Beware of This Expensive Ventilation Scam
Three marketers of crawl space fans rely on customers who don’t know the science of air and moisture
How much does an exhaust fan cost? Search online and you can find lots of them that move 200 cubic feet per minute (cfm) for $100 to $150. But, if you put one in a semi-attractive (emphasis on the "semi") package, create some fancy marketing materials, and target people who don't know much building science, you can charge $1,200 to $1,700 for that same fan. At least that seems to be the business plan for these three companies.
I found out about them only recently, but a quick search online shows that people have been discussing whether or not they work at least as far back as 2008. The systems I'm talking about are made by WAVE, EZ Breathe, and Humidex, and, for most people in the U.S., they won't work as promised.
What the marketers say
Reading through the crap on their websites would be funny if everyone knew enough building science to see through it. Here are a few of the things they say:
Using less energy than a 40-watt light bulb, WAVE Ventilation units expel harmful gases, toxins and pollutants, replenishing your home with fresh, clean, moisture-free air. [WAVE]
They don't tell you that the air you replenish your home with will probably contain even more moisture than the air you're exhausting.
Why use costly energy (in the form of electricity) to condense this water vapor into liquid form like traditional dehumidification products do? Simply remove this moisture from your home for pennies a day! [EZ Breathe]
They all seem to be targeting the dehumidifier market, but they say nothing about climate or the dew point of the outdoor air they're bringing in. They also conveniently ignore the cost of conditioning the outdoor air their systems bring in.
Generally moist, stale, polluted air tends to become trapped in the lowest part of your home. If it isn’t dealt with, it can quickly move to the upper levels of your home. [Humidex]
Ah, yeah. It gets trapped, but watch out! That trapped air can escape quickly.
In the summer, when there is no air conditioning in the upper levels, the warmer air flows downstairs raising the temperature, which lowers the relative humidity and raises the dew point resulting in less condensation. [WAVE]
Raising the dew point of indoor air does not result in less condensation. In fact, condensation is more likely.
What the fans are supposed to do
These systems are nothing more than glorified exhaust-only ventilationMechanical ventilation system in which one or more fans are used to exhaust air from a house and make-up air is supplied passively. Exhaust-only ventilation creates slight depressurization of the home; its impact on vented gas appliances should be considered. systems. The main target for these companies is someone with a humid, musty smelling basement or a damp crawl space. They promise that by exhausting air from the basement or crawl space, dry, conditioned air from the living space above will be brought down into the basement or crawl space. The result is a dry basement or crawl space. Or so they'd have you believe.
If you've been following this blog for a while, you probably know the pitfalls of an exhaust-only strategy. One of the main problems is that you don't know where the makeup air is coming from. For every cubic foot of air that gets exhausted through one of these fans, another cubic foot of air has to come into the house somewhere.
Interestingly, only one of the companies (EZ Breathe) shows you where that air comes in... and that's because they want to sell you another piece to go with that expensive fan. It's good that they acknowledge the need for outdoor air to be brought in from a known place. Their balanced system even tempers the outdoor air by mixing it with indoor air before delivering it to the house. The claim, however, that “the E·Z Breathe Advanced Balanced VentilationMechanical ventilation system in which separate, balanced fans exhaust stale indoor air and bring in fresh outdoor air in equal amounts; often includes heat recovery or heat and moisture recovery (see heat-recovery ventilator and energy-recovery ventilator). System delivers all the benefits of ERV(ERV). The part of a balanced ventilation system that captures water vapor and heat from one airstream to condition another. In cold climates, water vapor captured from the outgoing airstream by ERVs can humidify incoming air. In hot-humid climates, ERVs can help maintain (but not reduce) the interior relative humidity as outside air is conditioned by the ERV. and 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. systems at about a third of the cost” is probably not true.
The other two companies show you diagrams with arrows, like the one below (Image #2) from WAVE. But notice that they don't show you the arrows of outdoor air coming into the house. If you believe that diagram, it looks like they're ventilating the house with indoor air.
Their basic idea is that the air in the house will be more humid than the outdoor air enough of the time that exhausting indoor air and bringing in outdoor air results in a net drying effect of the air. What do you say, New Orleans? Care to try that?
