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Hyperbole of “balanced ventilation”

fitchplate | Posted in General Questions on

“Balanced ventilation” is just not making sense. ERV/HRV’s with same air volume in as out are “equalized” settings, not “balanced ventilation”. Here’s why:

Infiltration/exfiltration is a fact of even the tightest house – even passive’s (doors and windows jambs, range hood, dryer and bath fans, boiler and DHW vents/supply, cellar and attic doors)

– Woodstoves when fired are draws; when shut down are either incoming or outgoing drafts; and in certain seasons and weather are wind tunnels.

– Atmospheric pressure, natural house stack effect, prevailing winds causing +/- pressure differentials, exterior convection; mass features, emittance and heat retention, north side/south and high/low building features and temperature differentials.

– No house is in equilibrium, nor is any a closed system, so “equalized” settings in an ERV/HRV is not balanced ventilation. Balanced ventilation would be a solution that responds to pressure changes and the need for make-up air. Passive vents can do this. Pressure and volume regulating in/out air flows in fans and ERV/HRV’s might do it . Where do you find those in residential technology or design.

Stop misleading folks into believing ERV’s and HRV’s balance the atmosphere in a house. If anything, positive over pressure makes more sense to achieve balanced ventilation.

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  1. GBA Editor
    Martin Holladay | | #1

    No matter how outdoor air enters your home, and no matter how interior air leaves your home, the volume of air entering always equals the volume of air leaving.

    Air in = air out. That's a fact. Otherwise, your house would explode like a popped balloon, or it would implode, causing the walls to be pulled in to the center of the house.

    In that sense, all ventilation systems (and normal air leakage through random cracks) are "balanced."

    Most ventilation experts say that it's a good idea to try to control how air enters and escapes from your house. If you can control this process, you can make the ventilation process more consistent from season to season. You can do a better job of delivering the fresh air where you want it. You can do a better job of predicting where the outdoor air comes from. You can do a better job of exhausting stale air from stinky or humid locations in your house. And you can lower your energy bills. All of these are good goals.

    One can accomplish these goals by sealing random air leaks, and by installing a ventilation system with an HRV or an ERV that simultaneously exhausts stale air and pulls fresh air into your house.

    The better job you do sealing air leaks, the closer you will get to your goal. Passivhaus builders routinely reduce air leakage to very low levels (less than 0.6 ach50). Of course there is still some random leakage, due to the stack effect and the effect of wind. But the rate of random air leakage is very low.

  2. fitchplate | | #2

    Martin ... you really kind of said the same thing that I posted without acknowledging that "balanced ventilation" is a misrepresentation of the role of an ERV/HRV. As you yourself said, it is impossible to isolate the conditioned space so only a mechanical unit delivers fresh air and removes pollutants.

    An industry claiming that this $6000 - $7000 (ERV/HRV, its ducting, and installation) solution is giving one a "balanced environment in their house -- or allowing folks to think this way -- is nothing but self-serving political correctness in the building industry but not a legitimate proposition. Home buyers cannot get an isolated, static box that has a sealed perimeter and single-point, technologically controlled fresh air supplied.

    If the effectiveness of an exhaust-only system, or a hybrid exhaust with make-up air from multi-point or single point mechanical or passive approaches are compromised by natural pressure changes, wind, stack effect, air locking, stratification, etc, then so is the ERV/HRV’s equalized air supply/exhaust approach also compromised.

    If the ACH rate is just that good, then an ERV/HRV system is actually contributing, perhaps creating an imbalance. Wind and bulk air flow can over pressurize or under pressurize a building. It does that every moment. That’s why we have infiltration. Reality is, some quadrants and strata are negative and some positive at the same time in one building. Leeward sides are releasing the house atmosphere by exfiltration and windward sides are driving in air by infiltration. An equalized supply/exhaust volume will not be responding to the indoors/outdoors over or under pressure deficit. It believes there is a static equilibrium in what is really a dynamic reality.

    In the very low ACH home you refer to (which is the extraordinary exception to the 99.8% of houses being built today), a balanced ventilation solution is only available through passive or mechanical stop-cocks that allow rapid pressure equalization (delivered with diffusers for comfort). There are always fugitive exhaust and fugitive infiltration. No house is balanced without pressure sensitive controls (regulating volumes and rates of in and out in the ERV/HRV) or pressure responsive openings – intentional holes/cross-barrier ducts in the wall.


  3. GBA Editor
    Martin Holladay | | #3

    I'm not sure what your point is. I agree with you that exhaust-only and supply-only ventilation systems are often a good choice and work well. If you read what I have written, you'll find that I am not a particularly strong advocate for $7,000 HRVs.

