We typically find that installing a remote blower for a vent hood is sufficient without the need for any add-ons to mitigate noise. I suggest a try-it-and-see approach. Install the hood and remote blower, and determine if you need to do anything else to mitigate the sound level in the kitchen.

Remember some people are more sensitive to sound than others. My husband hated the sound of the dishwasher after dinner or the washer and dryer running (laundry room door closed) because of the configuration of our house, semi open floor plan. I, however, wanted to hear the buzzer when the dryer finished and the sound of the dishwasher was minimal to me. Both of us were unpleasantly surprised when we replaced our old oven with a new double oven because the fan was so much louder than the old oven. Carpet, upholstery, draperies all absorb some of the sound, so what I would choose for my house, and insist that it is quiet, might not suit your family.

I can assert that my Wolf Pro Island hood with 10 sq. ft. of entry aperture, ducted to the roof via 10-inch duct through a Fantech silencer to a Wolf/Broan 1500 CFM (zero static pressure rating) blower is quiet enough to converse under and across the hood. Dominant noise is baffle hiss. Blower fan blade turbulence noise is not noticeable.

I did not test this with the silencer absent. Noise without the silencer will very much depend on duct turbulence (should be OK with 10-inch duct) and fan blade tip turbulence of your particular blower choice. Note that the Fantech silencer is 14 inches in diameter, and I am unclear whether this would be visible in your configuration.

Your new 36 inch cooktop needs at least 42 inches of hood length, and as much front to back depth as is commonly available.

The quietest hood per bit of performance possible will be a commercial hood w/ either an inline or exterior mounted blower and a silencer. That's what I did and the results have been quite good.

More: https://www.houzz.com/discussions/5745986/commercial-range-hood-install

I said 'bit of performance' above because CFM is a poor measure of hood performance. Our hood will do better with capturing and exhausting effluent at 300 CFM than most consumer hoods at 600 CFM simply because of the large open containment area. Our's is also silent up to about 700 CFM.

Thanks everyone. I had read kaseki's past posts but didn't realize the configuration included similar Wolf parts, so that makes me feel a little better. opaone's comment is relevant -- I wanted to use a commercial hood but a number of factors (mostly remodeling cost) have stopped that.

I'm most worried about going through this effort and expense and ending up with something that is more loud than what we have now at the same level of performance. The worst case is a cost-overrun with that outcome. I wish a better framework for making my decision was known.

This is not technical info but as an aside, we just installed an integrated 52” 1200cfm Prizer hood and for the first 3 months it did not have a surround, ie it was just the exposed hood and 10” duct.. When we added the surround a few weeks ago, we had it well insulated inside and it made a big difference in sound. Pic in my profile “blue star time” ideabook.

spurpura wrote: "I wish a better framework for making my decision was known."

The best framework for almost any technically complex integration task is the systems engineering process, for which there is an immense body of literature available on-line. Boiled down to the barest of minima, it requires that you know your requirements (performance, cost, appearance, etc.) before looking for parts that, in concert, can achieve them. Performance requirements are what I try to help with, but these are also derived from published information; I don't do computational fluid dynamics analysis to flow-down hood and blower component requirements, and neither does almost anyone else.

The most funded source of functioning kitchen ventilation system analysis is for commercial kitchens, and literature for measurements and analyses are also on the Internet. For example, look for California Air Resources Board reports. Efficient and effective kitchen ventilation understanding starts with the commercial kitchen suppliers. However, there are differences between residential and commercial requirements -- for example, having hood flow rates vary thereby also MUA rates vary -- that affect component selection.

I think it best that one start with capture requirements (hood size and volume), then volumetric flow rate requirements (CFM), then ducting and blower requirements (the CFM you get is not the CFM on the label). Next, MUA requirements are similarly determined. This process is recursive because, excluding safety considerations, the MUA determines the house pressure, which affects the hood blower flow rate, with determines the required MUA, ... .

Agree totally with external blower and inline silencer. We've had that installation for over a decade and have loved it. Super quiet. Many years ago in the GardenWeb era, I started a thread about hood sound levels with some fun comments, including those from the perpetually present Kaseki:

Vent hods and noise

Sounds like you're on the right track. I think the silencer is important given the relatively short run of duct to your blower, and it's cheap enough that it makes no sense not to install one.

It would seem to me that going from a 250cfm blower to a 1200cfm blower will be a big performance improvement.

