More Building Science
Here we are early in another winter. Because of the weather, most of us spend more time indoors. And the people with whom we share those indoor spaces are getting colds, flu, and other winter maladies. So, what you can do to improve your indoor air quality (IAQ) during these cold, dark months of breathing a lot of indoor air? Well, I’ve got a few tips. Below are 7 good IAQ practices that can help you breathe a little easier as you wait for the return of nicer weather in the spring and summer.
1. Use the range hood
The holidays may be over, but many people are doing more cooking at home now since restaurant meals have become so expensive. And, as you may know, cooking is responsible for a lot of the indoor air pollutants in homes. I certainly see it in my IAQ monitors. There’s an easy-to-identify cooking spike in the graph of volatile organic chemical (VOC) measurements most evenings in my home. And that’s with the range hood turned on.
The biggest reason, though, that range hoods don’t help indoor air quality more than they do is…drum roll, please…they don’t get turned on. Yep. The number one problem with range hoods is that the cook doesn’t flip that switch. So while you’re cooking—especially if you cook with gas and even more especially if you bake with gas—hit that switch, please. Your body will thank you.
2. Turn on bath fans
Using the range hood helps not only to remove pollutants at the source, though. It also brings in outdoor air (through random leaks in the building enclosure, but that’s another issue) to dilute the pollutants that don’t get pulled up into the range hood. So you can run the range hood even when you’re not cooking to help with pollutant levels. And then turn on bathroom exhaust fans to increase the ventilation and help with other parts of the home.
Yeah, you’re not going to dilute indoor air pollutants if the air you bring in is worse than the air in the house, so check the outdoor air quality first. Just go online and search for something like “air quality near me.” Or just look at the weather app on your smartphone.
Exhaust-only ventilation isn’t great in humid climates in warm weather, so this advice works for most people in winter. If you’re in Miami and it’s 86 °F (30 °C) with a 70 °F (21 °C) dew point, you’ll want to moderate the amount of exhaust ventilation you do. But still use the range hood when you cook!
3. Set the thermostat fan to “on” (maybe!)
Speaking of humid climates, setting the thermostat fan to “on” is generally a bad idea in warm, humid weather. You can end up with high indoor humidity and mold problems. But the nice thing about winter (for those of us in the Northern Hemisphere anyway) is that the weather is cooler and drier.
So you can set the thermostat to “fan on” instead of “auto” without worrying so much about problems with high humidity. Doing so can help your IAQ by providing more filtration of the air. One thing I didn’t include as a separate tip in this list is having a clean filter. So before you change that fan setting, you might want to change the filter.
Caution: Even though you’re not likely to add moisture to the home by doing this in winter, it’s possible that other problems could make this tactic a bad idea. If you have significant duct leakage, you could make the indoor air too dry. You also may be more likely to put carbon monoxide into your home. This strategy is mainly for heating systems with good duct systems and good filtration.
4. Use standalone filtration
If you’re still worried about not getting enough filtration with the heating system fan running continuously, set up some standalone filtration systems. There are plenty of those available commercially. And if you’re reading this blog, you probably already know about the Corsi-Rosenthal box, a DIY box fan air cleaner with high-efficiency filters and a high clean air delivery rate. These devices are very good at removing the tiny invisible particles floating around in your indoor air.
5. Monitor carbon monoxide
I would be remiss not to mention carbon monoxide (CO) here. It’s a colorless odorless gas that can kill you at high levels. The standard CO detectors won’t alarm until the level is high enough to put you in the hospital. But you could have lower CO levels for days or months that can give you headaches, dizziness, weakness, rapid heartbeat, shortness of breath, chest pain, or disorientation.
The best thing you can do is to get a low-level carbon monoxide monitor. The standard CO detectors will allow you to breathe levels of carbon monoxide that you really don’t want replacing oxygen in your blood.
6. Monitor carbon dioxide
Carbon dioxide (CO2) is a different thing altogether. It’s not poisonous the way carbon monoxide is, at least not at the levels you’ll ever experience at home. It’s an indicator of how much dilution you’re getting for the indoor air. Most of the carbon dioxide in your home’s air is (or should be) the result of people breathing.
The air that comes out of your lungs has about 40,000 parts per million (ppm) of CO2 in it. That quickly gets diluted with the room air, but if there’s not enough air exchange with outdoor air, the indoor CO2 level rises. That indicates that other pollutants may be building up in your indoor air as well. The level most people take as threshold for indoor CO2 is 1,000 ppm. When it goes higher than that, do more of numbers 1 and 2 above. If that still doesn’t help, consider the last tip below.
7. Open windows
If the weather outdoors isn’t too bad, you can crack a window or two to get more air exchange and dilution of pollutants. Yes, you may have to run the heating system more and thus use more energy, but health is more important than energy use. Besides, if you have a bunch of people over, they’re helping you heat the house, too. Each person gives off about the same amount of heat as a 60 watt incandescent light bulb.
