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Mike Guertin fires back on bathroom venting

Brian Pontolilo, editor

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In addition to these three smart switches as seen in "A Buyer's Guide to Bath Fans," in Kitchens & Baths 2008 (FHB #199), Mike Guertin likes the simplicity of manual crank timers (not pictured).

The smartest switch? In HOUSES (FHB #203) Mike Guertin says that the Airetrak Advantage is the "easiest-to-use, full-function bath fan controller" he's seen.

In addition to these three smart switches as seen in "A Buyer's Guide to Bath Fans," in Kitchens & Baths 2008 (FHB #199), Mike Guertin likes the simplicity of manual crank timers (not pictured).

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From time to time we publish something that's controversial or that's just plain wrong. It’s our job to do everything we can to avoid the latter, but mistakes happen, and sometimes all we can do is print a correction in a future issue or online. Controversy, on the other hand, can be a good thing for a magazine. If we engage readers with a compelling argument for a particular technique, material, or design, for example, we ultimately create a conversation that extends the life and impact of that particular story. Bathroom venting may not be controversial and we didn’t make any mistakes in the story that I’m aware of, but we did generate an interesting and useful conversation between the author, a contributor, and a reader. Here’s how it all went down:

Last fall we published “A Buyer’s Guide to Bath Fans” in our annual Kitchens & Baths issue (FHB #199). Author Jefferson Kolle wrote, “Bathroom fans that are never turned on allow mold-inducing moisture to build up, and fans left on too long waste energy.” After describing a few fans that ensure use with integral humidity and motion sensors, Kolle continues, “For bath fans without onboard sensors, many companies, including fan manufacturers and electrical suppliers, sell wall switches with programmable timers (photos above).”

After reading the story, contributing editor Mike Guertin sent former editor Kevin Ireton a quick note, which Kevin decided was worth publishing two issues later. From “Letters,”  FHB #201:  

Crank timers are smart
I’d like to add one of my favorite “smart switches” to Jeff Kolle’s list. It may not be electronically “smart,” but it is a smart, simple, easy-to-use, and cost-effective choice. It’s a mechanical crank timer. I install the 60-minute version in new and retrofit baths. A full crank after a long shower or a quarter turn after a wake-up spritz does the trick. Technophobes appreciate the short learning curve and real-time feedback on function (you can clearly hear it grind away as the minutes tick down).
—Mike Guertin
East Greenwich, R.I.

So far, so good. Until Arne Waldstein read Mike’s letter and found fault with his suggested settings for a “long shower” verses a “wake-up spritz.” Here’s Arne:

Relocate your bath fan
If you need to keep a bathroom fan running for an hour after you’ve showered, as Mike Guertin suggests in his recent letter (FHB #201), you don’t have moisture issues, you have a design problem.

I urge my customers to buy separate light and exhaust-fan fixtures so that the light can go in the middle of the room and the fan can go above the showerhead, where it belongs. After all, you wouldn’t put the exhaust hood for your cooktop in the middle of the kitchen ceiling, would you?
—Arne Waldstein
Housatonic, Mass.

I thought Arne’s comments had merit and decided to publish his letter in our current issue (#204). I did so without consulting Mike. Fortunately for us, Mike’s not one to wait to be asked for his opinion and I received this response to Arne’s letter last week. I’m not going to publish it, because the original story is now more that six months old, but I though it was worth sharing. So, here’s Mike, again:

Arne,
Your practice of installing the exhaust port for a bathroom vent above a shower enclosure is great and is a perfect example of an eye for good design. I do it on most of my new construction projects.  But, your analogy is misleading. 

There's a big difference between a cooktop and range hood and a shower and exhaust fan. Chances are you don't pour water all over your cooktop and the nearby walls then turn off your range hood fan without wiping down the surfaces and wringing the sponge water down the sink drain. The only moisture the range hood fan has to deal with is the moisture generated when cooking is actually happening. Your well-placed exhaust fan may clear all of the air-born moisture from the bath, but the water clinging to the walls and floor of the shower enclosure will not be removed. That water will evaporate into the household air and increase the moisture level of the house. There's more water in liquid form that will evaporate over time than there is in vapor form at the moment of showering. 