If the external blower is just on the other side of the wall, I don't think an inline silencer will do much for you.

@weedmeister, you may be right that the silencer will have minimal effect. However, in consideration of the project goals and the cost, I have to buy it. Because buying and having extra ducting and a silencer is a minimal cost just compared to the cost to get the installation crew to show up for the day of work this is going to take to install. And, if it even drops a few Db, I will be ok with it.

My strategy, in general, is to buy a bigger (and efficient) CFM solution and run it on low most of the time so that we don't hear it. High would be a rare emergency situation. Larger fan blades run on low RPMs should be quieter.

@kaseki, I appreciate your answer and rigor. I have MUA solved. I have an $11k ERV system with pressure sensing that can provide make up air at a combined 7000 CFM to 3 different points in the house.

If there is enough room (duct length) for a silencer then it will make a significant difference that is noticeable to most people.

@kaseki, I appreciate your answer and rigor. I have MUA solved. I have an $11k ERV system with pressure sensing that can provide make up air at a combined 7000 CFM to 3 different points in the house.

@spurpura, what ERV system is this?

My strategy, in general, is to buy a bigger (and efficient) CFM solution and run it on low most of the time so that we don't hear it. High would be a rare emergency situation. Larger fan blades run on low RPMs should be quieter.

You are correct but you have to be careful. Too low of air velocity reduces the ability of baffles to remove grease and other particulate matter from the air stream which can result in buildup in the duct, particularly at bends.

You can also get buildup on the fan blades which makes noise much worse due to increased turbulence and the fan becoming unbalanced (which also shortens the life of the motor). Your fan should have a minimum speed below which it no longer effectively throws grease off of the blades.

Both of these can be fire hazards.

"make up air at a combined 7000 CFM to 3 different points in the house." Wow!!!

Also, @queen e's comment reminds me of another suggestion for suppressing noise: duct wrapping. Various blower vibrations can be ducted mechanically down the duct and be audible at the hood. I wrapped my ducting, and the silencer, in a brand of automotive door/floor damping material, Evercoat "Q-Pads." These are very heavy plastic like sheet with adhesive on one side, typically sold by the body shop departments of automotive parts suppliers. To assure long term retention, long Ty-wraps are used circumferentially.

Later, a commenter here also raised http://www.acoustiproducts.us/ as a potential source of acoustic damping products. I have no further information on their offerings.

There may be some confusion about ERVs.

In general, ERVs are designed to ensure indoor air quality by introducing a quantity of fresh air and exhausting an equivalent amount with some energy and moisture transfer in the process. Typically, ERVs are sized to provide 0.35 air changes/hour for a home. A rule of thumb is 50 cfm/1000 sq. ft. of living area, but there are alternative methods for sizing them.

A 7,000 cfm system would serve a really, really, really big house--the kind Mark Bischak probably owns to give his spouse adequate "space." Because their air flow is balanced, ERVs don't serve to supply a volume of make up air to mitigate the volume exhausted by a large vent hood.

@opaone 2 Ultimate Air ERVs and 1 Panasonic. We're testing the units to decide which we like and will standardize on it. We have 2 separate HVAC systems and a dedicated MUA solution with MERV 13 filtering. 2 HVAC systems comes in handy right now because a sick person can be isolated (with their own air, mixed with fresh air without humidity increase or significant energy loss) in one self-contained area of the house. We haven't tested yet whether the filters will work sufficiently If wildfires generate too much smoke outside. But even in that worst case, we don't use the hood and the ERVs can be shutoff to stop mixing outdoor air.

@opaone "low speed" for a remote 1200 CFM blower is going to result in a lot of air flow -- more than we have now in total. We've priced going even higher (up to 2500 CFM) but I just think it's overkill. I didn't even consider grease buildup on the remote blower fan blades and neither have any of our candidate installers. It seems like the solution to that is to end the session with a burst of higher output ventilation.

In general, my impression is that the installers think we're crazy for trying to reduce the noise level to as close to 60 dB as possible, but they're happy to take our money.

@Charles Ross Homes high end ERV systems (including a mix of other parts and computer and analog controls) can control the mix of indoor and outdoor air on the fly. Under sealed home conditions, this would result in positive, negative, or neutral pressurization for the home. When the vent hood is taken into consideration (providing a source of negative pressurization for the home), the ERV system can be set to mix more outdoor with indoor air to achieve positive/negative/neutral pressurization (as desired). High end systems can output significantly more than 50 CFM, but you're right that many people have not used them for MUA in the past.

