Do operable windows count as openings for mechanical ventilation? 2

[nuuvox000]

We do a lot of multi-family housing projects and typically we meet ventilation code using bathroom exhaust fans; they pull air into the unit at the same time they're exhausting.

With buildings getting tighter and tighter nowadays, I get worried that fresh air isn't getting in very well. Do operable windows count as openings for people to air out their units when they need to? Or does it need to be able to provide the minimum flowrate with all of the windows closed? The code doesn't really say much about making the openings operable or not so I'm wondering if anyone has any thoughts about this.

Thanks in advance.

 

[EnergyProfessional]

Check your local code what the building type requires. I have no idea if you are in Zimbabwe, or New York City or if you talk about a camping cabin, or the World Trade Center.

Where I live there is very limited provision to allow use of natural ventilation instead of mechanical ventilation. This often is limited to single person spaces, or residential living areas. But in most cases, mechanical exhaust is required in bathrooms.

I'm not sure if you mis-spoke. But bathrooms and similar spaces have an exhaust requirement. This means the air cannot be recirculated through other spaces, they have to be EXHAUSTED to the outside. You often can use transfer air from other spaces to make up for the exhausted air.

 

[nuuvox000]

This is in the USA; using the 2018 IMC. Natural ventilation won't work in this case because there is too much living area when compared to the outside air opening areas.

I don't see that I misspoke but probably wasn't clear. I am meeting the exhaust requirements in the bathrooms and exhausting to the outside. The IMC allows you to use the exhaust rate to count towards ventilation air since air out = air in (through windows).

 

[EnergyProfessional]

"using bathroom exhaust fans; they pull air into the unit at the same time they're exhausting."

This is not clear. Do you have separate fans to exhaust and fans to bring in make-up air? Or does make-up air just infiltrate?

 

[IRstuff]

air out = air in (through windows).

Or doors. While windows might be tight, doors often are not.

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[ME27272727]

Natural ventilation seems to be a grey area and up to interpretation. In my opinion, you should consider space type, climate zone, and whether occupants will actually keep windows open while the space is occupied (not going to happen for the great majority of locations).

 

[EnergyProfessional]

It actually is not a gray area since the code (at least in my area) clearly describes under what conditions (type and size of space) you can use natural ventilation and what conditions need to be met (e.g. area of opening). If the code is not clear, one always can ask JHA.

Without looking into the applicable code(s) the whole discussion is moot, IMHO.

 

[Champchops]

Natural ventilation is not mechanical ventilation by definition but in IMC you can comply with ventilation requirements through mechanical or natural ventilation.

The factors you need are the size of the area being ventilated, the operable area of the windows, and the maximum distance in the room from an operable window. Look in IMC on how to use these values to determine compliance. Be prepared to submit calculations to your AHJ as well.

All that being said; natural ventilation doesn't work nearly as well as mechanical ventilation. It is quite simply often used just to comply with code.