As we build tighter and tighter homes by virtue of the building material we use and energy-efficiency enhancements to the building code, homes must include mechanical ventilation systems in the bathrooms to manage the primary interior air pollutant—Moisture vapor. Building scientists, model green building programs, many utility sponsored energy efficiency programs, industry groups like ASHRAE, HVI, American Lung Association and others, and building codes recommend, require and mandate controlled exhaust ventilation that targets bathrooms. And one of the primary components of a bathroom ventilation system is timer control.

The product I reviewed in HOUSES (see “Fixtures & Materials” FHB #203 and photo above) goes beyond the benefits of a simple timer: it not only controls fan run time to rid more of the moisture than simply locating the fan differently would, but it also turns the bath fan into a whole-house ventilation system providing either low-level background ventilation, periodic background ventilation or both.
—Mike Guertin

At the end of the day, I think it is important to bring conversations like this to light for a number of reasons that go beyond creating a buzz for the benefit of Fine Homebuilding magazine. Mold- and rot-causing moisture problems are not only a house's worst enemy, they are the leading source of poor indoor air quality (look for "15 Ways to Improve the Air you Breathe" in our August/September issue, #205) which can create serious health problems for you and your family. We're lucky to have contributors and readers who care enough to share, debate and test every detail of something like the placement of a bath fan, and how long it needs to run, and the best switch to control it.

Thanks Mike and Arne. 

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Comments (5)

DBDB writes: It is silly to guess 15 minutes vs 60, even more so given the attempt at trying to justify the point. After the shower is over, assuming the fan was on during it, the amount of water left on the shower walls, whether a lingering or quicky shower, is essentially the same. Everything else has gone down the drain. Sure there might be a bit more mist on the walls in the bathroom, but not much more, especially if the fan is sized properly and enough makeup air is getting into the room, but certainly not enough to justify a 4 fold increase in fan usage. A humidity controlled switch should be used if at all possible.

And to address the heating appliance draft concerns, a BPI certified building analyst could determine if you have a problem and is so offer solutions for that as well as identify any other insulation and air flow issues you might have, to help bring your house to the right condition to allow for adequate air flow without losing needless heat to the randomness of turning on a bathroom fan.

If your writers have not been trained and certified in such areas, they should not be shooting from the hips based on what they've gleaned from a little exposure here and there.
Posted: 8:26 pm on August 28th

bobalu writes: I think we're OK with our gas furnace, since it draws its air from the outside, and the range hood is winning out over the both bathroom fans, but now that we've sealed up all the cracks in this 1937 cottage, it's obvious where the air makeup will be supplied from.

Is there a simple solution out there for a simple house of 750 sqft.?
Posted: 8:43 pm on June 9th

bobalu writes: My question is related to this subject of house ventilation. In our tiny cottage, we have two bathroom exhaust fans and a range hood for the gas stove. Within the same space, we have a stone fireplace burning a propane log set. What can we do to keep the exhaust fans from competing with the draft of the chimney? Even if the fire isn't lit, in the winter, the downdraft the fans cause is wasting expensive fuel.
I am considering a chimney cap which is linked to the gas logs in order to keep within code, but this doesn't help when the fans are in operation, pulling in the propane fumes.

I would appreciate some professional suggestions on this. I'm sure my situation is not unique, but is probably more obvious because of its size than most normal sized homes.
Thanks,
Bobalu
Posted: 8:35 pm on June 9th

BrianP writes: You make a good point, Mr. Fournier, which is that a house is a system. New homes must be designed and built with this in mind and just as important, remodelers must be mindful that an upgrade, as simple as a new bath- or range hood-fan, can affect how other parts of the house, the heating system or chimney for example, are performing.
Posted: 9:31 am on June 4th

MFournier writes: Ah yes the discussion of venting. Well this is is not just the bath as houses get tighter and tighter whole house ventilation with air/heat exchangers are needed.

And these systems must also be designed to avoid uneven air pressure that can drive moisture into the walls and can even cause CO dangers with gas furnaces and water heaters. When a high volume range hood is turned on it can cause a negative air pressure in the house that then sucks the exhaust gases of a water heater or furnace into the house.

That is why many areas require powered exhaust on heaters. Not to mention the temperature of the exhaust on a high efficiency heater is so low it no longer creates enough draft to properly vent with out the powered exhaust.

But again this too has been covered in several FHB articles. But yet many new homes are still built wrong.
Posted: 10:57 am on June 3rd

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