@Charles Ross Homes I should also note that a part of my installation cost is offset by a benefit for the HVAC vendor -- they will get a customer testimonial and a YouTube advertising video out of the documentation of our HVAC install, including documenting the flow rates and how to mitigate the air flow rates in the house from this type of setup.

@spurpura, did you mean 700 CFM of ERV or 7,000 CFM? If 7,000, why? How large is your house?

@spurpura, the system you described is one that is intended to address two different HVAC needs. Combining the two may sound efficient, but doing so has implications for increasing equipment size, complexity of controls, reliability, and cost.

Energy-Recovery Ventilators and Heat-Recovery Ventilators (ERVs and HRVs, respectively) are designed to promote indoor air quality. Typically, they exhaust a quantity of stale air and bring in an equivalent quantity of fresh air (i.e., they are pressure balanced.) There are a variety of control schemes. I prefer continuous, 24/7, steady-state operation. At 50 cfm/1000 SF of living area a 4,000 SF home would need a 200 cfm system. That's about the same flow rate produced by (3) 70 cfm bath vent fans.

By contrast, make-up air (MUA) systems associated with high-capacity cooktop and range vent hoods are needed only when those devices are operating. For residential applications, that might be an hour or less each day. MUA systems are intended to mitigate the hazards associated with depressurizing a home--mainly back drafting of combustion appliances, but also introducing air into the living space from unintended sources like attached garages. A pro-style vent hood at 1,000 cfm would require 600 cfm of make-up air to meet code in our area. That's three times the size of the required ERV or HRV to maintain air quality in a 4,000 SF home. So, for this example, combining the two systems results in equipment that's three times the size required 23+/- hours/day and requires the system to operate efficiently at a 3:1 turndown ratio 23/24 of the time.

In our coastal Virginia climate zone we've found installing a motorized make-up damper operated by a simple pressure switch in the vent exhaust duct and a duct introducing make up air in proximity to the range hood works well without the need for any supplemental heater or sophisticated controls. It might not be a good solution in Minnesota, but simple is usually less expensive and more reliable than complicated.

@Charles Ross Homes thanks. I don't really want to get into a debate about our multi-zone HVAC system. We have allergies. We have pets. We have washer/dryers. We have a small data center generating heat that must be expelled. We have a range hood. We sometimes have high smoke levels in the outside air from fires. We have physically separated areas of housing that would require impossible duct runs. And, when I exercise in the house, the 1,000 sq ft area can have dangerous levels of CO2 in less than 30 minutes. If 2 people exercise at the same time, it's 15 minutes. So, yes, running a modern house with people quarantined in it is complicated.

A few thoughts...

The numbers @Charles Ross Homes quotes of 50/1,000 ERV/HRV is a typical target in the U.S. But is often quite inadequate in an average new home. Far worse, this is often done with stale air pulled from the return duct and fresh air introduced in to the return duct.

A better solution, and what is used in other countries is to have stale air pulled from kitchens and bathrooms and fresh air introduced directly to bedrooms (as the biggest IAQ problems in homes is in bedrooms at night). This also combines the functions of bath exhaust and ERV/HRV so reduces or eliminates the wasted energy of separate bath exhausts. Unfortunately most U.S. HVAC people are still stuck in a 1960's mentality about this stuff.

7,000 CFM of MUA + ERV/HRV seems excessive and a huge waste of energy unless this is a massive house (in which case it would likely have more than just two HVAC systems). In a most cases 140CFM/1,000sqft of ERV/HRV will result in maximum fresh air for high occupancy (8 people/1,000 sq ft IIRC) and I believe 110 for average occupancy (4 people / 1,000 sq ft). Any more than that does nothing to improve IAQ nor help w/ allergies and only wastes energy. The exception would be something in the house that produces very high amounts of VOC's.

And then there is the question of what exhausting applications exist that require that much MUA?

You mentioned increasing CFM on your range hood. That will have little to no effect on anything but ego and the amount of energy wasted. High CFM's, above about 1200, sound impressive but are largely useless except in large commercial kitchens. High CFM's will not overcome poor hood design that lacks proper capture and containment area. (Well, they will but it takes massive amounts like 7x to overcome a 3" difference in aperture size).

