ERV for Bath Ventilation
Want to get an opinion on using an ERV as bath ventilation in lieu of dedicated bath fans in each bath. I am an Architect building a two story 2700 SF 4 BR / 3.5 bath residence with a fairly tight envelope. This is located in the Delaware Shore area. I expect to get 1 or better ACH/ 50pa on the blower door test. I am specifying a Panasonic intellibalance 100 ERV unit for whole house ventilation. The ERV will be ducted independently from the HVAC units. The ERV will have exhaust from each bath and kitchen and supplies to the bedrooms and Living areas. The unit has a boost feature to increase ventilation via remote switch locations. Trying to decide if I also need additional independent bath exhaust fans……I don’t like the idea of cutting additional holes in my building envelope for this but understand individual fans may perform better as far as reducing steam and odors compared to the ERV alone. My bath areas are relatively small 5′ x 6′ toilet / shower compartments except for one larger open bath of 6′ x 10′. Any opinions and shared experience with this situation is greatly appreciated.
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I'd like to tell you that it will work fine but I have suspicions that it won't. The problem is that the exhausts air flow will be divided equally between all the bathrooms and the one in the kitchen area. If the boost function goes to 100 cfm you will conservatively be dividing that 100 cfm rate by at least 4, i.e. 25 cfm per bathroom. I don't think it will work. It's too bad because using an ERV exhaust in the bathroom is an elegant solution otherwise.
There might be an interesting technological solution if someone could come up with it. One normally doesn't need exhaust to more than one bathroom at a time. If you could shut a damper to all the other bathroom exhausts and the kitchen exhaust if a boost switch is closed in one bathroom then it would work. Like solutions to most problems the trick would be to not introduce other related problem while creating that solution.
This question gets asked here regularly, and there are people who argue both sides convincingly. I don't remember anyone who has gone with an ERV + boost function who has regretted it though.
One question I have is whether the Panasonic 100 is large enough to supply sufficient ventilation? Using the ASHRAE formula it seems a bit undersized.
I have an ERV with Boost. It doesn't work. My master bathroom is constantly 20%+ higher humidity than the rest of the house. I've tried to balance it better, to pull more air from the room, but it just isn't enough. The ERV is technically oversized per the ASHRAE formula.
Alas, details of the system are needed in order to place this in any useful context. Too many things that can be at fault beyond "this doesn't work".
What is the CFM of the exhaust on boost mode?
Our bathroom is a six by fourteen foot open space. Two shower heads at one end. Hrv on boost clears the air well, no need for additional ventilation. We're in zone 6, PH level air tightness.
Stephen - what's the air flow that your HRV is exhausting from the bathroom?
To the best of my recollection, it's 24 cfm on boost, 12 on medium, which is what Zehnder set at commissioning for general ventilation. Total for the house is 72 cfm unless on boost.
Stephen - Thanks - very helpful! That's the size of our planned bath, same CZ, and I've been wondering what's needed.
We use our Panasonic Intellibalance ERV (without Boost Mode) for our bathroom ventilation. It seems to work fine for my wife and I 99% of the time. Under extreme and rare circumstances, we simply crack the window for a few seconds. We measure our RH continuously and it rarely exceeds 50%.
If I had three kids that needed to shower before bed, then I might reluctantly consider dedicated exhaust. I prefer increased air tightness over children.
Check the Aldes line of bathroom ventilation, their air dampener can pull from the bathroom that needs ventilation.
We just a did a similar sized house and also used the same ERV. I am also an HVAC contractor and we do a lot of higher end homes. My own house I used the ERV to pull exhaust out of the basement bathroom, powder room on the main floor and the laundry on the second floor. I ran independent lines to each with balancing dampers in each. I used Panasonic exhaust fans in our master bath as well as the kids bath. I set my ERV to supply positive pressure to try to make up some air that the stand alone fans remove. We have been very happy with this set up so far. I have found in the builds we do when the architect, engineer or whoever does the manual J S D and T if they spec a ERV for high moisture and heavily used areas like a master bath the owners are generally not very happy with the results. It is very common to have zoned systems in these houses and the thermostat is almost always in the master bedroom. A hot shower with inadequate ventilation in a tight house lets a lot of heat linger and can affect the entire zone. At my house the damper on the roof term for my bath fan was only opening maybe 1/3 if the way cutting my ventilation and it was not uncommon for the thermostat to raise
2 degrees after a shower. Once I figured that out and was able to get rid of the heat quickly things improved a lot
Thanks for that input. I am leaning towards a similar approach using a combination of bath fans and the ERV like you describe. Do you have the ERV running continuous or intermittent and can you explain the positive pressure a bit more? I understand the panasonic has two fans so you can set it so the house is slight negative or positive pressure? I envisioned having the fan run intermittently and keep it set for positive pressure or I look at it as pushing air out of house. Thanks again for your comments.
