Calif. Dwelling unit IAQ via bathroom fan?

[Yikes]

Existing concrete apartment building in Los Angeles is receiving a new heat pump system (ductless mini-splits), with new condensers up on the roof.
Previously, the only HVAC system in the apartments was radiant steam heat, and a bath exhaust fan.

The mechanical engineer says CA code will require fresh air supply for Indoor Air Quality at the existing apartments. In the past we've done a low-speed continuous bath exhaust fan (switches to high speed via occupancy sensor), and the front door of the unit would have a 1/2" undercut for fresh air supply from the corridor.

When I shared this with the engineer, they replied: "The front door undercut does not accept fresh air intake; you can only use it for bathrooms. You need to provide outside air with a supply fan."

Q: Do you know of anything in the codes that prohibits use of a door undercut to supply whole house IAQ, especially on an existing building?

 

[steveray]

NFPA 80...

7.2.3.3.4

Clearance under doors, in the closed position, shall not exceed 3⁄8 in. (10 mm) above raised noncombustible sills and not more than 3⁄4 in. (20 mm) above the floor where there is no raised noncombustible sill.

IBC

1020.6​

Corridors shall not serve as supply, return, exhaust, relief or ventilation air ducts.

Exceptions:

1. 1.Use of a corridor as a source of makeup air for exhaust systems in rooms that open directly onto such corridors, including toilet rooms, bathrooms, dressing rooms, smoking lounges and janitor closets, shall be permitted, provided that each such corridor is directly supplied with outdoor air at a rate greater than the rate of makeup air taken from the corridor.
2. 2.Where located within a dwelling unit, the use of corridors for conveying return air shall not be prohibited.
3. 3.Where located within tenant spaces of 1,000 square feet (93 m2) or less in area, utilization of corridors for conveying return air is permitted.
4. 4. Transfer air movement required to maintain the pressurization difference within health care facilities in accordance with ASHRAE 170.

 

[Yikes]

1. 1.Use of a corridor as a source of makeup air for exhaust systems in rooms that open directly onto such corridors, including toilet rooms, bathrooms, dressing rooms, smoking lounges and janitor closets, shall be permitted, provided that each such corridor is directly supplied with outdoor air at a rate greater than the rate of makeup air taken from the corridor.

I notice that the code allows it for ANY rooms that open directly into corridors. The phrase "including toilet rooms, bathrooms, dressing rooms..." is not an exhaustive list. So these studio apartments could get their makeup air from the corridors.

 

[wwhitney]

When I shared this with the engineer, they replied: "The front door undercut does not accept fresh air intake; you can only use it for bathrooms. You need to provide outside air with a supply fan."

Just wanted to comment that even if the red sentence is true, the next sentence doesn't logically follow from that. Physics-wise (not sure about code-wise), you could provide a fan for forced exhaust and some other passive inlet for the make up air, rather than using a second fan for forced makeup air.

Cheers, Wayne

 

[Yikes]

Just wanted to comment that even if the red sentence is true, the next sentence doesn't logically follow from that. Physics-wise (not sure about code-wise), you could provide a fan for forced exhaust and some other passive inlet for the make up air, rather than using a second fan for forced makeup air.

Cheers, Wayne

What the engineer wants is for me to remove a pane from an apartment window and replace it with an intake air grille, attached to a duct, attached to an intake supply fan that is mounted inside the unit.

Meanwhile, we have unconditioned corridors in a temperate West L.A. climate zone, with the ends open to the outdoors, for plenty of makeup air into the corridor.

 

[Yankee Chronicler]

I notice that the code allows it for ANY rooms that open directly into corridors. The phrase "including toilet rooms, bathrooms, dressing rooms..." is not an exhaustive list. So these studio apartments could get their makeup air from the corridors.

But outdoor ventilation air is not makeup air.

 

[Yikes]

But outdoor ventilation air is not makeup air.

Please explain further the difference between makeup air and outdoor ventilation air. More specifically, do you believe my proposal regarding achieving IAQ via a low speed continuous bath fan and apartment entry door undercut is code-compliant in California?

 

[Yankee Chronicler]

I have always regarded the key to understanding and applying the building codes as following a logical sequence, or path, through the codes. As the king said in Alice in Wonderland, "It is best to begin at the beginning, and go on until the end."

So the requirement we first need to satisfy is the IMC requirement for ventilation air, and the tables don't care about total air circulation, they tell us the minimum amount of outdoor air that must be provided.

401.2 Ventilation required. Every occupied space shall be
ventilated by natural means in accordance with Section 402
or by mechanical means in accordance with Section 403.
Dwelling units complying with the air leakage requirements
of the International Energy Conservation Code or ASHRAE
90.1 shall be ventilated by mechanical means in accordance
with Section 403. Ambulatory care facilities and Group I-2
occupancies shall be ventilated by mechanical means in
accordance with Section 407.

You're asking about mechanical ventilation, so that excludes section 402. So looking at section 403, we find:

403.1 Ventilation system. Mechanical ventilation shall be
provided by a method of supply air and return or exhaust air
except that mechanical ventilation air requirements for
Group R-2, R-3 and R-4 occupancies shall be provided by an
exhaust system, supply system or combination thereof. The
amount of supply air shall be approximately equal to the
amount of return and exhaust air. The system shall not be
prohibited from producing negative or positive pressure. The
system to convey ventilation air shall be designed and
installed in accordance with Chapter 6.

So far, so good. In apartment buildings (R-2), ventilation can be accomplished using exhaust fans -- IF the air intake openings comply with the code. To determine that, you then have to look at sections 401.4 through 401.6.

Completely aside from the undercut door probably not complying with code requirements for fire resistance, I don't think an undercut door satisfies all of the conditions required by 401.4 through 401.6. And 401.4 says:

401.4 Intake opening location. Air intake openings shall
comply with all of the following:

 

[Joe.B]

So the requirement we first need to satisfy is the IMC

California doesn't use IMC.

 

[Yankee Chronicler]

California doesn't use IMC.

Oops. I forgot -- California is spayshul.

Sorry.