Finally, wanting as close to 60 dB (I assume 'a' but could be 'c') as possible. 60dB(a) is still quite loud and would be unacceptable in many commercial kitchens. For reference, that is twice as loud as our hood on full (1400 CFM blower that produces actual measured 992 CFM @ 53.6dB(a)). Our old VAH was 54dB(a) at a rated 150 CFM (actual 64 CFM).

Possibly you have a good reason for needing that amount of ERV/HRV+MUA but I can't figure out what that would be.

My purpose in starting this thread was to break through the noise of information available from installation professionals for range hoods and blowers. The advice is all over the map and (of the 7 installers I've interviewed), not a single one would commit to a contract that assures even a 60 dBa solution or better. Several told me I was crazy to expect to obtain that level of performance on high at 800 CFM (the Wolf recommendation for my RangeTop and its environment).

This isn't the first time that I've remodeled a kitchen. And the last time was equally as frustrating only around the purchase and installation of a range hood/blower. All of the other kitchen components perform exactly as I've expected based on their specifications. The range hood market appears to benefit from significant consumer confusion.

Responses so far have basically agreed with my original assessment: maximum hood width/diameter capable for my installation, 10" duct work, and a 1200 CFM remote blower and (if possible) the silencer (muffler). The forum added that other sound dampening materials might also be helpful.

I agree that (based on everything I know right now) the 1200 CFM remote blower should be overkill. But the specs for the Wolf remote blowers show a clear projected efficiency gain for the 1200 CFM remote blower compared to the sub-1000 Wolf remote blowers. I am looking at Wolf primarily because of *service contracts preferences*. I'm sure other manufacturers provide equal and better blowers. My wife chose the range hood style she liked. A Wolf certified technician/installer interviewed for this job suggested a 2500 CFM blower solution and I thought it was likely a bad theory/suggestion, and the forum supports that conclusion.

For future people reading this thread, I'm not re-litigating the extensive and complicated research done for my whole house HVAC systems. The comments by others about my particular HVAC system, its requirements, or wasted energy associated with my system are completely speculative and uninformed because the people speculating about why it works the way it does and how it works do not know its requirements, its design, or how it functions. Relevant for this conversation, the functional requirement for the MUA system in the kitchen is to be able to supply the MUA needed to maintain neutral home pressurization for the kitchen under full hood load (which is likely significantly less than the rated 1200 CFM for the Wolf Remote Blower) on demand, regardless of what else is happening in the house and that this air (without compromising safety) should be filtered for pollutants. Also, I will not design a system that intentionally pulls untreated wild fire smoke into my kitchen. Thus, the filtering requirements. I have no concerns that my particular HVAC solution will be able to achieve the objectives for providing MUA in the kitchen for the Wolf 1200 CFM remote blower.

For those interested in the future, my HVAC vendor will have the ability to release sales related videos and full analytic documentation (including measured flow rates and energy loss) for their design of my HVAC systems *after* the system has been proven to achieve its functional requirements in my home. I'm not giving references before the job is done. As I mentioned earlier, at this time, a complete list of the actual components for my HVAC systems have not been decided upon (we are testing multiple versions of several components).

Thank you to everyone for your assistance.

Spurious information is what motivated me to research this area and continue to drive stakes into certain outlandish claims for performance as well as try to address lack of data for performance.

With respect to noise, for nominal residential purposes, the remote blower/silencer/baffle hood approach will provide reasonably low noise for operation. I don't know the actual noise level of my system; I have a sound meter but its previous owner modified it somewhat and I have never calibrated it.

More "extravagant" systems can be made quieter. Larger ducts, commercial blowers run at low blade tip speed, some careful selection of commercial baffles put into a compatible hood, might further drop the noise level relative to the residential nominal solution. (I am not aware of any noise data for commercial baffles, but manufacturers such as Flame Gard may have data that isn't published.)

Wow, this thread is fascinating - I appreciate everyone's thoughtful comments. I am really interested in the comment that spurpura made about exercise and air quality. I've lived in a 100 year old house that is very drafty for the last 15 years, and we are about to knock it down and start over again. Not sure what a new house will be like, but I appreciate that it will be more airtight. Trying to complete some research on a hood for a 48" Bluestar, and these links will help. Thank you all!

