VOC removal. A good activated carbon (with enough carbon to actually make a difference) is wonderful stuff. A 4 or 5" deep pleat high-MERV particle filter followed by a good 1" activated carbon filter in your central system is a great system if you have the space to accommodate. Make sure the filter slots are high quality and gasketed.
And seriously, don't trust the guy in the video.
Thank you for being so knowledgeable and so untrustworthy, Jeff my man.
Jeff is so good and its difficult for him to give direct answer as at the moment of asking him a question he probably sees hundred of variables and he gives relative answers. I just wish he answer's emails more often :D
@@HomePerformance Lol...Jeff knows all
ECM blowers are by design more efficient but when attached to overly restrictive ductwork and loaded filters can actually consume more energy than psc motors. In that situation your motor is likely to fail prematurely ( earlier in its lifetime and with less total run time ) don’t rely on modern tech to save your bacon. Hire HVAC companies that know about ducts. Not all do.
Corbett, The primary pollutant I worry about with lots of bodies in a pretty small space is CO2 that's being exhaled. For example, I share a 120sqr ft bedroom (960 cubic ft) with my wife and two dogs for about 8 hours each night. No amount of filtration will pull any CO2 out of the air. Is there an erv out there that can handle this kind of load in such a specific space while also working as a whole house solution?
I'm imagining a standard erv that's maybe 120 CFM but is split between bedroom, living room, office, etc. Etc. Which means something like 30 CFM going into the bedroom on boost mode. That means running for those 8 hours it only moves 240 cfm out of the room leaving most of the CO2 there. How do you address an issue like this?
We have companies here with economizer setups on the home ventilation. However its more about features to advertise than practicality imho. We call it summer kits. I made my own auto version but its all about keeping the ventilation running than trying to cool the house.
To retrofit our house, I settled on a Fantech HRV with ECM fans, and an ecotouch IAQ controller. It's great how it can be set to some reasonable lower CFM speed, but it adapts to extra activity based on the VOC sensor in the controller. It's fun to watch and seems to being working well in that regard. Question: do you know of an _outdoor_ incoming air sensor controller to detect if the outside air is poor (ie: wood stove smoke, not very often, but sometimes.), and use that to trigger recirc mode or turn off the HRV, so as not to bring in poor air. I believe the Build Equinox CERV has this type of feature, but I haven't seen any others.
IFTTT could be used based on local weather data and pollution but it wont tell you when your neighbor is using dryer, doing barbeque or he just remote started his car in the morning to warm it up :D Also VOC or CO sensors wont pick this up. I with that kind of sensor exist!
what about the CERV2 system by Build Equinox? Doesn't it use sensors to monitor the indoor air quality and "dilute" with outside air as needed... and only when needed?
I'm currently in the design phase for my home's HVAC retrofit. The house is ~1200 sqft in Phoenix, AZ. My plan was to use a mini-split with between 1-3 heads for heating and cooling. Then I was planning on using a small commercial ducted HEPA filtration system that would act as an air handler of sorts as well. It would have one centrally located return duct and then the supply ducts would be out in all of the rooms. In addition to this, the ERV would have exhaust vents in the kitchen, bathrooms, and laundry with the outside air dumping into the HEPA supply side so it is filtered before entering the home.
You mentioned people tweaking their setups based on the environment. I believe the system as described above wouldn't need to be tweaked, which I think is ideal for the average human. We just have too many other things to deal with in the average day. What I would like though is for the ERV to have a way to automatically bypass the core between certain temperatures. For example, it may be 90 for the high here in the fall or spring but the lows may be in the 60s. If the ERV were to bypass the core once the outside air is cooler than inside until the inside hits a set temperature that would save a ton on cooling here. I do believe this technology exists, just not at the price point I'm at. I could see that same device that does what I described being used to let less outdoor air in on high pollution days, but if you dump that air into a filter first does it really matter all that much? I suppose it would prolong the life of the filters.
ERV core bypass is currently available. i know of one brand that uses it as an economiser. as you describe. is it actually worth it ???
Out door pollution is an interesting question. it depends on what one you measure. ventilation air all comes through a filter anyway. so some pollutants are filtered out. i highly recommend using a separate filter and not relying on the built in filters of the erv.
@@tweake7175 Yeah, my plan was to dump the outside air from the ERV into the return of the filtration system so that air runs through the HEPA filter and then uses that ducting to reach the rooms.
