ERVs Still Get The Yellow Flag?

Posted by Home Energy on March 01, 2012
ERVs Still Get The Yellow Flag?
Energy Recovery Ventilator (KyotoCooling)

In September 2010, Mr. Max Sherman, Ph.D., a senior scientist at the Lawrence Berkeley National Laboratory published an article in Home Energy suggesting that Energy Recovery Ventilators (ERVs) may transfer formaldehyde in the same way that they transfer water molecules from the outgoing indoor air stream to the incoming fresh air stream.

Recently, Kurt Johnson, owner and operator of Fresh Air, a company that installs Venmar brand ERVs in new and existing homes in Maine, wrote to us with these questions in response to Max’s article: Are you suggesting that some of the pollutant being reintroduced to the house is really a serious health risk? Isn't the fact that a given house already had really high levels be the serious risk?

In an effort to answer the questions above, Venmar, a leading manufacturer of ERVs in North America, decided to run a few tests to see if Mr. Sherman was correct in his assumptions. Below you will first find Venmar’s procedure and the findings of their testing, which were submitted to us, followed by Mr. Sherman’s response.

About Formaldehyde

What is formaldehyde? Formaldehyde is used in many synthetic materials such as permanent adhesives, presswood, plywood, furniture, and other products made from engineered wood. Over the long term, these materials could release considerable quantities of formaldehyde. It is one of the most widespread indoor air pollutants in dwellings. Formaldehyde had previously been classified as a "presumable carcinogen" but is now considered to be a "true carcinogen" by the International Agency for Research on Cancer (IARC), part of the World Health Organization (WHO), and by the Environmental Protection Agency (EPA) in the United States. To avoid risks associated with this organic compound, it is recommended to renew indoor air with appropriate ventilation, especially in new dwelling units or those containing new floors, carpets or glued synthetic floor tiles, walls, ceilings or furniture with engineered wood.


Before explaining the results, it is important to know that the CSA C439-09 standard and HVI require that all heat- and energy recovery ventilators are tested with a "tracer" gas (SF6) in order to detect the contamination percentage of stale indoor air transferred back to the incoming air stream. This value is called the Exhaust Air Transfer Ratio (EATR), and must be as low as possible. Because the EATR value of the SF6 gas is known and published in the HVI Certified Products Directory, we wanted to see whether formaldehyde has the same behavior as SF6. To do so, we tested a Constructo® 1.0 ERV for one hour on both high and low speeds (approximately 100 and 50 cubic feet per minute, respectively). The Constructo 1.0 has a static (non-rotating) core and uses the same enthalpic material as all of Venmar's ERV models.


We measured formaldehyde transfer of only 0.9% in high speed (0.9% returned into the house versus 99.1% exhausted to outside). We also validated the SF6 gas transfer on the same ERV and obtained exactly the HVI-published EATR of 1.9%. At low speed, the measured formaldehyde transfer was 2.2%. Again, the result is better than the tracer gas transfer, which was 3.3% for the same ERV unit. By comparison, at the same speed, the ERV has a latent recovery or moisture transfer of 61% (at 0°Celsius or 32° Fahrenheit).


In conclusion, it is wrong to believe that ERVs transfer formaldehyde the same way they transfer moisture. Almost all of the formaldehyde is exhausted by the ERV, and not transferred to the incoming fresh air stream. Our tests confirm that a Venmar ERV will provide effective ventilation and protect the occupants by evacuating almost the totality of formaldehyde that could be present in indoor air.

Max Sherman replies:

Thank you for giving me the opportunity to provide an update. Since I wrote my editorial, “ERVs Get The Yellow Flag” we at the Lawrence Berkeley National Laboratory have made some measurements to help answer the question of whether formaldehyde transfer is an important issue. I had hoped to report back to HE before this time, but unfortunately the required measurements have proven more challenging than expected.

While we do not have definitive results yet, we do have preliminary measurements and I can report some of the tentative trends.

Procedure and Results

Our experiments were done on a single type of ERV, specifically a wheel-type unit. We have looked at both laboratory and field performance in various configurations. When we test the unit in a configuration consistent with the HVI rating tests, we do in fact get results that (to within our error) are consistent with the ratings of the unit (e.g. an Exhaust Air Transfer Ratio in the neighborhood of 10%). As far as formaldehyde is concerned, there is only a few percent transfer above and beyond the amount that would be expected from the EATR (due to leakage).

Such a result would suggest that formaldehyde transfer is not a big issue, but some of our other tests might suggest otherwise.  The tests above were done at high speed, at laboratory conditions, with balanced flows. When we varied the conditions away from those, the performance changed—sometimes substantially. When we changed to low speed, we saw significant air leakage (roughly 50% increase in EATR) and a substantially increased transfer of formaldehyde over and above that—perhaps six times as much.  The impact of these two together is that there was over twice as much formaldehyde being transferred as one would expect from the rated EATR.

We also looked at the impact of unbalanced air flows. For high speed, we found that if the supply was 70% of the exhaust flow, the EATR would again be over double the rated value. All of that had to do with air leakage and not with the chemical properties of formaldehyde. So it is not a specific formaldehyde concern, but it does indicate general performance problems for unbalanced situations.

One factor that was specific to formaldehyde that seemed to matter was “outdoor” temperature. When the intake air temperature was lower, substantially more formaldehyde was transferred. For example, in our limited testing, when the intake temperature was dropped to 40°F the total formaldehyde transferred rose to about 25%. This suggests that the formaldehyde performance would be much worse in the winter than the ratings would indicate.

I previously reported on the performance of an ERV unit with a static core. I cannot compare your current results to ours directly because the ERV technologies are different, but here are a few observations:

  • You report a lower EATR, which makes sense for this type of core.
  • You also report a lower total formaldehyde transfer than EATR. As stated, it is not physically possible, but the number quoted may actually be the formaldehyde transfer over and above that transferred from air leakage. Another possible explanation is the sensitivity of the result to small measurement errors.
  • Finally, it is not clear from either of the data sets, if the static core ERVs would be as sensitive to low flow, unbalancing or temperature as the wheel-type we have looked at.

The ERVs we tested do not transfer as much formaldehyde as they moisture. The issues of poor EATR performance and extra formaldehyde transfer, however, are still potentially significant—at least for some product classes. Any performance degradation could substantially alter the choice of unit or technology when one is trying to optimize the ventilation system. A better rating method than EATR at a single operating point is probably needed, along with some sort of formaldehyde rating. Since in-situ performance of ERVs may still be substantially poorer than one estimated from their specifications, I am not yet inclined to renounce my yellow flag.

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