@Kim S, if you sit around with 7 of your friends for book club in a sealed house in the dining room with no air flow, CO2 will buildup in the room and the house. if you engage in running on a treadmill, stationary cycling, dance cardio, weight lifting, yoga, isometrics, or even just stretching you will likely expel CO2 at a higher rate than normal. The more fit you are (or the bigger you are) the more CO2 you can generate in an hour. What happens if the levels of CO2 increase? You can get headaches, feel tired, and have other significant symptoms.

The normal outdoor concentration of CO2 is, let's say, 400 ppm. A well ventilated indoor concentration is 400-1,000ppm. At 1,000-2,000ppm, you will hear complaints of drowsiness and poor air. From 2000-5000 ppm, people will experience headaches, sleepiness and stagnant, stale, stuffy air. They will complain of poor concentration, loss of attention, increased heart rate and slight nausea. 5,000 ppm workplace exposure is limited to 8 hours per day by OSHA.

While it is not a perfect measuring device, if you buy an Awair Element, you can get an idea of the concentration of CO2 in any room. Professional testing is more accurate, but (in testing by labs at Cornell University) the Awair has been found to be a reasonable estimate for an off-the-shelf consumer device. Pro testing for HVAC system verification is more rigorous with calibrated instruments.

If I put the Awair Element in a normal sized American bedroom with carpeting and minimal space between the carpet and the door bottom, close the door, and exercise on a Peloton doing the Haleakala Challenge, I will drive the CO2 level in the room from normal (about 450 ppm in my house) to over 4,000 well before I finish the challenge. If I do the same challenge in a 1,000 sq ft room, I will also drive the CO2 level in the room from normal to over 4,000 well before I finish the challenge. I expend more CO2 per minute on a treadmill.

A simple way to solve the problem of CO2 concentration is to open a window in the room in which you're exercising. The CO2 levels will stabilize with the outside air very quickly. But so will humidity levels and heat. If you live in an area that gets wildfire smoke, you get that indoors too.

Another way to solve the problem is to open the door to the room to a larger hallway, which typically enables better air flow in typical American houses so that the room can more easily exchange air with the rest of the house. But the tighter your house is sealed, the more you and others work out, and the less you open the windows/doors, the more the CO2 problem builds up. Why don't you want to open the doors? Because of cold/heat/humidity/smoke/nosy neighbors/etc.

Many people first experience the problem of CO2 concentration in a poorly ventilated basement. If you build a home theater system or an exercise room in a basement without ducted AC or MUA and you have 8 to 10 people over to watch a movie or 2 people work out together, you will have CO2 increase problems pretty quickly.

The solution is simple theoretically -- if you don't have windows open in a room, you need consistent airflow in the room to keep CO2 levels and other contaminants from building up. opaone's is right that standard American home design has not been adequately considering air quality and its effect on people.

If you want to buy a modern luxury home with luxury air quality, you can't rely on just the typical forced air HVAC design that Americans have been using for decades. The solution is to build a plan for managing CO2, temperature, humidity, VOCs, dust levels, and (if you want to go all out) other trace chemical levels (radon, methane, etc.) in every livable room and design the HVAC system to mix inside air with outside air, control the contaminants, control the humidity, and manage the temperature automatically. High end smart home customers are building these systems today. Systems can be built that automatically work if 1 person is in a 5,000 sq ft house or 50 people are in the same house for a party.

When you think about a luxury home, do you expect wifi coverage in every room? I certainly do. And I have a sophisticated collection of networking equipment that guarantees that every room in our house has access to 500 mbps or higher Internet connectivity. I wouldn't imagine trying to live in a home where my cell phone or ipad doesn't work in the kitchen or in my bedroom. Similarly, I expect the air quality to be great in every room in the house. I can't be expected to wake up in the morning, open the windows in the basement at 6 am to manage my basement's air flow and expulsion of VOCs, and then shut the windows by 830 am so that the heat and humidity don't build up and make the entire basement unlivable for days.

To be clear, I do not work in this industry. I am a consumer. I have to solve real problems because they impact my family's life, just like other home owners. I don't want to empty a bucket of water from a dehumidifier every few hours to prevent a mold growth problem in my basement. I want to be able to exercise in my house while I sit in on all-hands Zoom calls. I want to be able to sleep at night with the door closed for privacy from children or in-laws without feeling like I'm breathing bad hot air or opening a window and increasing heat and humidity.

