How to install bathroom exhausts in an airtight house?
I am in the planning stage of my new home build. I am planning on using advance framing techniques with 2×6 studs, 2″ polyiso rigid foam on the exterior, open cell spray foam in the wall and unvented roof.
After all that effort and extra expense Im suppose to place 4, 6″ holes in my wall for my bathroom exhaust fans with nothing more than a meta flap to keep air from coming back in? Same for my dryer’s exhaust. Seems like a lot of air intrusion points.
I’ve been learning a lot about new construction techniques and materials, but this technology seems to be stuck in the 50’s. I’m also concerned about a whole home systems extra cost. An extra $5000 – $8000 will never be made up in the efficiency or comfort. I haven’t research whole home ventilation enough to have figure out how to tackle it in the most efficient matter yet. So maybe an EVR system is the way to go.
Im in Phoenix BTW, so I’m not concerned about being too humid. I can run a hot shower all day and my mirrors never fog.
Thank you for your help I really appreciate it.
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Replies
Jeffrey,
First of all, there is no such thing as an airtight house. All houses leak. The reason we perform a blower door test is to learn the air leakage rate.
Second, there are different duct termination kits available for bathroom exhaust fans. You don't have to choose the cheap aluminum flaps if you don't like them. Perhaps some GBA readers will suggest their favorite brand for an exterior duct termination.
Third, you can connect your bathroom exhaust grilles to an HRV or ERV if you want. That way your house will have a single exhaust termination.
Here is a link to an article with more information on this topic: Bathroom Exhaust Fans.
Jeffrey,
As Martin says, there are some very good duct terminations. I like these:
http://www.seiho.com/product/index6.html
If you are still uncomfortable trusting an external one you can always put an online flap anywhere in the duct. They are aviliable at most big box stores.
Thank you very much for your response! In planning for a more efficient home everything has a laser like focus on best practices. When it came to exhaust fans I found it odd that the practice was to cut holes in the envelope was so meticulously designed.
Thank you for your links. I think thin walled PVC ducting with duct terminations as close to the exterior as I can get them is the way to go. I was just imagining 112+ degree air filling up those ducts in my conditioned attic before terminating at the fan.
Thanks again.
In Arizona, I encourage you to utilize your local contractors' masonry experience. and build with concrete blocks or ICFs instead of wood. The Arizona climate is perfect for taking advantage of the thermal mass benefits of exterior-insulated masonry or an AAC product, and your house will be substantially immune to termites, a major concern in your climate. The up-charge of insulated mass walls shouldn't be too high compared to your current plan which involves expensive spray foam.
I live in neighboring New Mexico and I encourage you to use an ERV system. An HRV or exhaust-only ventilation system will keep the relative humidity in your house under 15% most of the time, which is not great for your skin and respiratory system. You don't need a huge, expensive Zehnder ducted system which will cost you thousands of dollars; there are plenty of cheaper, almost-as-effective systems you can get. At the recommendation of the pros here, I'm installing a Panasonic FV-04VE1 ERV.
How big is your house going to be, how many bedrooms, and how many occupants?
Do you or your builder have an air tightness goal that you are trying to reach...or does your builder have a track record of blower door results that they will match in your build?
I (and I'm sure others) can provide better advice based on this, but the advice (as others have alluded to) is in the direction that you may be better off going with a whole house ERV. This will serve your continuous ventilation needs and the bathroom ventilation needs, so no bathroom fans and multiple exhaust terminations needed.
What is with this thinking that low humidity is bad for health? I don't get that one bit. It is entirely unproven.
Entirely unproven?
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1474709/
http://www.sciencedirect.com/science/article/pii/S0954611108003429
Everyone's body is different, of course. But for me, at indoor humidity levels below 20%, my skin cracks and bleeds. I also get colds more often. Above about 30-35%, my skin is fine and I feel much healthier.
