Sunday - October 04, 2009

Mr. Maintenance

That’s one of the jobs I have to do today for my regular Sunday customer. The vent fan they have in the lab bathroom gave up the ghost, and they want me to put in a new one. It shouldn’t be a big deal, as the ceiling there is suspended fiberglass panels underneath rebar trussing. So I’ve got all the clearance room I’ll ever need. And the wires and switches are already in, so it’s just a matter of going up on a ladder, getting the old one out, and hooking the new one up. Gosh, I might have to cut a new hole if the new fan has a bigger faceplate. Looks like a 90 minute job.

Now it’s down to picking the proper fan. They don’t need one with a light built in, and they don’t need one with a heater built in. And it’s a semi-industrial setting, so the fan noise level isn’t much of a concern. Price is a concern, but I know where to get stuff on the cheap, because I am the GoogleMeister.

So, what fan to pick?



If you read the typical Fix Up Your Bathroom web pages, they will tell you that a bathroom fan should be able to change the air at least 8 times an hour. How do you calculate how much fan you need with that? It’s pretty easy:

Length X Width X Height X 60 minutes in an hour
-------------------------------------------------------- = Number of Cubic Feet Per Minute needed
8 air changes per hour

Thus, if you had a 10 x 10 x 8 bathroom, you’d get 8 air changes per hour with a 54 CFM fan. The problem is, 8 changes per hour is 7 1/2 minutes per change. While this is probably fine for your home bathroom, and probably fine for clearing out the steam from your shower, you want a bit more than that in a workplace. Just in case your trip to the bathroom ... is, um, aromatic.

So, how to go about finding how much fan you need to de-stink the place quickly, but not so much fan that it sucks the paint off the walls? If you think that 3 minutes is a typical length of visit, then divide those 3 minutes into an hour and you see that what you really want is 20 air changes per hour, not the leisurely recommended 8. Recalculate the above example, and you’ll see you need a fan that can flow 133 CFM. Now realize that with ducting, fans don’t operate at maximum efficiency, so move to the next model up. That means you want to install a 150 CFM unit. With that amount of ventilation, by the time the employees are done washing and drying their hands, the room is almost fully aired out. And if they visit for longer than that, then no problem. You really want to keep the number of air changes above 12. But let’s not go crazy. 30 changes per hour is quite excessive, unless you have a whole queue of folks lined up to use the room every day. In which case it’s really nice.

Just remember that you have to let air in to pull air out; you may need to install an air inlet or trim 3/4” off the bottom of the door. If the door to floor gap is about an inch, you’re fine.

Gosh, but aren’t fans that powerful both noisy and expensive? In the past they were, but no longer. Fans are getting better every year. Panasonic has a full line of high volume, super quiet fans that are very competitively priced. Their Whisper Ceiling fans cost much less than a similar CFM model by Brone, run much quieter, and last nearly forever. And they’re all Energy Star rated, pulling only 31 watts or less. Plus, if you shop around you can get one for nearly half price.

And quiet these days is defined by the “Sones” rating. Old fans ran at 3 - 5 Sones or more. Conversation is around 2 Sones. A couple years ago “quiet” fans were at 1.0 - 1.5. Today, a really quiet fan runs at 0.5 Sones, and if you use fiberglass wrapped flexible ducting (Air King makes this stuff) it cuts the noise even more. 0.5 Sones is so quiet you have to almost strain to hear it.

Another way to figure things is to just calculate the number of air changes per hour:

CFM rating of fan X 60
-------------------------- = number of air changes per hour
Length X Width X Height

So if you had a 6 foot wide X 12 foot long X 8 foot tall bathroom, then a 150CFM fan would give you ... 15.6 air changes per hour; once every 3 minutes and 50 seconds. Good enough.

The downside to these high powered fans is that the bigger ones use 6” ducting. And fiberglass insulated 6” ducting is actually a bit over 8” in diameter. So you aren’t going to fit these things in a downstairs bathroom when the upstairs is sitting on 2x6 joists. You have to find a low clearance fan that uses 4” duct. No worries, Panasonic has them too. This is their WhisperFit line, in which the same quiet fan is given a smaller lower housing. You’ll either get less airflow, or a bit more noise, depending on which model you want. But even 1.5 Sones is still very quiet.

And for you California folks, there is a WhisperGreen line that meets the new Title 24 specification. As an added advantage, these fans can sense the backpressure in your ducting, and will automatically adjust the motor speed so that they output the rated level of air. WhisperGreen appears to be the WhisperFit line, with this added variable speed feature. They’re Energy Star rated too, of course.

No, this isn’t a push for Panasonic products. Broan is a big player in the fan market, along with Air King, NuTone, and several others. And they all have a full line of products. What I’m pointing out here is that the fans available today are much more powerful, efficient, quiet, and cost effective than that 20 year old monster you might have in your bathroom. So it might be time to think about putting in a newer, better model.

I was able to locate the Panasonic FV-15VQ4 fan, a 150CFM model that uses only 31 watts and is 0.6 Sones quiet, at WAMhomecenter.com for only $124, with free shipping. I’ve seen this same fan being sold for $299 plus shipping. This is about the strongest fan you can find that runs at the dead quiet noise level. There are fans much more potent, but most of them are in the 3.0 Sones level, which is getting kind of noisy. A 25 foot run of Air King fiberglass insulated flexible ducting is about $30. FanTech sells a nearly identical product for just a little more. I was able to find a generic one, still UL listed, for just $17.75 ($26 delivered) at ComfortGurus.com.

Posted by Drew458     on 10/04/2009 at 11:56 AM   
Filed Under: • work and the workplace •  
• Comments (5) • Trackbacks(0)  Permalink •  

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