Why they won't work
That's the basic problem with these systems. Exhaust-only strategies are bad for humid climates because the outdoor air isn't drier than the indoor air most of the time. Along the Gulf Coast, there's almost never a time when you could benefit from one of these. Even farther north, they'll have limited effectiveness for much of the year anywhere east of the 100th meridian, the longitude that (roughly) separates the wet from the dry climates of North America.
I explained this problem last year when I wrote about why crawl space vents don't dry out crawl spaces in humid climates. The psychrometric chart below (Image #3; click the image to enlarge it) shows what happens on a summer day when you bring outdoor air inside and cool it down. If you're keeping the house at 75°F, it's even worse. The relative humidity of that air goes up to more than 80%.
During cold weather, when the outdoor air is dry, these systems will bring in cold, unconditioned air in any climate. That $2 to $4 per month they promise it will cost you to operate the system doesn't account for the extra cost of conditioning all the outdoor air you're bringing in. Yes, you'll dry out the indoor air in cold weather, but the more cold air you bring in, the more expensive these systems are. You may also experience comfort problems from drafts and heating systems that can't keep up, especially in a winter as cold as the one we just had.
What should you do for a humid basement or crawl space?
As with any problem, the first thing to do is go after the causes, not the symptoms. For crawl spaces, especially in humid climates, encapsulation is the best answer. Even in dry climates, it's a good idea to keep soil gases like radonColorless, odorless, short-lived radioactive gas that can seep into homes and result in lung cancer risk. Radon and its decay products emit cancer-causing alpha, beta, and gamma particles. out of your home.
If you've got a humid basement, look for sources of moisture that you can eliminate before doing anything with the air. First on the list is to look for exterior water problems. In many cases, bad gutters or incorrect slope in the yard are the culprits. If your home has a crawl space connected to the basement, it's probably adding a lot of water vapor. Also look for air leakage sites between your basement and the outdoors. Get a blower door test to find out how bad it really is and target your air sealing efforts.
Once you've eliminated all the sources of moisture you can do cost effectively, then it's time to start considering what to do with the air. Maybe adding air conditioning to the basement is all you need to do. Most basements don't have much cooling load, though, so the AC may not run long enough to dehumidify completely.
At that point, a dehumidifier will be a better solution than one of the ventilation systems made by Humidex, WAVE, or EZ Breathe. If you want to do it without adding a lot of heat and without adding a lot to your electricity bill, get one of the high efficiency, high capacity models, like the ones made by Thermastor. (Disclosure: Thermastor is an advertiser on my website, but I would make the same recommendation even if it weren't. In fact, I've been recommending Thermastor products much longer than they’ve been a client, and I installed them when I was a contractor.)
The three companies I named above (WAVE, EZ Breathe, and Humidex) are relying on people who don't understand how air and moisture work. Here's a quick rundown of the problems with these fans:
- The products are expensive ($1,200 to $1,700).
- The operating costs will be higher than advertised because the cost of conditioning the outdoor air the systems bring in isn't included.
- They don't work in all climates or during all times of year.
- They could cause backdraftingIndoor air quality problem in which potentially dangerous combustion gases escape into the house instead of going up the chimney. of combustion appliances because of the negative pressure they induce on the home, possibly resulting in carbon monoxide in your home.
- They could bring more radon into your home.
- If you run them at their highest rates (>200 cubic feet per minute), you'll almost certainly exceed ASHRAE 62.2 ventilation rates (unless you have a 5,000-square-foot, 7 bedroom house or larger).
If you make the mistake of getting one of these systems, you'll almost certainly be throwing your money away. And that might be your best outcome.
Allison Bailes of Decatur, Georgia, is a speaker, writer, energy consultant, RESNET-certified trainer, and the author of the Energy Vanguard Blog. Check out his in-depth course, Mastering Building Science at Heatspring Learning Institute, and follow him on Twitter at @EnergyVanguard.
- Images #1 and 2: WAVE
- Image #3: Energy Vanguard
Thu, 06/19/2014 - 06:00
Mon, 06/23/2014 - 11:33