House will be right at 2400 sq ft. 2 bedrooms, 2.5 baths with a laundry and office. All one story. Essentially just me and the wife, the kid will move out soon. The more I look into it a whole house ERV (Broan ERV90HCS, is what Im thinking) is probably the best solution. Material pricing isn't as big of a difference considering I needed 6 exhaust fans that this one system will replace. The unit itself is $758 on amazon and the ducting will cost may 50% more than six individual units. I was under the impression it was a 5-8,000 system. looks to be closer to 3K for my needs.
I feel great in ultra low humidity.
The Sonoran Desert would be uninhabited and uninhabitable if this was true.
Jeffrey,
Here is a link to a previous Q&A thread on this topic: What's a good damper for a bath fan / range hood vent?
Thank you Martin. Very helpful. I keep going back and forth in my head. I think I will have my 2 master bathroom fans (both 110 CFM Panasonic) ganged together with an additional damper put in place prior to the roof insulation before exiting. Same with the half bath and laundry room fans (adjacent rooms). The second bedroom bath will be on its own ducting. Then I will place Panasonic's smaller EVR in the main living space for fresh air ventilation.
I'm hoping with two dampers on each exhaust (one just inside the insulation and the other built into the fan) I can limit the movement of hot air entering. I will buy over-sized fans to compensate. Especially since they are not significantly more expensive to buy the larger size.
And all this can change as I finalize my budget and continue to educate myself. Thank you for your responses. They are very helpful.
Jeffrey,
Be cautious about burying additional dampers on the laundry room ducting. They often get clogged by lint and should be accessible for cleaning.
Very good point Malcolm. Thank you.
Jeffrey, why does your master bathroom need two 110 cfm fans?
Separate toilet (water closet) from the shower/ bath area.
the fan in the water closet doesn't need to be 110 CFM.
Why did you give up on the idea of using your ERV/HRV to exhaust from some of the baths instead of fans for each? It seems a smart, efficient and economic way to go. With your set up it would probably actually be a cost savings since you are planning an ERV/HRV regardless and as you mention eliminate many holes in your house envelope. (or at least consolidate them.)
I'm having a hard time reconciling bringing in 115 degree air temperature at a large enough volume for the whole house. I don't believe the ERV would be able to transfer enough conditioned air temperature to the in coming air at those high volumes of air. Even if its dropped by 20 degrees, Im still bringing in 95 degree air. In the summer in Phoenix we have 100+ degree temperature well past 10 PM and can have nighttime lows in the mid 90's. EVR's working constantly or part of every hour seem to be an issue in my mind. I will always be bringing in air that would need significant energy to drop its temp to comfortable levels.
With only a portion of the house having a EVR system I can lower the total amount of hot air entering. If I go completely exhaust only and place a 300 CFM exhaust fan in the kitchen/living room area, I can have the minimal amount of hot daytime air entering the house. Allowing me to control when to exhaust the air for recirculation.
Of the studies I read in the last week ERV's become less efficient in hotter climates. Their time to pay back their extra cost is around 15 years. Add in the fact that I can have my windows open 5 months of the year, the EVR is less cost effective.
Part of your reasoning seems slightly erroneous to me. If you need fresh air you need fresh air. And if you are concerned about bringing hot air in then that is exactly the reason to use an HRV/ERV. If you have a 300 CFM exhaust fan going your house will try to pull in 300 CFM of air from the outside or have a severe pressure differential. So air will infiltrate from somewhere - cracks, or even back venting from the bath fan and range hood etc. and in this case it will be 115 degree air not something lowered with an 80% efficiency rating. 300 CFM does seem rather high though - typically make up air is in the 100's from what I have read.
