Five Ways to Do Balanced Ventilation

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Five Ways to Do Balanced Ventilation

Including some you can use to convert an exhaust-only system

Posted on Apr 12 2017 by Allison A. Bailes III, PhD

Ventilation is a great thing. Bringing outdoor air into the home and exhausting stale indoor air improves indoor air quality. Well, most of the time, anyway. Sometimes the outdoor air quality is worse than indoor air. Sometimes you bring in too much humidity and start growing mold. And sometimes you bring in the wrong outdoor air. But the issue of outdoor air vs. indoor air is a topic for another article.

Probably the most common type of whole-house mechanical ventilation system in homes is an exhaust-only system. You put some controls on the exhaust fans that are already in the home and those fans are set to exhaust stale air from the home, either continuously or intermittently. The problem is this type of system sucks. Literally. And if your house is sucking from an attached garage, a moldy crawl space, or dirty attic, you could be making things worse.

One way to avoid having a house that sucks is to do 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). . You exhaust stale air from the house and you supply an equal amount of outdoor air directly rather than relying on the negative pressure of the house to bring in the outdoor air.

Here are five ways to do balanced ventilation. I've put them in increasing order of cost, complexity, and efficiency.

1. Open the windows

OK, technically I shouldn't include this one because it's not a real solution for most homes. This one works only if the home is in a mild climate that needs to little to no conditioning. But if that's your situation, you don't need a fancy ventilation system. Just open the windows.

2. Pair a central-fan integrated supply system with the exhaust fans

A lot of homes get exhaust-only whole-house ventilation (fans plus controls). One easy way to upgrade is to install a central-fan integrated supply system to complement the exhaust-only side. The two most commonly used controls for this are made by AirCycler and Honeywell.

These systems are integrated with the blower in the central heating and cooling system. They bring in outdoor air when the system is running and mix it with the indoor air circulating through the duct system. It gets filtered and conditioned before being introduced into the home. When tied to the exhaust-only controls, you get balanced ventilation.

The main drawback of this system is energy use in systems that don't have variable-speed blowers. In addition to bringing in fresh air when the system is heating or cooling, it can turn the blower on when the home doesn't need heating or cooling. And some blowers use a lot of power. Turning on a 400 watt fan to bring in 50 cubic feet per minute of outdoor air is overkill. If you have a high-efficiency heating and cooling system with a variable-speed blower, you should be able to do this at less than 50 watts.

And another drawback is moisture. In a humid climate, running the blower without the compressor on can evaporate moisture on the coil and put it back into the home. (I’ve shown my data on what happens when you leave the fan on continuously in the summer in an article called How Your Thermostat Can Grow Mold and Make You Uncomfortable.) This wouldn’t be quite as bad as that, but it can make things worse. Curt Kinder, an HVAC(Heating, ventilation, and air conditioning). Collectively, the mechanical systems that heat, ventilate, and cool a building. contractor in Jacksonville, Florida, wrote recently, "Data and experience in my area of operation, northeast Florida, suggest that operating the system fan independently of the compressor raises indoor relative humidity by upwards of 10%.” If that scares you, consider the next three options.

3. Pair a supply fan with the exhaust fans

Another way to get balanced ventilation is to use the exhaust fans with controls and also install a supply fan. You can do this with a bath fan installed to blow air into the home or you can use a fan made specially for this task. I'm thinking of the QuFresh fan made by Air King.

They have two basic models. One has a sensor for temperature and relative humidity, and the other does not. The purpose of the sensor is to limit the amount of ventilation when it's really cold, really hot, or really humid outside. It'll still run 15 minutes an hour so you'll keep getting some ventilation air.

I like the concept and the features in the QuFresh fan. I haven't had a chance to try one out yet, but they do a lot of good things. You can adjust the flow rate from 30 to 130 cfm. It has a slot for a 2 inch filter that could be up to MERV 13. It's quiet (0.5 sone at 50 cfm). And it's relatively inexpensive.

4. Pair a ventilating dehumidifier with the exhaust fans

The strategy here is to use controls on your exhaust fans, as in the previous two, and supply your ventilation air through a whole-house dehumidifier. Many models allow you to do this by providing two intake ports on the dehumidifier, the smaller of which attaches to a duct that goes to the outdoors. We like Ultra-Aire but you can also find good models from AprilAire, Honeywell, and others. (Disclosure: Therma-Stor, which makes Ultra-Aire dehumidifiers, advertises in the Energy Vanguard Blog.)

