Ventilation, Ventilation, Ventilation…
Hi Everyone,
We are building a net-zero home in Ontario, Canada with air tightness goal of 1-1.5 ACH50. Climate zone would be similar to 5A. We have cold dry winters and hot humid summers. We are building a 2100 sq/ft bungalow with 3 bedrooms and 2 bathrooms on the main floor, with a 2100sq/ft walkout basement. We do not intend on finishing the basement within the next 5 years; however we will have a roughed in bathroom and wetbar area. Ultimately, the basement could be fabricated as a in-law suite in the future.
We have been working with an Energy Consultant who has recommeneded an whole house ERV with an ECM motor. We have been put in contact with an HVAC Designer. The HVAC designer is recommending a simplified connection from the ERV to the air handler to handle the distribution of fresh air with supplemental bathroom fans. He is claiming that an HRV/ERV will not be able to handle to moisture loads in the bathrooms.
I have spent some time looking into and researching these systems. I understand that this question has been brought up in the past, it looks like a while ago now, and systems and methods we use change a lot over time, so I thought I would post my dilemma for some feedback/advice. I have read through previous articles, but did not find advice to my specific questions.
My plan or idea is going against the grain with both the Energy Consultant (who we have not discussed this with) and the HVAC Designer. Hense, my dilemma. I am not a professional in this field, but I am not convinced what is being suggested is the best solution. We would like install a whole house balanced HRV (Venmar E15 or VanEE equivalent) with a humidifier to the air handler. Fresh air would be supplied to bedrooms, great room and rec room while stale air would be pulled from the Laundry room, bathrooms, kitchen (not for the range hood). Our preference is to utilize an HRV instead of an ERV in an attempt not to introduce or hold onto any unnecessary moisture within the envelope during high humidity events, or from humid air from the bathrooms. We would lean on a properly sized ASHP to draw out access humidity/moisture during the summer months (supplemented by a dehumidifier if nesscessary) the humidifier during the dry winter months.
We do not want to install bath fans in the upstairs bathrooms as it seems redundant to add additional penetrations in the envelope, if it isn’t needed. Additionally, unless dedicated make-up air was provided for each exhaust fan. It would seem that every time a bath fans is ran, we would at be temporarily unbalancing the system. The same goes for the kitchen rangehood. We would be willing to add a bath fan in the downstairs bathroom due to he frequency that it will be used (not often, and not for many years.) I also know that occupant behaviours are impossible to predict. We will be installing a kitchen rangehood with less than 350CFM and a condensing dryer.
With that being said, here are my questions below:
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Has anyone had a similar setup to what I am suggesting, and do you have any concerns or issues with your system?
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Am I overthinking this situation. I do tend to overthink things; however, I like to ensure things make sense.
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Aside from contacting the suppliers to confirm the HRV can be the only source of moisture removal, have you had success with setting up only an HRV with a boost mode in the bathroom to deal with the excess moisture?
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Does temporarily unbalancing (depressurizing) the system with either a bathroom fan or a rangehood have a large negative impact, or is the amount negligible and not worth worrying about?
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If we eliminate the bathroom fans from the equation, would the rangehood still require make-up air?
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If providing make-up air for the rangehood is necessary, what would be your thoughts on running a loop of duct into the house and then back to the stove. My thoughts on this would be that if the pipe was uninsulated, it would have an opportunity to temper the air to match the indoor conditions before injecting it around the rangehood. I’m thinking of those days that will be -20 or +40.
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I am unable to find much information on a Simplified connection between the HRV and the Air Handler as the HVAC designer is suggesting. He says that what 90% their designs call for. In my eyes, this system would be highly dependant on the air handler running to distribute fresh air. And with all the losses/mixture of air, it would be almost impossible to verify how the air is being distributed properly. Is this a bad idea, or is it more common than I know?
Thank you for your time and advice, all comments are welcomed and will be much appreciated. Please remember, I am not an expert and I am not claiming to be.
Chris
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Replies
"Has anyone had a similar setup to what I am suggesting, and do you have any concerns or issues with your system?"
-Yes, I have and it's not at all uncommon. There should be no issue with evacuating humidity from the bathrooms. If I recall correctly, a continuous 20CFM in the bathroom satisfies the code requirement. It's a good idea to have an ERV/HRV with a boost function that you can turn on during showers, etc.