I have done it both ways but in my house the ASHRAE called for 94 CFM of ventilation which is just barley under the output of the ERV I installed. I have this one set to run continuous and I also run the blower on my furnace continuously at a very low speed. When we put in bigger ERVs or HRVs with boost features we will often interlock them with the air handler blower so they run when there is a call for heat or cool or when the boost feature is activated. Most people will prefer a positive pressure meaning you are pushing a little extra air into the house rather than pulling things into the house as would happen if it were negative. In my case I adjusted the ERV to supply about 100 and exhaust about 75. Between the two exhaust fans and also the kitchen exhaust running a couple times a day I wanted to make sure we were positively pressurized 'most' of the time. I haven't set my monometer to verify anything yet but so far it has been working well
It could be possible to vent all bath register ducting to a remote fan which would require only one hole in your envelope. Here's an example to which I refer: https://tinyurl.com/y4kufaqf
I have a Zehnder system that provides 36-38 CFM in each bathroom on boost and that's worked fine.
I have a Broan ERV (erv140te I think?) but haven't built my house yet. I've been trying to plan things out and have been pondering about all facets, and a similar predicament crossed my mind a few times.
I take hot showers and create lots of steam! I decided to call Broan and asked if it's OK to remove moisture/steam from a bathroom with this ERV. I was NOT advised to use the ERV in this fashion as it's not designed for this purpose.
I have an identical concern about popping more holes into my envelope. I hate to think about doing it. So I will use a Panasonic bath vent in the master and rely on the ERV for the other two baths that will not see the humidity that the master bed will. Please keep us posted on what you end up doing.
Personally I wouldn't use just one of these units for a 2 storey 2700sf home.
I bought one for each floor and would highly recommend doing so. You should be fine if you do that. Generally it's best to have the units run continuously, with boost function when needed.
I also went with a TP link Kasa WiFi switch for the boost function. The 3-way model. This allows mounting one switch in bathroom and one in kitchen, plus tying into google home / alexa for control, and also some programmability in the app if you want the switch on a timer.
Thanks all for the helpful comments. Based on one comment I have been looking at the Aldes electronically controlled dampers. These seem like a good system because you can set them to allow for continuous ventilation mode and then open in a specific bath when the boost switch is activated from that bath. I am finding that if I calculate based on ASHRAE for whole house ventilation on continuous mode that the CFM rating is coming in too low when trying to also vent bathrooms similar to a traditional fan. By increasing the CFM capacity and utilizing the zoned dampers from Aldes I believe I can build a good system that does both. The only other reservation that some have is that using an ERV to vent baths will mix back some of that humidity into the supply air stream. For the 10 to 15 minutes a day the shower is turning out steam I don't believe that will be that big an issue. Anyway I am still trying to decide how to proceed. Thanks again for all the great input.
I think the Aldes electronically controlled damper may be a good idea. I think at least one, or even two Panasonic sized ERVs would be appropriate for the size of your home depending of the occupancy number of your house. Two of them would certainly help with evacuating steam from a bathroom. In any case, before cutting an opening in an outside wall for a damper I would suggest partially opening a window in a bathroom to an area approximately the size that the damper would present. Then check if the ERV fan in boost mode clears the steam quickly after a hot shower. If it doesn't then you know an Aldes damper won't do it alone. Then it's time to consider an additional ERV or to remove an ERV exhaust to the lesser used bathrooms so it doesn't overload the existing ERV.
Note that the moisture recovery % of an ERV is reduce at higher airflow rates. That helps a little if you are boosting the speed as well as using dampers. I have a swappable core ERV/HRV, so for at least some of the time when I don't want that moisture recovery from showers, have the HRV core in place.
FYI - This is from the Broan website... Fresh Air Systems FAQ
"Must I also install bath fans if I choose to install a Fresh Air System?
A Fresh Air System cannot be as effective if the high levels of humidity generated by today's shower and tub systems is allowed to dissipate throughout the entire house. It should be removed at the source by running a bathroom exhaust fan for 20-30 minutes after each shower. Your bathrooms should be properly measured and fans for each room must be chosen with proper CFM (Cubic Feet of air per Minute). Then the house's general ventilating system can control the moisture."
"Can I ventilate my bath fans through a Fresh Air System's ductwork?
It is not recommended that you do this. When a Fresh Air System (FAS) has been properly sized and balanced, any vent fan that operates during operation of the FAS will unbalance that system, rendering it ineffective. The high humidity from the bathroom, along with any odors, may be circulated throughout the rest of the house."