@@robertcrowley9677 you can, but that doesn't remove the need for filter at the inlet. i would still run a hepa on the incoming supply before the erv. that keeps the erv core clean and you have clean air coming in regardless of what is happening with the other system. it builds in some redundancy. i'm also a fan of piping the fresh air direct to the rooms rather than the dump it in one room and circulate from there.
you want the ventilation system to still distribute clean fresh air regardless of what the hvac or filter system is doing.
also keep in mind of any airflow short circuits. whats the easiest route for the airflow to take. i've seen it where the ventilation bypasses the hvac and goes straight to the ventilation exhaust.
So you have taught us quite well about sizing HVAC, sizing circulation/cleansing, and sizing balanced fresh air, but not everyone has the luxury of treating them as separate systems like in your awesome house. It would be great to understand how to combine them all if you have to (coupling return vs supply and so forth) and what the priority would be for separating them if you could pull just one out on its own.
You do not put lipstick on the pig . Use multi split and small ducts for HRV
Ooh, video forthcoming about why I actually don’t advise that, Andrey! And yes, Todd, video forthcoming for you too.
@@andreycham4797 I submit that your proposal falls far short on filtration.
Note: in the background the door to the great outdoors is propped open with a 5 gallon bucket - that's real Hi Tech fellas!
What can cause double gas usage bill due too furnace?
Atmos replaced gas meter, the AC unit was checked by by an A/C engineer - a new air filter was installed-
all the vent joints seem secure?
But seeing double bill in winter 😮any idea ?
It’s as if the furnace is using double gas but not being felt in rooms. But i have been told by a/c engineer the furnace would shut down.
The air from vents don’t seem to blow abs when they do it seems cool air except in master bedroom.
Any suggestions ?
All this wonkiness is great, but in reality most of us have been living our whole lives in conditions much worse than this. So the question is where is the sweet spot between a 5 ton unit running continuously which none of us can afford, and reasonable air cleaning that won't break the bank?
Well, stay tuned, Larry, exploring options is what this channel’s about
I want titanium window screens . Like 2 , for my sunny rooms . Any leads ?
What sensors should I buy to test indoor air quality?
Yes!! This is all great info. and as an engineer learning a lot. I'll continue to research your videos, and I sure hope you address how to best measure the effectiveness of our system. I know I need an O2 sensor and the oxygen is important. Also of course temp & humidity sensors but I don't trust those electronic VOC sensors for their accuracy. This sure is a complex project I'm taking on in a small house that was built in the 40's...here in LA. I'm literally doing everything possible to make it a clean room like a hospital. MOLD...every home especially this one has it somewhere in the walls, ceilings or below and this alone is quite a challenge. I'll know when I've reached a clean livable place when I'm not congested 24/7 in here.
Fan “on” almost ALWAYS produces elevated humidity and microbial growth I. The southeastern us - during warm humid weather and no fresh air intake.
Dehumidifiers are important
Critical
Thanks for the video. Regarding the fresh air component, I try to control my system to maintain about 600 ppm max CO2. This takes ~50 cfm of outside air per occupant. However, in order to reduce the VOCs to acceptable levels it requires an enormous amount of outside air. Is this typical or is there something else I need to consider to reduce VOC level? Thanks.
I know Corbett hates air purifiers but Field Controls DUO-2000 will get it lower very quickly
Keep, as much as possible, VOCs out of the house to begin with. Use the safest unscented cleaning products, don't use incense or scented candles, out gas stinky stuff outdoors, use a kitchen fan hood when you are cooking.
What are some web sites you use to research the various brands and specs of available ventilation systems?
Broan-Nutone.com
AirCycler.com
Renewaire.com
You could check out HVI.org too, but their databases tend to get a bit labyrintine.
Fuking awesome. Kick ass
✊🏽
So, what kinds of pollution and levels of pollution are you looking for and what levels do you want to stay at or below, or vice-versa, at or above?
2 questions. 1) How do you recommend modeling the airflow in a house when designing the ventilation system? ideally I want a simulation and optimization of the vent placement room by room. 2) If I do not want to splurge on ventilation now but want to put in some duct work for the future, any recommendations?
I don’t know why you’d need a simulation, it’s fairly simple math. It’s a pretty deep topic though, check out our Ventilation playlist or book an hour consult with me and we can make your plan.