There you have it. A little roundup of things you can do to improve your indoor air quality during the winter. For more good info on IAQ, see the articles below, the EPA’s indoor air quality pages, and ROCIS (Reducing Outdoor Contaminants in Indoor Spaces). Also, check out the new podcast called Indoor Air Pod. I just did an interview with them last month, and it’ll be out sometime this month.
Here’s to safe, healthy, and happy winter!
____________________________________________________________________
Allison A. Bailes III, PhD is a speaker, writer, building science consultant, and the founder of Energy Vanguard in Decatur, Georgia. He has a doctorate in physics and is the author of a bestselling book on building science. He also writes the Energy Vanguard Blog. For more updates, you can subscribe to Energy Vanguard’s weekly newsletter and follow him on LinkedIn.
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17 Comments
Range hoods over islands are almost always useless. Put your stove against a wall!
Snorkels on islands are even worse
True. Also, recommended width for hoods on islands is for additional extension beyond the cooktop (see HVI website), which the image in this article does not show. I don't know of a good fix for island hoods, other than to install vertical range hood extensions or set up temporary air shields on the counter (See my slides & presentations at ROCIS.org Kitchen Range Hoods site).
The best location for a stove & hood is in a corner, based on some Dutch research.
I'm surprised there was no mention of needing make-up air, especially when you turn on the range hood fan. Since a lot of them exhaust over 400 cfm you can cause dangerous back-drafting within the house.
rockies63: I'd say the majority of range hoods do NOT exhaust at more than 400 cfm. And yeah, it's an important issue, but I can't cover every aspect of every topic in every article. Besides, what kind of discussion would that leave for the comments? :~)
I did write about makeup air recently, and it will be here at GBA before long. You can read it at the Energy Vanguard Blog, though. Here's the URL:
https://www.energyvanguard.com/blog/range-hood-makeup-air-the-basics/
You mention using the range hood when baking. Does a range hood effectively capture particulate from the oven? I am pretty skeptical of that.
Great article as usual Allison :-)
@thispage, we have a fully automated range hood system over the induction cook top which varies CFM based on the induction power use. Make up air is provided via the HRV system which runs in an asymmetrical profile during cook top use. This HRV supply is on the main floor, centrally located, on the same floor as the kitchen. This means that air is intentionally biased to exit the home via the kitchen exhaust when the cook top is in use. PM2.5 levels in the home therefore remain very low when cooking.
Allison makes a good point in that rated CFM is pretty much at zero static and nowhere close to rated at install. That said, I've found that capture rates with a standard converted hood, inline ECM fan, 24" over the 30" wide cook top are quite good at 110 to 160 CFM (measured at the hood). The system dials in extraction anywhere between 60 and 160 CFM (max) depending on power use by the cook top. The system works astonishingly well based on PM2.5 data over the last year or so.
Conversely, using the wall oven currently does not dial up the exhaust hood or supply air via HRV, and PM 2.5 rates will rise often from 1 ug/m3 to 70 ug/m3 on the main floor with oven use. I am looking for a way to tie this into automation without spending another $200 plus on a 220V power metering Zwave switch. I'm doing this because after 18 months of data on interior AQ, oven use really correlates with the PM 2.5 jump.
You really don't need all the IAQ sensor data to figure this out. Just use your nose. If you can smell cooking outside the kitchen, your setup is not ideal.
Dennis - Very interesting! How is your make up air provided by HRV? I thought the CFM would be too low.
I am aiming for 400 CFM on high speed for the exhaust but obviously it is mostly used on a lower speed so we could just open the window if using high speed for anything super smoky. I wonder if we can also do something with our ERV for make up air because the hvac installer quoted $8,600 CAD for the exhaust and active make up air unit that our engineer specified originally due to the wood oven/fire nearby.
I must find out what this Zwave switch is, would that be a wall switch in your kitchen to activate this imbalanced mode on your HRV so you can flip that on when using your oven? If so, $200 doesn’t seem too bad!
Izzy, I misquoted that switch it's "only" $144 CAD. Aeotec Zwave Heavy Duty Appliance Smart Switch 240V ; Part Number. ZW078 The induction cook top is connected to that switch, which also reports power use. The ECM inline kitchen exhaust fan is controlled by a Zooz Zen54 0-10V dimmer. That fan is a Terrabloom 6", with a metal housing.
A Hubitat automation hub wakes up the fan and controls it's speed depending on what Aeotec is reporting for power. The dimmer setting for the fan is (Cook top watts * .02) +40. The dimmer setting is a value from 0-99 that controls the fan speed. Send the value 50 to the fan and it will run at 50% speed or so, but only use 15-20 watts at that speed.
I also "pop the ball" on the Broan Ecovent hood by running the exhaust fan at 100% for a minute if temps are below freezing. Frozen hood flaps are a problem at our winter temps which get to -35 C. Higher air pressure at 100% fan speed pops the ball quite nicely, even at -20 C. Cool stuff you can do with a $100 automation hub!
