How Balanced Ventilation Systems Become Exhaust-Only
Joe Nagan sends out another one of his humorous e-mails
Unlike the homes of our great-grandparents, the homes of most Americans are served by an array of automatic appliances and systems.
When our great-grandparents returned home after a three-day absence, they would need to haul a bucket of water from the spring and light a fire in the kitchen stove before they could brew tea. Today’s homes, of course, have electricity for lighting, a furnace for warmth, an air conditioner for cooling, a water heater for showers, and internet access for Googling.
If one of our modern services is interrupted, residents usually notice within a few hours. Teenagers are often the first to sense that something has conked out. “Dad, there’s no hot water,” they shout, or “Mom! The internet is down!” When the furnace shuts down in January or the air conditioner breaks in July, it doesn’t take long for someone to figure out that something is wrong.
We love our comforts, so most of our appliances are coddled and cared for when they get sick. Yet no one notices the poor HRV(HRV). Balanced ventilation system in which most of the heat from outgoing exhaust air is transferred to incoming fresh air via an air-to-air heat exchanger; a similar device, an energy-recovery ventilator, also transfers water vapor. HRVs recover 50% to 80% of the heat in exhausted air. In hot climates, the function is reversed so that the cooler inside air reduces the temperature of the incoming hot air. in the basement, even when it’s broken. (Remember the children’s classic, Mike Mulligan and His Steam Shovel? Someone should write a children’s story titled Amy, the Aging HRV. The main character would surely be sad, neglected, and lonely.)
The last time I discussed neglected HRVs was in a 2012 blog called Broken Ventilation Equipment Goes Unnoticed for Years. My article was inspired by an e-mail from Joe Nagan, an energy consultant from Wisconsin who is known for his sense of humor. Like other consultants who make site visits, Nagan has a good collection of stories from the field. This week, his latest HRV tale landed in my In box.
An inspector’s eyes
The setting for Nagan’s story is a handsome older house in Door Country, Wisconsin. Although Nagan was summoned to provide advice about a roof leak, he couldn’t resist walking around the house and checking things out. (If you inspect a lot of houses, you can’t turn off your inspector’s eyes.)
“It's my nature to take a stroll around the house — any house,” Nagan wrote in his recent e-mail. “You never know what you may find. I somehow am attracted to ventilation stuff. Not sure why, but I take a shine to it. So I'm walking around this home, and I stumble across what look like two hoods from a ventilation system. (I'm not sure, because I haven't been in the house yet.) Anyway, it looks from the ground where I’m standing that there's something in one of the hoods.”
The mysterious obstruction was blocking the fresh air intake of a heat-recovery ventilator (HRV). “I usually find stuff in the intake hoods, as apparently pests tend to enjoy fresh air more than people living in the homes do.”
In this case, the obstruction was a very large wasps’ nest (see Image #2, below). In a followup e-mail, Nagan wrote, “Insects enjoy the weather protection provided by the hood, but most of all they enjoy the fresh air. If they were to hang around the exhaust vent, they would have to smell all the crap people have in their home. They’re smarter than we are. They like fresh air. I have yet to find any people stuck in the fresh air ducting. They're all in the house with the plug-in air-fresheners and the junk.”
Have you checked your intake lately?
Nagan copied a few people on his e-mail; one of the recipients was Mac Pearce, the well-known microbiologist and mold expert from St. Paul, Minnesota. Responding to Nagan’s anecdote, Pearce supplied one of his own.
Pearce wrote, “My cousin Bob was proudly showing off his new (two-year-old) palace. As we walked around the outside, I asked if he had an HRV. After a moment of confusion he replied that he thought so. I decided to take an opportunity for a teaching moment. As we strolled to the rear of the house I described the HRV intake and the clumps of plant fiber that often clog it. When we got there, though, it was clean as a whistle — and he lives in the woods!”
Some consultants are irked when their predictions prove to be wrong, but Pearce took this setback in stride. He was sure that close inspection of the HRV would reveal a dirty filter. “We took a trip to the basement,” Pearce continued. “The Venmar hung in the utility room. Bob told me he didn't know what it was or what it did and that he’d never touched the thing. I popped the door to show him the clogged filter. Again, the filter was spotless — like new!”
Hmm — what’s going on here? “Then I looked to the left and saw the dangling power cord,” Pearce wrote. “The thing had never been operated. That’s one way to maintain your equipment in mint condition, eh?”
Well, it started out as a balanced system
Nagan sees HRV problems all the time. “For years now, you’ve heard me whine about no one taking care of whole-house ‘balanced’ ventilation systems,” Nagan wrote in his e-mail. “After a while they morph into exhaust-only systems due to lack of awareness and ‘nobody cares’ type of no-maintenance. The intake gets restricted or plugged, while the exhaust side is unrestricted and is sucking on the building.”
According to Nagan, air intake grilles often get plugged by “debris in the air getting caught on the screen or mesh. What can also happen is that the hardware cloth or screen gets damp after the outside air temperature drops towards evening, primarily in the summer and fall. Everything on earth then gets a bit damp at night. If there's any air being drawn in, the particles start accumulating on the screen, just like dirt particles on an electrostatic air cleaner.”
While Nagan points his finger at ignorant homeowners — “it is my firm belief that homeowners know ‘nothing-about-nothing,’ and then some” — I don’t think it’s reasonable to expect homeowners to pay attention to HRV maintenance. Since this problem is pervasive, the construction industry needs to come up with a technical solution to the problem; blaming the homeowner won’t solve anything.
Are the cobbler's children ill-shod?
I’m sure that a few ventilation experts are reading this story, thinking, “Why can’t homeowners clean the intake screens of their HRVs?”
If you are such an expert, I have a a few questions for you. First, when was the last time you attached a garden hose to your water heater and flushed out the scale that accumulates at the bottom of the tank? (You know that it’s a good idea to do that once a year, don’t you?) Second, when was the last time that you disassembled your clothes dryer’s exhaust duct to clean out all the lint? What? You haven’t done that recently?
Nagan may be cynical, but his sense of humor is intact. Here’s how he described his emotions after discovering the wasps’ nest: “As I stood there, as legally excited as I could get, I could hear Kate Smith singing away to the tune of ‘God Bless America.’ ”
After all, Nagan is an energy consultant. He concluded, “We won’t likely run out of work for quite a while.”
Martin Holladay’s previous blog: “Universal Design.”
- All photos: Joe Nagan
- Image #3: Virginia Lee Burton
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