@@HomePerformance Well I guess I wonder about the fluid dynamics of the ventilation - where do the vents go in the room to ensure the air quality? If the supply and return are too close, presumably it's not good, but what are the metrics? Seems like compute is cheap enough these days that finite element simulations could be done to get precise answers to design questions. Maybe overkill, but I'm curious what the gold standard is for modeling and simulation for ventilation design.
@@ThisIsNotAVideo wow, lots of words man. the further the supply and the return are away from each other, the the more space is influenced by the flow differential. This is high school shit. You dont need computational fluid dynamics and Navier-Stokes equations ffs.
Hey Ray Man, I hear where you’re coming from, but the good news/bad news is we are literally making this stuff up right now. We are the ones we’ve been waiting for.
@@theastuteangler High school shit...lol...I don't remember learning this in HS or by any of our horrible US doctors in allergies or immunologist my entire life. We live 75% + indoors yet our total crap medical system has done ZIP in this research for the American people. Doctors are supposed to help people with their health...right? All the doctors I've know, and a lot of them, just care about how much they're making and all have their trophy wives or in my cousin's case trophy new 20 year old girlfriend every few months
corbett do you have merv 13 or 16 filters in your home ?
I have 13
Hello,If you have a leaky house and installing a erv is not a option,would be a positive fresh air supply system a good option? Thanks
My understanding (and someone who knows more than me will likely comment too) is that you still want the ventilation balanced to try and avoid pushing or pulling air through the leaky house. Just forcing the outbound air out through all the cracks and crevices doesn't seem like a good idea based on what I've learned so far.
Postive pressure is recommended unless your in cold climate where you have to run negative pressure to avoid moist inside air hitting cold walls and condensing or frosting. Balanced systems are pointless when there is more air leakage than ventilation air flow.
Thanks,I’m in Fl,humidity is a concern
Yes. Fraction of cost, and dispenses with the additional filters and heat exchanger, which need continual maintenance.
When a house is deemed to be leaky, based on a blower door test under 50 pascals of pressure, it doesn't mean that the home has adequate ventilation. That is a myth. When it is calm out the natural air change can be minimal, and the indoor air quality can be poor. I agree that standards established like ASHRAE 62.2 are nonsense. Air quality needs to be monitored and controlled based on the air quality, not the size of the building and the number of occupants. Without a demand controlled ventilation system, every home is either over ventilated or under ventilated. A ventilation system should be as close to being balanced as possible, with a slight positive pressure in humid climates and slight negative pressure in cold climates. The problem with a strong pressure difference is in all climates there are certain conditions that a strong pressure difference can create a problem.
Good morning. I am looking for a profesional design company for a new house in south texas. Do you have a recommendation? Thank you
homediagnosis.tv/pro
Where is this 5-6 air turnovers (a turnover defined as passing the equivelent enclosed volume of air through the filter) per hour coming from? Is this based on Gage and Bidwell law of dilution? Just because you pass the equivalent enclosed volume of air through the filter, doesn't mean you have filtered 100% of the enclosed air. Gage and Bidwell would say only about 63% of the air has been passed through the filter in the first turnover do to mixing of the air. At the 5th turnover you have filtered 99.3% of the air and at the 6th, you are at 99.7%.
I’d say the effectiveness would have a lot to do with room and duct arrangement. 5-6 per hour was used in COVID classrooms as an ideal for standalone air cleaners with no ductwork at all.
@@HomePerformance I would agree supply/return size, relative position and velocity will impact the turnovers required to achieve filtration of 90+% of the space air. I was curious as to where the 5-6 for standalone filtration in a covid classroom came from. Assuming there is science and not conjecture backing up the recommendation.
Hmmm… running the ac system fan full time with leaking duct work or ductwork which passes through an unconditioned air has proven to be disastrous. Also, running the fan full time after a cooling cycle will turn it into a humidifier. No bueno. Not all houses are airtight and thoughtfully built.
It’s a system, absolutely
Isn’t this decide by AHJ? You guys make this video for them?
Who is AHJ? We don’t make videos FOR anyone, we partner with others when it serves a story we’re excited to tell.
@@HomePerformance authority having jurisdiction.
Oh my god please no. Even the people who write the codes have no idea about indoor air quality generally.
Jk . You house air is bad. Probably even if you really think its good and spent a ton of money on filters . Unless your next to a coal plant outdoor air tests better. Its another infinite energy problem