Have you heard about the
Have you heard about the HOMECHEM project? They are studying indoor air quality rigorously.

@Trey, you may not need MUA
@Trey, you may not need MUA for bath fans (you’ll need to test for that), but conventional clothes dryers typically pull > 200 CFM, so you’ll need to tie that to the damper control (or use a barometric damper).

Here is another issue with
Here is another issue with exhaust fan depressurization in tight homes. Drain traps. In a previous job, we built some research houses that were quite tight. We put in quiet, high-performance bathroom exhaust fans. They were so quiet that they often got left on. Whenever that happened, I noticed sewer gas smells. The house was unoccupied, so I had to keep adding water to the drains to keep the traps full, but I would still get that sewer smell when the bath fan was left running. I finally figured out that it was coming from a floor drain in the mechanical room. Pouring water in it did not help, so I contacted the plumber and he admitted that he did not install a trap on that drain, since these types of drains are rarely used so would likely be dry. He was intending to put a rubber “dry trap” (one-way check valve) in that drain, but he forgot it when he trimmed out the house. He came back and installed it and the problem went away. The moral of the story is that drains can be your source of make-up air if you are not careful. The second moral of the story is that there may be an advantage to having noisy bathroom exhaust fans.

@David, we will have a make
@David, we will have a make up air duct with a motorized damper and a current sensing relay that is connected to the kitchen vent hood. Im not sure if we could connect that same damper to the bathroom vent hoods as well or exactly how that would work but will have to look into it. I agree that we would want some sort of make up air if we do have bath exhaust fans.

I’m still not convinced that we need the bath fans/additional make-up air since we will be exhausting continuously from the bathrooms anyway with the ERV. Without them we might have occasional positive enthalpy exchange (which would be taken care of by the dehu) but with them we would have added loads from the make-up air.

Thanks for your feedback on this, BTW, much appreciated 🙂

@Trey, since you mentioned
@Trey, since you mentioned yours is a ‘Passive House’ project (e.g., super tight), you’ll almost certainly need a makeup air source, mostly for the range hood. A single makeup vent will serve kitchen, baths and laundry. Ideally it should be barometric, meaning that it won’t open until the house reaches a negative 4 or 5 Pascals, thus avoiding becoming a source of infiltration. (If someone knows who makes one of these, please post here. The one I used to specify is no longer produced.)

In general, there are two arguments for makeup air: a) a makeup air vent allows for filtration rather, otherwise it’s pulled in though building cavities (or worse, the garage); and (b) it’s important to avoid negative pressure in hot-humid climates, as that could cause condensation on the back side of drywall, especially where supply diffusers are directed toward the wall (a bad idea in any case).

It’s easy to test whether makeup air is needed once the house is fully sealed. I’m not sure what Passive House requires along those lines but I recommend zonal pressure diagnostics for all homes, especially super tight homes. If a enclosure is leaky enough to not require makeup air (range hood + clothes dryer + bath fan don’t pull a negative 5 Pascals), then a makeup air vent won’t fix what’s already broken!

Thanks David. In that case,
Thanks David. In that case, would you recommend a bathfan with a timer hooked up to a make-up air system, or do you think that the temporary depressurization is not an issue?

Debbie, the whole-house
Debbie, the whole-house ventilation requirements are not based on cooking or gas combustion processes. They are primarily based on occupant and building material contaminant sources. There are separate exhaust ventilation requirements for cooking, regardless of whether it is gas or electric. I commend you for building your “super tight” house without any combustion appliances, but research shows that cooking with electric also generates significant contaminant levels, especially with electric ranges with high temperature heating elements. If you want to really minimize your exposure from cooking, you might consider the newer induction cooktops, but Std. 62.2 still requires exhaust ventilation due to the other food-generated contaminants. I guess the bottom line is that it is OK to eat that stuff, just don’t inhale it.