Is my bathroom fan venting into unvented space between ceiling and flat roof??

Motorapido

My 1920s three story brick house has a 1950 one story bedroom/ bathroom addition. The addition has a flat rubber roof. The exterior brick toward the roof on the addition has no vents to vent the air above the finished ceiling inside and the flat roof. The bathroom ceiling powered fan vent draws lots of moist air out of the bathroom very effectively, but without visible vents on the brick exterior between the ceiling level and rubber roof level, all I can assume is that the moist air is simply getting dumped into the unvented space between the ceiling and roof. I'm in Pennsylvania, where we have very hot, humid summers and very cold winters. I've owned the house three years, and I see no evidence of condensed water damage on the ceiling of this addition, and when I walk on the roof membrane, I don't detect springy, wet wood structure beneath. I would expect that dumping all the highly humid bathroom shower exhaust air into the unvented space would create evident damage. The roof has three equal diameter plumbing vent stacks. Is it possible that the fan exhausts through one of them? I can't imagine that, since the stacks are straight pipe with open tops. I put my ear to the opening of each stack while the fan was running below and heard no fan sounds and felt no exhaust air. Any guesses on where this exhaust air is going? A real long shot guess is that the fan might exhaust through a duct that would take a long journey to the wall between the addition room and the kitchen and tie into the kitchen exhaust duct, but that is a long shot guess. Thoughts?

STEVEusaPA

I doubt they would pipe it that far.
It would most likely come out of the wall, but you said you looked and didn't see one. It could be dumping into the dead space. Can you get up there and look? I'd be concerned about mold, and possibly rotting the underside of the roof (deck).
You can also have someone spray Fabreeze into the fan and someone else go on a sniffing expedition.
Is the roof vented anywhere around the house?

JUGHNE

I have seen these cases where there is no duct on the exhaust at all. If you remove the fan motor/blower you can feel thru the damper if any duct connected. If there is none then it goes nowhere.
Some believed putting just a short pipe on would achieve something, perhaps get the exhaust above the insulation.

Motorapido

As a steam heat lover who respects the deep wisdom of The Dead Men of steam, I wish that there had been similarly wise Dead Men building and ventilating this addition nearly 70 years ago. Good idea on the Fabreze trick. I'll try it. But with no external vents anywhere I can find, I'll probably just confirm my fears when I can't smell anything. I'll also remove as much of the bathroom fan as I can without risking damage to the plaster ceiling, to see if I discovered a duct. Wish me luck.

JUGHNE

Just removing the grill and fan motor/wheel assembly should get you to the discharge damper.
Most ceiling fans were nailed to the ceiling rafters, with the nails inaccessible after the ceiling is installed.

Fred

Are you sure your exhaust fan isn't using one of the cavities between the roof rafters and one of those three vent stacks isn't just penetrating the roof deck at that particular cavity, with no pipe between the stack and the fan? That's not the way to do it, unless that cavity is lined in some way but people are creative in the construction industry. If that's the case, you may well not hear the fan motor or have enough air velocity to feel it at the top of the stack.

Also, do you have eave or soffit vents on the exterior overhang on the house? It could be vented to one of those.

Leonard

Maybe a USB camera on a cable to look up there. Possible fan is venting into ceiling cavity , them a short pipe vents that cavity thru roof...... no connecting intermediate pipe. DIY plumbing

If it's just dumping into ceiling , I'ld be very concerned about humid air condenseing on rafters and wood roof deck in winter. Would at least get mold, eventual possible rot of structural rafters

EBEBRATT-Ed

If it moves air as effectively as you say than I would think it has to be going somewhere. Exhausting into the roof space would be like a dead ended duct

ChrisJ

I've seen many fart fans without any duct. It's amazing.

None of us can tell you where yours is going, only that yes, many times hacks install them like that and it's very bad.

Motorapido

Thanks for all these comments and insights. I love this forum. Here's a follow-up question. If one of the vertical wide open at the top vent stacks is used to vent air beneath the flat rubber roof, what prevents rain from falling into the pipe and then into the space beneath the roof deck? Do these stacks ever have a. P-trap? If so, I could imagine that just above the p-trap you could have a tee that could either connect to duct to the fan or just open to vent out the positive pressure created by the fan. It's odd to think somebody would engineer it that way, but we've all seen many a corner cutting hack. The rubber roof is adhered to the perimeter wall and protected with copper flashing. There is no overhang and no soffit and no vents. Despite the lack of visible vents, the fact that the plaster ceiling has lasted for the 70 years since the addition was built leads me to believe that there must be a way that the hot humid air from the fan can vent. Could my idea be correct that one of the vent stack pipes might have a p-trap and a tee fitting to allow the air to escape? I forgot to mention that the fan appears to be about a 1970 vintage, so 20 years newer than the addition, but still plenty old.