If what you are saying is you will only ventilate at night at a 300 CFM rate rather than more consistently across that day at 100 CFM, i guess that makes sense if you aren't around during the day. But still you could run the ERV for longer at night an accomplish that same thing. If you are buying high quality exhaust fans at $250 a pop it only takes replacing 3-4 of them with an ERV to be a straight even cost trade (the fans need ductwork whether you have an ERV/HRV or not). Not counting the cost of whatever 300 CFM fan you would also have to buy for exhaust only. You could even buy a few Panasonic spot ERV/HRV units instead of the bath fans and not go whole house. The ability to exhaust from baths with an HRV/ERV makes a huge difference in the cost equation.
I am not an expert so others feel free to pick apart my logic, I'd like to hear the pro's and cons from others as well.
I think air leakage would be less with ERV rather than a bunch of fans and added penetrations. And I second that you don't need such a powerful fan in the WC.
I really appreciate everyone's input. After reading more about ERV controls and setting up individual switches in the bathrooms, etc it sounds like I will have the control I thought I was losing with a ERV.
Thank you for the responses and allowing me to work through the issue in my head. Hopefully I can find a subcontractor to help me size the system correctly so I will pass exhaust CFM codes in the bathrooms.
Jeffrey,
Here is a link to a GBA article that may help you: Does a Home with an HRV Also Need Bath Fans?
Thank you very much Martin. I'm comfortable without exhaust fans as moisture has never been an issue in my bathrooms. Even during monsoon season.
My new home will also have 34" x 72" casement windows in the full bathrooms.
Thanks again.
Hi all. I came here to post nearly the same question. I live in Central KY, mixed humid, zone 4A, 4610 HDD (?). I think I need an ERV.
It has been difficult to wade through all the different things to think about and try to determine what is best. All strategies have their pros and cons and for Joe Homeowner, it is hard to work through all the facts.
After reading several articles here and elsewhere (but need to read those articles posted regarding bath fans), I like the idea of connecting the bath exhausts to the ERV and exhausting them together out of one hole. Fortunately, for plumbing efficiency, we grouped the baths together and over top of a plumbing chase that will run down the 1st floor wall into the basement. I believe I would have room to run the exhaust ducts through this chase as well, as long as there is no other reason the ductwork can't run that distance or that direction.
My only other question would be supply runs. I guess if I am exhausting from the 2nd floor baths it would be OK to supply the ventilation somewhere in the floor of the 1st floor? Would that be enough supply or do I need supplies on each floor?
ETA: Well rats! Nevermind! After reading "Does a Home with HRV Also Need Bath Fans", I see in the next to last paragraph that ERVs might not be good for bath exhaust because they don't get rid of the humidity. That would not be good here during our humid summers.
An ERV is good for air conditioned houses in humid zones, since it lowers the latent load of the ventilation air. But exhausting humid bathroom through an ERV retains some of that bathroom moisture, returning it to the incoming air stream, redistributing it to the rest of the house. But the moisture recovery isn't really all that high, percentage-wise.
Unless the shower is running for hours every day, those pulses of returned moisture from the ERV when the bathroom is foggy-mirror humid don't really add up to much. ERVs absolutely DO get rid of the bathroom humidity, just not quite as rapidly as an HRV or exhaust fan does, and it moderates the amount of moisture coming in from outdoors when the air conditioning is running.
If you want high ventilation rates during the dog-days of summer, an ERV would be somewhat more comfortable than an HRV, but it's a bit easy to over-think this. In a gulf coast climate I'd personally opt for ERV, but in central Kentucky it's a bit of a coin-toss- if you want high ventilation rates go with an ERV, otherwise, HRVs are fine.
Dana, upstate NY zone 5- ERV with an added bath fan in shower, or HRV???
Joe,
Here are links to two articles which will help you answer that question:
HRV or ERV?
Does a Home with an HRV Also Need Bath Fans?
Joe-I'm in Maine, zone 6. My HRV on boost setting takes care of shower humidity with no problems, even if both shower heads are flowing at the same time. Exhaust port is in the shower ceiling. I also use boost in the kitchen when boiling water or cooking something smelly like onions. Exhaust port is in kitchen, but about 8' from cooktop.