Well, I'm in way over my head, but the notion that indoor exercise can raise CO2 levels to a toxic level just seems counter-intuitive. Here's my attempt to understand the impact of exercise in a 1000 sf room:

Estimates vary, but one estimate of CO2 production during exercise (Int J Sports Exerc Med, 2018, 4:095) shows that a young healthy individual exercising at 100% of capacity produces 62 mL of CO2 per kg per minute. For an 80 kg exerciser, that's 4960 ml/min. Rounding off to 5 L/min, that suggests that over 30 minutes of maximal exercise, a total of 150 L of CO2 are produced. Assuming 8 ft ceilings, the exercise room is 8000 cu ft, or roughly 226,500 liters in volume. If, improbably, 100% of produced CO2 remains trapped in the room (absolutely no exchange ventilation), this equates to an additional 66 ppm of CO2. This is nearly two orders of magnitude lower than the concentration of CO2 that you apparently measured ("over 4000") when exercising.

The only explanation for the breathtaking (excuse the pun) level of CO2 you are reporting would be some kind of weird air stagnation in which airflow is so impaired that CO2 is not diffusing away from you. Perhaps you're exercising in a hazmat suit?

Another common sense way of asking the same question is to consider how often we have exercised in a commercial gym, in a 1000 sf room (quite large), with, say, 8 or 10 people on treadmills, bikes, rowers, etc? By your calculation, those 10 people would experience toxic hypercapnia in 3 minutes. Agree that air circulation is a mitigating factor in this setting, but I'd argue that even without active ventilation, any room short of a sealed airtight "clean room" would allow that many people to exercise continuously without suffering from respiratory acidosis and subsequent symptomology.

But I could be wrong :-)

@catinthehat, how far away were you standing? 5' in front w/ the mic 5'6" (avg ear height) seems kind of the standard.

You were measuring dB(a), not dB(c)? IIRC the NIOSH app defaults to dB(a) and changing that is quite buried.

Overall your numbers seem kind of high for a remote blower + silencer. What hood do you have?

OP, given how many variables there are and people's lack of understanding I doubt anyone would give you a noise guarantee so that's not surprising.

Your 7,000 CFM of MUA+ERV/HRV is rather fantastical. Perhaps there's a valid reason for it but I can't think of one and you seem to be studiously avoiding providing one.

Hi opaone, nice to hear from you, enjoy reading about your setup. I took the measurement maybe 6 inches away. Yes dB(a). When I stand 5 ft back the low value hardly changes, the medium drops to 52 dB, and high is 62 dB. Just a standard bluestar hood with commercial-style baffles.

@clinresga for someone with a bike or a treadmill, the meter required to replicate the test is $100 to $150. Then shutoff the air flow and run/bike.

I happen to have the meter to measure wild fire smoke particulates. It was recommended by our medical group. When the numbers get too large, evacuation is recommended. Again, the home meter is directional and relative order of magnitude. It's accuracy is not assumed nor necessary for the purpose. We bought a second from a different vendor to test 2 different areas. They both report the same results.

@opaone asking me to explain the MUA for my entire house is beyond the scope of the discussion.

Spurpura, I get that directional CO2 production could produce locally high concentrations of CO2 during exercise. If that's the concern, then just running any kind of fan would seem to eliminate the issue: once you dilute the exercise-produced CO2 into the entire room (particularly if there's active ventilation or even an open door), based on my calculations, any increase in CO2 concentrations would be small and clinically negligible.

The exercise scenario is highly different than the wildfire situation, where the entire house is surrounded by products of combustion including CO, CO2, and particulates. In that case, there's "no escape" as bringing in air from outside is not a solution. But I remain quite skeptical that indoor exercise in a room with anything approaching normal airflow could lead to symptomatic hypercapnia.

@clinresga while I appreciate what you expect to happen, I had professionals measure it and it doesn't happen as you think without taking active measures to diffuse. You are right that relatively simple active measures like a fan blowing air around in the room with the door open helps but the situation is more complex than I want to get into in a discussion about range hoods. For instance, in our first attempt to clear CO2 from our 1000 sq ft exercise room, we used a fan to "blow it" towards a bathroom exhaust fan. That works ... and it took 4 to 6 hours to clear it to baseline from a 1200 ppm reading in the 1,000 sq ft room.

@spurpura: I don't argue that controlling airflow can be complex. But your situation seems to violate some basic principals, like conservation of matter. It just isn't physically possible for humans exercising to generate this level of CO2.

