February 27 , 2009

Sleuthing the Noise in Our Ventilation

This house has a lot of ventilation. We have a total of 5 Broan SmartSense® ventilation fans in bathrooms and garage, humidity sensing fans in the bath and shower areas, and standard ventilation fans in the laundry, master toilet area and master closet.

Proper ventilation exhausts stale air and replaces it with fresh air. This minimizes mold and mildew growth, and helps remove gases and particles not trapped by filtration units. It also reduces indoor pollutants such as household cleaners, VOCs, off-gassing formaldehyde from building materials, carpets and other furnishings. 

I never gave much thought to ventilation in a home until this project, but now I am convinced that it is something that every homeowner needs to understand and oversee when building a new home. First of all, good ventilation saves a homeowner time and money. Consider the amount of time you spend with a toothbrush cleaning out mold and mildew from tile grout in showers.  And if your family is like mine, and rarely thinks to turn on a fan when you take a shower, consider how quickly paint tends to peel and break down in the bathroom due to excessive moisture.  Good ventilation helps minimize – perhaps even eliminate – some of these not-so-joyous aspects of owning and caring for a home.

How it Works:
The SmartSense system automatically coordinates the operation of the ventilation fans in my home, running them intermittently throughout the day. Regular operation can be temporarily interrupted by manually switching any fan off or on. However, the SmartSense will automatically turn off a fan that was left on after a certain amount of time has passed and it will also deduct any extra manually induced exhausting from the total CFM for which the system is set to exhaust daily.  It’s really pretty cool.

These higher CFM exhaust systems (especially the kitchen oven exhaust) came in  handy for flushing the indoor air prior to occupancy. By flushing the house for a full 48 hours (with all fans running and the windows open) we were able to earn a LEED point under Indoor Environmental Quality. The SmartSense System will also help us earn additional points for enhanced ventilation measures.

Lessons Learned So Far
The downside to enhanced ventilation is that most contractors are not up to speed on the strategies, and that can lead to some headaches, grumbling, and the occasional finger pointing.

With our own project, the frustrations began with the number and size of ventilation fans. No one anticipated that our SmartSense fans (which pull more CFM than the typical ventilation fan) would be larger.  Had we known, we probably would have made space in the floor joist during framing.  However, we didn’t, so in a few locations we had to do some cutting to make these fans fit.  It’s not really anyone’s fault.  Contractors simply assume the fans one homeowner chooses are going to be pretty much like the last 100 or so they installed. But times are changing and ventilation is one of those areas that is likely to upset the apple cart.

There was also the sheer number of fans that we installed.  Usually there is one fan per bathroom and one in the kitchen.  More fans means more duct.  More duct means more exit points to the outside.  More exit points means more exit covers to be installed. (Exit covers is not the proper terminology.  What I mean are the “cosmetic vent thingies” that go on the soffit so you just don’t have exposed duct hanging out of your soffit.) 

It’s a good idea to let your contractors know all of this ahead of time. In all fairness, they probably are not quoting the job based on this many fans, and they will spend some more time. The electrician bears the greatest burden.  All of those fans have to be wired and wired correctly. The HVAC contractor will have to run more duct.  And, at least in our case, the exterior trim contractor will have to install the exits.  I can tell you right now that during this process (which was a learning process for us all) I wasn’t at the top of anyone’s Christmas list. But, I give credit to BJ Christie, my electrical contractor for sticking with the job until everything worked properly.

Speaking of which, we did have some issues once the fans were installed.  A few of the fans were too noisy. Karen Collins, of Broan-Nutone recognized this immediately when she was here in December to present to about two dozen builders at the Greenspiration Builder Lunch & Learn. She put Rick Nowlin, Broan-Nutone’s area Construction Sale Manager on the case. Rick suspected from the beginning that the noise was due to restricted flow somewhere within the ductwork, but he did test all of the fans before he came to this final conclusion. 

Various things can cause restricted flow – one of which is duct that is sized too small for the fan.  We had one or two like this. The SmartSense fans all require 6-inch duct.  However, 4-inch duct is what most contractors are used to installing on most houses. Too many bends in the flex duct can also be a problem. Ideally, ventilation duct should run straight up and exit the roof.  However, it would have been a bit expensive to go back and redo all of that. And, we actually had very few bends in any of our duct, although it does have to make a 90-degree turn to exit out of the soffit.  Finally, the exit itself can be a problem and this was the culprit for most of the noise we were experiencing..

This is a really important tip. At least in this area, trim contractors typically have one exit piece that they use and it has about a 3-inch opening. They don’t question it, and in all likelihood no one else thinks to.  But the fact was, we were restricting flow through a 6-inch duct down to about 3 ½  inches at the exit point, and that was causing most of our noise.

I have to say, the trim guys weren’t very much help with this, and in fairness, ventilation is not their expertise. (How it came to be that they are the ones that get saddled with this particular task in construction, I do not know.)  They didn’t know of any other product to use. It was Rick Nowlin who found the solution, which is shown in the picture.  This product is sold under two different names: Deflecto-O and also Fantech. Deflect-O states that it is suitable for up to 5” duct, while Fantech states that it is good for up to 6” duct.  We gave Fantech the benefit of the doubt and used it for our 6-inch duct. 

Since installing these vents, our noise issues have gone away. We are keeping check on our CFM to see how the ducts are performing – not just relying on the Energy Star verification, but seeing how close the fans come to their published CFM. An actual installation will never reflect what a published CFM is because these numbers do not reflect bends or other obstructions in ductwork, but the numbers should be in the same ballpark.

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