Complex challenge with bath exhaust fan - need help with solution!

Don’t know if this is an electric or HVAC question, but here is my problem …

we have a 60’s brick ranch house that we are remodeling … one story with a full basement … it has 2 small baths that stack on top of each other, both on the back wall of the house … the exterior wall on the top bath is brick veneer on wood frame and the the exterior wall on the lower bath is 10" concrete block … now, the issue we have …

neither bath has an exhaust fan … I don’t want to just exhaust the upper bath into the attic space and going through the brick wall to the outside would be a pain; however, going into the attic and piping to the soffit (we have a fairly wide overhang) seems like a reasonable solution … but, what about …

the lower bath? … the only options I can come up with to vent to the outside is to go through the concrete block (ugh!), go into the space between the two floors and then through the brick wall above (not easy either), or lastly …

go up and through the upstairs bath and tie into the exhaust pipe in the attic (in other words, share the same exit pipe with the upstairs bath) … this could be done fairly easily since both baths are currently torn down to the studs … my question is …

can or should this be done? … I’ve never seen it done before … it’s a long way for the exhaust to go up and out from the lower bath to the soffit on the upper floor …

any ideas or suggestions about how to solve this exhaust challenge? …

if my idea makes sense, how should I size each of the exhaust fans? again, both baths are small (about 6’ x 8’).

Thanks in advance, Bill

You can install one fan to control both bathrooms. The lower bathroom hose is going to be quite long but it should be fine. If your concerned about condensation build-up in the lower bathroom then you have no choice but to penetrate the solid wall.

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Thanks for your help, David. Just emailed a question to the fan company.

Steam from the lower bath can’t be exhausted up and out?

I think 2 fans sharing one stack will end up sending a significant portion of the air down to the other fan. Bathroom 1 will steam up bathroom 2

Not with a back flow damper…

Have someone cut a hole in the concrete for you. It’s not as bad as it sounds.

You don’t want to take the exhaust through a soffit if the soffit has vents to the attic.


I do have soffit vents and a ridge cap vent to ventilate the attic. Why should I not exhaust these two baths into the attic and out through the soffit? … of course, the soffit vent for the bath exhaust would be ducted.



I don’t see a problem with a bathroom vent being installed in a soffit, even if the soffit is being utilized for venting of the attic.

Where can one buy an outlet vent for a soffit application? Seems like all of the exhaust fans at Lowe’s and Home Depot are geared for an exterior wall application with the flapper vents, which wouldn’t work in a horizontal installation.

What is the bath exhaust setup used in most new houses today?

The covers you are looking for can be found at most hardware stores. If you having a hard time trying to locate one locally, order one on-line here for 12 bucks.


[Quote: Bill]
but, what about … the lower bath? … the only options I can come up with to vent to the outside is to go through the concrete block (ugh!), go into the space between the two floors and then through the brick wall above (not easy either), or lastly … [End Quote]
[FONT=Arial]Cutting through "concrete block" is very easy. I would strongly recommend that you vent this basement bathroom to the outside wall.[/FONT]

[FONT=Arial]When you pull the permits for this job ask your local town code compliance inspector what they recommend.[/FONT]

  • **If you do this renovation without permits you could wind up having to tear it down and “redo it according to code.”
    ****[FONT=Arial]Looking for the most current information?Here is some information that you might find useful;:smiley:

The 2006 International Residential Code for One and Two Family Dwellings

Air that is conveyed to or from occupied areas through ducts which are not part of the heating or air-conditioning system, such as ventilation for human usage, domestic kitchen range exhaust*, *bathroom exhaust and domestic clothes dryer exhaust.

IRC, Section Are 303, Light, Ventilation, and Heating.
R303.3 Bathrooms.
Bathrooms, water closet compartments and other similar rooms shall be provided with aggregate glazing area in windows of not less than 3 square feet (0.3 m2), one-half of which must be openable.
Exception: The glazed areas shall not be required where artificial light and a mechanical ventilation system are provided. The minimum ventilation rates shall be 50 cubic feet per minute (24 L/s) for intermittent ventilation or 20 cubic feet per minute (10 L/s) for continuous ventilation. Ventilation air from the space shall be exhausted directly to the outside.**

M1507.1 General.
Where toilet rooms and bathrooms are mechanically ventilated, the ventilation equipment shall be installed in accordance with this section.

M1506.2 Recirculation of air.
Exhaust air from bathrooms and toilet rooms shall not be recirculated within a residence or to another dwelling unit and shall be exhausted directly to the outdoors. Exhaust air from bathrooms and toilet rooms shall not discharge into an attic, crawl space or other areas inside the building.

M1507.3 Ventilation rate.
Ventilation systems shall be designed to have the capacity to exhaust the minimum air flow rate determined in accordance with Table M1507.3. Mechanical exhaust capacity of 50 CFM intermittent or 20 CFM continuous

2006, International Mechanical Code
502.18 Specific rooms.
Specific rooms, including bathrooms, locker rooms, smoking lounges and toilet rooms, shall be exhausted in accordance with the ventilation requirements of Chapter 4.

2006, International Property Maintenance Code
BATHROOM. A room containing plumbing fixtures including a bathtub or shower.

Chapter 4, Light, Ventilation, and Occupancy Limitations

403.2 Bathrooms and toilet rooms.
Every bathroom and toilet room shall comply with the ventilation requirements for habitable spaces as required by Section 403.1, except that a window shall not be required in such spaces equipped with a mechanical ventilation system. Air exhausted by a mechanical ventilation system from a bathroom or toilet room shall discharge to the outdoors and shall not be recirculated.

**403.4 Process ventilation. **
Where injurious, toxic, irritating or noxious fumes, gases, dusts or mists are generated, a local exhaust ventilation system shall be provided to remove the contaminating agent at the source. Air shall be exhausted to the exterior and not be recirculated to any space.

2006 International Plumbing Code
BATHROOM GROUP. A group of fixtures consisting of a water closet, lavatory, bathtub or shower, including or excluding a bidet, an emergency floor drain or both. Such fixtures are located together on the same floor level.

2006 International Building Code
IBC, 1203.4.2.1 Bathrooms.
Rooms containing bathtubs, showers, spas and similar bathing fixtures shall be mechanically ventilated in accordance with the International Mechanical Code.
{See Chapter 15, SECTION M1507 MECHANICAL VENTILATION, M1507.1 General. located above}

2006, ICC Performance Code for Buildings and Facilities
Chapter 9 Moisture, Section 903 Internal Moisture
903.3 Performance requirements.
903.3.1 Excess moisture removal and protection.
An adequate means shall be provided to remove excess moisture or protect the structure from the effects of excess moisture and condensation to all habitable spaces, bathrooms, laundries and other locations where moisture may be generated.

**I hope that this information can be of some help.:smiley: :nachi: **