To generate 1200 ppm of CO2, using the hypothetical assumptions:

• We are using 80 kg humans, exercising at 100% capacity for 30 consecutive minutes (impossible)
• 100% of CO2 produced stays completely confined in the room (again, impossible outside of a clean room environment)
• We assume 5 L/minute of CO2 produced per human (per my prior reference)

it would require over 50 humans exercising in your 1000 sf room for 30 minutes.

It's just physics. You cannot achieve that level of CO2 via human exercise. The only rational explanation is that you have an intentionally or unintentionally unvented combustion source in your house, dumping POC into your exercise room. If so, it's not the CO2 you should be worrying about, it's the CO.

@clinresga I will indulge your scenario only to say that your expectation of a 30 minute workout is not what I stated. My original example was a hill climb challenge frequently undertaken by 30, 40, 50, 60, and 70 year old women (and men) who ride a Peloton for fitness. My wife is interested in it. Each person, of course, has a varying degree of body mass but I never stated I was measuring a 175 lb adult for 30 minutes. This hill climb challenge will take longer than 30 minutes.

I am not listing the actual weights of myself, spouse, and others on the Internet. For you to be right about the impossibility of the measurements in my home, PhD accredited scientists would have had to have faked a test result and a falsified a report. Additionally, I have specifically described a scenario to reproduce the tests with a $100 to $150 device in someone's home for them to see how their environment behaves for them You have not a done a single environmental test.

My personal daily indoor bike training workout has a twenty minute low intensity warmup, a 20 minute to 5 hour workout varying between light endurance and high intensity, and a 5 minute to 35 minute cool down at low intensity. The average number of minutes spent on the bike for the past 6 months is about 70 per workout day (the round numbers are generated by the fitness tracking solution). The average gain of CO2 for 70 minutes at endurance level rides in our 1,000 sq ft room without ventilation enabled is just under 1,000 ppm for just the bike workout portion.

I'm struggling w/ CO2 of 4,000 with a single person in a 1,000 sq ft room. In winter I will frequently do a 1-3 hour workout on a TACX Neo 2 in an attic room that is about 300 sq ft and with a very low sloped ceiling and poor ventilation. I'm 155lbs and for a typical workout I average about 172w and 143bpm with maximums of about 500w and 170bpm so I'm breathing pretty hard for 2 or 3 hours (I'm old and not nearly as fit as I'd like to be ).

I have a uRAD A3 environmental monitor in there and have never seen over 1600 and that high is rare. More typical is about 1200 (which is still too high and why I've much better ventilation in our new house).

The public gym I go to has an IQAir that I don't believe I've ever seen over 2,000 ppm. My guess is that this is about 25x40 so pretty close to 1,000 sq ft and it's not unusual for there to be 5 to 10 of us in there doing a variety of workouts from HIIT to weight lifting.

A study of fitness centers a couple of years back was showing, IIRC, around 2,000ppm in a 2,000 sq ft room with 9 people in a spin class.

This is all anecdotal but I just can't imagine a single person or even two or three people being able to produce anywhere near 4,000 ppm in a 1,000 sq ft room no matter what they are doing. CO2 (and other bits of poor air quality) is certainly a concern in workout facilities, including home gyms, and I know that some multi-user facilities have likely exceeded 10,000ppm CO2, but I'd guesstimate that it'd take perhaps 10 people working out really hard to get to 4,000 in a 1,000 sq ft room.

@opaone again, this is off-topic. I only consider it mildly related because I have numerous friends with Pelotons in their dining room/kitchen areas since the pandemic has put people at home. Remember, I described numbers with no ventilation. I hope your gym has some ventilation.

My studies began by accident -- looking at the Awair alerts and saying, "that can't be right." The Awair was supposed to be looking for smoke particulates. Why is it alerting about CO2? That progressed to academic friends loaning me measuring equipment to validate and then professionally measuring my house. And then these same academics measured their basement treadmill workouts for marathon training and becoming more concerned about ventilation.

I'm not going to post stats about my workouts because I'm tired of people in the forum questioning whether I (and other engineering professionals) can read meters. I am likely significantly taller & bigger than you are, and I have no comment on my cycling power-to-weight ratio other than I won't be winning the TdF any time soon. I cycle to avoid diabetes, but I have raced in cat 1 cycling races in my lifetime. I need a range hood because we are excellent cooks; good enough that I sometimes struggle to out-ride my fork.