"Am I overthinking this situation. I do tend to overthink things; however, I like to ensure things make sense.
Aside from contacting the suppliers to confirm the HRV can be the only source of moisture removal, have you had success with setting up only an HRV with a boost mode in the bathroom to deal with the excess moisture?"
-I have HRV exhausts in the bathroom, and never had any issue with humidity (not from that, anyway). I never even run the boost in the bathroom, though it is there.
"Does temporarily unbalancing (depressurizing) the system with either a bathroom fan or a rangehood have a large negative impact, or is the amount negligible and not worth worrying about? "
-It's a concern if you have combustion appliances in the house. If not, as long as the range hood is below 400cfm it should not be a big deal. 400cfm is the threshold for requiring make-up air for the range hood.
" If we eliminate the bathroom fans from the equation, would the rangehood still require make-up air?"
-No.
" If providing make-up air for the rangehood is necessary, what would be your thoughts on running a loop of duct into the house and then back to the stove. My thoughts on this would be that if the pipe was uninsulated, it would have an opportunity to temper the air to match the indoor conditions before injecting it around the rangehood. I’m thinking of those days that will be -20 or +40. "
-You have to keep the make up air source a good distance away from the range hood, otherwise you will have some short circuiting (the return air getting pulled into the range hood without collecting any pollutants). The potential thermal gains from what you describe are quite small.
"I am unable to find much information on a Simplified connection between the HRV and the Air Handler as the HVAC designer is suggesting. He says that what 90% their designs call for. In my eyes, this system would be highly dependant on the air handler running to distribute fresh air. And with all the losses/mixture of air, it would be almost impossible to verify how the air is being distributed properly. Is this a bad idea, or is it more common than I know?"
-Install a standalone HRV/ERV with its own ducts. This is far and away the best way.
As far as HRV vs ERV goes, we have an HRV and I'm strongly considering replacing the core with an ERV core. All of the humidity issues we've experienced have been driven by outdoor ambient conditions. In the summer and shoulder seasons, the indoor humidity is too high but not as high as outdoors. So an ERV would help reject some of that moisture from getting into the house. In the winter, it tends to be on the drier side. Not enough to be much of a concern, but at the same time it probably isn't going to hurt to limit the moisture being expelled from the house. If you buy a Zehnder unit, you have swappable cores, so you could have an ERV one season, then an HRV the next. As far as I know, they are the only brand in North America with that feature.
For reference, I am also in SW Ontario, 2500ft house on two stories (no basement), 0.22ACH50.
If it's feasible, I would be shopping around for a different designer. The system he's suggesting is widely known to be less than ideal in the building science community.
Hi Trevor, I appreciate the insight. Thank you. How long ago did you build? May I ask who completed your HVAC design?
I would love to install a Zehnder, although the price tag for a full system on our particular house was 10k without installation or delivery. That's a tough pill to swallow.
Again, many thanks.
The build was substantially complete about 2 years ago. The V part of the HVAC design was done by Zehnder, and then re-done (after the system was installed) by Trevor Day & Associates, to satisfy a pernicious building inspector.
Try just comparing the cost of the HRVs themselves. You don't have to use Zehnder's duct, fittings, etc. That's where the bulk of the cost difference is.
> 400cfm is the threshold for requiring make-up air
Note how crazy code is to use the same number for say a small 0.22 ACH50 house and a large 1.5 ACH50 house.
That's a good point, it really should depend on how much make-up air can be provided by leaks in the house. Once I replace my recirculating hood with a proper one, I'll be going with the low tech "open a window" strategy for makeup air.
Obviously more bathroom exhaust CFM will clear odors and shower humidity better/faster. I'm not aware of any non-anecdotal data regarding "how fast is fast enough" - it will change with climate, the bathroom wall/ceiling design and personal preferences. Code (the worst you can legally build) may not be the best answer.
When is comes to concerns about unbalanced ventilation, convert the losses to dollars/year.
Our Zehnder HRV on boost clears humidity from showers quite well in just a few minutes.