The ERV/HRV supply air is a lot tougher to do with an out of the box product. I've removed the motor from a "dumb" HRV and am using two ECM fans (again controlled by the Hubitat) which allows me to run the system in an asymmetric supply setup while the cook top is in use..also when using our high efficiency fireplace. I'm finding that 60 CFM supply (via HRV) works great for the kitchen exhaust, which runs (measured at hood) 80 to 160 CFM out. Our home is a heavily retrofitted 1905 vintage build which has gotten quite tight over the years, to the point of IAQ issues.
I've written a fair bit about the newer (as in last 2-3 years) possibilities controlling ECM fans with off the shelf 0-10 volt automation bits: https://community.hubitat.com/t/success-0-10-volt-control-of-ac-infinity-or-any-ec-fan-motor-using-leviton-zs057-d0z-zigbee-dimmer-or-zooz-zen54-zwave-0-10v-dimmer/104450
This is a game changer IMO for improving IAQ while lowering energy use, particularly as IAQ sensors become cost effective and reliable. I'm using an Ecowitt WH45 and a few AirThings Wave Plus to report air quality back to the Hubitat device so as Allison suggests, am monitoring for CO2, PM2.5, VOC and Radon.
You must be an engineer… I only partially understand this, but I think this is exactly what I wanted to do I just totally lack the technical knowledge to do so.
I was planning to buy AirThings and I had a hope they might some day be integrated with the HVAC system. I was looking at Aranet sensors too and they look really good. Endless possibilities but sadly I don’t know how to do anything myself in this regard.
Do you happen to live in southern Ontario? I’m not sure who will help me with this, but I’ll save your response in a note and see if it’s something I can ask our mechanical engineer, or HVAC installer, or electrician about…
I also need to find out who runs GBA because this website is pretty terrible and the need for a notification/alert system for comments is very high!
The comment system is a bit limiting for sure. A forum would work better, particularly to search.
Not an engineer, and sadly, about 1400 kms away from TO in Northern Ontario :-(
HVAC guys will not likely help as 99% of the guys are “on the clock” and unless there are prepackaged systems with manufacturer support, it’s not practical or profitable. Broan’s “AI” system is working to this end, but there is still a largely untapped market IMO for more efficient IAQ systems.
re: #1, range hoods: thanks for reminding folks to use the hoods. But many are not very effective. We suggest putting a reminder label on the hood for users, among other things.
More info (and resources) on how to improve hood effectiveness, including easy steps, @ ROCIS.org Kitchen Range Hood Guide & webinars, https://rocis.org/range-hood-guide-update-jan-2024/.
See also, new health risk assessment re: indoor pollutants: indoor PM is the highest lifetime risk: Morantes et al 2024, ES&T, https://pubs.acs.org/doi/10.1021/acs.est.3c07374
BTW: nice graphic, but the fumes should be spilling out around the island hood, per your comment and common experience.
It's interesting that humid climates are mentioned, but there is zero mention of any IAQ issues related to super dry air when it's cold... Tips on humidifying old homes would be great to share!
People may also want to check the power used by their furnace fan before turning it to "on," it turns out my regular old Carrier furnace fan burns 1018 watts, which would cost over $100 extra per month to run 24/7.
A number of newer thermostats have settings that run the fan intermittently, which can give you a lot of the IAQ benefits with much less cost.
@doug , with the caveat that this power use reflects a furnace with PSC motor, not an ECM. The NRC here in Canada ran some tests in their twin home project with PSC vs ECM. ECM power use in circ mode (around 432 CFM) was 16.7 watts.
https://nrc-publications.canada.ca/eng/view/accepted/?id=97997ac4-834d-44ff-a5ec-fd4a3f890d39#:~:text=The%20power%20use%20of%20the,and%20490%20W%20in%20heating.
We updated to a high efficiency furnace with ECM motor 10 years ago and although the furnace is rated much higher than the outgoing unit at around 98% efficiency, the biggest difference wasn't in gas use, but rather power use.
Doug Horgan and Dennis Wood are right to consider the increased electric use of running air handlers continuously: https://inspectapedia.com/heat/Electric-Side-of-Gas-Heaters-Pigg.pdf
PSC furnace blower motors "averaged about 500 watts of power draw, compared
to about 100 watts for the ECM models."
For up-to-date info on range hood and air handler solutions: https://rocis.org/building-solutions/ (ROCIS:Reducing Outdoor Contaminants in Indoor Spaces)
I also recommend reading Don Fugler's research on what furnace filters can actually accomplish: https://www.researchgate.net/publication/236433764_Effects_of_improved_residential_furnace_filtration_on_airborne_particles (Activity of people is more important than furnace efficiency. Portable air cleaners such as the DIY box fan offer some advantages.)
More of Don Fugler's research history:
https://www.iaqradio.com/blogs/659.pdf
Residential furnace filters (1999): https://publications.gc.ca/collections/collection_2015/schl-cmhc/NH15-318-1999-eng.pdf (Take your shoes off when entering the house. Use a vacuum with HEPA filtration)
RE: Turning on kitchen range hoods: the other big hurdle is that most of the hoods on the market are NOT very effective and/or quiet. So there may be a will, but not an easy way to get good exhaust ventilation with most installed vented/ducted range hoods in homes.
Of course, unvented/recirculating range hoods are basically worthless too.
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