One drawback of dehumidifiers is the heat they put into your home. The Ultra-Aire model SD12 eliminates that problem by being a split-system dehumidifier. It removes the humidity indoors but puts the heat outdoors. That means it even provides a bit of cooling (about a third of a ton).

5. Use a heat-recovery or energy-recovery ventilator (HRV or ERV)

This is what most people think of when someone mentions balanced ventilation. The photo at the top of the article shows the inside of a typical ERV, with arrows to show the two air streams. (An HRV looks the same but uses a different material in the heat exchangerDevice that transfers heat from one material or medium to another. An air-to-air heat exchanger, or heat-recovery ventilator, transfers heat from one airstream to another. A copper-pipe heat exchanger in a solar water-heater tank transfers heat from the heat-transfer fluid circulating through a solar collector to the potable water in the storage tank..)

The operation is simple. It has two fans, one to exhaust stale indoor air, one to bring in fresh outdoor air. It filters both air streams. The two air streams pass through a heat exchanger, a capillaryForces that lift water or pull it through porous materials, such as concrete. The tendency of a material to wick water due to the surface tension of the water molecules. core in most models. The two air streams pass near each other and exchange heat in an HRV and heat and moisture in an ERV. But the two air streams don't mix.

This is a great way to ventilate a home. It's also more expensive than the methods mentioned above. Panasonic does have a small "spot" ERV called the Whisper Comfort, but aside from that model, you're probably looking at $1,000 or more for an ERV or HRV. The biggest difference between this type of balanced ventilation and the previous ones is the heat exchanger. You get balanced ventilation with recovery, which means you don't need to do as much conditioning of the outdoor air you bring in.

Finding balance

There's your quick rundown of the main ways to do balanced ventilation. We're seeing a lot of creativity in the ventilation market these days because ventilation is a big deal. I think we've gotten to the point where we rarely have to fight the battle about the need for airtight houses. The old myth that a house needs to breathe, while not completely gone, has mostly been relegated to the dustbin of bad thinking.

But let’s be clear about what balanced ventilation really means. It doesn’t mean the building is always at neutral pressure with respect to outdoors. Wind, stack effectAlso referred to as the chimney effect, this is one of three primary forces that drives air leakage in buildings. When warm air is in a column (such as a building), its buoyancy pulls colder air in low in buildings as the buoyant air exerts pressure to escape out the top. The pressure of stack effect is proportional to the height of the column of air and the temperature difference between the air in the column and ambient air. Stack effect is much stronger in cold climates during the heating season than in hot climates during the cooling season., and other mechanical systems can always unbalance a building. When we talk about a balanced ventilation system, we mean simply that that particular system doesn’t result in the building going positive or negative because it’s exhausting and supplying equal amounts of air.

Another point here is that my main motivation in writing this article was to show some ways you can convert an exhaust-only system to a balanced system. Methods 2 and 3 above show how you can do that relatively easily and inexpensively. Method 4 would be a good way to do it in the humid climates of the southeastern US.

And one more thing. I was going to make this a list of six ways to do balanced ventilation but decided to save the other one for a separate article. Going a step beyond the ERV, you could go with a souped-up ERV. There are two companies making devices that include balanced ventilation with recovery, a small heat pump, better filtration, and more. One is the Conditioning ERV, or CERV, by Build Equinox. The other is the Minotair by Minotair Ventilation. We've got two HVAC design jobs going right now that will be using these devices, so stay tuned for more on these later.

Meanwhile, try to stay in balance. Or at least be positive.

Allison Bailes of Decatur, Georgia, is a speaker, writer, building science consultant, and the author of the Energy Vanguard Blog. You can follow him on Twitter at @EnergyVanguard.

Tags: , ,

Image Credits:

  1. Energy Vanguard
  2. AirCycler
  3. QuFresh

Apr 12, 2017 2:17 PM ET

small house ventilation
by Anders Lewendal

Allison: Thank you for the article on balanced ventilation. Since we are building tighter homes, I am sure this issue will come up again many times.

I do have an issue that you might help me with. I volunteer with the city of Bozeman and its Community Affordable Housing Advisory Board. We are collaborating with MSU's architecture department and some local non profits to build some very small, affordable, transitional housing.

