ACIN Flow Finder Mk 2

October 30, 2014
November/December 2014
A version of this article appears in the November/December 2014 issue of Home Energy Magazine.
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By definition, energy-efficient homes need to be airtight, so the ventilation system is vital to a healthy, durable home. Yet in Ontario, where new homes are being built more airtight, one can still build a compliant home with exhaust-only “ventilation” controlled by a binary switch. Some high-performance builders and architects are starting to see the value in commissioning their heat recovery ventilation (HRV) systems to (1) balance the incoming and outgoing flows, and (2) ensure that the system delivers no more or less than the designed flows to the intended rooms. Generally, home performance pros are beginning to realize that it is necessary to focus on commissioning HRV systems. At my company in Canada, BlueGreen Consulting Group, Incorporated, we recently took the plunge and bought the ACIN Flow Finder Mk 2 from U.S. distributor Retrotec (also available through TrueTech Tools). Though the Flow Finder is a pleasure to use, it had a few quirks that need to be resolved.

Greg Labbé
is co-owner of BlueGreen Consulting Group, a Toronto-based high-performance home consulting firm. (Greg Labbé)

First and foremost, what’s unique about this machine is that unlike most balometers, which passively measure airflow, this one uses a small, light, powered fan. As Lawrence Berkeley National Laboratory says in one of its technical papers, “To date, no nonpowered flow hood has been able to measure outlet flows with an acceptable level of accuracy.” The Flow Finder does have this ability.

At $4,000, this new machine is expensive. Ours is the 246th unit produced, and we’re probably the first company in Canada to take it for a test run.

Having been accused of measuring a turd with a micrometer in the past, we felt the investment in top-of-the-line equipment was necessary for our clients’ sake and to bolster our detail-oriented image.

How It Works

There are two ways of measuring airflow with a flow capture hood—passively or actively. Most balometers use passive sensors that measure the air passing through them with an array of anemometers. But the Flow Finder Mk 2 uses an active method that exhausts the air trapped inside the capture hood, using a small, precisely controlled fan that ramps up until the pressure inside the capture hood is the same as the pressure inside the room.

As delivered, the Flow Finder Mk 2 package came from Retrotec with the parts shown here, except the square extension, which we ordered and received later. It came with an assembly manual, but no user’s manual. By the time this is published, a new, more extensive user’s manual should be available for download.

Passive versus active is perhaps an unfair way to compare balometers, but the Flow Finder is easy to use for residential purposes, and the digital reading eliminates the parallax and the operator bias typical of meters with needles that move.


Table 1. Comparison of ACIN Flow Finder Mk 2 and Alnor ABT701

Table 1. Comparison of ACIN Flow Finder Mk 2 and Alnor ABT701

If you live in North America, make sure you get the attachments you want. The collapsible hood would be very useful, and so would the rectangular extension shown above on an Alnor balometer. Note that Retrotec does not issue the rugged hard case shown in the photo at left but a large red carrying case that a fellow elevator rider mistook for a pizza delivery case. (Greg Labbé)

When the Flow Finder Mk 2 is placed over a supply grille, for example, the motorized fan expels the air trapped in the hood’s enclosure and accelerates the fan until the pressure in the hood is equal to the atmospheric pressure in the room. All this happens with the push of a little red button cleverly placed at the handle for one-handed starts. It takes no more than ten seconds to depressurize or pressurize the enclosure and spit out a reading. The Flow Finder measures air temperature and relative humidity (RH), too. The fully pressure-compensated readings range from 6 CFM to 323 CFM, but Flow Finder will read up to 500 CFM using calculated compensation. For residential flows, we anticipate staying well below the 323 CFM.

It should be noted that unless your supply or return register grille is flat and less than 8 inches square, you’ll need a hood attachment in order to get readings. It’s important to know what kind of grilles you’re going to measure from, and we highly recommend that as part of your order, you get the right combination of hoods, if Retrotec can supply them. For residential purposes—given that the typical residential HVAC supply grille is 4 inches x 10 inches—the clear hood supplied by Retrotec works well, and the fact that it’s clear means you can see inside the enclosure to confirm positioning and check the seal around the edges—a brilliant idea. Having said that, the classic longer cloth- type hood—see photo of the Alnor flow meter on the next page—would mean less bending down and less ladder work for ceiling grills. No hood attachment can prepare you for every scenario in the field, so bring lots of cardboard and tape to make flanges and custom attachments.

Retrotec claims that the battery can measure active readings for 12 hours of operation, and so far we have no reason to doubt that claim.

For HRV grilles that are on ceilings, or worse, between ceilings and closet trim casings, a narrower hood attachment might be very useful. On our first couple of assignments, let’s just say we used a lot of cardboard cutouts and tape to get some readings.


We’re pleased to report that the Flow Finder Mk 2 does what it’s supposed to do. We compared two balometers by placing the hood on the supply grille on center and at the corner (see Table 1). At Low, the flows were too low to detect with the Alnor. (In fairness, it’s a commercial unit.) The Medium and High flow rates produced ratings for both balometers. The standard deviation was consistently lower with the ACIN, and the difference between corner readings and middle readings were an order of magnitude less noticeable. Splitting hairs for measuring air flows? Perhaps, but when you can measure more precisely, why not?

Once we downloaded the user’s manual from Retrotec, we were pleased to learn that we didn’t have to learn Dutch to operate the unit. (The Flow Finder is manufactured in Holland by ACIN Instrumenten.) The touch screen offers two modes: continuous reading, or sample reading. For the sample reading, it takes less than ten seconds to adjust the speed of the fan until pressure parity is achieved inside and outside the hood. There is an option to custom-enter the names of rooms and store readings for each of those rooms. This feature is quirky and, in our case, it didn’t work.

The first unit we received randomly locked the screen for a dozen minutes when we tried to store readings. Thankfully, Retrotec was fairly attentive and sent us a new replacement unit that works. The store function captures basic information in a comma-delineated table that includes temperature and RH for each measurement location. Though this function should eliminate transcription errors, it would be nice if the machine could spit out a more formal and simple report including the unit’s calibration date, serial number and model number.

Finally, living in Canada might as well be living in Madagascar when it comes to dealing with warranty or calibration issues. We all thought the Free Trade Agreement and NAFTA were going to make the border less of a barrier to small to-medium-sized enterprises like our BlueGreen, but it’s still a struggle. Shipping over the international border to resolve issues of this kind is expensive, and it’s a hassle. Though the manual suggests the calibration interval be set at one year, Retrotec is still working out the details of where (Europe or United States) the interval can be extended and how much to charge for a calibration. The new replacement machine we had shipped to us was last calibrated in December of 2013, which means the certificate expires less than five months after we received the unit—we’ll keep you posted.

learn more

Lawrence Berkeley National Laboratory. Measuring Residential Ventilation System Airflows: Part 2—Field Evaluation of Airflow Meter Devices and System Flow Verification, Berkeley, California: LBNL, 2012. Download a copy of this report.

The bottom line: As homes get more airtight—by design or by happenstance—home performance pros need to take ventilation rates seriously, and the Flow Finder Mk 2, with its sleek, easy-handling, simple interface; its long battery life; and its accuracy won’t disappoint the user. Yes, it’s orders of magnitude more expensive than a garbage bag test, but it looks more professional and is less awkward to use. If supply accuracy is important to you and you value your time in the field, the ACIN Flow Finder Mk 2 should be part of your tool kit whenever you commission ventilation systems or do diagnostics of discomfort due to flow imbalance.

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