I'm not sure you need or want a separate bathroom fan. Architect recommended HRV, not ERV, for northern climates.
How do you folks who use your vent. system as your bathroom exhaust deal with the longer duct runs from the bathroom? Do you install the system close to your bathrooms? I'm guessing 2nd floor bathrooms would be difficult to reach for a basement ERV?
Clay,
The airflow rates are not particularly high -- 50 cfm or less. If there are long duct runs with several elbows, you can upgrade from 4-inch duct to 6-inch duct.
Duct run locations need to be figured out at the design phase, not after the house is framed.
Clay: My HRV has a separate 4" plastic duct for each exhaust and supply vent. The HRV unit is about 50 feet or so from the bathroom exhaust location, although there is probably more like a 70 foot piece of duct, since it goes up into the utility chase in the ceiling.
The system was commissioned and produced the proper level of ventilation set forth in the design. It really works very well for venting shower moisture.
Joe: In your climate there's not enough up-side for an ERV, so HRV it would be. During higher humidity days in summer you can dial back the ventilation rates &/or run a dehumidifier if the AC in a high-R/low-load house isn't taking care of the humidity at the higher ventilation rate.
Thank you, all. I knew it was one offer the other but after reading that article Martin recommended a few times, I was still unsure. I am nt hit on ambiguity. Anyway, I was hoping Panasonic made an HRV, but no such luck. Can anyone recommend a brand? I do not wish to tie it into my furnace/heat pump/forced air system. I prefer to have a separate HRV ventilation system. I stacked my bathrooms and have a third first floor bath not far from the main bath as well. I know my duct runs in the pantry and close try which I positioned in the center of the plan. But my particular strategy is to settle on a brand, rough in duct with 6" runs, make all my penetrations and have a space to put the unit in basement. Then after we have insulation, run the blower door to determine how much ventilation I truly need. Then I can select the size. Is this a poor strategy or a good one? Hopefully Jeffrey (OP) is still tuned in bc this is a universal answer to a universal question, I believe.
Joe,
Q. "After we have insulation, I'll run the blower door to determine how much ventilation I truly need. Then I can select the size of the HRV. Is this a poor strategy or a good one?"
A. You don't use the results of your blower-door test to determine your ventilation rate -- except in a very crude way. (In other words, if you have an old Victorian house that tests at 12 ach50, you know that you don't need an HRV.)
The way you size an HRV is by the ASHRAE 62.2 standard. The standard calls for 7.5 cfm per occupant plus 3 cfm for every 100 square feet of occupiable floor area. (That's how you size the equipment. Once the equipment is installed, you are free to ventilate at a lower rate if you want to, and in fact many experts recommend experimenting with lower ventilation rates.)
Here is a link to an article that explains what you need to know: Designing a Good Ventilation System.
Joe- we have a Zehnder HRV. It was expensive, (about $6500 installed) but works very well. It is extremely quiet. If you send Zehnder your plans, they'll design the system and provide all the parts you need. My installer was impressed with the system and how well the components go together. Part of the cost included someone from Zehnder coming to the house and commissioning the system.
Thanks Martin. I guess I need to decide if 50 cfm is adequate for a steamy bathroom (the wife loves hot showers). As you mention in your "Does a Home With an HRV Need Bath Fans?" article, there are opinions on both sides.
For reference another nice article from Canada on ERV/HRV's:
https://hpo.bc.ca/sites/www.hpo.bc.ca/files/download/Publications/HRV%20Guide%20for%20Houses-%20Compiled_web.pdf
Martin and Stephen, how does Zehnder know how much your house leaks before they tell you what amount of ventilation you need. Martin, I read that article a half dozen times. Once you blower door test, I think you are at the stage at which you have an sea of the exact amount of air changes you need to have. Otherwise, you can only guess. I am hoping that my house will be rather sealed. But once blower foor is done I will know really how much leakage I have.