    Of course the pressure dynamics in a typical house are complicated. Among the factors affecting the air in a house are the stack effect, wind, exhaust fans, unbalanced forced-air heating systems, central vacuum cleaners, and clothes dryers. So what?

    GBA has been writing articles on these topics for years.

    If you don't like the use of the term "balanced" to refer to a ventilation system that simultaneously introduces fresh air and exhausts stale air, I think you are being so literal that your insistence on precision is interfering with ordinary communication. It's useful to have a word to distinguish the type of system that has an exhaust fan as well as a supply fan from other types of systems; "balanced" is a useful descriptor.

    No one here at GBA is unaware of the fact that, even when an HRV is operating, the stack effect and wind still affect a house.

    We do, however, strongly urge all readers to do their best to seal random air leaks in their homes, so that the stack effect and the effect of wind are reduced.

  4. Expert Member
    Dana Dorsett | | #4

    ERV/HRV are "balanced" in the sense that(when properly set up) they do not actively pressurize or depressurize the house while running, unlike exhaust only or supply only ventilation schemes.

    That's it- there are no other functional aspects implied by the term when applied to ventilation schemes, no implicit balancing of natural wind/stack effect/other infiltration forces, only that the mechanical system itself is designed & set up to have minimal effect on infiltration air movement through the unintended air leaks.

  5. fitchplate | | #5

    So I think we agree that "balanced ventilation" is not in fact "balanced ventilation" and more importantly, it is not, even as the phrase implies, creating a "balanced environment". That said, it might be commercial misrepresentation and professional sleight of hand to allow, if not to claim, that the equalized intake/outflow of an E/HRV is “balanced ventilation” when it is in fact, only equalized air flow settings.

    A house with a distributed or single point E/HRV solution is always working to return itself to a state of balance or equilibrium. So all that is equalized by the E/HRV is the air volumes through the E/HRV. The house itself may in fact be significantly out of balance and the E/HRV ventilator is relevant only to (1) air quality, if and where it can dominate the building’s atmosphere; (2) some energy recovery, which may not be at all cost-effective return on investment; along with – depending on climate and ventilator -, (3) some de/humidification, also where it can dominate the atmosphere (i.e. overcome routine pressure imbalances imposed by other factors and forces).

    I suggest E/HRV’s are used much more often in irrelevant applications than not (i.e. where they are really not needed and are little more than bling); where the house is too leaky, where the other venting mechanicals, along with stoves and chimneys, and most of all, prevailing winds are all causing imbalanced and differential pressure zones on, around and inside the envelope. Frankly, the idea or proposition of “balanced ventilation” has mislead the designer/builder/buyer to install the newest technology because it sounds attractive, is politically correct, gets a green energy tax deduction, impresses visitors; etc.

    Martin, you are right about my objective. But its not language I am trying to shape, its truth I am trying to shape and paradigms needing to be shifted.

    First of all, all ventilation systems are balanced systems. Not because the mechanical unit equalizes in and out airflow, but because pressures will always equalize on their own. Passive, exhaust only, exhaust with passive inlets, supply only, and E/HRV’s in a very tight or a not so tight envelopes are balanced by natural forces. You, Martin, above anyone continuously remind the reader that no house is absolutely airtight. And most builders and do it yourselfers who insist they have built an airtight house are usually shocked by their blower door test.

    GBA has several articles and postings challenging with good numbers the cost-effectiveness of E/HRV ventilation; comparing the more efficient and cheaper buy and install of exhaust solutions, the too long payback period of even the most efficient E/HRV (maintenance and replacement before pay back is achieved) and the fact that $5000 into air sealing, insulation and energy efficient central heating units are leaps and bounds more efficient investments than E/HRV’s.

    Yet this site and others sound like advertisements for E/HRV’s. If I want someone to favor a particular solution; then I will call it "balanced".

    You cannot legitimately claim that to make language more accurate and less misleading is to interfere with communications. Stop referring to and allowing this systemic misrepresentation of E/HRV’s by differentiating them as “balanced ventilation” solutions and by this, elevating them in popular language and building jargon as having better relative performance characteristics than the other, often more efficient and significantly lower capital cost forms of home ventilation. E/HRV’s are just one way and a most expensive way to condition fresh air and probably the most expensive way to distribute it (i.e. push fresh air around). And let’s stop assuming that E/HRV’s are predominantly in use in truly airtight houses; were, by the way, pressure imbalances are greatest.

  6. GBA Editor
    Martin Holladay | | #6

    I guess we'll just have to agree to disagree on this one. I have stated my position.

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