Here's where you come in: These homes are about 170 square feet with a 1 ACH or less. I just finished a house that tested .35 ACH at completion. You can imagine with one person living, showering, cooking in a very small unit that is so tight there are virtually no air exchanges, there are going to be moisture issues. I asked the architecture students where they think all of the moisture is going with only one bath fan. We should consider that the tenant may turn off that fan. A couple of them speculated, correctly, that the moisture would end up in the walls.

Do you have a low cost solution? How much moisture do we need to remove? Will a Panasonic fan/ERV solve the problem or do they need a more elaborate solution? Opening the windows when it is zero outside probably will not cut it.

Let me know if you have any ideas?

Apr 12, 2017 2:37 PM ET

Response to Anders Lewendal
by Martin Holladay

An exhaust-only system using a high-quality bathroom exhaust fan like the Panasonic will work. Of course, the homeowners have to use the fan properly. If the fan is disabled or turned off, it clearly won't work.

The other option is a pair of Lunos fans.

-- Martin Holladay

Apr 12, 2017 3:14 PM ET

Question for Martin
by Steve Knapp CZ 3A Georgia

What about the TwinFresh? (I'm not familiar with this products.) It makes a single room ERV and HRV. Both units are low-cost and good to -4 degrees.

Apr 12, 2017 11:24 PM ET

Panasonic Whisper ERV family
by Armando Cobo

IMO, for high-performing houses there is no other choice than ERV/HRVs. Panasonic ERVs are very affordable with wide range outputs, from 40/20 cfm for small houses, to 80-150 cfm ranges for mid and large homes, and the best part is that all are between $250-$500 plus install. Broan has some fairly affordable units too in the mid-rage size.

Apr 13, 2017 5:01 AM ET

Response to Steve Knapp (Comment #3)
by Martin Holladay

I have no direct experience with the TwinFresh products. I agree with you that the prices are low.

-- Martin Holladay

Apr 13, 2017 12:24 PM ET

Edited Apr 13, 2017 12:33 PM ET.

by Ethan T ; Climate Zone 5A ; ~6000HDD

In addition to the Twinfresh and Panasonic Whispercomfort, the Lunos ( also has an in-wall solution for HRV functionality. The Lunos units are paired to create a ventilation system. It seems like a great idea, though perhaps not a cost savings (depending on what the ductwork costs.). To echo Anders' question above, I don't see how an HRV can take care of humidity. Minotair has an interesting ERV+dehumidificatino system ( but again we are getting into higher cost and higher complexity. I also worry about the fabled toaster+coffeemaker problem (or DVD+TV) problem, which ties two separate systems together making it impossible to upgrade just one, and rendering the system useless if 1/2 breaks.

Apr 13, 2017 12:42 PM ET

IMO, there there should be
by Jon R

IMO, there there should be more emphasis on "pressure managed" ventilation (vs balanced ventilation). There is potential to improve things, not just leave them unchanged.

Also note that a HRV can easily cause unbalanced or non-pressure-neutral ventilation. For example, when sharing ducts with an intermittent furnace. Or a supply duct in a room with no return duct.

Apr 13, 2017 2:37 PM ET

More info on VENTS-US HRV
by Ethan T ; Climate Zone 5A ; ~6000HDD

I was able to track down the VENTS-US single room HRV at an orange big box store for about $450. Interestingly, it is listed under Hydroponic Gardening - Grow Room Ventilation. Perhaps this has to do with UL listing (just speculating here). It is intersting to compare the VENTS-US website documentation of the TwinFresh Comfo RA1-50-2 with its USA marketing as a grow room ventilator.

Apr 13, 2017 2:45 PM ET

CERV/Minotair pricing
by Ethan T ; Climate Zone 5A ; ~6000HDD

Again, back to my toaster+coffeemaker analogy, is there any cost savings to combining conditioning with an ERV system? Or is the impetus to do so enhanced functionality? Could combining these systems be detrimental by creating enhanced complexity and be prone to system failure? The thought of it kind of makes me long for Option 1 (opening some windows).

Apr 16, 2017 10:54 AM ET

If all you need to deliver is
by Jon R

If all you need to deliver is ventilation air and dehumidification, then combining ducts can be a significant cost savings.

Apr 16, 2017 11:21 AM ET

what's wrong with...
by Ethan T ; Climate Zone 5A ; ~6000HDD

What's wrong with a simple (through wall?) ERV or HRV and a stand alone dehumidifier like we used to run in the old days. Seems to me the less ductwork the better.

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