A blower door test doesn't tell you anything at all as to how much natural ventilation you are actually getting (or at least not with any accuracy) since it only measures the size of the aggregate hole, not where the leaks are. Clustering of leakage at the foundation sill and another clustering at the top floor ceiling delivers a lot more convection driven infiltration than holes of similar size halfway between grade an the the ceiling. It could be an order of magnitude different.
Joe- as far as I know, the amount of ventilation required is not related to how much a house leaks air. The amount for my house was determined by the size of the house, without reference to the blower door test results. For my house, with about 1650 of interior conditioned space, the ventilation rate was 72 cfm. We had some back and forth among me, Zehnder and our architect over whether volume, as opposed to square footage, controlled and the eventual consensus was that our high ceilings (varying from 8-14') didn't materially impact the needed ventilation rate. For what it's worth, we usually run the HRV at low speed, even though the design cfm is at medium speed. We get no condensation at all and no odors.
As Martin said, if a house is extremely leaky, you may not need additional mechanical ventilation until you tighten it up.
Joe,
As others have said, and as my article states, the way to size a ventilation system is according to the ASHRAE 62.2 formula. Of course you can choose to operate your equipment any way you want. You can leave it off, or you can run it 24/7 on "high."
Ventilation systems are not sized according to blower-door results.
Ok, that is solved then! Thank you!
I'm currently in the middle of this discussion about venting bathrooms with our builder and HVAC contractor, too. We're in zone 5 (Colorado Springs area). We'll have an HRV (Broan HRV150TE) connected to an air handler on the intake side, so not separate ducting. The contractor is reluctant to vent the bathrooms to the main duct system due to the humidity, so I'm looking at direct venting options. Our builder likes the Panasonic Whisper fans, which seem to have a reasonable external damper. I'm also wondering about a multi-port fan since our bathrooms are grouped together and that should minimize external penetrations. The contractor's initial response was that he is concerned about cold air backflow into the bathrooms where the fan isn't operating if the wind is 'just right.' I've been reading through the articles here again looking for comments about that but haven't seen anything. Am I missing something?
A.W.,
First of all, here is a link to an article that you and your HVAC contractor may want to read: Ducting HRVs and ERVs.
In that article, I describe several ways to duct HRVs, including a method called "exhaust-ducted." I wrote, "An exhaust-ducted system straddles the fence between a fully ducted system and a simplified system. This installation has dedicated exhaust ductwork, but as with a simplified system, the HRV/ERV dumps the fresh air into the main return duct of the forced-air system."
You may also be interested in reading this article: Does a Home with an HRV Also Need Bath Fans?
Q. "The contractor's initial response was that he is concerned about cold air backflow into the bathrooms where the fan isn't operating if the wind is 'just right.'"
A. This type of backflow can happen, whether you install bathroom exhaust fans that are individually ducted, or whether you install a multi-port exhaust fan. However, the amount of such backflow is usually negligible in most homes -- not enough to be irritating to occupants. If you get troublesome backflow, you can install a supplementary backflow damper in the exhaust duct.
Thank you, Martin. I just spoke with the HVAC contractor and clarified his concern. It wasn't actually backflow, but that the vent fan would not be able to overcome pressure against the damper if the wind is hitting it head on. He followed that by stating that in his opinion, "houses these days are too tight...", so he tries to install make up air in all of the houses he does. I'm hoping our house will be "pretty good" tight, but we certainly won't be PH tight. Is it difficult to install a make up air system/vent after completion if we think we need it?
I've struggled with the range hood vent, too. We're currently planning one that is 400CFM, with the hope that it will be adequate with recirculating filtration so that I can close off the outside vent.
Thanks again, Alex
Alex,
Here is a link to an article with more information on providing makeup air for exhaust fans: Passive Air Inlets Usually Don’t Work.
Whether or not you will be satisfied with a circulating range hood (instead of a range hood that vents to the outdoors) depends in part on what type of cooking you do.