One trick for testing ductwork is to use a theatrical fog generator with a Duct Blaster to introduce a visible vapor into the duct system …
Credit: Michael Uniacke One trick for testing ductwork is to use a theatrical fog generator with a Duct Blaster to introduce a visible vapor into the duct system …
The fog makes it easy to find leaks in ductwork.
Credit: Michael Uniacke The fog makes it easy to find leaks in ductwork.

Note: This is Part 3 in a series. To see Part 1: Clearing the Air, click here. To see Part 2: Choosing a Whole-House Ventilation Strategy, click here.

"It is only when they go wrong that machines remind you how powerful they are." ~ Clive James

The best-designed ventilation system in the world may not help you much if it's not installed properly. But how do you know if it's installed properly or not? Can you just look at it and tell? Listen to it? Ask the contractor who installed it?

No, it needs to be commissioned. We don't talk about commissioning a whole lot in the residential world, but it's a word that needs to gain a foothold there. An example of commissioning you may be familiar with is a HERS (Home Energy Rating System) rating. When a HERS rater rates a new home, especially if the rating process includes a pre-drywall inspection and minimum thresholds for things like insulation grade and duct leakage, they're commissioning the home to determine if it's likely to work as well as it should.

Likewise, with a ventilation system, the design and installation should be followed by commissioning so the ventilation system has the greatest likelihood of doing what it's supposed to do. And it's not nearly as difficult as it is important.

Here are some of the major things to include in the commissioning process for residential ventilation systems:

Design. Was the system installed the way it was designed? Make sure the proper type of system was installed, with the inlets and outlets in the proper places. Take the time to do a thorough visual inspection of the system as well to make sure.

Controls. Do the controls for the ventilation system do what they're supposed to do? Are they accessible to the occupants? Will the occupants be able to figure it out? Are the controls labeled? At a minimum, the occupant should be able to turn the system off so it doesn't run when they don't need it (e.g., when the windows are open).

Source of ventilation air. Where is the ventilation air coming from? It needs to come from outdoors, not another unit in a multifamily building or a garage, attic, or other buffer space. Are the inlets separated from exhaust outlets for combustion appliances, dryers, and other fans? Are they high enough off the ground or the roof?

Air flow. Does the system move as much air as it was designed to move? Flow hoods (balometers), anemometers, and even garbage bags can be used to measure how much air moves through the system. (Yes, really! See the Home Energy Magazine article by Iain Walker to learn more about using garbage bags to measure air flow.)

Balance. If you're installing an ERV or HRV, is it really balanced? You have to measure the air flow to find out. There's no guarantee that every system in the "balanced" category is indeed balanced. The air flow through the two sides is determined by the fan and the ductwork attached to it. Just because you have two identical fans doesn't mean you have identical air flows. A kink, malfunctioning wall cap, or a greater length of duct on one side can make a big difference. It might be necessary to install and adjust balancing dampers to get the air flow right.

Duct insulation. A run of uninsulated rigid duct above the drywall in the basement ceiling will give you an unwelcome surprise come winter. The water spots appearing on the ceiling will be evidence of condensation from the relatively humid indoor air on the cold duct. (I found this out the hard way.)

Sound. Is the system making noises it shouldn't be making? Is it obnoxiously loud? Systems that are deemed too loud are often turned off.

Local ventilation. Don't forget that the bath fans and range hood are an important part of the home's ventilation. It's easy to measure the flow of bath fans with a manometer and a calibrated box, such as the Energy Conservatory's Exhaust Fan Flow Meter.

Filtration. If the ventilation system is not an exhaust-only type, the outdoor air should be filtered. Check to see that a filter is installed properly and in the right place. ERVs, HRVs, and standalone supply-only systems will need filters. A central fan integrated supply system will use the filter that's already in the heating and cooling system.

Comfort red flags. Even if it was installed according to the design, it could still cause comfort problems. You don't want cold ventilation air blowing directly on people, so make sure the ventilation outlets are placed so they will ensure mixing without hitting people directly. Also, if you're using a system that tempers the air before delivering it, how tempered is the air being delivered? You may need to adjust dampers to get it right.

So, that should give you an idea of what to do. Of course, the devil's always in the details, and you can find some good assistance online. Even if you're not getting the house certified in the ENERGY STAR new homes program, you can use their materials. Download the program requirements and inspection checklists for assistance with the details. The California Energy Commission also has a good document on residential ventilation systems that will help with the process.

Indoor air quality is as important as energy efficiency. A good ventilation system design, competent installation, and proper commissioning will allow the occupants to breathe easier.

Allison Bailes owns Energy Vanguard, a home performance and training firm in Decatur, Ga.