@opaone: your numbers, while still higher than my estimates, are at least within an order of magnitude, which in this business probably is reasonable correlation. I agree that this could rise to a significant concern with 10 people really cranking away in a poorly ventilated room. So we're on the same wavelength.

@spurpura: you are correct in that I've not invested in air quality monitoring devices or hired PhD's to test my house. But my calculations are grounded in simple physics. The only assumption I have made is in the estimate of CO2 production during exercise, and that was from an academic sports physiology laboratory, authored by a PhD and published in a peer-reviewed journal. If you have figures showing that CO2 production during exercise is roughly 10 times higher than my estimate (which is what would be needed to support your observations), I'll await the citation.

There are really only three possible scenarios:

1. You are measuring local concentrations of CO2, presumably close to where you are exhaling.
2. Your PhD consultants and their equipment are wrong.
3. There's an exogenous unidentified source of CO2 infiltrating your exercise room.

Enough of that dead end discussion. But...as to your original question, I think you're on the right track. As noted upthread, our 1200 cfm hood runs through a straight run of 10" duct, about 25' upwards, with an attic-mounted Fantech LD10 silencer and FKD10XL blower. It measures 60db (LCS weighted, ear level, roughly 4' from baffles) on high. So we hit the mark you are shooting for and I expect your setup will too. Good luck!

@clinresga as I've told you, your calculations are wrong because your input data is wrong. Send me the citation you used to compute the numbers and I'll send back the comments from the team. And a bill for their time to educate you.

I am a bit late to the, ahem, race, here, but I will say, on a completely unrelated note: I love my dehumidifier, but I don't blame anyone for not wanting to empty it. Also, I look forward to having a hood for my kitchen that doesn't directly vent into the attic (someone thought THAT was a good idea around 1930 - and it wasn't.)

And I'm not an engineer or a particularly fit person, but I really have enjoyed the discussion. I can tell that @spurpura is thinking about health and comfort. I have learned many things - even if not everyone on this thread agrees on the physics. I tend to think, in your house, you should do what makes you healthy and comfortable. Also, somewhat unrelated, I own the IQAir, and while I felt silly buying it, I do really think it has improved our indoor air quality and it has made me want to ensure better air quality going forward (you can imagine that if I am running a dehumidifier in my house in California now, there is probably a mold issue.) We live in a place that was described by my grandfather as having the weather on earth - warm during the day, but cool at night and best for sleeping. I realize that is unusual - and we have the luxury of opening windows at night to capture that cool air. Having traveled extensively and lived in a variety of places, I know how unrealistic that is for most of the country. I think having an HVAC setup that allows you to sleep well and breathe well is brilliant.

@spurpura

Here's the link to source Source

@catinthehat, could you provide more detail as to where your MUA vents are located and the general airflow? (I think you said you put them under the range.)

Does that area get hot/cold in the summer winter?

Do you feel the MUA air when using the range?

Thanks so much for the help.

In general, MUA should be directly or indirectly vented into the kitchen such that when the MUA reaches the cooking zone it does so with minimal turbulence. Otherwise, the uprising cooking plumes will be disturbed and all the "theory" about how much wider a hood should be will not account for the effective size and offset of the plume when so disturbed.

One approach used by commercial kitchens is to dump the MUA under the cooking appliance (which in commercial applications will have legs). This may or may not affect the plume structure. One commenter here tried to use the kick zone under the cooktop but found that with an island/peninsula across from the vent the MUA became turbulent at the cooking zone.

If the air comes from above the kitchen, I recommend a ceiling diffuser that if nearby directs the air away from the hood across the ceiling, or if distant towards the hood. MUA coming from below should be released in a way that allows it to "straighten out" somewhat by the time it gets to the hood area.

As I recall, Greenheck addresses MUA approaches in its guide, available here:

https://www.tagengineering.ca/wp-content/uploads/2015/02/KVSApplDesign_catalog.pdf

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Edit: note that a diffuser has a different vane shape than a register; see Hart & Cooley for details.

Also, in comments earlier in this thread, I recall the mention of passive MUA (no blower). One must be aware that if the intake of MUA is to be filtered, the pressure loss of the filter will be commensurate with the hood baffles, depending on filter effectiveness and area. This means that a blower is needed to keep the house at exterior pressure if called for by the presence of combustion appliances susceptible to back-drafting. If passive MUA is acceptable on back-draft grounds, the filter pressure loss still must be accounted for in determining the actual CFM that the hood system can vent.