Trevor covered your concerns quite well. A few more items of note:
The best thing to do here is to find an HVAC designer who knows more about designing high efficiency systems, especially if you are trying for net zero. Easier said than done, I know.
If you are doing a direct ducted approach, which is without a doubt the best way, you will need a post-heater in the cold winter months so that fresh air being put into your living room isn't too cold. On those -26°C days, the fresh air delivery temp will be in the range of 12°C. That feels like a very cold draft! And that's on low speed, performance drops further when you bump it up to high speed. Electric duct heater is usually how this is done.
Zehnder makes a fantastic unit for a net zero house. If you are serious about a certified Net Zero, you may even find the efficiency of that unit makes your life easier in achieving that goal. There have been some permitting issues with some of their models since they don't test with the same standards as Canadian manufacturers, so just know that ahead of time and clear it with your building inspector. Otherwise, you should consider the Vanee V160H75RS. Essentially the same energy performance as the Venmar unit you've chosen (which used to be their best unit) but with way better features. The auto-balancing is genius and the controls are really spiffy.
You are correct about the simplified system, there is no way to know exactly where your fresh air is going and the air handler has to run whenever the HRV does. It is how most systems in Ontario are installed. The extended exhaust and simplified fresh air is also a common method. Both of those methods avoid the issues with tempering the fresh air.
I agree with Trevor about the ERV. They make good sense for tight houses in our climate. But if you are going to have separate controls for humidity, not a necessity.
You will need makeup air in a tight house if you expect your range hood to move the amount of air it is rated for. This can be a simple as an cracked window or you can do a LARGE passive duct or a makeup air fan such as this: https://shop.fantech.net/en-CA/muas--750--makeup--air--system/p111416
I'll reaffirm what Trevor said about an HRV exhaust being adequate for bathroom exhaust. It usually is slower than a properly installed bathroom fan but definitely works just fine. If you can't handle your bathroom mirror being foggy for longer than a few minutes, you probably want a bathroom fan or just design your HRV to provide a nice high flow rate similar to a bathroom fan on Boost mode.
Source: I regularly design these systems
You will not need a Humidifier attached to the air handler, in a tight house you may need Dehumidifier.
I live in your area. I have an ERV. I have no bathroom fans.
I wish I did, at least for the master bath. It's currently sitting at 70% humidity, there's no good spot to put a dehumidifier in there, and the ERV vent doesn't do anything.
It's the vent that's furthest away from the ERV, and even in boost mode, it doesn't do much. I've tried to balance the ERV better but ultimately, being two floors away, and a full house back is too much to overcome. I'm considering installing a single room ERV as a solution.
I run a dehumidifier every night to try and reduce humidity in the house to help dry the bathroom. I spend a fortune in energy because I can't get airflow to this room.
What is the size of your house? What's the make and model of your ERV?
Appreciate the comment.
Chris
2100 Sq Ft. I have a Venmar E15 ECM.
The Master bath is just not well connected with the rest of the house.
Steve, would it be correct to say that the problem you have is that the ERV ducting wasn't designed/tested to pull the required 20 CFM from the bathroom? I find it hard to believe that 20 CFM wouldn't eventually bring bathroom humidity close to the rest of the house - at least under most wind conditions.
I mean, probably. But have you ever seen an HVAC tech use an engineered drawing for the ERV piping? It's not common practice around here. They run the same size pipe everywhere and rely on changing the restriction at the vent to 'balance' but they don't really try. I don't need a fan in every bathroom, but having a decent ventilation source for my most used shower would be super nice.
Instead of an expensive 2nd ERV, consider an in-line duct booster fan to get the bathroom CFM to what it should be.
Have you seen the new update to the Panasonic Intelli-balance ERV? I'd strongly recommend looking into it. FV10-VEC2 is the model. I just bought 2 from Vaughan Electrical in Ontario. I don't think there's anything out there that comes close for the price tag. The one thing people were hesitant about with the old model was no boost function. When I saw they added it in the new version that sealed the deal for me. I haven't installed it yet, but I couldn't be more impressed with the quality and I measured it at a 16w power draw running at 50cfm, 90w at full power.
I bought one for each floor and will be skipping bathroom fans and installing a Kasa smart wifi switch in the bathroom connected to the 100% boost function. This way I have a little programmability in the app if I want a timer on it, along with the option to activate the boost from anywhere in the house via Alexa or Google Assistant.
