Panasonic bathroom fan install

[Green Genie]

I'm in the planning stages of back to back bathroom remodels. Neither one has a bath fan. My teenage son never opens the window before showering so the ceiling is showing signs of mold spots. They both have attic access with a new wood shake roof. Ensuite is 9x6 and main bath is 9x7ft.

Questions:
Which panasonic ventilation fan would you recommend?
I'm leaning to the WhisperGreen 80 CFM Continuous and Spot Ventilation Fan with Motion Sensor as that would solve the issue of forgeting to turn on the fan before showering. Other options could be same model at 130CFM, or a basic model with a timer switch mounted on wall.

Venting:
Since it is a new shake roof, I would prefere to run the ducts perpendicular across the ceiling joists to the gable wall instead of hiring a roofer to cut holes in the roof. The ensuite run would be 5ft to the gable wall and the main bath would be about 10ft away. The 130cfm whispergreen model uses 6in ducts and the 80cfm uses 4in ducts. To vent to the side wall I would have to go up and across the 2x10 joists, creating 2 / 90 deg. elbows right after the fan unit. I'm thinking of using insulated flex vent pipe. Would this be too restrictive for a 80cfm flow? Should I have to angle the airflow down so there is no condensation worries?

Wiring:
It seems redunant, but does the Continuous and Spot Ventilation Fan with Motion Sensor model require a wall mounted turn off switch or can it be hard wired direct? The only time I think you would need to turn it off would be when cleaning. Does the Canadian Electricial Code require a turn off switch?

Thanks for your expert help.
Dan

[jch]

I just installed a WhisperGreen 80cfm fan (without motion sensor) in a 10' x 6' sloped-ceiling bathroom. (FV-08VKS2) I got it for 126 bucks + 25 shipping online.

It uses 3 elbows in its 4" ducting plus about 2 feet of straight pipe, angled down slightly towards vent hood in the gable wall. Everything smooth aluminum with insulating jacket. Taped with foil tape, not screwed.

Broan ecoVent (EV-100) vent hood (the one with the styrofoam ball valve rather than a flapper door) so no banging noises on windy nights. In hindsight, this hood is *not* a good match for Panasonic pressure-sensing fans due to resonance of the styrofoam ball. I'll explain further in a separate post if asked.

The one very noticable feature about this fan is that it is almost silent (eerily so) when it has no downstream loading. Once the ducting is connected to the vent hood (the largest resistance in the whole setup), the fan speed automatically ramps up to about 3x the original motor speed to attain the rated 80cfm.

The resultant sound is all white wind noise (though still very quiet) with no discernable motor noise.

Because this particular fan will increase its speed to guarantee 80cfm, I'd recommend going with it rather than the 130cfm model. You'll get less backflow resistance (and less likelihood of condensation pooling) if you use smooth metal ducting.

Instead of using the motion-sense model with a turn-off switch, consider using the non-motion-detector fan model with a humidistat--that'll keep the fan on high-speed long enough to guarantee a condensation-free bathroom rather than having to guess how many minutes delay your motion-detector should be set for.

The wall switch is meant to handle the case where you want to be able to force the fan off, say, if you have the Idle Air Volume switch set to a non-zero value. If you set the Air Volume switch to zero, then theoretically you won't need a wall switch. Not sure about Cdn code requirments though.

Does this help?

[Thatguy]

vent hood (the largest resistance in the whole setup)

Do you have a link for the total equivalent length of straight pipe for this fixture, elbows and 4":3" reducers? I can't find any link that shows resistances for commonly available round duct work fixtures.

[jch]

Do you have a link for the total equivalent length of straight pipe for this fixture, elbows and 4":3" reducers? I can't find any link that shows resistances for commonly available round duct work fixtures.

No I don't

However, I know that the fan speed barely increased when I added my curvy ducting.

It wasn't until I plugged the ducting into the vent hood that the fan speed jumped.

The other (flapper) hoods were even worse for back pressure. Especially the ones with metal (i.e. heavy) flappers. I've returned quite a few to the store while trying to figure this out...

I doubt that you'd find EDL (equivalent duct length) numbers for adjustable elbows because the resistance will depend on how sharp of an angle you have them adjusted to.