EBEBRATT-Ed

Could this fan be vented back into the attic of the main house?

Intplm.

There should never be any type of air from a exhaust fan connected to a plumbing drainage waste and vent system. This should never be done.

Your suspicions that it may be hooked up that way, or any other odd way when nothing else is visible are understandable.

I would check the entire building a few more times. Look for side wall registers, roof (again) or under an eave. Sometimes a registers used to vent bathroom exhaust can closely match the decor of the building including eave vents.

Using a device that emits a smell is an idea but a smell can travel in a way that is tough to trace.

What I would do is use smoke or something that carries like smoke does. If you do use smoke, have some fans ready to blow any excess out. Of course you can only judge whether or not to use smoke, and how much can be used safely in your home.

Leonard

This is the reason cities require permits and inspections........ but that doesn't stop incompetent DIY installations.

In past I've seem a China ~ 1/2 inch diameter "pencil" USB camera on ~ 25 ft cord on ebay for ~ $10.

Tape small LED penlight on it and push it thru past fan and see if there's a duct. Then note turns, left and right, and distances and you can likely guess at where it comes out of house, if it does,

Motorapido

Good plan on the USB camera. Now I have an excuse to buy one.

Larry Weingarten

Hello, Ultimately it sounds like two options are to install duct from the current fan run to an exterior wall, or to install a wall mounted fan and seal up the present one. I suppose a third option would be to penetrate the rubber roof, and use the current fan, but that seems risky. A new, quiet, Panasonic fan would be better than keeping the 1970s fan.
You could try the smoke test to see if there is anything to be discovered, but use "theatrical smoke" to test with. In theory, it's less toxic than real smoke. How's that for a jumble of thoughts?
Yours, Larry

Motorapido

Good thoughts

ChrisJ

I installed a Panasonic low profile fan in my bathroom that has a flat roof. It was stressful because I didn't know exactly what I was getting into but I wanted a fan.

The low profile one fits in the shallow space and then I snaked 4" insulated flex into the main attic where that ceiling connects into the house. I then vented it through the roof.

In my case it worked and the Panasonic fans are amazing. I also couldn't live without the night light these days.

JUGHNE

Could you install a soffit, with a new fan, perhaps above the WC, then vent out thru the outside wall?

In building our house the design purposely included soffits above the WC for two baths. The adjacent inside wall of 2 x 6 was used to enclose the 4" duct down thru the floor to the joists and then out thru the outside wall. Another 1/2 bath had the fan mounted in the wall and vented down with 3" in the same manner.
No holes in the ceiling, avoiding air infiltration, no roof penetration for leak potential.
No downflow of cold air thru the ducting.

Just some ideas.

Motorapido

Jughne, that's a great design

JUGHNE

All 4 of our WC's are in 36" pockets of the rooms.
It instills more privacy even though the room door can be locked.

Also since having hip problems myself and wife with recent knee surgery, installing helper bars on each side was quite easy.
Delta has a great TP dispenser that doubles as a grab bar, BTW, only available at the big box stores I was told.

Fred

JUGHNE said:

All 4 of our WC's are in 36" pockets of the rooms.
It instills more privacy even though the room door can be locked.

Also since having hip problems myself and wife with recent knee surgery, installing helper bars on each side was quite easy.
Delta has a great TP dispenser that doubles as a grab bar, BTW, only available at the big box stores I was told.

The chair height WC's are great too.

JUGHNE

Just put one in the master bath.
Put grab bar at the same height across from TP grab bar.
After needing these a little I realize the proper ADA height is too high.....good for an old man to lean on standing....too high, for most people, to launch yourself up from the throne though.

ChrisJ

I'm still hoping to get around to restoring the vent-away. Though that isn't chair height I'm surprised it doesn't come with an ottoman.

Intplm.

Chair height is very nice. Elongated with soft close seat extra nice.

Leonard

For dad I installed helper arm rails to the porcine throne , bolts to same holes that hold the regular seat. Use arms to help lift, worked well.

Helped make my bad back better , use arms to mussle up, less stress on back