Chris,
Just beware of the stated CFM of range hoods. My tight house means our rated 300 cfm fan is enough to make the woodstove give up a smell from drawing air down the stack, but not enough to send the onion smell out of the kitchen on the very noisey high setting. I have only 5 feet of 6" duct to make it outside and it still feels asthmatic. It is pretty, but unconvincing.
I would recommend a hood style that is wider than the cook top area and preferably with a lip all the way around. Ours has a fancy sheet of glass that looked appealing online, but has proven to be a pig for cleaning. It also has the additional surprise of staying cold enough that steam will condense on the underside. Not too surprising, but the edge of the glass stops just at the edge of the cook top, so drips come very close to falling into the larger fry pans or stew pots.
You can save extra vent holes if you use a central fan with ducts back the bath ceilings. I installed one for someone that had a steam shower and a separated toilet room. The roof was tile, so I was stuck with one existing vent. I didn't want back flow issues from trying to connect two individual fans to one exit, so a Fantech unit did the trick.
Regarding bath fans, I went with Panasonics that claimed 80 cfm and reasonable WC values. Even with 6" smooth metal pipe, taped and two wide bends they labor for 15-20 minutes to show progress. The runs are 7' and 18' and show little difference. I will definitely be planning on more aggressive cfm on my next project.
> 300 cfm fan is enough to make the woodstove give up a smell
Given the back-draft and pollution safety issues and the downsides to anything that would discourage tight houses, code should require balanced push/pull kitchen supply/exhaust.
Chris and Jon R.,
My bad for a poorly rendered observation about air flow. The woodstove is right next to the door to the kitchen, so the depressurization of the kitchen when using high fan is enough to extend to the living room. The flue for the stove is dead straight up so during cold weather there is already a fair amount of heavy cold air in it waiting for an imbalance to overcome the warm air leakage/pressure going the other way.
The frustrating part of the range hood is the poor selectivity of air collection, which allows food smells to billow around the hood perimeter. If a slow stew is cooking, we have found the best way to limit the spread of smells is to crack a window in the living room rather than the kitchen. Score one for magic air arrows not doing what your think they should.
Oddly, the standard venting dryer we have should create the same effect when running, but being down the hall a short ways causes it to pull air from other parts of the house, not the stove stack. The bath fans tend to only pull air from close to the ceiling, which is fine for steamy showers, not so fine when trying to resolve other IAQ problems. The work around is to close the door and force the room into a negative pressure situation with "make-up air" slipping in under the door. That stirs things up and results in a more complete exchange of air in the room.
I suspect the very low cfm of HRV or ERV per opening would make them inherently ineffective for getting rid of bath humidity or other air qualities. The additional resistance from extensive ducts or tubes can't be of much help either. Increasing the size of the cfm is a questionable notion unless each intake can be isolated on demand. Using an HRV/ERV for slow, low volume air exchange makes sense, using them for bathroom venting does not IMHO. The idea of having a stale air pick up in the kitchen runs counter to others recommendations due to the potential for picking up greasy air. The range hood traps show just how greasy.
The new mandate for make-up air for hoods over 400cfm is commendable, but how and where to introduce that air is heavily dependent on kitchen layout and general floor plan. We do not like open floor plans, so the kitchen is a box that should have had good venting thanks to a short duct run and a make-up air window 10ft from the cooktop. Doesn't work. An open floor plan with the kitchen wide open to living areas are problematic. We lived with that condition while building and confirmed our dislike of open floor plans.
I did fantasize about creating air slots on either side of the cooktop where make-up air would create a bit of an air curtain to help capture errant cooking vapors... spouse, money and design time killed that notion pretty quickly. Also, a spill on the cooktop would certainly fall into the slots and create a monstrous mess.
Focusing codes on range hoods for a push/pull air balance is commendable, but ignores the many other potentials for creating imbalances, particularly venting dryers. As for combustion pollution problems, I don't have them thanks to being 100% electric. The few occasions when I get a little campfire odor is not a danger. I would probably have some difficulty starting a stove fire with the rangehood on high, but we know not to do that.