One of the Panasonics' main strengths is its decreased sensitivity to back pressure. It'll bump up the speed until it's at rated cfm airflow.

[Thatguy]

One of the Panasonics' main strengths is its decreased sensitivity to back pressure. It'll bump up the speed until it's at rated cfm airflow.

So it simulates a positive displacement pump. I guess they do it with a King's Law flowmeter and a variable speed motor.

Performance vs. price vs. ease of installation may be hard to judge
nexta*.com/bathroom-fans/shop-html

[jch]

Not sure what type of flow meter they're using but, yes, it's a variable-speed DC motor.

At 0.1" back pressure, it only uses 10.6W and makes <0.3 sones. It guarantees 80cfm all the way up to 0.3" back pressure (and uses only 16.2W). At a whopping 0.5" back pressure, it still moves 30cfm.

For comparison, my old noisebox used 85W, generated 1.5 sones and was lucky to move 90cfm with the fan not connected to anything.

Really easy to install. Solid. No obvious leaks in the case (i.e. airtight). Very impressed/satisfied.

[Thatguy]

I guess as the price of electronic hardware drops these high tech things will become more commonplace. The downside is they can't be repaired by the owner and they may be vulnerable to "dirty power" [transients and such]. Also, high complexity generally equals short Mean Time Between Failures.

[jch]

Time will tell. The DC motor is brushless so that should help.

[Harry V]

Broan ecoVent (EV-100) vent hood (the one with the styrofoam ball valve rather than a flapper door) so no banging noises on windy nights. In hindsight, this hood is *not* a good match for Panasonic pressure-sensing fans due to resonance of the styrofoam ball. I'll explain further in a separate post if asked.

John,

I'd be interested to know what the issue is using an EcoVent with the bathroom fan.

I have an EcoVent for my dryer, which works well, and was considering getting one for a new Panasonic bathroom fan. The typical dampers sold here are really flimsy. Thanks.

Harry

[jch]

My advice would be to buy an EcoVent (Big Orange has them) and keep it in returnable condition while you test it on the Panasonic fan.

The problem I had was that the airflow would get going so fast (80 cfm) that the styrofoam ball in the EcoVent would start to resonate against the foam housing. Would usually take a few minutes before this happened--for the airflow to just hit amount needed to sustain the resonance. Once the ball started resonating, it sounded like someone had a sabre saw cutting through the wall of our house -- you could hear it 2 floors away!

There are 5-6 air slots in the EcoVent's critter guard (plus 1 on each side to relieve the pressure above the ball).

The solution was to cover 2 of one side's air slots (without covering the outermost one) so that the airflow was now exiting the vent off-center. This presses the ball to one side of the vent (it tries to stay centred in the airflow). I used aluminum tape to cover the slots -- we'll see how well that lasts.

My guess is that for constant-speed (vs. constant airflow) fans you wouldn't have any resonance issues. It's just that the Panasonic adjusts its speed based on the measured airflow and happens to settle at an airflow that causes resonance in the EcoVent.

Now the EcoVent is super-silent (even on windy nights) and the Panasonic fan runs nice and quiet.

Does this help?

[hj]

qutote; It guarantees 80cfm all the way up to 0.3" back pressure

Since one room is about 430 cu.ft, and the other is 500, that would give one complete air exchange every FIVE minutes in one case, and about SIX and one half for the other. Both of which would probably range on the side of "ineffectual" for removing humdity in the rooms, and that assumes sufficient air replacement to give a full exchange.

[jch]

Don't you typically aim for 5-8 air changes per hour for bathrooms? (7-12 minutes per air-change)

[Harry V]

The problem I had was that the airflow would get going so fast (80 cfm) that the styrofoam ball in the EcoVent would start to resonate against the foam housing. [...] The solution was to cover 2 of one side's air slots (without covering the outermost one) so that the airflow was now exiting the vent off-center. [...]

John,

Thanks a lot for the informative reply. (Sorry for not replying sooner; I just saw your post now.) I'm installing two Panasonic fans, 50 and 80 cfm. Will see if the resonance issue occurs with either one.

Harry